Why scientists adjust temperature records, and how you can too

Author

1. 

   Neville Nicholls

   Professor emeritus, School of Earth, Atmosphere and Environment at Monash University
   Original link:   http://theconversation.com/why-scientists-adjust-temperature-records-and-how-you-can-too-36825
   

Disclosure Statement

Neville Nicholls in the 1990s initiated and led the efforts by the Bureau of Meteorology to adjust raw meteorological observations to reduce the effect of changes of exposure etc., to build a credible picture of how Australia's climate has been changing. He is a member of the National Council of the Australian Meteorological and Oceanographic Society.

What does Paraguay have to do with the global temperature record? dany13/Flickr, CC BY

An article in The Australian today has once again raised the question of why scientists, in trying to estimate how the global and regional surface temperatures of Earth may have changed over the past century or so, “adjust” the raw temperature data.

It is important to note, first off, that no data have been “altered” or destroyed in this process – all the raw data remain available for investigation by anyone who has the inclination (as I’ll show below).

But this process can lead to large adjustments to the raw data, and in at least some instances the adjusted data can suggest long-term warming even when the raw data indicate cooling.

This appears to have happened at the Paraguay stations mentioned in the article – the raw temperature recordings suggest cooling over decades, whereas warming appears after the raw data have been adjusted by NASA and NOAA.

The figure below shows this at one station in Paraguay. I have obtained the data from this station (raw and adjusted) from Berkeley Earth, an independent group who have, quite separately from NASA and NOAA, checked global temperature data for these so-called “inhomogeneities” and adjusted the raw data themselves.

Their results provide an independent check for the NASA and NOAA groups doing this adjustment. The raw data (blue line) at this station suggest cooling, whereas the “adjusted” data (pink line) indicate warming.

Berkeley Earth, Author provided

The problem with thermometers

So why do scientists “adjust” the raw data – why don’t they simply accept that the raw data are the best estimate of how the temperature has changed over decades?

The underlying problem is that whether or not a specific thermometer reading is a good estimate of the air temperature depends on how the thermometer is exposed.

Take a thermometer and attach it to a wall, and then compare the temperature you read from that thermometer with the reading from an identical thermometer in a modern Stevenson Screen located nearby.

 

This shows the thermometer screens at the Adelaide Observatory in 1888. Charles Todd established a very long experiment (it ran well into the 20th century) to compare temperature observations in the three different exposures illustrated here. His data show that the summer daytime temperatures measured in the typical 19th century thermometer exposure, the open stand shown on the right, were biased warm compared with the typical 20th century exposure in the Stevenson Screen shown on the left. So simply comparing the raw data from the 19th century with data from the 20th century would be misleading.

On a warm summer day the thermometer on the wall will usually record higher temperatures than the one in the Stevenson Screen. As well, any trees around the observing site, or buildings or roads or car parks, as well as many other factors, can all affect the recorded temperature.

Because nearly all long-term records of temperature anywhere in the world have been affected by such factors, for instance as a rural station or airport gets surrounded by suburbs and roads, the scientific thing to do is to make sure you take these factors into account when trying to get a picture of how the world may have warmed.

How to adjust data scientifically

It would be nice if we had a compete record of all the changes to all the temperature recording sites around the world, listing in forensic detail when and where stations were moved (even a few metres can make a difference), when trees around the site were planted or removed, when car parks nearby were built, and all the buildings for tens of metres around the site.

And we would need all these details stretching back over many decades.

Unfortunately, no station exists with such comprehensive information for the last century or so. But even if these “metadata” did exist, we could not just use the raw data at a single station alone to work out how much to adjust the raw data for changes in exposure and location.

So scientists identify other “comparison” stations (as many as they can find) with which to compare the raw data at the “target” station (such as the station in the graph from Paraguay). These comparison stations are selected because their temperature variations from year-to-year generally track the changes at the “target” station.

If, however, the target station temperatures change suddenly and that change is not matched by similar changes in all the comparison stations, it is reasonable to conclude that something has happened to corrupt the raw data at the target station. The relationship between temperatures at the target and comparison stations is then used to adjust the raw data at the target station.

The details of the way this adjustment process is done varies between the groups who do this. The result of the adjustments made by Berkeley Earth for a station in Paraguay is shown in the figure above.

Both the raw and adjusted data show warming over the past forty or so years, but before the mid-1960s the data are quite different. Even looking at the raw data alone, a scientist would worry that some change in exposure has corrupted the data, because of the sudden large drop in temperature.
But the Berkeley Earth scientists have objectively adjusted for this drop, through their comparisons with other stations in the region. Their adjustments remove the sudden drop in the mid-1960s, and indicate that temperatures in the region have been warming for more than the 40 years shown by the raw data.

Do it yourself

I encourage anyone who worries about the sort of adjustments made by NASA or NOAA, or in Australia by the Bureau of Meteorology, to go to the Berkeley Earth website, look at their independent results, and perhaps even do some calculations themselves to check what these other groups have done.

But don’t just think that the raw data will tell you much more than that the way the thermometer has been exposed has changed, or a car park has been built nearby, or a suburb now surrounds what once was a rural station.

You need to do the science and adjust for these corrupting factors, if you really want to work out how global and regional temperatures have changed. I’ve never been to Paraguay and I know almost nothing about the station whose data are in the graphs above. But scientists around the world have made these data available so we can do this work from our desktops.

I think this is great fun, but then I’m a nerdy meteorologist, so I would think that, wouldn’t I?

Logic

From Wikipedia, the free encyclopedia

Logic (from the Ancient Greek: λογική, logike)^[1] is the use and study of valid reasoning.^[2][3] The study of logic features most prominently in the subjects of philosophy, mathematics, and computer science.

Logic was studied in several ancient civilizations, including India,^[4] China,^[5] Persia and Greece. In the West, logic was established as a formal discipline by Aristotle, who gave it a fundamental place in philosophy. The study of logic was part of the classical trivium, which also included grammar and rhetoric. Logic was further extended by Al-Farabi who categorized it into two separate groups (idea and proof). Later, Avicenna revived the study of logic and developed relationship between temporalis and the implication. In the East, logic was developed by Buddhists and Jains.

Logic is often divided into three parts: inductive reasoning, abductive reasoning, and deductive reasoning.

The study of logic[edit]

“	Upon this first, and in one sense this sole, rule of reason, that in order to learn you must desire to learn, and in so desiring not be satisfied with what you already incline to think, there follows one corollary which itself deserves to be inscribed upon every wall of the city of philosophy: Do not block the way of inquiry.	”
—Charles Sanders Peirce, "First Rule of Logic"

The concept of logical form is central to logic, it being held that the validity of an argument is determined by its logical form, not by its content. Traditional Aristotelian syllogistic logic and modern symbolic logic are examples of formal logics.

• Informal logic is the study of natural language arguments. The study of fallacies is an especially important branch of informal logic. The dialogues of Plato^[6] are good examples of informal logic.
• Formal logic is the study of inference with purely formal content. An inference possesses a purely formal content if it can be expressed as a particular application of a wholly abstract rule, that is, a rule that is not about any particular thing or property. The works of Aristotle contain the earliest known formal study of logic. Modern formal logic follows and expands on Aristotle.^[7] In many definitions of logic, logical inference and inference with purely formal content are the same. This does not render the notion of informal logic vacuous, because no formal logic captures all of the nuances of natural language.
• Symbolic logic is the study of symbolic abstractions that capture the formal features of logical inference.^[8][9] Symbolic logic is often divided into two branches: propositional logic and predicate logic.
• Mathematical logic is an extension of symbolic logic into other areas, in particular to the study of model theory, proof theory, set theory, and recursion theory.

Logical form

Logic is generally considered formal when it analyzes and represents the form of any valid argument type. The form of an argument is displayed by representing its sentences in the formal grammar and symbolism of a logical language to make its content usable in formal inference. If one considers the notion of form too philosophically loaded, one could say that formalizing simply means translating English sentences into the language of logic.
This is called showing the logical form of the argument. It is necessary because indicative sentences of ordinary language show a considerable variety of form and complexity that makes their use in inference impractical. It requires, first, ignoring those grammatical features irrelevant to logic (such as gender and declension, if the argument is in Latin), replacing conjunctions irrelevant to logic (such as "but") with logical conjunctions like "and" and replacing ambiguous, or alternative logical expressions ("any", "every", etc.) with expressions of a standard type (such as "all", or the universal quantifier ∀).

Second, certain parts of the sentence must be replaced with schematic letters. Thus, for example, the expression "all As are Bs" shows the logical form common to the sentences "all men are mortals", "all cats are carnivores", "all Greeks are philosophers", and so on.

That the concept of form is fundamental to logic was already recognized in ancient times. Aristotle uses variable letters to represent valid inferences in Prior Analytics, leading Jan Łukasiewicz to say that the introduction of variables was "one of Aristotle's greatest inventions".^[10] According to the followers of Aristotle (such as Ammonius), only the logical principles stated in schematic terms belong to logic, not those given in concrete terms. The concrete terms "man", "mortal", etc., are analogous to the substitution values of the schematic placeholders A, B, C, which were called the "matter" (Greek hyle) of the inference.

The fundamental difference between modern formal logic and traditional, or Aristotelian logic, lies in their differing analysis of the logical form of the sentences they treat.

• In the traditional view, the form of the sentence consists of (1) a subject (e.g., "man") plus a sign of quantity ("all" or "some" or "no"); (2) the copula, which is of the form "is" or "is not"; (3) a predicate (e.g., "mortal"). Thus: all men are mortal. The logical constants such as "all", "no" and so on, plus sentential connectives such as "and" and "or" were called "syncategorematic" terms (from the Greek kategorei – to predicate, and syn – together with). This is a fixed scheme, where each judgment has an identified quantity and copula, determining the logical form of the sentence.
• According to the modern view, the fundamental form of a simple sentence is given by a recursive schema, involving logical connectives, such as a quantifier with its bound variable, which are joined by juxtaposition to other sentences, which in turn may have logical structure.
• The modern view is more complex, since a single judgement of Aristotle's system involves two or more logical connectives. For example, the sentence "All men are mortal" involves, in term logic, two non-logical terms "is a man" (here M) and "is mortal" (here D): the sentence is given by the judgement A(M,D). In predicate logic, the sentence involves the same two non-logical concepts, here analyzed as and , and the sentence is given by , involving the logical connectives for universal quantification and implication.
• But equally, the modern view is more powerful. Medieval logicians recognized the problem of multiple generality, where Aristotelian logic is unable to satisfactorily render such sentences as "Some guys have all the luck", because both quantities "all" and "some" may be relevant in an inference, but the fixed scheme that Aristotle used allows only one to govern the inference. Just as linguists recognize recursive structure in natural languages, it appears that logic needs recursive structure.

Deductive and inductive reasoning, and abductive inference

Deductive reasoning concerns what follows necessarily from given premises (if a, then b). However, inductive reasoning—the process of deriving a reliable generalization from observations—has sometimes been included in the study of logic. Similarly, it is important to distinguish deductive validity and inductive validity (called "cogency"). An inference is deductively valid if and only if there is no possible situation in which all the premises are true but the conclusion false. An inductive argument can be neither valid nor invalid; its premises give only some degree of probability, but not certainty, to its conclusion.

The notion of deductive validity can be rigorously stated for systems of formal logic in terms of the well-understood notions of semantics. Inductive validity on the other hand requires us to define a reliable generalization of some set of observations. The task of providing this definition may be approached in various ways, some less formal than others; some of these definitions may use mathematical models of probability. For the most part this discussion of logic deals only with deductive logic.

Abduction^[11] is a form of logical inference that goes from observation to a hypothesis that accounts for the reliable data (observation) and seeks to explain relevant evidence. The American philosopher Charles Sanders Peirce (1839–1914) first introduced the term as "guessing".^[12] Peirce said that to abduce a hypothetical explanation from an observed surprising circumstance is to surmise that may be true because then would be a matter of course.^[13] Thus, to abduce from involves determining that is sufficient (or nearly sufficient), but not necessary, for .

Consistency, validity, soundness, and completeness

Among the important properties that logical systems can have:

• Consistency, which means that no theorem of the system contradicts another.^[14]
• Validity, which means that the system's rules of proof never allow a false inference from true premises. A logical system has the property of soundness when the logical system has the property of validity and uses only premises that prove true (or, in the case of axioms, are true by definition).^[14]
• Completeness, of a logical system, which means that if a formula is true, it can be proven (if it is true, it is a theorem of the system).
• Soundness, the term soundness has multiple separate meanings, which creates a bit of confusion throughout the literature. Most commonly, soundness refers to logical systems, which means that if some formula can be proven in a system, then it is true in the relevant model/structure (if A is a theorem, it is true). This is the converse of completeness. A distinct, peripheral use of soundness refers to arguments, which means that the premises of a valid argument are true in the actual world.

Some logical systems do not have all four properties. As an example, Kurt Gödel's incompleteness theorems show that sufficiently complex formal systems of arithmetic cannot be consistent and complete;^[9] however, first-order predicate logics not extended by specific axioms to be arithmetic formal systems with equality can be complete and consistent.^[15]

Rival conceptions of logic

Logic arose (see below) from a concern with correctness of argumentation. Modern logicians usually wish to ensure that logic studies just those arguments that arise from appropriately general forms of inference. For example, Thomas Hofweber writes in the Stanford Encyclopedia of Philosophy that logic "does not, however, cover good reasoning as a whole. That is the job of the theory of rationality. Rather it deals with inferences whose validity can be traced back to the formal features of the representations that are involved in that inference, be they linguistic, mental, or other representations".^[16]
By contrast, Immanuel Kant argued that logic should be conceived as the science of judgement, an idea taken up in Gottlob Frege's logical and philosophical work. But Frege's work is ambiguous in the sense that it is both concerned with the "laws of thought" as well as with the "laws of truth", i.e. it both treats logic in the context of a theory of the mind, and treats logic as the study of abstract formal structures.

History

Aristotle, 384–322 BCE.

In Europe, logic was first developed by Aristotle.^[17] Aristotelian logic became widely accepted in science and mathematics and remained in wide use in the West until the early 19th century.^[18] Aristotle's system of logic was responsible for the introduction of hypothetical syllogism,^[19] temporal modal logic,^[20][21] and inductive logic,^[22] as well as influential terms such as terms, predicables, syllogisms and propositions. In Europe during the later medieval period, major efforts were made to show that Aristotle's ideas were compatible with Christian faith. During the High Middle Ages, logic became a main focus of philosophers, who would engage in critical logical analyses of philosophical arguments, often using variations of the methodology of scholasticism. In 1323, William of Ockham's influential Summa Logicae was released. By the 18th century, the structured approach to arguments had degenerated and fallen out of favour, as depicted in Holberg's satirical play Erasmus Montanus.

The Chinese logical philosopher Gongsun Long (c. 325–250 BCE) proposed the paradox "One and one cannot become two, since neither becomes two."^[23] In China, the tradition of scholarly investigation into logic, however, was repressed by the Qin dynasty following the legalist philosophy of Han Feizi.

In India, innovations in the scholastic school, called Nyaya, continued from ancient times into the early 18th century with the Navya-Nyaya school. By the 16th century, it developed theories resembling modern logic, such as Gottlob Frege's "distinction between sense and reference of proper names" and his "definition of number", as well as the theory of "restrictive conditions for universals" anticipating some of the developments in modern set theory.^[24] Since 1824, Indian logic attracted the attention of many Western scholars, and has had an influence on important 19th-century logicians such as Charles Babbage, Augustus De Morgan, and George Boole.^[25] In the 20th century, Western philosophers like Stanislaw Schayer and Klaus Glashoff have explored Indian logic more extensively.

The syllogistic logic developed by Aristotle predominated in the West until the mid-19th century, when interest in the foundations of mathematics stimulated the development of symbolic logic (now called mathematical logic). In 1854, George Boole published An Investigation of the Laws of Thought on Which are Founded the Mathematical Theories of Logic and Probabilities, introducing symbolic logic and the principles of what is now known as Boolean logic. In 1879, Gottlob Frege published Begriffsschrift, which inaugurated modern logic with the invention of quantifier notation. From 1910 to 1913, Alfred North Whitehead and Bertrand Russell published Principia Mathematica^[8] on the foundations of mathematics, attempting to derive mathematical truths from axioms and inference rules in symbolic logic. In 1931, Gödel raised serious problems with the foundationalist program and logic ceased to focus on such issues.

The development of logic since Frege, Russell, and Wittgenstein had a profound influence on the practice of philosophy and the perceived nature of philosophical problems (see Analytic philosophy), and Philosophy of mathematics. Logic, especially sentential logic, is implemented in computer logic circuits and is fundamental to computer science. Logic is commonly taught by university philosophy departments, often as a compulsory discipline.

Types of logic

Syllogistic logic

The Organon was Aristotle's body of work on logic, with the Prior Analytics constituting the first explicit work in formal logic, introducing the syllogistic.^[26] The parts of syllogistic logic, also known by the name term logic, are the analysis of the judgements into propositions consisting of two terms that are related by one of a fixed number of relations, and the expression of inferences by means of syllogisms that consist of two propositions sharing a common term as premise, and a conclusion that is a proposition involving the two unrelated terms from the premises.
Aristotle's work was regarded in classical times and from medieval times in Europe and the Middle East as the very picture of a fully worked out system. However, it was not alone: the Stoics proposed a system of propositional logic that was studied by medieval logicians. Also, the problem of multiple generality was recognized in medieval times. Nonetheless, problems with syllogistic logic were not seen as being in need of revolutionary solutions.

Today, some academics claim that Aristotle's system is generally seen as having little more than historical value (though there is some current interest in extending term logics), regarded as made obsolete by the advent of propositional logic and the predicate calculus. Others use Aristotle in argumentation theory to help develop and critically question argumentation schemes that are used in artificial intelligence and legal arguments.

Propositional logic (sentential logic)

A propositional calculus or logic (also a sentential calculus) is a formal system in which formulae representing propositions can be formed by combining atomic propositions using logical connectives, and in which a system of formal proof rules establishes certain formulae as "theorems".

Predicate logic

Predicate logic is the generic term for symbolic formal systems such as first-order logic, second-order logic, many-sorted logic, and infinitary logic.

Predicate logic provides an account of quantifiers general enough to express a wide set of arguments occurring in natural language. Aristotelian syllogistic logic specifies a small number of forms that the relevant part of the involved judgements may take. Predicate logic allows sentences to be analysed into subject and argument in several additional ways—allowing predicate logic to solve the problem of multiple generality that had perplexed medieval logicians.

The development of predicate logic is usually attributed to Gottlob Frege, who is also credited as one of the founders of analytical philosophy, but the formulation of predicate logic most often used today is the first-order logic presented in Principles of Mathematical Logic by David Hilbert and Wilhelm Ackermann in 1928. The analytical generality of predicate logic allowed the formalization of mathematics, drove the investigation of set theory, and allowed the development of Alfred Tarski's approach to model theory. It provides the foundation of modern mathematical logic.

Frege's original system of predicate logic was second-order, rather than first-order. Second-order logic is most prominently defended (against the criticism of Willard Van Orman Quine and others) by George Boolos and Stewart Shapiro.

Modal logic

In languages, modality deals with the phenomenon that sub-parts of a sentence may have their semantics modified by special verbs or modal particles. For example, "We go to the games" can be modified to give "We should go to the games", and "We can go to the games" and perhaps "We will go to the games". More abstractly, we might say that modality affects the circumstances in which we take an assertion to be satisfied.
Aristotle's logic is in large parts concerned with the theory of non-modalized logic. Although, there are passages in his work, such as the famous sea-battle argument in De Interpretatione § 9, that are now seen as anticipations of modal logic and its connection with potentiality and time, the earliest formal system of modal logic was developed by Avicenna, whom ultimately developed a theory of "temporally modalized" syllogistic.^[27]

While the study of necessity and possibility remained important to philosophers, little logical innovation happened until the landmark investigations of Clarence Irving Lewis in 1918, who formulated a family of rival axiomatizations of the alethic modalities. His work unleashed a torrent of new work on the topic, expanding the kinds of modality treated to include deontic logic and epistemic logic. The seminal work of Arthur Prior applied the same formal language to treat temporal logic and paved the way for the marriage of the two subjects. Saul Kripke discovered (contemporaneously with rivals) his theory of frame semantics, which revolutionized the formal technology available to modal logicians and gave a new graph-theoretic way of looking at modality that has driven many applications in computational linguistics and computer science, such as dynamic logic.

Informal reasoning

The motivation for the study of logic in ancient times was clear: it is so that one may learn to distinguish good from bad arguments, and so become more effective in argument and oratory, and perhaps also to become a better person. Half of the works of Aristotle's Organon treat inference as it occurs in an informal setting, side by side with the development of the syllogistic, and in the Aristotelian school, these informal works on logic were seen as complementary to Aristotle's treatment of rhetoric.
This ancient motivation is still alive, although it no longer takes centre stage in the picture of logic; typically dialectical logic forms the heart of a course in critical thinking, a compulsory course at many universities.

Argumentation theory is the study and research of informal logic, fallacies, and critical questions as they relate to every day and practical situations. Specific types of dialogue can be analyzed and questioned to reveal premises, conclusions, and fallacies. Argumentation theory is now applied in artificial intelligence and law.

Mathematical logic

Mathematical logic really refers to two distinct areas of research: the first is the application of the techniques of formal logic to mathematics and mathematical reasoning, and the second, in the other direction, the application of mathematical techniques to the representation and analysis of formal logic.^[28]

The earliest use of mathematics and geometry in relation to logic and philosophy goes back to the ancient Greeks such as Euclid, Plato, and Aristotle.^[29] Many other ancient and medieval philosophers applied mathematical ideas and methods to their philosophical claims.^[30]

One of the boldest attempts to apply logic to mathematics was undoubtedly the logicism pioneered by philosopher-logicians such as Gottlob Frege and Bertrand Russell: the idea was that mathematical theories were logical tautologies, and the programme was to show this by means to a reduction of mathematics to logic.^[8] The various attempts to carry this out met with a series of failures, from the crippling of Frege's project in his Grundgesetze by Russell's paradox, to the defeat of Hilbert's program by Gödel's incompleteness theorems.

Both the statement of Hilbert's program and its refutation by Gödel depended upon their work establishing the second area of mathematical logic, the application of mathematics to logic in the form of proof theory.^[31] Despite the negative nature of the incompleteness theorems, Gödel's completeness theorem, a result in model theory and another application of mathematics to logic, can be understood as showing how close logicism came to being true: every rigorously defined mathematical theory can be exactly captured by a first-order logical theory; Frege's proof calculus is enough to describe the whole of mathematics, though not equivalent to it. Thus we see how complementary the two areas of mathematical logic have been.^{[citation needed]}

If proof theory and model theory have been the foundation of mathematical logic, they have been but two of the four pillars of the subject. Set theory originated in the study of the infinite by Georg Cantor, and it has been the source of many of the most challenging and important issues in mathematical logic, from Cantor's theorem, through the status of the Axiom of Choice and the question of the independence of the continuum hypothesis, to the modern debate on large cardinal axioms.

Recursion theory captures the idea of computation in logical and arithmetic terms; its most classical achievements are the undecidability of the Entscheidungsproblem by Alan Turing, and his presentation of the Church–Turing thesis.^[32] Today recursion theory is mostly concerned with the more refined problem of complexity classes—when is a problem efficiently solvable?—and the classification of degrees of unsolvability.^[33]

Philosophical logic

Philosophical logic deals with formal descriptions of ordinary, non-specialist ("natural") language. Most philosophers assume that the bulk of everyday reasoning can be captured in logic if a method or methods to translate ordinary language into that logic can be found. Philosophical logic is essentially a continuation of the traditional discipline called "logic" before the invention of mathematical logic. Philosophical logic has a much greater concern with the connection between natural language and logic. As a result, philosophical logicians have contributed a great deal to the development of non-standard logics (e.g. free logics, tense logics) as well as various extensions of classical logic (e.g. modal logics) and non-standard semantics for such logics (e.g. Kripke's supervaluationism in the semantics of logic).
Logic and the philosophy of language are closely related. Philosophy of language has to do with the study of how our language engages and interacts with our thinking. Logic has an immediate impact on other areas of study. Studying logic and the relationship between logic and ordinary speech can help a person better structure his own arguments and critique the arguments of others. Many popular arguments are filled with errors because so many people are untrained in logic and unaware of how to formulate an argument correctly.^{[citation needed]}

Computational logic

Logic cut to the heart of computer science as it emerged as a discipline: Alan Turing's work on the Entscheidungsproblem followed from Kurt Gödel's work on the incompleteness theorems. The notion of the general purpose computer that came from this work was of fundamental importance to the designers of the computer machinery in the 1940s.

In the 1950s and 1960s, researchers predicted that when human knowledge could be expressed using logic with mathematical notation, it would be possible to create a machine that reasons, or artificial intelligence. This was more difficult than expected because of the complexity of human reasoning. In logic programming, a program consists of a set of axioms and rules. Logic programming systems such as Prolog compute the consequences of the axioms and rules in order to answer a query.

Today, logic is extensively applied in the fields of Artificial Intelligence, and Computer Science, and these fields provide a rich source of problems in formal and informal logic. Argumentation theory is one good example of how logic is being applied to artificial intelligence. The ACM Computing Classification System in particular regards:

• Section F.3 on Logics and meanings of programs and F.4 on Mathematical logic and formal languages as part of the theory of computer science: this work covers formal semantics of programming languages, as well as work of formal methods such as Hoare logic;
• Boolean logic as fundamental to computer hardware: particularly, the system's section B.2 on Arithmetic and logic structures, relating to operatives AND, NOT, and OR;
• Many fundamental logical formalisms are essential to section I.2 on artificial intelligence, for example modal logic and default logic in Knowledge representation formalisms and methods, Horn clauses in logic programming, and description logic.

Furthermore, computers can be used as tools for logicians. For example, in symbolic logic and mathematical logic, proofs by humans can be computer-assisted. Using automated theorem proving the machines can find and check proofs, as well as work with proofs too lengthy to write out by hand.

Bivalence and the law of the excluded middle; non-classical logics

The logics discussed above are all "bivalent" or "two-valued"; that is, they are most naturally understood as dividing propositions into true and false propositions. Non-classical logics are those systems that reject bivalence.

Hegel developed his own dialectic logic that extended Kant's transcendental logic but also brought it back to ground by assuring us that "neither in heaven nor in earth, neither in the world of mind nor of nature, is there anywhere such an abstract 'either–or' as the understanding maintains. Whatever exists is concrete, with difference and opposition in itself".^[34]

In 1910, Nicolai A. Vasiliev extended the law of excluded middle and the law of contradiction and proposed the law of excluded fourth and logic tolerant to contradiction.^[35] In the early 20th century Jan Łukasiewicz investigated the extension of the traditional true/false values to include a third value, "possible", so inventing ternary logic, the first multi-valued logic.^{[citation needed]}

Logics such as fuzzy logic have since been devised with an infinite number of "degrees of truth", represented by a real number between 0 and 1.^[36]

Intuitionistic logic was proposed by L.E.J. Brouwer as the correct logic for reasoning about mathematics, based upon his rejection of the law of the excluded middle as part of his intuitionism. Brouwer rejected formalization in mathematics, but his student Arend Heyting studied intuitionistic logic formally, as did Gerhard Gentzen. Intuitionistic logic is of great interest to computer scientists, as it is a constructive logic and can be applied for extracting verified programs from proofs.

Modal logic is not truth conditional, and so it has often been proposed as a non-classical logic. However, modal logic is normally formalized with the principle of the excluded middle, and its relational semantics is bivalent, so this inclusion is disputable.

"Is logic empirical?"

What is the epistemological status of the laws of logic? What sort of argument is appropriate for criticizing purported principles of logic? In an influential paper entitled "Is logic empirical?"^[37] Hilary Putnam, building on a suggestion of W. V. Quine, argued that in general the facts of propositional logic have a similar epistemological status as facts about the physical universe, for example as the laws of mechanics or of general relativity, and in particular that what physicists have learned about quantum mechanics provides a compelling case for abandoning certain familiar principles of classical logic: if we want to be realists about the physical phenomena described by quantum theory, then we should abandon the principle of distributivity, substituting for classical logic the quantum logic proposed by Garrett Birkhoff and John von Neumann.^[38]

Another paper of the same name by Sir Michael Dummett argues that Putnam's desire for realism mandates the law of distributivity.^[39] Distributivity of logic is essential for the realist's understanding of how propositions are true of the world in just the same way as he has argued the principle of bivalence is. In this way, the question, "Is logic empirical?" can be seen to lead naturally into the fundamental controversy in metaphysics on realism versus anti-realism.

Implication: strict or material?

The notion of implication formalized in classical logic does not comfortably translate into natural language by means of "if ... then ...", due to a number of problems called the paradoxes of material implication.

The first class of paradoxes involves counterfactuals, such as If the moon is made of green cheese, then 2+2=5, which are puzzling because natural language does not support the principle of explosion. Eliminating this class of paradoxes was the reason for C. I. Lewis's formulation of strict implication, which eventually led to more radically revisionist logics such as relevance logic.

The second class of paradoxes involves redundant premises, falsely suggesting that we know the succedent because of the antecedent: thus "if that man gets elected, granny will die" is materially true since granny is mortal, regardless of the man's election prospects. Such sentences violate the Gricean maxim of relevance, and can be modelled by logics that reject the principle of monotonicity of entailment, such as relevance logic.

Tolerating the impossible

Hegel was deeply critical of any simplified notion of the Law of Non-Contradiction. It was based on Leibniz's idea that this law of logic also requires a sufficient ground to specify from what point of view (or time) one says that something cannot contradict itself. A building, for example, both moves and does not move; the ground for the first is our solar system and for the second the earth. In Hegelian dialectic, the law of non-contradiction, of identity, itself relies upon difference and so is not independently assertable.

Closely related to questions arising from the paradoxes of implication comes the suggestion that logic ought to tolerate inconsistency. Relevance logic and paraconsistent logic are the most important approaches here, though the concerns are different: a key consequence of classical logic and some of its rivals, such as intuitionistic logic, is that they respect the principle of explosion, which means that the logic collapses if it is capable of deriving a contradiction. Graham Priest, the main proponent of dialetheism, has argued for paraconsistency on the grounds that there are in fact, true contradictions.^[40]

Rejection of logical truth

The philosophical vein of various kinds of skepticism contains many kinds of doubt and rejection of the various bases on which logic rests, such as the idea of logical form, correct inference, or meaning, typically leading to the conclusion that there are no logical truths. Observe that this is opposite to the usual views in philosophical skepticism, where logic directs skeptical enquiry to doubt received wisdoms, as in the work of Sextus Empiricus.

Friedrich Nietzsche provides a strong example of the rejection of the usual basis of logic: his radical rejection of idealization led him to reject truth as a "... mobile army of metaphors, metonyms, and anthropomorphisms—in short ... metaphors which are worn out and without sensuous power; coins which have lost their pictures and now matter only as metal, no longer as coins."^[41] His rejection of truth did not lead him to reject the idea of either inference or logic completely, but rather suggested that "logic [came] into existence in man's head [out] of illogic, whose realm originally must have been immense. Innumerable beings who made inferences in a way different from ours perished".^[42] Thus there is the idea that logical inference has a use as a tool for human survival, but that its existence does not support the existence of truth, nor does it have a reality beyond the instrumental: "Logic, too, also rests on assumptions that do not correspond to anything in the real world".^[43]

This position held by Nietzsche however, has come under extreme scrutiny for several reasons. He fails to demonstrate the validity of his claims and merely asserts them rhetorically. Although, since he is criticising the established criteria of validity, this does not undermine his position for one could argue that the demonstration of validity provided in the name of logic was just as rhetorically based. Some philosophers, such as Jürgen Habermas, claim his position is self-refuting—and accuse Nietzsche of not even having a coherent perspective, let alone a theory of knowledge.^[44] Again, it is unclear if this is a decisive critique for the criteria of coherency and consistent theory are exactly what is under question. Georg Lukács, in his book The Destruction of Reason, asserts that, "Were we to study Nietzsche's statements in this area from a logico-philosophical angle, we would be confronted by a dizzy chaos of the most lurid assertions, arbitrary and violently incompatible."^[45] Still, in this respect his "theory" would be a much better depicition of a confused and chaotic reality than any consistent and compatible theory. Bertrand Russell described Nietzsche's irrational claims with "He is fond of expressing himself paradoxically and with a view to shocking conventional readers" in his book A History of Western Philosophy.^[46]

Cannabis (drug)

From Wikipedia, the free encyclopedia

Cannabis
Flowering cannabis plant
Botanical	Cannabis
Source plant(s)	Cannabis sativa, Cannabis sativa forma indica, Cannabis ruderalis
Part(s) of plant	flower
Geographic origin	Central and South Asia.[1]
Active ingredients	Tetrahydrocannabinol, cannabidiol, cannabinol, tetrahydrocannabivarin
Main producers	Afghanistan,[2] Canada,[3] China,[4][not in citation given] Colombia,[5] India,[2] Jamaica,[2] Mexico,[6] Morocco,[2] Netherlands, Pakistan, Paraguay,[6] Spain,[2] Thailand, Turkey, United States[2]

Cannabis, commonly known as marijuana^[7] and by numerous other names,^a[›] is a preparation of the Cannabis plant intended for use as a psychoactive drug and as medicine.^[8][9] Pharmacologically, the principal psychoactive constituent of cannabis is tetrahydrocannabinol (THC); it is one of 483 known compounds in the plant,^[10] including at least 84 other cannabinoids, such as cannabidiol (CBD), cannabinol (CBN), tetrahydrocannabivarin (THCV),^[11][12] and cannabigerol (CBG).

Cannabis is often consumed for its psychoactive and physiological effects, which can include heightened mood or euphoria, relaxation,^[13] and an increase in appetite.^[14] Possible side-effects include a decrease in short-term memory, dry mouth, impaired motor skills, reddening of the eyes,^[13] and feelings of paranoia or anxiety.^[15]

Modern uses of cannabis are as a recreational or medicinal drug, and as part of religious or spiritual rites; the earliest recorded uses date from the 3rd millennium BC.^[16] Since the early 20th century cannabis has been subject to legal restrictions with the possession, use, and sale of cannabis preparations containing psychoactive cannabinoids currently illegal in most countries of the world; the United Nations deems it the most-used illicit drug in the world.^[17][18] In 2004, the United Nations estimated that global consumption of cannabis indicated that approximately 4% of the adult world population (162 million people) used cannabis annually, and that approximately 0.6% (22.5 million) of people used cannabis daily.^[19] Medical marijuana refers to the use of the Cannabis plant as a physician-recommended herbal therapy, which is taking place in Canada, Belgium, Australia, the Netherlands, Spain, and several U.S. states.

Effects

Main short-term physical effects of cannabis

Cannabis has psychoactive and physiological effects when consumed.^[20] The immediate desired effects from consuming cannabis include relaxation and mild euphoria (the "high" or "stoned" feeling), while some immediate undesired side-effects include a decrease in short-term memory, dry mouth, impaired motor skills and reddening of the eyes.^[21] Aside from a subjective change in perception and mood, the most common short-term physical and neurological effects include increased heart rate, increased appetite and consumption of food, lowered blood pressure, impairment of short-term and working memory,^[22][23] psychomotor coordination, and concentration.

A 2013 literature review said that exposure to marijuana had biologically-based physical, mental, behavioral and social health consequences and was "associated with diseases of the liver (particularly with co-existing hepatitis C), lungs, heart, and vasculature".^[24]

Cannabis has been used to reduce nausea and vomiting in chemotherapy and people with AIDS, and to treat pain and muscle spasticity.^[25] According to a 2013 review, "Safety concerns regarding cannabis include the increased risk of developing schizophrenia with adolescent use, impairments in memory and cognition, accidental pediatric ingestions, and lack of safety packaging for medical cannabis formulations."^[25]

The medicinal value of cannabis is disputed. The American Society of Addiction Medicine dismisses the concept of medical cannabis because of concerns about its potential for dependence and adverse health effects. The US Food and Drug Administration (FDA) states that the herb cannabis is associated with numerous harmful health effects, and that significant aspects such as content, production, and supply are unregulated. The FDA approves of the prescription of two products (not for smoking) that have pure THC in a small controlled dose as the active substance.^[26][27]

Neurological

A 2013 review comparing different structural and functional imaging studies showed morphological brain alterations in long-term cannabis users which were found to possibly correlate to cannabis exposure.^[28] A 2010 review found resting blood flow to be lower globally and in prefrontal areas of the brain in cannabis users, when compared to non-users. It was also shown that giving THC or cannabis correlated with increased bloodflow in these areas, and facilitated activation of the anterior cingulate cortex and frontal cortex when participants were presented with assignments demanding use of cognitive capacity.^[29] Both reviews noted that some of the studies that they examined had methodological limitations, for example small sample sizes or not distinguishing adequately between cannabis and alcohol consumption.^[28][29]

Gateway drug

The Gateway Hypothesis states that cannabis use increases the probability of trying "harder" drugs. The hypothesis has been hotly debated as it is regarded by some as the primary rationale for the United States prohibition on cannabis use.^[30][31] A Pew Research Center poll found that political opposition to marijuana use was significantly associated with concerns about health effects and whether legalization would increase marijuana use by children.^[32]
Some studies state that while there is no proof for the gateway hypothesis,^[33] young cannabis users should still be considered as a risk group for intervention programs.^[34] Other findings indicate that hard drug users are likely to be poly-drug users, and that interventions must address the use of multiple drugs instead of a single hard drug.^[35] Almost two-thirds of the poly drug users in the "2009/10 Scottish Crime and Justice Survey" used cannabis.^[36]

The gateway effect may appear due to social factors involved in using any illegal drug. Because of the illegal status of cannabis, its consumers are likely to find themselves in situations allowing them to acquaint with individuals using or selling other illegal drugs.^[37][38] Utilizing this argument some studies have shown that alcohol and tobacco may additionally be regarded as gateway drugs;^[39] however, a more parsimonious explanation could be that cannabis is simply more readily available (and at an earlier age) than illegal hard drugs. In turn alcohol and tobacco are easier to obtain at an earlier point than is cannabis (though the reverse may be true in some areas), thus leading to the "gateway sequence" in those individuals since they are most likely to experiment with any drug offered.^[30]

An alternative to the gateway hypothesis is the Common Liability to Addiction theory (CLA). It states that some individuals are, for various reasons, willing to try multiple recreational substances. The "gateway" drugs are merely those that are (usually) available at an earlier age than the harder drugs. Researchers have noted in an extensive review, Vanyukov et al., that it is dangerous to present the sequence of events described in gateway "theory" in causative terms as this hinders both research and intervention.^[40]

Safety

Fatal overdoses associated with cannabis use have not been reported as of 2008.^[41] There has been too little research to determine whether cannabis users die at a higher rate as compared to the general population, though some studies suggest that fatal motor vehicle accidents and death from respiratory and brain cancers may be more frequent among heavy cannabis users. It is not clear whether cannabis use affects the rate of suicide.^[41]
THC, the principal psychoactive constituent of the cannabis plant, has low toxicity, the dose of THC needed to kill 50% of tested rodents is very high,^[42] and human deaths from overdose are extremely rare, usually following the injection of hashish oil.^[43]

Evaluations of safety and tolerability of Sativex, a pharmacological preparation made from a low dose of cannabinoids, have concluded that it is indeed well-tolerated and, in one class of patients, useful.^[44]

Many studies have looked at the effects of smoking cannabis on the respiratory system. Cannabis smoke contains thousands of organic and inorganic chemical compounds. This tar is chemically similar to that found in tobacco smoke,^[45] and over fifty known carcinogens have been identified in cannabis smoke,^[46] including; nitrosamines, reactive aldehydes, and polycylic hydrocarbons, including benz[a]pyrene.^[47] Combustion products are not present when using a vaporizer, consuming THC in pill form, or consuming cannabis foods.

There is serious suspicion among cardiologists, spurring research but falling short of definitive proof, that cannabis use has the potential to contribute to cardiovascular disease. Cannabis is believed to be an aggravating factor in rare cases of arteritis, a serious condition that in some cases leads to amputation. Because 97% of case-reports also smoked tobacco, a formal association with cannabis could not be made. If cannabis arteritis turns out to be a distinct clinical entity, it might be the consequence of vasoconstrictor activity observed from delta-8-THC and delta-9-THC.^[48] Other serious cardiovascular events including myocardial infarction, stroke, sudden cardiac death, and cardiomyopathy have been reported to be temporally associated with cannabis use. Research in these events is complicated because cannabis is often used in conjunction with tobacco, and drugs such as alcohol and cocaine.^[49] These putative effects can be taken in context of a wide range of cardiovascular phenomena regulated by the endocannabinoid system and an overall role of cannabis in causing decreased peripheral resistance and increased cardiac output, which potentially could pose a threat to those with cardiovascular disease.^[50]

Varieties and strains

Types of cannabis

CBD is a 5-HT_1A receptor agonist, which may also contribute to an anxiolytic effect.^[51] This likely means the high concentrations of CBD found in Cannabis indica mitigate the anxiogenic effect of THC significantly.^[51] The effects of sativa are well known for their cerebral high, hence its daytime use as medical cannabis, while indica is well known for its sedative effects and preferred night time use as medical cannabis.^[51]

Concentration of psychoactive ingredients

According to the United Nations Office on Drugs and Crime (UNODC), "the amount of THC present in a cannabis sample is generally used as a measure of cannabis potency."^[52] The three main forms of cannabis products are the flower, resin (hashish), and oil (hash oil). The UNODC states that cannabis often contains 5% THC content, resin "can contain up to 20% THC content", and that "Cannabis oil may contain more than 60% THC content."^[52]

A scientific study published in 2000 in the Journal of Forensic Sciences (JFS) found that the potency (THC content) of confiscated cannabis in the United States (US) rose from "approximately 3.3% in 1983 and 1984", to "4.47% in 1997". The study also concluded that "other major cannabinoids (i.e., CBD, CBN, and CBC)" (other chemicals in cannabis) "showed no significant change in their concentration over the years".^[53] More recent research undertaken at the University of Mississippi's Potency Monitoring Project found that average THC levels in cannabis samples between 1975 and 2007 steadily increased,^[54] for example THC levels in 1985 averaged 3.48% by 2006 this had increased to an average of 8.77%.^[54]

Australia's National Cannabis Prevention and Information Centre (NCPIC) states that the buds (flowers) of the female cannabis plant contain the highest concentration of THC, followed by the leaves. The stalks and seeds have "much lower THC levels".^[55] The UN states that leaves can contain ten times less THC than the buds, and the stalks one hundred times less THC.^[52]

After revisions to cannabis rescheduling in the UK, the government moved cannabis back from a class C to a class B drug. A purported reason was the appearance of high potency cannabis. They believe skunk accounts for between 70 and 80% of samples seized by police^[56] (despite the fact that skunk can sometimes be incorrectly mistaken for all types of herbal cannabis).^[57][58] Extracts such as hashish and hash oil typically contain more THC than high potency cannabis flowers.^[59]

Preparations

• 

  Dried flower
• 

  Kief
• 

  Hashish
• 

  Tincture
• 

  Hash oil
• 

  Infusion (dairy butter)
• 

  Pipe resin

Marijuana

Marijuana consists of the dried flowers and subtending leaves and stems of the female Cannabis plant.^[60][61] This is the most widely consumed form, containing 3% to 20% THC,^[62] with reports of up-to 33% THC.^[63] In contrast, cannabis varieties used to produce industrial hemp contain less than 1% THC and are thus not valued for recreational use.^[64]

This is the stock material from which all other preparations are derived. It is noted that cannabis or its extracts must be sufficiently heated or dehydrated to cause decarboxylation of its most abundant cannabinoid, tetrahydrocannabinolic acid (THCA), into psychoactive THC.^[65]

Kief

Kief is a powder, rich in trichomes,^[66] which can be sifted from the leaves and flowers of cannabis plants and either consumed in powder form or compressed to produce cakes of hashish.^[67] The word "kif" derives from colloquial Arabic كيف kēf/kīf, meaning pleasure.^[68]

Hashish

Hashish (also spelled hasheesh, hashisha, or simply hash) is a concentrated resin cake or ball produced from pressed kief, the detached trichomes and fine material that falls off of cannabis flowers and leaves.^[69] It varies in color from black to golden brown depending upon purity and variety of cultivar it was obtained from.^[70] It can be consumed orally or smoked.^[71]

Tincture

Cannabinoids can be extracted from cannabis plant matter using high-proof spirits (often grain alcohol) to create a tincture, often referred to as "green dragon".^[72] Nabiximols is a branded product name from a tincture manufacturing pharmaceutical company.^[73]

Hash oil

Hash oil is obtained from the cannabis plant by solvent extraction, and contains the cannabinoids present in the natural oils of cannabis flowers and leaves.^[74] The solvents are evaporated to leave behind a very concentrated oil. Owing to its purity, hash oil is consumed by smoking, vaporizing, eating, or topical application. Hash oil is very different from both hemp seed oil and cannabis flower essential oil.^[75]

Infusions

There are many varieties of cannabis infusions owing to the variety of non-volatile solvents used. The plant material is mixed with the solvent and then pressed and filtered to express the oils of the plant into the solvent. Examples of solvents used in this process are cocoa butter, dairy butter, cooking oil, glycerine, and skin moisturizers. Depending on the solvent, these may be used in cannabis foods or applied topically.^[76]

Adulterated cannabis

Contaminants may be found in hashish obtained from "soap bar"-type sources.^[77] The dried flowers of the plant may be contaminated by the plant taking up heavy metals and other toxins from its growing environment,^[78] or by the addition of glass.^[79] In the Netherlands, chalk has been used to make cannabis appear to be of a higher quality.^[80] Increasing the weight of hashish products in Germany with lead caused lead intoxication in at least 29 users.^[81]

Despite cannabis being generally perceived as a natural product,^[82] in a recent Australian survey^[83] one in four Australians consider cannabis grown indoors under hydroponic conditions to be a greater health risk due to increased contamination, added to the plant during cultivation to enhance the plant growth and quality.

Consumption

A joint prior to rolling, with a paper handmade filter on the left

Woman selling cannabis and bhang in Guwahati, Assam, India

A forced-air vaporizer. The detachable balloon (top) fills with vapors that are then inhaled

Methods of consumption

Cannabis is consumed in many different ways:^[84]

• smoking, which typically involves inhaling vaporized cannabinoids ("smoke") from small pipes, bongs (portable versions of hookahs with water chamber), paper-wrapped joints or tobacco-leaf-wrapped blunts, roach clips, and other items.^[85]

• vaporizer, which heats herbal cannabis to 165–190 °C (329–374 °F),^[86] causing the active ingredients to evaporate into a vapor without burning the plant material (the boiling point of THC is 157 °C (315 °F) at 760 mmHg pressure).^[87]

• cannabis tea, which contains relatively small concentrations of THC because THC is an oil (lipophilic) and is only slightly water-soluble (with a solubility of 2.8 mg per liter).^[88] Cannabis tea is made by first adding a saturated fat to hot water (e.g. cream or any milk except skim) with a small amount of cannabis.^[89]

• edibles, where cannabis is added as an ingredient to one of a variety of foods.

Marijuana vending machines for selling or dispensing cannabis are in use in the United States and are planned to be used in Canada.^[90]

Mechanism of action

The high lipid-solubility of cannabinoids results in their persisting in the body for long periods of time.^[91] Even after a single administration of THC, detectable levels of THC can be found in the body for weeks or longer (depending on the amount administered and the sensitivity of the assessment method).^[91] A number of investigators have suggested that this is an important factor in marijuana's effects, perhaps because cannabinoids may accumulate in the body, particularly in the lipid membranes of neurons.^[92]
Not until the end of the 20th century was the specific mechanism of action of THC at the neuronal level studied. Researchers have subsequently confirmed that THC exerts its most prominent effects via its actions on two types of cannabinoid receptors, the CB₁ receptor and the CB₂ receptor, both of which are G-protein coupled receptors.^[93] The CB1 receptor is found primarily in the brain as well as in some peripheral tissues, and the CB2 receptor is found primarily in peripheral tissues, but is also expressed in neuroglial cells.^[94] THC appears to alter mood and cognition through its agonist actions on the CB1 receptors, which inhibit a secondary messenger system (adenylate cyclase) in a dose dependent manner. These actions can be blocked by the selective CB1 receptor antagonist SR141716A (rimonabant), which has been shown in clinical trials to be an effective treatment for smoking cessation, weight loss, and as a means of controlling or reducing metabolic syndrome risk factors.^[95] However, due to the dysphoric effect of CB1 antagonists, this drug is often discontinued due to these side effects.^[96]

Via CB1 activation, THC indirectly increases dopamine release and produces psychotropic effects. Cannabidiol also acts as an allosteric modulator of the mu and delta opioid receptors.^[97] THC also potentiates the effects of the glycine receptors.^[98] The role of these interactions in the "marijuana high" remains elusive.^{[citation needed]}

Detection of consumption

THC and its major (inactive) metabolite, THC-COOH, can be measured in blood, urine, hair, oral fluid or sweat using chromatographic techniques as part of a drug use testing program or a forensic investigation of a traffic or other criminal offense.^[99] The concentrations obtained from such analyses can often be helpful in distinguishing active use from passive exposure, elapsed time since use, and extent or duration of use. These tests cannot, however, distinguish authorized cannabis smoking for medical purposes from unauthorized recreational smoking.^[100] Commercial cannabinoid immunoassays, often employed as the initial screening method when testing physiological specimens for marijuana presence, have different degrees of cross-reactivity with THC and its metabolites.^[101] Urine contains predominantly THC-COOH, while hair, oral fluid and sweat contain primarily THC.^[99] Blood may contain both substances, with the relative amounts dependent on the recency and extent of usage.^[99]
The Duquenois-Levine test is commonly used as a screening test in the field, but it cannot definitively confirm the presence of cannabis, as a large range of substances have been shown to give false positives. Despite this, it is common in the United States for prosecutors to seek plea bargains on the basis of positive D-L tests, claiming them definitive, or even to seek conviction without the use of gas chromatography confirmation, which can only be done in the lab.^[102] In 2011, researchers at John Jay College of Criminal Justice reported that dietary zinc supplements can mask the presence of THC and other drugs in urine.^[103]

Production

It is often claimed by growers and breeders of herbal cannabis that advances in breeding and cultivation techniques have increased the potency of cannabis since the late 1960s and early '70s, when THC was first discovered and understood. However, potent seedless cannabis such as "Thai sticks" were already available at that time. Sinsemilla (Spanish for "without seed") is the dried, seedless inflorescences of female cannabis plants. Because THC production drops off once pollination occurs, the male plants (which produce little THC themselves) are eliminated before they shed pollen to prevent pollination. Advanced cultivation techniques such as hydroponics, cloning, high-intensity artificial lighting, and the sea of green method are frequently employed as a response (in part) to prohibition enforcement efforts that make outdoor cultivation more risky. It is often cited that the average levels of THC in cannabis sold in United States rose dramatically between the 1970s and 2000, but such statements are likely skewed because of undue weight given to much more expensive and potent, but less prevalent samples.^[104]
"Skunk" refers to several named strains of potent cannabis, grown through selective breeding and sometimes hydroponics. It is a cross-breed of Cannabis sativa and C. indica (although other strains of this mix exist in abundance). Skunk cannabis potency ranges usually from 6% to 15% and rarely as high as 20%. The average THC level in coffee shops in the Netherlands is about 18–19%.^[105]

Price

The price or street value of cannabis varies widely depending on geographic area and potency.^[106]
In the United States, cannabis is overall the number four value crop, and is number one or two in many states including California, New York and Florida, averaging $3,000/lb.^[107][108] It is believed to generate an estimated $36 billion market.^[109] The United Nations Office on Drugs and Crime claims in its 2008 World Drug Report that typical U.S. retail prices are $10–15 per gram (approximately $280–420 per ounce). Street prices in North America are known to range from about $40 to $400 per ounce, depending on quality.^[110] In Washington and Colorado, however, the two states that have legalized marijuana for recreational use, illicit dealers have suffered now that their lucrative underground market has all but disappeared, and as a result, prices have fallen sharply (they cannot compete with the genuine, professionally grown and superior quality crop, the price of which they also cannot compete with). Buyers from nearby states have further damaged the illegal market, putting several thousands of illegal dealers out of business.

The European Monitoring Centre for Drugs and Drug Addiction reports that typical retail prices in Europe for cannabis varies from €2 to €20 per gram, with a majority of European countries reporting prices in the range €4–10.^[111]

History

The Chinese character for hemp (麻 or má) depicts two plants under a shelter.^[112] Cannabis cultivation dates back at least 3000 years in Taiwan.^[113]

Cannabis is indigenous to Central and South Asia.^[114] Evidence of the inhalation of cannabis smoke can be found in the 3rd millennium BCE, as indicated by charred cannabis seeds found in a ritual brazier at an ancient burial site in present day Romania.^[115] In 2003, a leather basket filled with cannabis leaf fragments and seeds was found next to a 2,500- to 2,800-year-old mummified shaman in the northwestern Xinjiang Uygur Autonomous Region of China.^[116][117] Evidence for the consumption of cannabis has also been found in Egyptian mummies dated about 950 BC.^[118][119]
Cannabis is also known to have been used by the ancient Hindus of India and Nepal thousands of years ago. The herb was called ganjika in Sanskrit (गांजा,ganja in modern Indo-Aryan languages).^[120][121] Some scholars suggest that the ancient drug soma, mentioned in the Vedas, was cannabis, although this theory is disputed.^[122]

Cannabis was also known to the ancient Assyrians, who discovered its psychoactive properties through the Aryans.^[123] Using it in some religious ceremonies, they called it qunubu (meaning "way to produce smoke"), a probable origin of the modern word "cannabis".^[124] Cannabis was also introduced by the Aryans to the Scythians, Thracians and Dacians, whose shamans (the kapnobatai—"those who walk on smoke/clouds") burned cannabis flowers to induce a state of trance.^[125]

Cannabis sativa from Vienna Dioscurides, 512 AD

Cannabis has an ancient history of ritual use and is found in pharmacological cults around the world. Hemp seeds discovered by archaeologists at Pazyryk suggest early ceremonial practices like eating by the Scythians occurred during the 5th to 2nd century BCE, confirming previous historical reports by Herodotus.^[126] It was used by Muslims in various Sufi orders as early as the Mamluk period, for example by the Qalandars.^[127]

A study published in the South African Journal of Science showed that "pipes dug up from the garden of Shakespeare's home in Stratford-upon-Avon contain traces of cannabis."^[128] The chemical analysis was carried out after researchers hypothesized that the "noted weed" mentioned in Sonnet 76 and the "journey in my head" from Sonnet 27 could be references to cannabis and the use thereof.^[129] Examples of classic literature featuring cannabis include Les paradis artificiels by Charles Baudelaire and The Hasheesh Eater by Fitz Hugh Ludlow.

John Gregory Bourke described use of "mariguan", which he identifies as Cannabis indica or Indian hemp, by Mexican residents of the Rio Grande region of Texas in 1894. He described its uses for treatment of asthma, to expedite delivery, to keep away witches, and as a love-philtre. He also wrote that many Mexicans added the herb to their cigarritos or mescal, often taking a bite of sugar afterward to intensify the effect. Bourke wrote that because it was often used in a mixture with toloachi (which he inaccurately describes as Datura stramonium), mariguan was one of several plants known as "loco weed". Bourke compared mariguan to hasheesh, which he called "one of the greatest curses of the East", citing reports that users "become maniacs and are apt to commit all sorts of acts of violence and murder", causing degeneration of the body and an idiotic appearance, and mentioned laws against sale of hasheesh "in most Eastern countries".^{[130][131][132]}

Cannabis indica fluid extract, American Druggists Syndicate, pre-1937

Cannabis was criminalized in various countries beginning in the early 20th century. In the United States, the first restrictions for sale of cannabis came in 1906 (in District of Columbia).^[133] It was outlawed in South Africa in 1911, in Jamaica (then a British colony) in 1913, and in the United Kingdom and New Zealand in the 1920s.^[134] Canada criminalized cannabis in the Opium and Drug Act of 1923, before any reports of use of the drug in Canada. In 1925 a compromise was made at an international conference in The Hague about the International Opium Convention that banned exportation of "Indian hemp" to countries that had prohibited its use, and requiring importing countries to issue certificates approving the importation and stating that the shipment was required "exclusively for medical or scientific purposes". It also required parties to "exercise an effective control of such a nature as to prevent the illicit international traffic in Indian hemp and especially in the resin".^[135][136]

In the United States in 1937, the Marihuana Tax Act was passed, and prohibited the production of hemp in addition to cannabis. The reasons that hemp was also included in this law are disputed—several scholars have claimed that the act was passed in order to destroy the US hemp industry,^{[137][138][139]} with the primary involvement of businessmen Andrew Mellon, Randolph Hearst, and the Du Pont family.^[137][139] But the improvements of the decorticators, machines that separate the fibers from the hemp stem, could not make hemp fiber a very cheap substitute for fibers from other sources because it could not change that basic fact that strong fibers are only found in the bast, the outer part of the stem. Only about 1/3 of the stem are long and strong fibers.^{[137][140][141][142]}The company DuPont and many industrial historians dispute a link between nylon and hemp. They argue that the purpose of developing the nylon was to produce a fiber that could be used in thin stockings for females and compete with silk.^{[143][144][145]}

In New York City, more than 41,000 pounds of marijuana, which was growing like weeds throughout the boroughs until 1951, when the "White Wing Squad", headed by the Sanitation Department General Inspector John E. Gleason, was charged with destroying the many pot farms that had sprouted up across the city. The Brooklyn Public Library reports: this group was held to a high moral standard and was prohibited from "entering saloons, using foul language, and neglecting horses." The Squad found the most weed in Queens but even in Brooklyn dug up "millions of dollars" worth of the plants, many as "tall as Christmas trees". Gleason oversaw incineration of the plants in Woodside, Queens.^[146]

The United Nations' 2012 Global Drug Report stated that cannabis "was the world's most widely produced, trafficked, and consumed drug in the world in 2010", identifying that between 119 million and 224 million users existed in the world's adult (18 or older) population.^[147]

Medical marijuana

Medical marijuana refers to the use of the Cannabis plant as a physician-recommended herbal therapy as well as synthetic THC and cannabinoids. So far, the medical use of cannabis is legal only in a limited number of territories, including Canada, Belgium, Australia, the Netherlands, Spain, and several U.S. states. This usage generally requires a prescription, and distribution is usually done within a framework defined by local laws.

Legal status

Cannabis propaganda sheet from 1935

Since the beginning of the 20th century, most countries have enacted laws against the cultivation, possession or transfer of cannabis.^[148] These laws have impacted adversely on the cannabis plant's cultivation for non-recreational purposes, but there are many regions where, under certain circumstances, handling of cannabis is legal or licensed. Many jurisdictions have lessened the penalties for possession of small quantities of cannabis, so that it is punished by confiscation and sometimes a fine, rather than imprisonment, focusing more on those who traffic the drug on the black market.

In some areas where cannabis use has been historically tolerated, some new restrictions have been put in place, such as the closing of cannabis coffee shops near the borders of the Netherlands,^[149] closing of coffee shops near secondary schools in the Netherlands and crackdowns on "Pusher Street" in Christiania, Copenhagen in 2004.^[150][151]

Some jurisdictions use free voluntary treatment programs and/or mandatory treatment programs for frequent known users. Simple possession can carry long prison terms in some countries, particularly in East Asia, where the sale of cannabis may lead to a sentence of life in prison or even execution. More recently however, many political parties, non-profit organizations and causes based on the legalization of medical cannabis and/or legalizing the plant entirely (with some restrictions) have emerged.

In December 2012, the U.S. state of Washington became the first state to officially legalize cannabis in a state law (Washington Initiative 502) (but still illegal by federal law),^[152] with the state of Colorado following close behind (Colorado Amendment 64).^[153] On January 1, 2013, the first marijuana "club" for private marijuana smoking (no buying or selling, however) was allowed for the first time in Colorado.^[154] The California Supreme Court decided in May 2013 that local governments can ban medical marijuana dispensaries despite a state law in California that permits the use of cannabis for medical purposes. At least 180 cities across California have enacted bans in recent years.^[155]

In December 2013, Uruguay became the first country to legalize growing, sale and use of cannabis.^[156] However, as of August 2014, no cannabis has yet been sold legally in Uruguay. According to the law, the only cannabis that can be sold legally must be grown in the country by no more than five licensed growers, and these have yet to be selected; in fact the call for applications did not go out until August 1, 2014.^[157] In the elections of October, 2014, there is a significant chance that lawmakers opposed to legal cannabis will come to control the legislature, and the law will be repealed before it has fully taken effect.^{[158][159][160]}

Constraints on open research

Cannabis research is challenging since the plant is illegal in most countries.^{[161][162][163][164][165]} Research-grade samples of the drug are difficult to obtain for research purposes, unless granted under authority of national governments.
There are also other difficulties in researching the effects of cannabis. Many people who smoke cannabis also smoke tobacco.^[166] This causes confounding factors, where questions arise as to whether the tobacco, the cannabis, or both that have caused a cancer. Another difficulty researchers have is in recruiting people who smoke cannabis into studies. Because cannabis is an illegal drug in many countries, people may be reluctant to take part in research, and if they do agree to take part, they may not say how much cannabis they actually smoke.^[167]

However many universities in different countries outside the US have published hundreds of studies on effects of cannabis.^[168]