Monday, May 18, 2015

Differential equation

From Wikipedia, the free encyclopedia

Visualization of heat transfer in a pump casing, created by solving the heat equation. Heat is being generated internally in the casing and being cooled at the boundary, providing a steady state temperature distribution.

A differential equation is a mathematical equation that relates some function with its derivatives. In applications, the functions usually represent physical quantities, the derivatives represent their rates of change, and the equation defines a relationship between the two. Because such relations are extremely common, differential equations play a prominent role in many disciplines including engineering, physics, economics, and biology.

In pure mathematics, differential equations are studied from several different perspectives, mostly concerned with their solutions—the set of functions that satisfy the equation. Only the simplest differential equations are solvable by explicit formulas; however, some properties of solutions of a given differential equation may be determined without finding their exact form.

If a self-contained formula for the solution is not available, the solution may be numerically approximated using computers. The theory of dynamical systems puts emphasis on qualitative analysis of systems described by differential equations, while many numerical methods have been developed to determine solutions with a given degree of accuracy.

History

Differential equations first came into existence with the invention of calculus by Newton and Leibniz. In Chapter 2 of his 1671 work "Methodus fluxionum et Serierum Infinitarum",^[1] Isaac Newton listed three kinds of differential equations: those involving two derivatives (or fluxions)

\dot{x},\dot{y}

and only one undifferentiated quantity

x

; those involving

\dot{x},\dot{y},x

and

y

; and those involving more than two derivatives. As examples of the three cases, he solves the equations:

$\dot{y}\dot{y}=\dot{x}\dot{y}+\dot{x}\dot{x}xx$ ,

$\dot{y}ax-\dot{x}xy-aa\dot{x}=0$ , and

$2\dot{x}-\dot{z}+\dot{y}x=0$ , respectively.

He solves these examples and others using infinite series and discusses the non-uniqueness of solutions.

Jacob Bernoulli solved the Bernoulli differential equation in 1695.^[2] This is an ordinary differential equation of the form

y'+ P(x)y = Q(x)y^n\,

for which he obtained exact solutions.^[3]

Historically, the problem of a vibrating string such as that of a musical instrument was studied by Jean le Rond d'Alembert, Leonhard Euler, Daniel Bernoulli, and Joseph-Louis Lagrange.^[4]^[5]^[6]^[7] In 1746, d’Alembert discovered the one-dimensional wave equation, and within ten years Euler discovered the three-dimensional wave equation.^[8]

The Euler–Lagrange equation was developed in the 1750s by Euler and Lagrange in connection with their studies of the tautochrone problem. This is the problem of determining a curve on which a weighted particle will fall to a fixed point in a fixed amount of time, independent of the starting point.

Lagrange solved this problem in 1755 and sent the solution to Euler. Both further developed Lagrange's method and applied it to mechanics, which led to the formulation of Lagrangian mechanics.

Fourier published his work on heat flow in Théorie analytique de la chaleur (The Analytic Theory of Heat),^[9] in which he based his reasoning on Newton's law of cooling, namely, that the flow of heat between two adjacent molecules is proportional to the extremely small difference of their temperatures. Contained in this book was Fourier's proposal of his heat equation for conductive diffusion of heat. This partial differential equation is now taught to every student of mathematical physics.

Example

For example, in classical mechanics, the motion of a body is described by its position and velocity as the time value varies. Newton's laws allow (given the position, velocity, acceleration and various forces acting on the body) one to express these variables dynamically as a differential equation for the unknown position of the body as a function of time.

In some cases, this differential equation (called an equation of motion) may be solved explicitly.

An example of modelling a real world problem using differential equations is the determination of the velocity of a ball falling through the air, considering only gravity and air resistance. The ball's acceleration towards the ground is the acceleration due to gravity minus the acceleration due to air resistance.

Gravity is considered constant, and air resistance may be modeled as proportional to the ball's velocity. This means that the ball's acceleration, which is a derivative of its velocity, depends on the velocity (and the velocity depends on time). Finding the velocity as a function of time involves solving a differential equation and verifying its validity.

Main topics

Ordinary differential equations

An ordinary differential equation (ODE) is an equation containing a function of one independent variable and its derivatives. The term "ordinary" is used in contrast with the term partial differential equation which may be with respect to more than one independent variable.
Linear differential equations, which have solutions that can be added and multiplied by coefficients, are well-defined and understood, and exact closed-form solutions are obtained. By contrast, ODEs that lack additive solutions are nonlinear, and solving them is far more intricate, as one can rarely represent them by elementary functions in closed form: Instead, exact and analytic solutions of ODEs are in series or integral form. Graphical and numerical methods, applied by hand or by computer, may approximate solutions of ODEs and perhaps yield useful information, often sufficing in the absence of exact, analytic solutions.

Partial differential equations

A partial differential equation (PDE) is a differential equation that contains unknown multivariable functions and their partial derivatives. (This is in contrast to ordinary differential equations, which deal with functions of a single variable and their derivatives.) PDEs are used to formulate problems involving functions of several variables, and are either solved by hand, or used to create a relevant computer model.
PDEs can be used to describe a wide variety of phenomena such as sound, heat, electrostatics, electrodynamics, fluid flow, elasticity, or quantum mechanics. These seemingly distinct physical phenomena can be formalised similarly in terms of PDEs. Just as ordinary differential equations often model one-dimensional dynamical systems, partial differential equations often model multidimensional systems. PDEs find their generalisation in stochastic partial differential equations.

Linear and non-linear

Both ordinary and partial differential equations are not broadly classified as linear and nonlinear.

A differential equation is linear if the unknown function and its derivatives appear to the power 1 (products of the unknown function and its derivatives are not allowed) and nonlinear otherwise. The characteristic property of linear equations is that their solutions form an affine subspace of an appropriate function space, which results in much more developed theory of linear differential equations. Homogeneous linear differential equations are a further subclass for which the space of solutions is a linear subspace i.e. the sum of any set of solutions or multiples of solutions is also a solution. The coefficients of the unknown function and its derivatives in a linear differential equation are allowed to be (known) functions of the independent variable or variables; if these coefficients are constants then one speaks of a constant coefficient linear differential equation.

There are very few methods of solving nonlinear differential equations exactly; those that are known typically depend on the equation having particular symmetries. Nonlinear differential equations can exhibit very complicated behavior over extended time intervals, characteristic of chaos. Even the fundamental questions of existence, uniqueness, and extendability of solutions for nonlinear differential equations, and well-posedness of initial and boundary value problems for nonlinear PDEs are hard problems and their resolution in special cases is considered to be a significant advance in the mathematical theory (cf. Navier–Stokes existence and smoothness). However, if the differential equation is a correctly formulated representation of a meaningful physical process, then one expects it to have a solution.^[10]

Linear differential equations frequently appear as approximations to nonlinear equations. These approximations are only valid under restricted conditions. For example, the harmonic oscillator equation is an approximation to the nonlinear pendulum equation that is valid for small amplitude oscillations (see below).

Examples

In the first group of examples, let u be an unknown function of x, and c and ω are known constants.

Inhomogeneous first-order linear constant coefficient ordinary differential equation:

\frac{du}{dx} = cu+x^2.

Homogeneous second-order linear ordinary differential equation:

\frac{d^2u}{dx^2} - x\frac{du}{dx} + u = 0.

Homogeneous second-order linear constant coefficient ordinary differential equation describing the harmonic oscillator:

\frac{d^2u}{dx^2} + \omega^2u = 0.

Inhomogeneous first-order nonlinear ordinary differential equation:

\frac{du}{dx} = u^2 + 4.

Second-order nonlinear (due to sine function) ordinary differential equation describing the motion of a pendulum of length L:

L\frac{d^2u}{dx^2} + g\sin u = 0.

In the next group of examples, the unknown function u depends on two variables x and t or x and y.

Homogeneous first-order linear partial differential equation:

\frac{\partial u}{\partial t} + t\frac{\partial u}{\partial x} = 0.

Homogeneous second-order linear constant coefficient partial differential equation of elliptic type, the Laplace equation:

\frac{\partial^2 u}{\partial x^2} + \frac{\partial^2 u}{\partial y^2} = 0.

Third-order nonlinear partial differential equation, the Korteweg–de Vries equation:

\frac{\partial u}{\partial t} = 6u\frac{\partial u}{\partial x} - \frac{\partial^3 u}{\partial x^3}.

Existence of solutions

Solving differential equations is not like solving algebraic equations. Not only are their solutions oftentimes unclear, but whether solutions are unique or exist at all are also notable subjects of interest.
For first order initial value problems, it is easy to tell whether a unique solution exists. Given any point

(a,b)

in the xy-plane, define some rectangular region

Z

, such that

Z = [l,m]\times[n,p]

and

(a,b)

is in

Z

. If we are given a differential equation

\frac{\mathrm{d}x}{\mathrm{d}t} = g(x,t)

and an initial condition

x(t_{0}) = x_{0}

, then there is a unique solution to this initial value problem if

g(x,t)

and

\frac{\partial g}{\partial x}

are both continuous on

Z

. This unique solution exists on some interval with its center at

a

.

However, this only helps us with first order initial value problems. Suppose we had a linear initial value problem of the nth order:

f_{n}(x)\frac{\mathrm{d}^n y}{\mathrm{d}x^n} + \cdots + f_{1}(x)\frac{\mathrm{d} y}{\mathrm{d}x} + f_{0}(x)y = h(x)

such that

y(x_{0})=y_{0}, y'(x_{0}) = y'_{0}, y''(x_{0}) = y''_{0}, \cdots

For any nonzero

f_{n}(x)

, if

\{f_{0},f_{1},\cdots\}

and

g

are continuous on some interval containing

x_{0}

y

is unique and exists.
^[11]

Related concepts

A delay differential equation (DDE) is an equation for a function of a single variable, usually called time, in which the derivative of the function at a certain time is given in terms of the values of the function at earlier times.

A stochastic differential equation (SDE) is an equation in which the unknown quantity is a stochastic process and the equation involves some known stochastic processes, for example, the Wiener process in the case of diffusion equations.

A differential algebraic equation (DAE) is a differential equation comprising differential and algebraic terms, given in implicit form.

Connection to difference equations

The theory of differential equations is closely related to the theory of difference equations, in which the coordinates assume only discrete values, and the relationship involves values of the unknown function or functions and values at nearby coordinates. Many methods to compute numerical solutions of differential equations or study the properties of differential equations involve approximation of the solution of a differential equation by the solution of a corresponding difference equation.

Applications and connections to other areas

In general

The study of differential equations is a wide field in pure and applied mathematics, physics, and engineering. All of these disciplines are concerned with the properties of differential equations of various types. Pure mathematics focuses on the existence and uniqueness of solutions, while applied mathematics emphasizes the rigorous justification of the methods for approximating solutions. Differential equations play an important role in modelling virtually every physical, technical, or biological process, from celestial motion, to bridge design, to interactions between neurons. Differential equations such as those used to solve real-life problems may not necessarily be directly solvable, i.e. do not have closed form solutions. Instead, solutions can be approximated using numerical methods.

Many fundamental laws of physics and chemistry can be formulated as differential equations. In biology and economics, differential equations are used to model the behavior of complex systems. The mathematical theory of differential equations first developed together with the sciences where the equations had originated and where the results found application. However, diverse problems, sometimes originating in quite distinct scientific fields, may give rise to identical differential equations. Whenever this happens, mathematical theory behind the equations can be viewed as a unifying principle behind diverse phenomena. As an example, consider propagation of light and sound in the atmosphere, and of waves on the surface of a pond. All of them may be described by the same second-order partial differential equation, the wave equation, which allows us to think of light and sound as forms of waves, much like familiar waves in the water. Conduction of heat, the theory of which was developed by Joseph Fourier, is governed by another second-order partial differential equation, the heat equation. It turns out that many diffusion processes, while seemingly different, are described by the same equation; the Black–Scholes equation in finance is, for instance, related to the heat equation.

In physics

Classical mechanics

So long as the force acting on a particle is known, Newton's second law is sufficient to describe the motion of a particle. Once independent relations for each force acting on a particle are available, they can be substituted into Newton's second law to obtain an ordinary differential equation, which is called the equation of motion.

Electrodynamics

Maxwell's equations are a set of partial differential equations that, together with the Lorentz force law, form the foundation of classical electrodynamics, classical optics, and electric circuits. These fields in turn underlie modern electrical and communications technologies. Maxwell's equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents. They are named after the Scottish physicist and mathematician James Clerk Maxwell, who published an early form of those equations between 1861 and 1862.

General relativity

The Einstein field equations (EFE; also known as "Einstein's equations") are a set of ten partial differential equations in Albert Einstein's general theory of relativity which describe the fundamental interaction of gravitation as a result of spacetime being curved by matter and energy.^[12] First published by Einstein in 1915^[13] as a tensor equation, the EFE equate local spacetime curvature (expressed by the Einstein tensor) with the local energy and momentum within that spacetime (expressed by the stress–energy tensor).^[14]

Quantum mechanics

In quantum mechanics, the analogue of Newton's law is Schrödinger's equation (a partial differential equation) for a quantum system (usually atoms, molecules, and subatomic particles whether free, bound, or localized). It is not a simple algebraic equation, but in general a linear partial differential equation, describing the time-evolution of the system's wave function (also called a "state function").^[15]^:1–2

Other important equations

Euler–Lagrange equation in classical mechanics
Hamilton's equations in classical mechanics
Radioactive decay in nuclear physics
Newton's law of cooling in thermodynamics
The wave equation
The heat equation in thermodynamics
Laplace's equation, which defines harmonic functions
Poisson's equation
The geodesic equation
The Navier–Stokes equations in fluid dynamics
The Diffusion equation in stochastic processes
The Convection–diffusion equation in fluid dynamics
The Cauchy–Riemann equations in complex analysis
The Poisson–Boltzmann equation in molecular dynamics
The shallow water equations
Universal differential equation
The Lorenz equations whose solutions exhibit chaotic flow.

In biology

Predator-prey equations

The Lotka–Volterra equations, also known as the predator–prey equations, are a pair of first-order, non-linear, differential equations frequently used to describe the dynamics of biological systems in which two species interact, one as a predator and the other as prey.

Other important equations

Verhulst equation – biological population growth
von Bertalanffy model – biological individual growth
Replicator dynamics – found in theoretical biology
Hodgkin–Huxley model – neural action potentials

In chemistry

Rate equation

The rate law or rate equation for a chemical reaction is a differential equation that links the reaction rate with concentrations or pressures of reactants and constant parameters (normally rate coefficients and partial reaction orders).^[16] To determine the rate equation for a particular system one combines the reaction rate with a mass balance for the system.^[17]

In economics

Important equations

The key equation of the Solow–Swan model is: $\frac{\part k(t)}{\part t} = s [k(t)]^\alpha - \delta k(t)$
The Black–Scholes PDE
Malthusian growth model
The Vidale–Wolfe advertising model

An Estimate of The Centennial Variability of Global Temperatures

By Philip J. Lloyd

Original link: http://multi-science.atypon.com/doi/abs/10.1260/0958-305X.26.3.417

Unfortunately, you have to pay $35 to get the entire article, but the abstract alone gives important data. Basically, according to ice core temperature (Antarctic? Greenland? Both?) readings, changes of temperature up to a degree C per century are normal. The 0.8 degree C temperature increase in the 20'th century may then be largely duty to natural variation, although rising CO2 levels must be a contributor too. But beware: it's not clear from the abstract whether these temperature trends truly are global or just local; that must be in the actual report (assuming a minimum of peer review), so if you're willing the $35, please let me know

Abstract

There has been widespread investigation of the drivers of changes in global temperatures. However, there has been remarkably little consideration of the magnitude of the changes to be expected over a period of a few decades or even a century. To address this question, the Holocene records up to 8000 years before present, from several ice cores were examined. The differences in temperatures between all records which are approximately a century apart were determined, after any trends in the data had been removed. The differences were close to normally distributed. The average standard deviation of temperature was 0.98 ± 0.27 °C. This suggests that while some portion of the temperature change observed in the 20th century was probably caused by greenhouse gases, there is a strong likelihood that the major portion was due to natural variations.

Sunday, May 17, 2015

Warming Defied…Data, Studies Show NO WARMING In Antarctica…Southern Ocean Cooling Down

By Dr. Sebastian Lüning and Prof. Fritz Vahrenholt
[Translated by P Gosselin]

Original link: http://notrickszone.com/2015/05/13/warming-defied-data-studies-show-no-warming-in-antarctica-southern-ocean-cooling-down/#sthash.zmCrIax1.aOpsuotj.dpbs

In Antarctica if a single piece of ice breaks off, the media worldwide go into a frenzy: How could it happen? That’s got to be climate change. Yes, global warming is striking Antarctica with full force and is rearing its ugly head.
Every iceberg that breaks off at the edge of the ice sheet is a sign of climate catastrophe. Amen.

But also during pre-industrial times chunks of ice broke off regularly. This is how ice sheets work: Snow builds up on the continent and then gradually moves towards the coast. What’s new?

So just how much has Antarctica warmed over the last years and decades? One reads or hears very little about this in the media. Therefore we’d like to take this knowledge deficit as an occasion to look more carefully at the temperature history of the great white continent.

Paul Homewood once posted on the temperature development of the past 35 years, using the satellite measurements:

There’s been no detectable warming. It was cold earlier and it is cold today! No Trend.
Perhaps the thermometer at the Amundsen Scott Base at the South Pole has found warming? Based on GISS data, Paul Homewood generated the following curve:

Also in the region of the South Pole station there has been no detectable warming, and that over the past 50 years.
In the next step we leave the mainland and examine the ocean to see if it may have warmed around Antarctica. Bob Tisdale put together the temperature curve based on the KNMI Climate Explorer data:

Again we find no warming here as well. To the contrary the Southern Ocean has even cooled over the past 35 years.
In June 2014 Marshall et al. confirmed the cooling trend in a Paper in the Philosphical Transactions A. The abstract states:

In recent decades, the Arctic has been warming and sea ice disappearing. By contrast, the Southern Ocean around Antarctica has been (mainly) cooling and sea-ice extent growing.

In the paper’s main section the authors add:

Over the last few decades, the two polar regions of our planet have exhibited strikingly different behaviours, as is evident in observed decadal trends in surface air temperature shown in figure 1. The Arctic has warmed, much more than in the global average, primarily in winter, while Arctic sea-ice extent has decreased dramatically. By contrast, the eastern Antarctic and Antarctic plateau have cooled, primarily in summer, with warming over the Antarctic Peninsula and Patagonia . Moreover, sea-ice extent around Antarctica has modestly increased.

Appearing in the same year in the Annals of Glaciology was a paper by Ekaykin et al., where the temperature development of Central Antarctica was reconstructed over the past 350 years. The researchers found characteristic 30-50 years cycles. Interestingly it was warmer than today back in the 1940s than today. The following is the paper’s abstract:

Multiple climate shifts in the Southern Hemisphere over the past three centuries based on central Antarctic snow pits and core studies
Based on the results of geochemical and glaciological investigations in snow pits and shallow cores, regional stack series of air temperature in central Antarctica (in the southern part of Vostok Subglacial Lake) were obtained, covering the last 350 years. It is shown that this parameter varied quasi-periodically with a wavelength of 30–50 years. The correlation of the newly obtained record with the circulation indices of the Southern Hemisphere (SH) shows that the central Antarctic climate is mainly governed by the type of circulation in the SH: under conditions of zonal circulation, negative anomalies of temperature and precipitation rate are observed, whereas the sign of the anomalies is positive during meridional circulation. In the 1970s the sign of the relationship between many climatic parameters changed, which is likely related to the rearrangement of the climatic system of the SH. The data suggest that during the past 350 years such events have taken place at least five times. The stable water isotope content of the central Antarctic snow is governed by the summer temperature rather than the mean annual temperature, which is interpreted as the influence of ‘post-depositional’ effects.

And when we look even further back in the past, we find more surprises. During the last interglacial, the Eem Warm Period of 130,000 years ago, it was 3.5 to 4.0°C warmer than today. This was reported by Parennin et al. in a publication appearing in February 2015 in the Climate of the Past Discussions.

On this matter a paper by Conway et al. appearing in 1999 in Science is interesting. Back then the authors recognized that the West Antarctic ice sheet shrank foremost during the mid Holocene, i.e. some 5000 years ago.
The scientists suspect that the melting process started already during the early Holocene some 10,000 years ago and has continued on without any external influences until today:

Past and Future Grounding-Line Retreat of the West Antarctic Ice Sheet
The history of deglaciation of the West Antarctic Ice Sheet (WAIS) gives clues about its future. Southward grounding-line migration was dated past three locations in the Ross Sea Embayment. Results indicate that most recession occurred during the middle to late Holocene in the absence of substantial sea level or climate forcing. Current grounding-line retreat may reflect ongoing ice recession that has been under way since the early Holocene. If so, the WAIS could continue to retreat even in the absence of further external forcing.

Today we would like to conclude with a curious “discovery” On May 23, 2014. Spiegel Online brought us a frightening climate alarm story:

Ice melt: Irreversible chain reaction feared in Antarctica
[…] “A large piece of the ice cap in West Antarctica finds itself at a stage or irreversible retreat,” NASA scientist Eric Rignot of the University of California, Irvine. In the previous calculations by the IPCC concerning sea level rise the phenomenon was not adequately taken into account. In a study that was recently published in the “Geophysical Research Letters” the scientists lead by Rignot studied the retreat of all six large glaciers.”

Just awful…so, who brings us this terrible news? Does Eric Rignot really know what he’s doing? Hold on to your seat: Rignot is in fact not a climate scientist. He’s an electrical engineer…just in case someone complains later on that a non-Phd does not qualify anyone to participate in the climate discussion…

First Evidence for Primordial Ripples in Space

Image: Swinburne Astronomy Productions

By: World Science Festival Staff

Original link: http://www.worldsciencefestival.com/2014/03/first_evidence_for_primordial_ripples_in_space/

Today’s announcement from the Harvard-Smithsonian Center for Astrophysics, about the detection of “gravitational waves” emanating from the universe’s first moments, is tremendously exciting, but a little tough for the layman to grasp. We caught up with Brian Greene, in Vancouver to give a TED talk on 3/18, and asked him to break it down for us.

“The dominant scientific approach to cosmology, called the ‘inflationary theory,’ predicts that that just after the birth of the universe, space experienced a tremendous burst of expansion, causing it to swell from far smaller than the size of an atom to perhaps even farther than we can now see with our most powerful telescopes, all within a minuscule fraction of a second. Tiny variations in the original space would have been stretched out in the expansion—and much as a pulled piece of spandex reveals the pattern of its weave, these stretched “quantum jitters” would be imprinted on the residual heat from the universe’s earliest moments and would be detectable as a pattern of subtle temperature variations in the night sky. We’ve been finding and mapping these variations—a specific pattern of hot and cold spots in the cosmic microwave background radiation — with ever-greater precision since the early 1990s, a triumph of modern cosmology.

“Today, researchers at Harvard-Smithsonian Astrophysical Observatory, leading a team of researchers using a facility at the South Pole, say they’ve found, for the first time, a long-predicted second kind of fluctuation: ripples in the fabric of space itself, set down in the universe’s earliest moments. Believed also to be generated by quantum processes, these spatial vibrations are inferred from a delicate twist they impart to the cosmic background radiation.

“If the results stand, they are a landmark discovery. They provide our first look into energy scales that are perhaps a million million times larger than that of the Large Hadron Collider, and will greatly sharpen our theoretical understanding of events that happened perhaps a billionth of a billionth of a billionth of a billionth of a second after the Big Bang. The results also affirm, once again, the astounding power of mathematical analysis to lead the way into the most remote corners of creation.”

Saturday, May 16, 2015

How rivers regulate global carbon cycle

how-rivers-regulate-global-carbon-cycle.html

Plants convert carbon dioxide from the atmosphere into organic carbon via photosynthesis. Most of this carbon eventually returns to the atmosphere when plant material (or animals that eat plants) decompose. A small fraction of this material, however, ends up in rivers. They carry it out to sea, where some settles to the seafloor and is buried and disconnected from the atmosphere for millions of years and eventually makes its way back to the surface in the form of rocks. At the same time, rivers also erode carbon-containing rocks into particles carried downstream. The process exposes carbon to air, oxidizing the previously locked-up carbon into carbon dioxide that can leak back out to the atmosphere.
Credit: Illustration by Eric Taylor, Woods Hole Oceanographic Institution

Humans concerned about climate change are working to find ways of capturing excess carbon dioxide (CO2) from the atmosphere and sequestering it in the Earth. But Nature has its own methods for the removal and long-term storage of carbon, including the world's river systems, which transport decaying organic material and eroded rock from land to the ocean.

While river transport of carbon to the ocean is not on a scale that will bail humans out of our CO2 problem, we don't actually know how much carbon the world's rivers routinely flush into the ocean -- an important piece of the global carbon cycle.

But in a study published May 14 in the journal Nature, scientists from Woods Hole Oceanographic Institution (WHOI) calculated the first direct estimate of how much and in what form organic carbon is exported to the ocean by rivers. The estimate will help modelers predict how the carbon export from global rivers may shift as Earth's climate changes.

"The world's rivers act as Earth's circulatory system, flushing carbon from land to the ocean and helping reduce the amount that returns to the atmosphere in the form of heat-trapping carbon dioxide," said lead author and geochemist Valier Galy. "Some of that carbon--'new' carbon--is from decomposed plant and soil material that is washed into the river and then out to sea. But some of it comes from carbon that has long been stored in the environment in the form of rocks-- 'old' carbon--that have been eroded by weather and the force of the river."

The scientists, who included Bernhard Peucker-Ehrenbrink, and Timothy Eglinton (now at ETH Zürich), amassed data on sediments flowing out of 43 river systems all over the world, which cumulatively account for 20 percent of the total sediments discharged by rivers. The representative rivers also encompassed a broad range of climates, vegetation, geological conditions, and levels of disturbance by people.

From these river sediment flow measurements, the research team calculated amounts of particles of carbon-containing plant and rock debris that each river exported. They estimated that the world's rivers annually transport 200 megatons (200 million tons) of carbon to the ocean. The total equals about .02 percent of the total mass of carbon in the atmosphere. That may not seem like a lot, but over 1000 to 10,000 years, it continues to add up to significant amounts of carbon (20 and 200 percent) extracted from the atmosphere.

Generally, plants convert CO2 from the atmosphere into organic carbon via photosynthesis. But most of this carbon eventually returns to the atmosphere when plant material (or animals that eat plants) decompose. A small fraction of this material, however, ends up in rivers. They carry it out to sea, where some settles to the seafloor and is buried and disconnected from the atmosphere for millions of years and eventually makes its way back to the surface in the form of rocks.

At the same time, rivers also erode carbon-containing rocks into particles carried downstream. The process exposes carbon to air, oxidizing the previously locked-up carbon into carbon dioxide that can leak back out to the atmosphere. Until now, scientists had no way to distinguish how much of the carbon whisked away by rivers comes from either the biospheric or petrogenic (rock) sources. Without this information, scientists' ability to model or quantitatively predict carbon sequestration under different scenarios was limited.

To solve this dilemma, the scientists found a novel way to distinguish for the first time the sources of that carbon--either from eroded rocks or from decomposed plant and soil material. They analyzed the amounts of carbon-14, a radioactive isotope, in the river particles. Carbon-14 decays away within about 60,000 years, so it is present only in material that came from living things, and not rocks. Subtracting the portion of particles that did not contain carbon-14, the scientists calculated the percentage that was derived from the terrestrial biosphere: about 80 percent.

But even though biospheric carbon is the major source of carbon exported by rivers, the scientists also discovered that rivers surrounded by greater amounts of vegetation didn't necessarily transport more carbon to the ocean. Instead, the export was "primarily controlled by the capacity of rivers to mobilize and transport" particles. Erosion is the key factor--the more erosion occurs along the river, the more carbon it transfers to sea and sequesters from the air.

"The atmosphere is a small reservoir of carbon compared to rocks, soils, the biosphere, and the ocean," the scientists wrote in Nature. "As such, its size is sensitive to small imbalances in the exchange with and between these larger reservoirs."

The new study gives scientists a firmer handle on measuring the important, and heretofore elusive, role of global rivers in the planetary carbon cycle and enhances their ability to predict how riverine carbon export may shift as Earth's climate changes.

"This study will provide geochemical modelers with new insights on an important link between the global carbon and water cycles," says Don Rice, program director in the National Science Foundation's Division of Ocean Sciences, a major funder of the research.

Reference:
Valier Galy, Bernhard Peucker-Ehrenbrink, Timothy Eglinton. Global carbon export from the terrestrial biosphere controlled by erosion. Nature, 2015; 521 (7551): 204 DOI: 10.1038/nature14400

Note: The above story is based on materials provided by Woods Hole Oceanographic Institution.

Understanding the Problems with the Climate and with Climate Science Communication

Posted By: FQtQ Contributoron: May 16, 2015

Original link: http://www.fromquarkstoquasars.com/understanding-problems-climate-climate-science-communication/

Earth and Sun, Global Warming from Shutterstock

Research from Yale University shows that climate science literacy is unrelated to public acceptance of human-caused global warming.

Deep public divisions over climate change are unrelated to differences in how well ordinary citizens understand scientific evidence on global warming, according to a new study published by Professor Dan Kahan.

In fact, members of the public who score the highest on a climate-science literacy test are the most politically polarized on whether human activity is causing global temperatures to rise.

These were the principal findings of a Yale-led study published recently in the journal Advances in Political Psychology. In the study, a nationally representative sample of 2,000 U.S. adults completed a test measuring their knowledge of prevailing scientific consensus on the causes and consequences of climate change. They also indicated whether they believed that human activity is responsible for global temperature increases in recent decades.

Consistent with national opinion surveys generally, the study found that the American public is split on the existence of human-caused climate change.

“The study participants were deeply divided along partisan lines, with about 50% saying they do believe in human-caused climate change and 50% saying they don’t,” said Kahan, the Elizabeth K. Dollard Professor of Law and Professor of Psychology at Yale Law School and the lead researcher on the study.

Disagreement did not diminish, however, as the study subjects’ climate-literacy test scores increased. On the contrary, “those with the highest scores were even more politically polarized,” Kahan said.

The climate-science literacy test consisted of questions derived from reports issued by the U.N.’s Intergovernmental Panel on Climate Change and by the U.S. National Oceanic and Atmospheric Administration and the National Aeronautics and Space Administration.

“Generally speaking,” said Kahan, “both those who accept human-caused climate change and those who don’t displayed very poor comprehension of climate science.” For example, he said, most participants recognized that carbon dioxide increases global temperatures, yet mistakenly indicated that rising levels of atmospheric CO2 are expected to “reduce photosynthesis in plants.”

“If you know carbon dioxide is a ‘greenhouse gas’ but think it kills the things that live in greenhouses, then it’s safe to say you don’t know much about climate science,” said Kahan.

Regardless of whether participants said they accepted that human activity caused climate change, most recognized that scientists expect climate change to create serious environmental dangers, including increased coastal flooding. However, the vast majority of study participants also associated global warming with risks wholly contrary to scientific evidence, such as an increase in the incidence of skin cancer.

Study participants who scored highest on a general-science-literacy test did the best on the study’s climate-literacy test. But contrary to the researchers’ expectations, those participants were not more likely to agree on whether human activity is causing climate change, according to the study.

“Despite consistently giving the correct answers to climate-literacy questions,” Kahan noted, “the most science literate study participants were even more politically polarized.”

Previous studies, Kahan said, have found the more science-literate members of the public are more polarized. “Nevertheless, one might reasonably have supposed that those individuals must at least differ in their levels of climate-science literacy, maybe because of biased interpretations of the evidence. But apparently that’s not what’s going on,” said Kahan.

Kahan dismissed as “ridiculous” the suggestion that the study implies there is no value in climate education. “We need even more research on how to communicate climate science effectively, so people can make informed individual and collective decisions,” he said.

Nevertheless, Kahan said the results justify reassessing at least some popular common science-communication strategies. “One conclusion is that it’s misguided to fixate on what percentage of the respondents in an opinion survey say they ‘believe in’ climate change,” said Kahan. “What people say they believe about global warming is not a measure of how much they know, or even how worried they are about it; it is an expression of their cultural identities.”

According to Kahan, the study also casts doubt on the value of social-marketing campaigns that feature the message that “97% of climate scientists” accept human-caused climate change.

“Republicans and Democrats alike already understand that climate scientists have shown we face huge risks from global warming,” said Kahan. “Just telling people that over and over — something advocacy groups have been spending millions of dollars doing for over a decade — misses the point: Positions on climate change have become symbols of whose side you are on in a cultural conflict divorced from science.”

“That’s what has to change if as a society we are going to make use of all we know about the dangers we face and how to abate them,” he added.

Kahan pointed to the success of local political leaders in southeast Florida in depoliticizing discussions of climate science, an example that is discussed at length in the study.

The study was sponsored jointly by the Cultural Cognition Project at Yale Law School, the Annenberg Public Policy Center of the University of Pennsylvania, and the Skoll Global Threats Fund.

Salon pulls out all the stops in dissing New Atheists

by Sam Harris

Original link: https://whyevolutionistrue.wordpress.com/2015/05/10/salon-pulls-out-all-the-stops-in-dissing-new-atheists/

If you want to see every shopworn criticism of New Atheism rolled up into one splenetic article, then it’s this one (in Salon, of course): “New atheism’s fatal arrogance: The glaring intellectual laziness of Bill Maher & Richard Dawkins.” The writer is Sean Illing, a graduate student in political science at Louisiana State University, who professes to be an atheist. And, like Maru, this is a box I cannot help but enter. I will try to be brief, but will probably fail.

So what exactly is the intellectual laziness of Bill Maher and Richard Dawkins? It is one of Illing’s several accusations leveled at New Athiests, which I’ll summarize below:

1. New Atheists are just too stupid to realize that religion isn’t about truths, but about fictions that make people feel good, and structure their lives. Yes, Illing appears to be a nonbeliever, and sees religion as promulgating untruths, but that doesn’t matter, for those untruths give people meaning. This is a variant on the “Courtier’s Reply” trope, in which believers fault us for not tackling the Most Sophisticated Forms of Theology™ (the so-called “best arguments”). In this case, defenders of faith like Illing simply admit that religious “truth claims” are all bogus, but they don’t really care. In fact, the people who are at fault are not the believers who structure their morality and behavior around those bogus claims, but the atheists who take believers at their word, apparently thinking erroneously that believers really believe. That, says Illnig, is the fatal weakness of Maher and Dawkins (my emphasis):

But there’s something missing in their critiques, something fundamental. For all their eloquence, their arguments are often banal. Regrettably, they’ve shown little interest in understanding the religious compulsion. They talk incessantly about the untruth of religion because they assume truth is what matters most to religious people. And perhaps it does for many, but certainly not all – at least not in the conventional sense of that term. Religious convictions, in many cases, are held not because they’re true but because they’re meaningful, because they’re personally transformative. New Atheists are blind to this brand of belief.

It’s perfectly rational to reject faith as a matter of principle. Many people (myself included) find no practical advantage in believing things without evidence. But what about those who do? If a belief is held because of its effects, not its truth content, why should its falsity matter to the believer? Of course, most religious people consider their beliefs true in some sense, but that’s to be expected: the consolation derived from a belief is greater if its illusory origins are concealed. The point is that such beliefs aren’t held because they’re true as such; they’re accepted on faith because they’re meaningful.

The problem is that the New Atheists think of God only in epistemological terms. Consequently, they have nothing to say to those who affirm God for existential reasons. New Atheist writers tend to approach religion from the perspective of science: They argue that a particular religion isn’t true or that the empirical claims of religious texts are false. That’s easy to do. The more interesting question is why religions endure in spite of being empirically untrue. There are, of course, millions of fundamentalists for whom God is a literal proposition. Their claims concerning God are empirical and should be treated as such. For many [JAC: How many? Most?], though, God is an existential impulse, a transcendent idea with no referent in reality. This conception of God is untouched – and untouchable – by positivist science; asking if God is true in this sense is like asking how much the number 12 weighs – it’s nonsensical.

Now, really? How many religious people wouldn’t give a hoot if they were told that what they believed was false? Would they say, “I don’t care: I have existential reasons for believing in God.” As I wrote yesterday:

Sadly, the data show that while religion does have these other functions, it’s simply not the case that truth is irrelevant. Even theologians (the honest ones) admit that without an underpinning of beliefs about what’s really true about the universe, religion crumbles. Where would Christianity be if adherents thought that Jesus’s divinity, crucifixion, and resurrection were just a fictitious but convenient framework on which to hang their emotions? Would Mormons wear their sacred underwear if theyknew Joseph Smith was really a con man who fabricated those plates? Do the Sophisticated Critics really believe that if Muslims knew for certain that Muhammed didn’t get the Qur’an from the mouth of God, via an angel, but made it up himself, that Islam would have the sway it does? Get serious.

I challenge Illing to stand on the steps of any mosque in Pakistan or Iran and tell believers that it doesn’t matter whether what they think about Muhammad or the inerrancy of the Qur’an is irrelevant; all that matters is that the beliefs motivate their behavior. I suspect his longevity would be severely reduced. And there are 1.6 billion Muslims on this planet.

Note as well that Illing really does admit that believers must undergird their behavior with acceptance of factual propositions, for he says this:

“Of course, most religious people consider their beliefs true in some sense, but that’s to be expected: the consolation derived from a belief is greater if its illusory origins are concealed.”

I’m not sure what he means by “true in some sense”, but I suspect that the 57% of Americans who think that Jesus was born of a virgin take it as a real fact that Mary was not penetrated by a human male before baby Jesus was born. And I think the 42% of Americans who think that humans were created by God in their present form within the last 10,000 years are really thinking of actual years and an actual creator God. (By the way, if the facts here aren’t all that important, why do creationists keep trying to get this stuff taught in public schools?)

And what about this?:

The point is that such beliefs aren’t held because they’re true as such; they’re accepted on faith because they’re meaningful.

Illing has not thought this through. What is accepted on faith is the religious epistemology: statements about the existence of God and Jesus, Mohammed or Moroni, and the moral codes that stem from the scriptures. They may not look at these propositions too closely, but they believe them, and they undergird the faith of everyone except for the highly rarefied and well-fed theologians who eschew the need for truth.

But really, religion is not treated like fiction. Religious people don’t act like all of scripture is fictional, nor do they act like they don’t care whether scripture is fictional. At least some truths matter. (For Christians, the one non-negotiable is the salvific effect of Jesus’s death and resurrection.) You don’t see people basing their lives and hopes and morality and meanings on things that are palpably untrue, like the Harry Potter series or even The Brothers Karamazov. If you’re a normal person (i.e., not Karen Armstrong or David Bentley Hart), you must accept some fundamental truths about your faith if it’s to inspire you.

Hell, this is kindergarten stuff, realized even by theologians. I’ll give a few quotes, starting with the Bible itself:

But if there be no resurrection of the dead, then is Christ not risen:And if Christ be not risen, then is our preaching vain, and your faith is also vain.—Paul, 1 Cornithians 15:13-14

A religious tradition is indeed a way of life and not a set of abstract ideas. But a way of life presupposes beliefs about the nature of reality and cannot be sustained if those beliefs are no longer credible.—Ian Barbour

I cannot regard theology as merely concerned with a collection of stories which motivate an attitude toward life. It must have its anchorage in the way things actually are, and the way they happen.—John Polkinghorne

Likewise, religion in almost all of its manifestations is more than just a collection of value judgments and moral directives. Religion often makes claims about ‘the way things are.’ —Karl Giberson & Francis Collins

That’s only a small sample; I have more for Illing if he wants them. And here is what Americans actually believe to be true (percentage of all Americans accepting the propositions below). This is not a small minority of Americans—it’s MOST OF THEM:

A personal God concerned with you 68%
Absolutely certain there is a God 54%
Jesus was the son of God 68%
Jesus was born of a virgin 57%
Jesus was resurrected 65%
Miracles 72%
Heaven 68%
Hell and Satan 58%
Angels 68%
Survival of soul after death 64%

2. Without the (false) verities of religion, people’s lives will lose meaning.

For [Dostoyevsky’s] part, God was a bridge to self-transcendence, a way of linking the individual to a tradition and a community. The truth of Christ was therefore less important than the living faith made possible by belief in Christ. . .

“I’ve never seen anyone die for the ontological argument,” Camus wrote, but “I see many people die because they judge that life is not worth living. I see others getting killed for ideas or illusions that give them a reason for living.” Today is no different; people continue to kill and die in defense of beliefs that give their lives meaning and shape.

. . . The New Atheists don’t have a satisfactory alternative for such people. They argue that religion is false; that it’s divisive; that it’s unethical; that it makes a virtue of self-deception; that it does more harm than good – and maybe they’re right, but if they don’t understand that, for many, meaning is more important than truth, they’ll never appreciate the vitality of religion. To his credit, Sam Harris’ most recent book, “Waking Up,” grapples with these issues in truly fascinating ways. Indeed, Harris writes insightfully about the necessity of love, meaning and self-transcendence. But he’s a fringe voice in the New Atheist community. Most are too busy disproving religion to consider why it is so persistent, and why something beyond science will have to take its place in a Godless world.

What we see here is the incredibly arrogant and condescending Little People Argument: while rationalists like Illing can easily reject religion’s truths and get along fine without them—he says, “It’s perfectly rational to reject faith as a matter of principle. Many people [myself included] find no practical advantage in believing things without evidence”—the Little People can’t. They need their faith! I guess the Little People who populate much of Northern Europe don’t count.

Let us make one thing clear: it is a benefit to humanity to rid it of false beliefs, even if you have nothing to put in their place. Many people in the South structured their lives around the implicit assumption that whites were far superior to blacks, and that a decent society demanded the subjugation of blacks. Did the civil rights movement offer something to replace the need of Southern whites to feel superior? Nope; the movement simply rid society of a false and invidious notion that people were inherently unequal and thus should be treated unequally.

Likewise, New Atheists rid society of the belief that it’s being monitored and tended by a celestial dictator. That alone is a good, for it’s better to see the truth. I don’t see it as an inherent responsibility of atheists to replace religion with something else that gives people meaning, for I think that most people (as they have in atheistic Europe) will find such meaning for themselves, and that it will differ from person to person. I bet if you asked most Swedes how they can possibly find meaning in their lives without religion, they’d just look like you were crazy.

Which brings us to the last point:

3. New Atheists should be faulted for attacking religion without at the same time suggesting replacements for religion.

The New Atheists have an important role to play. Reason needs its champions, too. And religion has to be resisted because there are genuine societal costs. One can draw a straight line between religious dogma and scientific obscurantism or moral stagnation, for example. That’s a real problem. But if religion is ineradicable, we have to find a way to limit its destructive consequences. Satire and criticism are necessary, but they’re not sufficient.

People like Harris and the late Christopher Hitchens make a powerful case for a more humanistic ethics. Harris writes admirably about the need to be more attentive to the present, to the suffering of other human beings. I agree. But if we want to encourage people to care about the right things, we should spend as much time encouraging them to care about the right things as we do criticizing their faith.

Here we see more arrogance—not from the New Atheists but from Illing. Who is he to tell us how to spend our time? In fact, some of us criticize religion, while others, like Phil Kitcher, Chris Stedman and Alain de Botton—spend their time finding the substitutes for religion. Isn’t that just as good as all of us spending our time doing both?

After all, we have the principle of comparative advantage at work: let each of us do what he or she is good at. I am not good at suggesting religion substitutes because I don’t believe that we need formal substitutes, and the evidence from modern Europe supports me. Nor do we have good studies to show a). what will count as a religion substitute for people, and b). whether people really need those things to have a meaningful life. Since I think that religion is on balance a harmful superstition, standing in the way of rational discourse, and as a scientist who’s read theology I can do something about that, that’s what I do. I’m not keen on finding religion substitutes, and neither Illing nor I (nor anyone, I think) is well qualified to tell people what can replace church. As water finds its own level, so will people find their own meaning.

In the end, it’s not the New Atheists who are arrogant. How could we be, if we’re wedded to rationality, doubt, and the use of evidence? Who asks themselves more often questions like, “Could I be wrong?”, or “How would I know if I were wrong?” Hint: it’s not the believers.

No, it’s Illing who’s the arrogant one, for he presumes that he, who sits proudly at the Big People’s Table and can dispense with the need for religion, must preach to all of us that those Little People at the Children’s Table must have their ~~pabulum~~ faith—or a substitute for it. It is he who doubts the ability of people to live without convenient fictions. I have more faith in humanity than that, and I use the word “faith” as a metaphor.

Sam Harris: ‘Morally confused’ liberals thought I lost debate with Noam Chomsky — but they don’t get it

Travis Gettys

15 May 2015 at 12:34 ET

Neuroscientist Sam Harris speaking at TED2010 (Steve Jurvetson/Flickr)

Sam Harris offered what amounts to a 10-minute author rebuttal to a negative book review in a podcast on his disastrous debate with Noam Chomsky.

The pair recently engaged in an email exchange on the ethical importance of intentions – and while Harris agrees it was a disaster, he’s not sure it was actually a debate instead of a conversation.

“They’re superficially similar when the parties disagree, but to have one’s mind changed in a debate is to lose the debate and very likely to lose face before one’s audience,” Harris said. “Now this is an incredibly counterproductive way to frame any inquiry into what is true.”

Harris published the exchange, which he had hoped would be “a civil conversation on an important topic with a very influential thinker,” as a way to salvage something of value from what turned out to be “a truly pointless exercise.”

He said Chomsky’s supporters accused him of trying to “steal some measure of his fame” and immediately found himself out of his depth when the famed linguist “devastated (him) with the evidence of my own intellectual misconduct and my ignorance of history and my blind faith in the goodness of the U.S. government.”

The neuroscientist said he was “flabbergasted” by that response.

“Anyone who thinks I lost a debate here just doesn’t understand what I was trying to do,” he said.

Harris said he had hoped to learn what Chomsky actually believes about the ethics of intent, and he hoped his own arguments would steer leftists away from their “masochistic” tendencies.

He said Chomsky’s followers believe the U.S. was morally worse than ISIS because it had, through “selfishness and ineptitude,” created ISIS and victimized millions of people in other nations.

“This kind of masochism and misreading of both ourselves and of our enemies has become a kind of religious precept on the left,” Harris said. “I don’t think an inability to distinguish George Bush or Bill Clinton from Saddam Hussein or Hitler is philosophically or politically interesting, much less wise.”

He said most people who hold this “morally confused” view “Chomsky as their patriarch, and I suspect that’s not an accident.”

Harris complained that he encountered “contempt and false accusation and highly moralizing language” throughout his exchange with Chomsky – and he now wishes he had addressed those points immediately and directly.

“Highly moralizing accusations work for people who think they are watching a debate,” Harris said. “They convince most of the audience that where there is smoke there must be fire. For instance, when Ben Affleck called me and Bill Maher racist, that was all he had to do to convince 50 percent of the audience.”

Harris said he’s never approached debates like a “high school exercise,” where he remains committed to his point of view, because he doesn’t “want to be wrong for a moment longer than I need to be.”

“I wanted to talk to him to see if there was some way to build a bridge off of this island of masochism so that these sorts of people that I’ve been hearing from for years could cross over to something more reasonable, and it didn’t work out,” he said. “The conversation, as I said, was a total failure, but I thought it was an instructive one.”

Fact Sheet on Biological Effects of Radiation (NRC)

Background

Radiation is all around us. It is naturally present in our environment and has been since the birth of this planet.

Consequently, life has evolved in an environment which has significant levels of ionizing radiation. It comes from outer space (cosmic), the ground (terrestrial), and even from within our own bodies. It is present in the air we breathe, the food we eat, the water we drink, and in the construction materials used to build our homes. Certain foods such as bananas and brazil nuts naturally contain higher levels of radiation than other foods. Brick and stone homes have higher natural radiation levels than homes made of other building materials such as wood. Our nation's Capitol, which is largely constructed of granite, contains higher levels of natural radiation than most homes.

Levels of natural or background radiation can vary greatly from one location to the next. For example, people residing in Colorado are exposed to more natural radiation than residents of the east or west coast because Colorado has more cosmic radiation at a higher altitude and more terrestrial radiation from soils enriched in naturally occurring uranium. Furthermore, a lot of our natural exposure is due to radon, a gas from the earth's crust that is present in the air we breathe.

About half of the total annual average U.S. individual's radiation exposure comes from natural sources. The other half is mostly from diagnostic medical procedures. The average annual radiation exposure from natural sources is about 310 millirem (3.1 millisieverts or mSv). Radon and thoron gases account for two-thirds of this exposure, while cosmic, terrestrial, and internal radiation account for the remainder. No adverse health effects have been discerned from doses arising from these levels of natural radiation exposure.

Man-made sources of radiation from medical, commercial, and industrial activities contribute about another 310 mrem to our annual radiation exposure. One of the largest of these sources of exposure is computed tomography (CT) scans, which account for about 150 mrem. Other medical procedures together account for about another 150 mrem each year. In addition, some consumer products such as tobacco, fertilizer, welding rods, exit signs, luminous watch dials, and smoke detectors contribute about another 10 mrem to our annual radiation exposure.

The pie chart on the following page shows a breakdown of radiation sources that contribute to the average annual U.S. radiation dose of 620 mrem. Nearly three-fourths of this dose is split between radon/thoron gas and diagnostic medical procedures. Although there is a distinction between natural and man-made radiation, they both affect us in the same way.
Sources of Radiation Exposure

Above background levels of radiation exposure, the NRC requires that its licensees limit maximum radiation exposure to individual members of the public to 100 mrem (1mSv) per year, and limit occupational radiation exposure to adults working with radioactive material to 5,000 mrem (50 mSv) per year. NRC regulations and radiation exposure limits are contained in Title 10 of the Code of Federal Regulations, Part 20

Biological Effects of Radiation

We tend to think of biological effects of radiation in terms of their effect on living cells. For low levels of radiation exposure, the biological effects are so small they may not be detected. The body has repair mechanisms against damage induced by radiation as well as by chemical carcinogens. Consequently, biological effects of radiation on living cells may result in three outcomes: (1) injured or damaged cells repair themselves, resulting in no residual damage; (2) cells die, much like millions of body cells do every day, being replaced through normal biological processes; or (3) cells incorrectly repair themselves resulting in a biophysical change.

The associations between radiation exposure and the development of cancer are mostly based on populations exposed to relatively high levels of ionizing radiation (e.g., Japanese atomic bomb survivors, and recipients of selected diagnostic or therapeutic medical procedures). Cancers associated with high-dose exposure (greater than 50,000 mrem) include leukemia, breast, bladder, colon, liver, lung, esophagus, ovarian, multiple myeloma, and stomach cancers. Department of Health and Human Services literature also suggests a possible association between ionizing radiation exposure and prostate, nasal cavity/sinuses, pharyngeal and laryngeal, and pancreatic cancer.

The period of time between radiation exposure and the detection of cancer is known as the latent period and can be many years. Those cancers that may develop as a result of radiation exposure are indistinguishable from those that occur naturally or as a result of exposure to other carcinogens. Furthermore, National Cancer Institute literature indicates that other chemical and physical hazards and lifestyle factors (e.g., smoking, alcohol consumption, and diet) contribute significantly to many of these same diseases.

Although radiation may cause cancers at high doses and high dose rates, currently there are no data to establish unequivocally the occurrence of cancer following exposure to low doses and dose rates – below about 10,000 mrem (100 mSv).

Even so, the radiation protection community conservatively assumes that any amount of radiation may pose some risk for causing cancer and hereditary effect, and that the risk is higher for higher radiation exposures. A linear, no-threshold (LNT) dose response relationship is used to describe the relationship between radiation dose and the occurrence of cancer. This dose-response hypothesis suggests that any increase in dose, no matter how small, results in an incremental increase in risk. The LNT hypothesis is accepted by the NRC as a conservative model for determining radiation dose standards, recognizing that the model may over estimate radiation risk.

High radiation doses tend to kill cells, while low doses tend to damage or alter the genetic code (DNA) of irradiated cells. High doses can kill so many cells that tissues and organs are damaged immediately. This in turn may cause a rapid body response often called Acute Radiation Syndrome. The higher the radiation dose, the sooner the effects of radiation will appear, and the higher the probability of death. This syndrome was observed in many atomic bomb survivors in 1945 and emergency workers responding to the 1986 Chernobyl nuclear power plant accident.
Approximately 134 plant workers and firefighters battling the fire at the Chernobyl power plant received high radiation doses – 80,000 to 1,600,000 mrem (800 to 16,000 mSv) – and suffered from acute radiation sickness. Of these, 28 died within the first three months from their radiation injuries. Two more patients died during the first days as a result of combined injuries from the fire and radiation.

Because radiation affects different people in different ways, it is not possible to indicate what dose is needed to be fatal. However, it is believed that 50% of a population would die within thirty days after receiving a dose of between 350,000 to 500,000 mrem (3500 to 5000 mSv) to the whole body, over a period ranging from a few minutes to a few hours. This would vary depending on the health of the individuals before the exposure and the medical care received after the exposure. These doses expose the whole body to radiation in a very short period of time (minutes to hours). Similar exposure of only parts of the body will likely lead to more localized effects, such as skin burns.

Conversely, low doses – less than 10,000 mrem (100 mSv) – spread out over long periods of time (years) don't cause an immediate problem to any body organ. The effects of low doses of radiation, if any, would occur at the cell level, and thus changes may not be observed for many years (usually 5-20 years) after exposure.

Genetic effects and the development of cancer are the primary health concerns attributed to radiation exposure. The likelihood of cancer occurring after radiation exposure is about five times greater than a genetic effect (e.g., increased still births, congenital abnormalities, infant mortality, childhood mortality, and decreased birth weight). Genetic effects are the result of a mutation produced in the reproductive cells of an exposed individual that are passed on to their offspring. These effects may appear in the exposed person's direct offspring, or may appear several generations later, depending on whether the altered genes are dominant or recessive.

Although radiation-induced genetic effects have been observed in laboratory animals (given very high doses of radiation), no evidence of genetic effects has been observed among the children born to atomic bomb survivors from Hiroshima and Nagasaki.

NRC regulations strictly limit the amount of radiation that can be emitted by a nuclear facility, such as a nuclear power plant. A 1991 study by the National Cancer Institute, "Cancer in Populations Living Near Nuclear Facilities," concluded that there was no increased risk of death from cancer for people living in counties adjacent to U.S. nuclear facilities. At the NRC's request, the National Academy of Sciences is currently engaged in a state-of-the-art update to the earlier study. The new study will examine cancer rates in communities around operating and decommissioned nuclear power plants, as well as nuclear fuel cycle facilities.

October 2011

Page Last Reviewed/Updated Friday, December 12, 2014

Monazite sand does not cause excess cancer incidence

Original link: http://www.thehindu.com/todays-paper/tp-features/tp-sci-tech-and-agri/article671607.ece

Cancer risk: The study found that there is no excess cancer risk to people living in the area of high natural background radiation in Kerala.

Now it is official. In the January 2009 issue of the Health Physics Journal, researchers from the Regional Cancer Centre (RCC), Thiruvananthapuram, and their collaborators have shown that there is no excess cancer risk to people living in the area of high natural background radiation in Kerala from exposure to terrestrial gamma radiation.

The Journal highlighted the importance of the paper by carrying a photo of the beaches in its cover page.

Gamma radiation

The coastal belt of Karunagappally, Kerala, is known for high background radiation (HBR) from thorium-containing monazite sand.

In the coastal panchayats, the median outdoor gamma radiation levels are more than 4 mGy y{+-}{+1} and in certain locations, the levels are as high as 70mGy y {+-}{+1}.(Gy is a unit of radiation dose; mGy is one thousandth of a Gy; the annual gamma radiation level in normal locations is on an average one mGy).

During 1990-97, survey teams collected data on 359,619 subjects in 71,674 households using a standardised questionnaire which covered socio-demographic factors, lifestyle, dietary habits and tobacco and alcohol use.

Follow up study

Based on radiation level measurements, by a method perfected by scientists of the Bhabha Atomic Research Centre, they chose a radiation sub cohort consisting of 173,067 residents and analysed the cancer incidence in the sub cohort, aged 30 to 84y (N=69958 followed up for 10.5 years).

They estimated the cumulative radiation dose to each individual in the age group based on the radiation doses received indoors and outdoors and taking into account how long and where they stayed during the period.

By the end of 2005, they identified 1379 cases of cancer including 30 cases of leukaemia.

The results

Statistical analysis of the data showed no excess cancer risk from exposure to terrestrial gamma radiation.

In site-specific analysis, they did not find any cancer site or leukaemia to be significantly related to cumulative radiation dose.

“Although the statistical power of the study might not be adequate due to the low dose, our cancer incidence study, together with previously reported cancer mortality studies in the HBR area of Yangjiang, China suggests it is unlikely that estimates of risk at low doses are substantially greater than currently believed,” the researchers concluded.

It appears that the researchers were in a hurry to publish the paper. They did not use the complete data but selected four coastal panchayats (Chavara, Neendakara, Panmana and Alappad) which had HBR and two control areas (Oachira and Thevalakkara) which have relatively low natural radiation levels.

They estimated the excess risk as -0.13 Gy{+-}{+1} (95 per cent confidence limit:-0.58, 0.46). The authors pointed out that the upper limit of 95 per cent confidence limit was lower than 0.97, which other researchers got for pooled analysis for nuclear workers from 15 countries (BMJ, 2005) and slightly lower than 0.47 Gy{+-}{+1} reported in the study of atomic bomb survivors in Hiroshima and Nagasaki (Radiation Research, 2007)

Authors highlighted some unique features of their data. Unlike the nuclear workers study, RCC study included smoking habits, an important contributing factor. The estimate of atomic bomb survivors is a sex-averaged estimate for solid cancer unlike the RCC study. The currently accepted radiation risk estimate is mostly based on atomic bomb survivor study.

Regrettably, the researchers did not estimate the substantial contribution of airborne radon and thoron daughters to the individual radiation dose. This may not affect the main conclusion that there is no excess cancer in areas of high natural background radiation.

The limitations

Though the analysis limited to six panchayats cannot be faulted scientifically, they should use complete data including internal dose from all panchayats for a reanalysis to do justice to the project and to examine whether precise radiation risk estimate can be arrived at from this study

Highlighting the negative radiation risk coefficient of -0.13 Gy{+-}{+1}, proponents of those who believe in the beneficial effects of radiation (hormesis theory) may argue that low level radiation is helping to lower cancer risks!

They may not agree that lack of statistical power may be the reason for the negative result.

K.S. PARTHASARATHY
FORMER SECRETARY, AERB

ksparth@yahoo.co.uk

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