Convergent and Divergent Evolution

Condensed from Wikipedia, the free encyclopedia

Original Links:  http://en.wikipedia.org/wiki/Convergent_evolution and

                           http://en.wikipedia.org/wiki/Divergent_evolution

 

Convergent Evolution

Example: Two succulent plant genera, Euphorbia and Astrophytum, are only distantly related, but have independently converged on a similar body form.

 

Convergent evolution describes the independent evolution of similar features in species of different lineages. Convergent evolution creates analogous structures that have similar form or function, but that were not present in the last common ancestor of those groups.^[1] The cladistic term for the same phenomenon is homoplasy, from Greek for same form.^[2] The recurrent evolution of flight is a classic example of convergent evolution. Flying insects, birds, and bats have all evolved the capacity of flight independently. They have "converged" on this useful trait.

 

Functionally similar features arising through convergent evolution are termed analogous, in contrast to homologous structures or traits, which have a common origin, but not necessarily similar function.^[1]

The British anatomist Richard Owen was the first scientist to recognise the fundamental difference between analogies and homologies.^[3] Bat and pterosaur wings constitute an example of analogous structures, while the bat wing is homologous to human and other mammal forearms, sharing an ancestral state despite serving different functions. The opposite of convergent evolution is divergent evolution, whereby related species evolve different traits. On a molecular level, this can happen due to random mutation unrelated to adaptive changes; see long branch attraction.

 

Convergent evolution is similar to, but distinguishable from, the phenomena of parallel evolution. Parallel evolution occurs when two independent but similar species evolve in the same direction and thus independently acquire similar characteristics—for instance gliding frogs have evolved in parallel from multiple types of tree frog.

 

Causes

In morphology, analogous traits will often arise where different species live in similar ways and/or similar environment, and so face the same environmental factors. When occupying similar ecological niches (that is, a distinctive way of life) similar problems lead to similar solutions.^[4]

 

In biochemistry, physical and chemical constraints on mechanisms cause some active site arrangements to independently evolve multiple times in separate enzyme superfamilies (for example, see also catalytic triad).^[5]

Significance

Convergence has been associated with Darwinian evolution in the popular imagination since at least the 1940s. For example, Elbert A. Rogers argued: "If we lean toward the theories of Darwin might we not assume that man was [just as] apt to have developed in one continent as another?"^[6]

 

In his book Wonderful Life, Stephen Jay Gould argues that if the tape of life were re-wound and played back, life would have taken a very different course.^[7] Simon Conway Morris disputes this conclusion, arguing that convergence is a dominant force in evolution, and given that the same environmental and physical constraints are at work, life will inevitably evolve toward an "optimum" body plan, and at some point, evolution is bound to stumble upon intelligence, a trait presently identified with at least primates, corvids, and cetaceans.^[8]

 

Convergence is difficult to quantify, so progress on this issue may require exploitation of engineering specifications (as of wing aerodynamics) and comparably rigorous measures of "very different course" in terms of phylogenetic (molecular) distances.^{[citation needed]}

Distinctions

Convergent evolution is a topic touched by many different fields of biology, many of which use slightly different nomenclature. This section attempts to clarify some of those terms.

Diagram of cladistic definition of homoplasy, synapomorphy, autapomorphy, apomorphy and plesiomorphy.

Cladistic definition

In cladistics, a homoplasy or a homoplastic character state is a trait (genetic, morphological etc.) that is shared by two or more taxa because of convergence, parallelism or reversal.^[9] Homoplastic character states require extra steps to explain their distribution on a most parsimonious cladogram.

Homoplasy is only recognizable when other characters imply an alternative hypothesis of grouping, because in the absence of such evidence, shared features are always interpreted as similarity due to common descent.^[10] Homoplasious traits or changes (derived trait values acquired in unrelated organisms in parallel) can be compared with synapomorphy (a derived trait present in all members of a monophyletic clade), autapomorphy (derived trait present in only one member of a clade), or apomorphies, derived traits acquired in all members of a monophyletic clade following divergence where the most recent common ancestor had the ancestral trait (the ancestral trait manifesting in paraphyletic species as a plesiomorphy).

Re-evolution vs. convergent evolution

In some cases, it is difficult to tell whether a trait has been lost then re-evolved convergently, or whether a gene has simply been 'switched off' and then re-enabled later. Such a re-emerged trait is called an atavism. From a mathematical standpoint, an unused gene (selectively neutral) has a steadily decreasing probability of retaining potential functionality over time. The time scale of this process varies greatly in different phylogenies; in mammals and birds, there is a reasonable probability of remaining in the genome in a potentially functional state for around 6 million years.^[11]

Parallel vs. convergent evolution

Evolution at an amino acid position. In each case, the left-hand species changes from incorporating alanine (A) at a specific position within a protein in a hypothetical common ancestor deduced from comparison of sequences of several species, and now incorporates serine (S) in its present-day form. The right-hand species may undergo divergent, parallel, or convergent evolution at this amino acid position relative to that of the first species.

 

For a particular trait, proceeding in each of two lineages from a specified ancestor to a later descendant, parallel and convergent evolutionary trends can be strictly defined and clearly distinguished from one another.^[12] However the cutoff point for what is considered convergent and what is considered parallel evolution is assigned somewhat arbitrarily. When two species are similar in a particular character, evolution is defined as parallel if the ancestors were also similar and convergent if they were not. However, this definition is somewhat murky. All organisms share a common ancestor more or less recently, so the question of how far back to look in evolutionary time and how similar the ancestors need to be for one to consider parallel evolution to have taken place is not entirely resolved within evolutionary biology. Some scientists have argued parallel evolution and convergent evolution are more or less indistinguishable from one another.^[13] Others have argued that we should not shy away from the gray area and that there are still important distinctions between parallel and convergent evolution.^[14]

 

When the ancestral forms are unspecified or unknown, or the range of traits considered is not clearly specified, the distinction between parallel and convergent evolution becomes more subjective. For instance, the striking example of similar placental and marsupial forms is described by Richard Dawkins in The Blind Watchmaker as a case of convergent evolution,^[15] because mammals on each continent had a long evolutionary history prior to the extinction of the dinosaurs under which to accumulate relevant differences. Stephen Jay Gould describes many of the same examples as parallel evolution starting from the common ancestor of all marsupials and placentals. Many evolved similarities can be described in concept as parallel evolution from a remote ancestor, with the exception of those where quite different structures are co-opted to a similar function. For example, consider Mixotricha paradoxa, a microbe that has assembled a system of rows of apparent cilia and basal bodies closely resembling that of ciliates but that are actually smaller symbiont micro-organisms, or the differently oriented tails of fish and whales. On the converse, any case in which lineages do not evolve together at the same time in the same ecospace might be described as convergent evolution at some point in time.

 

The definition of a trait is crucial in deciding whether a change is seen as divergent, or as parallel or convergent. In the image above, note that, since serine and threonine possess similar structures with an alcohol side-chain, the example marked "divergent" would be termed "parallel" if the amino acids were grouped by similarity instead of being considered individually. As another example, if genes in two species independently become restricted to the same region of the animals through regulation by a certain transcription factor, this may be described as a case of parallel evolution — but examination of the actual DNA sequence will probably show only divergent changes in individual base-pair positions, since a new transcription factor binding site can be added in a wide range of places within the gene with similar effect.

 

A similar situation occurs considering the homology of morphological structures. For example, many insects possess two pairs of flying wings. In beetles, the first pair of wings is hardened into wing covers with little role in flight, while in flies the second pair of wings is condensed into small halteres used for balance. If the two pairs of wings are considered as interchangeable, homologous structures, this may be described as a parallel reduction in the number of wings, but otherwise the two changes are each divergent changes in one pair of wings.

 

Similar to convergent evolution, evolutionary relay describes how independent species acquire similar characteristics through their evolution in similar ecosystems, but not at the same time (dorsal fins of sharks and ichthyosaurs).

________________________________________

Divergent Evolution

Darwin's finches are a clear and famous example of divergent evolution, in which an ancestral species radiates into a number of descendant species with both similar and different traits.

Divergent evolution is the accumulation of differences between groups which can lead to the formation of new species, usually a result of diffusion of the same species to different and isolated environments which blocks the gene flow among the distinct populations allowing differentiated fixation of characteristics through genetic drift and natural selection. Primarily diffusion is the basis of molecular division can be seen in some higher-level characters of structure and function that are readily observable in organisms. For example, the vertebrate limb is one example of divergent evolution. The limb in many different species has a common origin, but has diverged somewhat in overall structure and function.^{[citation needed]}

Alternatively, "divergent evolution" can be applied to molecular biology characteristics. This could apply to a pathway in two or more organisms or cell types, for example. This can apply to genes and proteins, such as nucleotide sequences or protein sequences that derive from two or more homologous genes. Both orthologous genes (resulting from a speciation event) and paralogous genes (resulting from gene duplication within a population) can be said to display divergent evolution. Because of the latter, it is possible for divergent evolution to occur between two genes within a species.

In the case of divergent evolution, similarity is due to the common origin, such as divergence from a common ancestral structure or function has not yet completely obscured the underlying similarity. In contrast, convergent evolution arises when there are some sort of ecological or physical drivers toward a similar solution, even though the structure or function has arisen independently, such as different characters converging on a common, similar solution from different points of origin. This includes analogous structures.

Usage

J. T. Gulick founded the usage of this term^[1] and other related terms, which can vary slightly from one researcher to the next. Furthermore, the actual relationships might be more complex than the simple definitions of these terms allow. "Divergent evolution" is most commonly meant when someone invokes evolutionary relationships and "convergent evolution" is applied when similarity is created by evolution independently creating similar structures and functions. The term parallel evolution is also sometimes used to describe the appearance of a similar structure in closely related species, whereas convergent evolution is used primarily to refer to similar structures in much more distantly related clades. For example, some might call the modification of the vertebrate limb to become a wing in bats and birds to be an example of parallel evolution. Vertebrate forelimbs have a common origin and thus, in general, show divergent evolution. However, the modification to the specific structure and function of a wing evolved independently and in parallel within several different vertebrate clades. Also, it has much to do with humans and the way they function from day to day.

In complex structures, there may be other cases where some aspects of the structures are due to divergence and some aspects that might be due to convergence or parallelism. In the case of the eye, it was initially thought that different clades had different origins of the eye, but this is no longer thought by some researchers. It is possible that induction of the light-sensing eye during development might be diverging from a common ancestor across many clades, but the details of how the eye is constructed—and in particular the structures that focus light in cephalopods and vertebrates, for example—might have some convergent or parallel aspects to it, as well.^[2]

A good example of a divergent evolution is Darwin's finches, which now have over 80 varieties which all diverged from one original species of finch. (John Barnes)Another example of divergent evolution are the organisms having the 5 digit pentadactyle limbs like the humans, bats, and whales.
They have evolved from a common ancestor but, today they are different due to environmental pressures

Divergent species

Comparison of allopatric, peripatric, parapatric and sympatric speciation.

Divergent species are a consequence of divergent evolution. The divergence of one species into two or more descendant species can occur in four major ways:^[3]

• Allopatric speciation occurs when a population becomes separated into two entirely isolated subpopulations. Once the separation occurs, natural selection and genetic drift operate on each subpopulation independently, producing different evolutionary outcomes.
• Peripatric speciation is somewhat similar to allopatric speciation, but specifically occurs when a very small subpopulation becomes isolated from a much larger majority. Because the isolated subpopulation is so small, divergence can happen relatively rapidly due to the founder effect, in which small populations are more sensitive to genetic drift and natural selection acts on a small gene pool.
• Parapatric speciation occurs when a small subpopulation remains within the habitat of an original population but enters a different niche. Effects other than physical separation prevent interbreeding between the two separated populations. Because one of the genetically isolated populations is so small, however, the founder effect can still play a role in speciation.
• Sympatric speciation, the rarest and most controversial form of speciation, occurs with no form of isolation (physical or otherwise) between two populations.

Species can diverge when a part of the species is separated from the main population by a reproductive barrier. In the cases of allopatric and peripatric speciation, the reproductive barrier is the result of a physical barrier (e.g. flood waters, mountain range, deserts). Once separated, the species begins to adapt to their new environment via genetic drift and natural selection. After many generations and continual evolution of the separated species, the population eventually becomes two separate species to such an extent where they are no longer able to interbreed with one another. One particular cause of divergent species is adaptive radiation.

An example of divergent species is the apple maggot fly. The apple maggot fly once infested the fruit of a native Australian hawthorn. In the 1860s some maggot flies began to infest apples. They multiplied rapidly because they were able to make use of an abundant food supply. Now there are two distinct species, one that reproduces when the apples are ripe, and another that continues to infest the native hawthorn. Furthermore, they have not only evolved different reproductive timing, but also now have distinctive physical characteristics.

Corporate Profits Grow and Wages Slide

APRIL 4, 2014

From Link:  http://www.nytimes.com/2014/04/05/business/economy/corporate-profits-grow-ever-larger-as-slice-of-economy-as-wages-slide.html?_r=1

 

CORPORATE profits are at their highest level in at least 85 years. Employee compensation is at the lowest level in 65 years.

 

The Commerce Department last week estimated that corporations earned $2.1 trillion during 2013, and paid $419 billion in corporate taxes. The after-tax profit of $1.7 trillion amounted to 10 percent of gross domestic product during the year, the first full year it has been that high. In 2012, it was 9.7 percent, itself a record.

 

Until 2010, the highest level of after-tax profits ever recorded was 9.1 percent, in 1929, the first year that the government began calculating the number.

Before taxes, corporate profits accounted for 12.5 percent of the total economy, tying the previous record that was set in 1942, when World War II pushed up profits for many companies. But in 1942, most of those profits were taxed away. The effective corporate tax rate was nearly 55 percent, in sharp contrast to last year’s figure of under 20 percent.

 

The trend of higher profits and lower effective taxes has been gaining strength for years, but really picked up after the Great Recession temporarily depressed profits in 2009. The effective rate has been below 20 percent in three of the last five years. Before 2009, the rate had not been that low since 1931.

 

The statutory top corporate tax rate in the United States is 35 percent, and corporations have been vigorously lobbying to reduce that, saying it puts them at a competitive disadvantage against companies based in other countries, where rates are lower. But there are myriad tax credits, deductions and preferences available, particularly to multinational companies, and the result is that effective tax rates have fallen for many companies.

 

The Commerce Department also said total wages and salaries last year amounted to $7.1 trillion, or 42.5 percent of the entire economy. That was down from 42.6 percent in 2012 and was lower than in any year previously measured.

 

Including the cost of employer-paid benefits, like health insurance and pensions, as well as the employer’s share of Social Security and Medicare contributions, the total cost of compensation was $8.9 trillion, or 52.7 percent of G.D.P., down from 53 percent in 2012 and the lowest level since 1948.

Profits High, Wages Low

After-tax corporate profits in 2013 rose to a record of 10 percent of gross domestic product, while total compensation of employees slipped to a 65-year low. Corporate tax rates — under 20 percent of pretax corporate income in three of the last five years — have not been that low since Herbert Hoover was president. During the Obama administration, profits have taken a higher share of national income than during any administration since 1929.

After-tax corporate profits

Employee compensation

As a percentage of G.D.P.

Effective corporate tax rate*

 

As a percentage of G.D.P.

RECESSION YEARS

10

%

60

%

60

%

50

58

8

40

56

6

30

54

4

20

52

2

10

50

0

48

0

’30

’50

’70

’90

’13

’30

’50

’70

’90

’13

’30

’50

’70

’90

’13

By presidential term

AFTER-TAX

CORPORATE PROFITS

EFFECTIVE

CORPORATE

TAX RATE

 

EMPLOYEE

COMPENSATION

 

CHANGE IN S.&P. 500

Highest in each

category is highlighted

AS A PCT. OF G.D.P.

AS A PCT. OF G.D.P.

TOTAL CHANGE

ANNUALIZED

Obama

G.W. Bush

Clinton

G.H.W. Bush

Reagan

Carter

Ford

Nixon

Johnson

Kennedy

Eisenhower

Truman

F.D. Roosevelt

Hoover

9.3

7.2

6.0

4.8

5.2

5.8

5.5

5.4

7.2

6.1

5.8

5.6

5.1

5.4

%

20.5

26.0

31.0

32.9

31.7

36.7

37.3

39.0

36.1

41.1

44.1

47.3

44.2

14.7

%

53.2

55.0

55.5

55.9

55.6

56.3

56.1

57.4

55.5

55.2

55.1

53.6

52.9

51.0

%

+

–

+

+

+

+

+

–

+

+

+

+

+

–

133

40

210

51

118

28

27

20

46

16

129

86

141

77

%

+

–

+

+

+

+

+

–

+

+

+

+

+

–

17.7

6.2

15.2

10.9

10.2

6.3

10.4

4.0

7.6

5.4

10.9

8.3

7.5

30.8

%

Sources: Bureau of Economic Analysis, via Haver Analytics; Standard & Poor’s, via Bloomberg; National Bureau of Economic Research.

In profit and compensation calculations, presidents are given credit for years in which they served for the majority of the year. Stock market gains reflect Standard & Poor’s 500 price changes from inauguration to end of term. For President Obama, they are through March 31. Recession shading indicates the economy was in recession during all or part of the year shown. *No figure is given for 1932 and 1933, which were years of corporate losses.

Benefits were a steadily rising cost for employers for many decades, but that trend seems to have ended. In 2013, the figure was 10.2 percent, the lowest since 2000.

 

One way to look at the current situation is to compare 2013 with 2006, the last full year before the recession began. Adjusted for inflation, corporate profits were 28 percent higher, before taxes, last year. But taxes were down by 21 percent,so after-tax profits were up by 36 percent. At the same time, total employee compensation was up by 5 percent, or less than the 7 percent increase in the working-age population over the same period.

 

Several reasons that have been offered as explanations for the declining share of national income going to workers, including the effects of globalization that have shifted some jobs to lower-paid overseas workers and the declining bargaining power of unions.

 

The accompanying charts compare President Obama’s administration with each of his predecessors, going back to Herbert Hoover. After-tax corporate profits in President Obama’s five years in office have averaged 9.3 percent of G.D.P. That is a full two percentage points higher than the 7.2 percent averages under Lyndon B. Johnson and George W. Bush, previously the presidents with the highest ratios of corporate profits.

 

The stock market has reflected that strong performance. Through the end of March, the Standard & Poor’s 500-stock index was up 133 percent since Mr. Obama’s inauguration in 2009. Of the 13 presidents since 1929, only Bill Clinton and Franklin D. Roosevelt saw a larger total increase. On an annualized basis, the Obama administration gains come to 17.7 percent a year, higher than any of the previous presidents. The figures reflect price changes, and are not adjusted for dividends or inflation.

The Incredible Shrinking Dinosaurs

 

Saturday, August 2, 2014 18:22

Original Link:  http://beforeitsnews.com/alternative/2014/08/the-incredible-shrinking-dinosaurs-video-3005106.html

 

For decades, paleontologists have been uncovering the remarkable evolutionary relationships between fearsome, two-legged, meat-eating dinosaurs and birds.

A new study suggests that the pace of the transition from one to the other was quick by dinosaur standards. In the 50 million years preceding the appearance of the first birds some 163 million years ago, the size and weight of theropods along the direct line of descent to birds shrank one group after another – slowly at first, but going into free fall during the final 10 to 15 million years once Maniraptors took the evolutionary baton from their direct ancestors, the Coelurosaurs.

The skeletal changes taking place during the 50-million-year dinosaur-to-bird transition were occurring four times faster than for dinosaurs as a whole, according to the analysis, conducted by an international team of researchers led by Michael Lee, with the South Australia Museum in Adelaide.

Rapid rates of change in body size have appeared before in the fossil record. Following a mass extinction at the end of the Cretaceous period some 65 million years ago, an event that drove non-avian dinosaurs extinct, the size and diversity of mammals exploded over a 15-million-year period, researchers say. This came as mammals began to fill ecological niches vacated by the late, great dinosaurs.

The interplay between evolution and ecological niches was likely at work for the ancestors to birds as well – in this case, the Great Escape.

Some researchers surmise that the changes in body size and skeletal structures that led to the first birds, particularly during the phase of accelerated change, could have occurred as the now-smaller theropods moved into trees to escape becoming another animal’s meal or to take advantage of new sources of food.

The continuing reduction in size needed to succeed as tree dwellers would have triggered a cascade of evolutionary changes, suggests University of Bristol paleontologist Mike Benton. These changes would have improved vision, improved the aerodynamics of forelimbs to allow for increasingly ambitious leaps from tree to tree, or encouraged the evolution of feathers to insulate the new tree dwellers.

“Being smaller and lighter in the land of giants, with rapidly evolving anatomical adaptations, provided these bird ancestors with new ecological opportunities,” Dr. Lee said in a prepared statement.

Past studies of animal sizes in the run-up to birds had looked at individual branches of the avian ancestral tree or used trees that used physical traits to establish relationships, but no dates.

Lee and colleagues were able to take advantage of the explosion of small feathered theropod fossils coming out of China since the mid-1990s, known collectively as Paraves. These animals were trying to exploit various ways of getting from tree to tree – jumping, gliding, or parachuting, notes Dr. Benton in an article in the current issue of the journal Science. The article accompanies the analysis Lee and his colleagues performed.

The researchers gathered data on 1,549 skeletal traits from 120 species of theropods, including the length of the thigh bones and the ages of the specimens. The team used the femur as a marker of body mass. They then applied sophisticated statistical techniques to reconstruct the relationships among the species, their chronology, and track their evolutionary changes.

Some 200 million years ago, direct ancestors of the first birds tipped the scales at about 360 pounds. By about 175 million years ago, the typical weight of a new generation of direct ancestor had fallen to 100 pounds. Over the next 10 million to 15 million years, body weights would plummet, winding up at about a pound for the first birds.

The study is significant on two levels, suggests Daniel Field, a PhD candidate in paleontology at Yale University and a predoctoral fellow at the university’s Peabody Museum of Natural History.

Researchers have a good idea of what the pattern of evolutionary relationships are along that lineage, he says, “but we don’t have quite as good an idea of how those evolutionary transitions actually played out,” he says. The analysis Lee and his colleagues have performed help fill in that information.

But the study has broader implications, Mr. Field adds. The team amassed a remarkable set of data that will be valuable in its own right and raises additional, intriguing questions.

For instance, the Great Jurassic Shrink Off was apparent at each of 12 or more points along the main line of evolution between theropods and birds. Those points represent branches in the family tree where other theropods went off in their own evolutionary directions – directions in which body size either remained stable or often increase significantly, in one case giving the world Tyrannosaurus rex. It’s a pattern that repeats along each branch. Explaining that repetition even as the avian lineage was yielding ever smaller animals over the same time span is a fresh mystery the data present, according to Field.

Click to zoom

Source: http://www.ascensionearth2012.org/2014/08/the-incredible-shrinking-dinosaurs-video.html

A Yellowstone Super Eruption: Another Doomsday Scenario put to Rest

August 2, 2014 Science
From Link:  http://www.fromquarkstoquasars.com/a-yellowstone-super-eruption-another-doomsday-scenario-put-to-rest/      

Image Credit: Nina B via Shutterstock

If you’ve heard of Yellowstone National Park then, chances are, you’ve heard doomsday scenarios about Yellowstone National park. The 2005 movie “Supervolcano” highlights how these scenarios generally play out: Yellowstone erupts; people are drowned beneath mountains of lava; a looming cloud of sulfur dioxide gets carried over the globe; the Earth plunges into a volcanic winter; we all die.

Fun times…

In truth, Yellowstone is quite massive…and so is its underground magma reservoir. At 3,472 square miles (8,987 square km), the park is larger than Rhode Island and Delaware combined. And as we all know, a portion of the park sits on top of a giant volcanic caldera (an earthen cap that covers a huge reservoir of superhot liquid rock and gasses). The underground magma chamber is about 37 miles long (60 km), 18 miles wide (30 km), and 3 to 7 miles deep (5 to 12 km). That may sound rather terrifying; however, fortunately for us, all that magma is tucked safely beneath the surface of the Earth.

Image Source

But what if it wasn’t? What if Yellowstone erupted? Would the Earth be plunged into a volcanic winter, as some sources indicate?

Geologist Jake Lowenstern (scientist-in-charge of the Yellowstone Volcano Observatory) has the answers that we seek. According Lowenstern, although the Yellowstone magma source is enormous, walls of lava won’t come pouring across the continent if there’s a super eruption. Instead, the lava flows would be limited to a 30-40 mile radius. Of course, this is still widespread enough to cause significant devastation. There would be no hope for any life forms living within this radius, and the surrounding areas would be engulfed in flames—forest fires would likely rage out of control…but a majority of the immediate damage would be contained within the surrounding area.

A bit dramatic, but you get the idea.
Photograph by Carlos Gutierrez/UPI/Landov via National Geographic

Most of the long-range damage would come from “cold ash” and pumice borne on the wind. 4 or more inches (10cm) would cover the ground in a radius of about 500 miles. This would prevent photosynthesis and destroy much of the plant life in the region. Lighter dustings would traverse the United States– polluting farms in the Midwest, covering cars in New York, and contaminating the Mississippi River. It would clog waterways and agricultural areas with toxic sludge. Thus, the worst outcome of this event would be the destruction of our food supplies and waterways.

It’s likely that we’d see a global effect on temperatures from all the extra particles in the Earth’s atmosphere. However, these effects would only last a few years as Yellowstone isn’t nearly big enough to cause the long-term catastrophes that we see play out in doomsday scenarios (so no need to worry about a new ice age).

Moreover, contrary to what Hollywood would have you believe, the eruption won’t come without warning.

A super eruption, like all volcanic eruptions, begins with an earthquake. And if Yellowstone were to have a super eruption, we’d have some big ones. These earthquakes would begin weeks or months before the final eruption. So this eruption wouldn’t come out of nowhere. In fact, most scientists agree that such an eruption won’t come at all as the caldera has gone through many regular eruptions that release pressure.

So it seems that you can add “A Yellowstone Super Eruption” to your list of ways that the world will not end (Yay!).

Deep Oceans Are Cooling Amidst A Sea of Modeling Uncertainty: New Research on Ocean Heat Content

Deep Oceans Are Cooling Amidst A Sea of Modeling Uncertainty: New Research on Ocean Heat Content

Posted on July 21, 2014 by Guest Blogger 

Original Link:  http://wattsupwiththat.com/2014/07/21/deep-oceans-are-cooling-amidst-a-sea-of-modeling-uncertainty-new-research-on-ocean-heat-content/          

Guest essay by Jim Steele, Director emeritus Sierra Nevada Field Campus, San Francisco State University and author of Landscapes & Cycles: An Environmentalist’s Journey to Climate Skepticism

Two of the world’s premiere ocean scientists from Harvard and MIT have addressed the data limitations that currently prevent the oceanographic community from resolving the differences among various estimates of changing ocean heat content (in print but available here)^.3 They point out where future data is most needed so these ambiguities do not persist into the next several decades of change.
As a by-product of that analysis they 1) determined the deepest oceans are cooling, 2) estimated a much slower rate of ocean warming, 3) highlighted where the greatest uncertainties existed due to the ever changing locations of heating and cooling, and 4) specified concerns with previous methods used to construct changes in ocean heat content, such as Balmaseda and Trenberth’s re-analysis (see below).¹³ They concluded, “Direct determination of changes in oceanic heat content over the last 20 years are not in conflict with estimates of the radiative forcing, but the uncertainties remain too large to rationalize e.g., the apparent “pause” in warming.”


Wunsch and Heimbach (2014) humbly admit that their “results differ in detail and in numerical values from other estimates, but the determining whether any are “correct” is probably not possible with the existing data sets.”

They estimate the changing states of the ocean by synthesizing diverse data sets using models developed by the consortium for Estimating the Circulation and Climate of the Ocean, ECCO. The ECCO “state estimates” have eliminated deficiencies of previous models and they claim, “unlike most “data assimilation” products, [ECCO] satisfies the model equations without any artificial sources or sinks or forces. The state estimate is from the free running, but adjusted, model and hence satisfies all of the governing model equations, including those for basic conservation of mass, heat, momentum, vorticity, etc. up to numerical accuracy.”

Their results (Figure 18. below) suggest a flattening or slight cooling in the upper 100 meters since 2004, in agreement with the -0.04 Watts/m2 cooling reported by Lyman (2014).⁶ The consensus of previous researchers has been that temperatures in the upper 300 meters have flattened or cooled since 2003,⁴ while Wunsch and Heimbach (2014) found the upper 700 meters still warmed up to 2009.

The deep layers contain twice as much heat as the upper 100 meters, and overall exhibit a clear cooling trend for the past 2 decades. Unlike the upper layers, which are dominated by the annual cycle of heating and cooling, they argue that deep ocean trends must be viewed as part of the ocean’s long term memory which is still responding to “meteorological forcing of decades to thousands of years ago”. If Balmaseda and Trenberth’s model of deep ocean warming was correct, any increase in ocean heat content must have occurred between 700 and 2000 meters, but the mechanisms that would warm that “middle layer” remains elusive.

The detected cooling of the deepest oceans is quite remarkable given geothermal warming from the ocean floor. Wunsch and Heimbach (2014) note, “As with other extant estimates, the present state estimate does not yet account for the geothermal flux at the sea floor whose mean values (Pollack et al., 1993) are of order 0.1 W/m2,” which is small but “not negligible compared to any vertical heat transfer into the abyss.³ (A note of interest is an increase in heat from the ocean floor has recently been associated with increased basal melt of Antarctica’s Thwaites glacier. ) Since heated waters rise, I find it reasonable to assume that, at least in part, any heating of the “middle layers” likely comes from heat that was stored in the deepest ocean decades to thousands of years ago.

Wunsch and Heimbach (2014) emphasize the many uncertainties involved in attributing the cause of changes in the overall heat content concluding, “As with many climate-related records, the unanswerable question here is whether these changes are truly secular, and/or a response to anthropogenic forcing, or whether they are instead fragments of a general red noise behavior seen over durations much too short to depict the long time-scales of Fig. 6, 7, or the result of sampling and measurement biases, or changes in the temporal data density.”

Given those uncertainties, they concluded that much less heat is being added to the oceans compared to claims in previous studies (seen in the table below). It is interesting to note that compared to Hansen’s study that ended in 2003 before the observed warming pause, subsequent studies also suggest less heat is entering the oceans. Whether those declining trends are a result of improved methodologies, or due to a cooler sun, or both requires more observations.

Study	Years Examined	Watts/m2
9Hansen 2005	1993-2003	0.86 +/- 0.12
5Lyman 2010	1993-2008	0.64 +/- 0.11
10von Schuckmann 2011	2005-2010	0.54 +/- 0.1
3Wunsch 2014	1992-2011	0.2 +/- 0.1

No climate model had predicted the dramatically rising temperatures in the deep oceans calculated by the Balmaseda/Trenberth re-analysis,¹³ and oceanographers suggest such a sharp rise is more likely an artifact of shifting measuring systems. Indeed the unusual warming correlates with the switch to the Argo observing system. Wunsch and Heimbach (2013)² wrote, “clear warnings have appeared in the literature—that spurious trends and values are artifacts of changing observation systems (see, e.g., Elliott and Gaffen, 1991; Marshall et al., 2002; Thompson et al., 2008)—the reanalyses are rarely used appropriately, meaning with the recognition that they are subject to large errors.”³
More specifically Wunsch and Heimbach (2014) warned, “Data assimilation schemes running over decades are usually labeled “reanalyses.” Unfortunately, these cannot be used for heat or other budgeting purposes because of their violation of the fundamental conservation laws; see Wunsch and Heimbach (2013) for discussion of this important point. The problem necessitates close examination of claimed abyssal warming accuracies of 0.01 W/m2 based on such methods (e.g., Balmaseda et al., 2013).” ³

So who to believe?

Because ocean heat is stored asymmetrically and that heat is shifting 24/7, any limited sampling scheme will be riddled with large biases and uncertainties. In Figure 12 below Wunsch and Heimbach (2014) map the uneven densities of regionally stored heat. Apparently associated with its greater salinity, most of the central North Atlantic stores twice as much heat as any part of the Pacific and Indian Oceans. Regions where there are steep heat gradients require a greater sampling effort to avoid misleading results. They warned, “The relatively large heat content of the Atlantic Ocean could, if redistributed, produce large changes elsewhere in the system and which, if not uniformly observed, show artificial changes in the global average.” ³



Furthermore, due to the constant time-varying heat transport, regions of warming are usually compensated by regions of cooling as illustrated in their Figure 15. It offers a wonderful visualization of the current state of those natural ocean oscillations by comparing changes in heat content between1992 and 2011. Those patterns of heat re-distributions evolve enormous amounts of heat and that make detection of changes in heat content that are many magnitudes smaller extremely difficult. Again any uneven sampling regime in time or space, would result in “artificial changes in the global average”.

Figure 15 shows the most recent effects of La Nina and the negative Pacific Decadal Oscillation. The eastern Pacific has cooled, while simultaneously the intensifying trade winds have swept more warm water into the western Pacific causing it to warm. Likewise heat stored in the mid‑Atlantic has likely been transported northward as that region has cooled while simultaneously the sub‑polar seas have warmed. This northward change in heat content is in agreement with earlier discussions about cycles of warm water intrusions that effect Arctic sea ice, confounded climate models of the Arctic and controls the distribution of marine organisms.

Most interesting is the observed cooling throughout the upper 700 meters of the Arctic. There have been 2 competing explanations for the unusually warm Arctic air temperature that heavily weights the global average. CO2 driven hypotheses argue global warming has reduced polar sea ice that previously reflected sunlight, and now the exposed dark waters are absorbing more heat and raising water and air temperatures. But clearly a cooling upper Arctic Ocean suggests any absorbed heat is insignificant. Despite greater inflows of warm Atlantic water, declining heat content of the upper 700 meters supports the competing hypothesis that warmer Arctic air temperatures are, at least in part, the result of increased ventilation of heat that was previously trapped by a thick insulating ice cover.⁷
That second hypothesis is also in agreement with extensive observations that Arctic air temperatures had been cooling in the 80s and 90s. Warming occurred after subfreezing winds, re‑directed by the Arctic Oscillation, drove thick multi-year ice out from the Arctic.¹¹

Regional cooling is also detected along the storm track from the Caribbean and along eastern USA. This evidence contradicts speculation that hurricanes in the Atlantic will or have become more severe due to increasing ocean temperatures. This also confirms earlier analyses of blogger Bob Tisdale and others that Superstorm Sandy was not caused by warmer oceans.


In order to support their contention that the deep ocean has been dramatically absorbing heat, Balmaseda/Trenberth must provide a mechanism and the regional observations where heat has been carried from the surface to those depths. But few are to be found. Warming at great depths and simultaneous cooling of the surface is antithetical to climate models predictions. Models had predicted global warming would store heat first in the upper layer and stratify that layer. Diffusion would require hundreds to thousands of years, so it is not the mechanism. Trenberth, Rahmstorf, and others have argued the winds could drive heat below the surface. Indeed winds can drive heat downward in a layer that oceanographers call the “mixed-layer,” but the depth where wind mixing occurs is restricted to a layer roughly 10-200 meters thick over most of the tropical and mid-latitude belts. And those depths have been cooling slightly.

The only other possible mechanism that could reasonably explain heat transfer to the deep ocean was that the winds could tilt the thermocline. The thermocline delineates a rapid transition between the ocean’s warm upper layer and cold lower layer. As illustrated above in Figure 15, during a La Nina warm waters pile up in the western Pacific and deepens the thermocline. But the tilting Pacific thermocline typically does not dip below the 700 meters, if ever.⁸

Unfortunately the analysis by Wunsch and Heimbach (2014) does not report on changes in the layer between 700 meters and 2000 meters. However based on changes in heat content below 2000 meters (their Figure 16 below), deeper layers of the Pacific are practically devoid of any deep warming.

The one region transporting the greatest amount of heat into the deep oceans is the ice forming regions around Antarctica, especially the eastern Weddell Sea where annually sea ice has been expanding.¹² Unlike the Arctic, the Antarctic is relatively insulated from intruding subtropical waters (discussed here) so any deep warming is mostly from heat descending from above with a small contribution from geothermal.

Counter‑intuitively greater sea ice production can deliver relatively warmer subsurface water to the ocean abyss. When oceans freeze, the salt is ejected to form a dense brine with a temperature that always hovers at the freezing point. Typically this unmodified water is called shelf water. Dense shelf water readily sinks to the bottom of the polar seas. However in transit to the bottom, shelf water must pass through layers of variously modified Warm Deep Water or Antarctic Circumpolar Water.
Turbulent mixing also entrains some of the warmer water down to the abyss. Warm Deep Water typically comprises 62% of the mixed water that finally reaches the bottom. Any altered dynamic (such as increasing sea ice production, or circulation effects that entrain a greater proportion of Warm Deep Water), can redistribute more heat to the abyss.¹⁴. Due to the Antarctic Oscillation the warmer waters carried by the Antarctic Circumpolar Current have been observed to undulate southward bringing those waters closer to ice forming regions. Shelf waters have generally cooled and there has been no detectable warming of the Warm Deep Water core, so this region’s deep ocean warming is likely just re-distributing heat and not adding to the ocean heat content.

So it remains unclear if and how Trenberth’s “missing heat” has sunk to the deep ocean. The depiction of a dramatic rise in deep ocean heat is highly questionable, even though alarmists have flaunted it as proof of Co2’s power. As Dr. Wunsch had warned earlier, “Convenient assumptions should not be turned prematurely into ‘facts,’ nor uncertainties and ambiguities suppressed.” … “Anyone can write a model: the challenge is to demonstrate its accuracy and precision… Otherwise, the scientific debate is controlled by the most articulate, colorful, or adamant players.” ¹

To reiterate, “the uncertainties remain too large to rationalize e.g., the apparent “pause” in warming.”

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