Extinctions and shutting down the Gulf Stream

By Andy May

This is part four of our series on climate change costs and hazards. The first three parts were on humans and the environment, population and the food supply, and the cost of global warming. In this part we examine the assertion that man-made climate change, the growth of the human population, and other human activities are causing an increase in species extinctions. We also examine the polar bear controversy.

And we examine the assertion that man-made climate change will cause an influx of fresh water into the North Atlantic from melting glaciers on Greenland and shut down the North Atlantic thermohaline circulation and/or the Gulf Stream. This will then, supposedly, cause a major cooling akin to the one seen 8,180 to 8,340 years ago when the ice dam holding Lake Agassiz onto North America broke, spilling a huge amount of fresh water into the Atlantic.

Global warming is causing a “great extinction” event.

Besides the potential financial costs of global warming, some claim that the modest 0.8°C of warming we have experienced since the mid-19th century is causing more species to become extinct, others say it is the growth of the human population. In fact, National Geographic has claimed we are in the “sixth great extinction in the Earth’s history.” Nadia Drake proclaims that the current extinction rate may be 100 times the normal rate. This is also the subject of a book entitled The Sixth Extinction, by Elizabeth Kolbert. If true, this is a considerable cost of either global warming or human population growth.

Experts in the past five extinction events do not support this idea. Smithsonian paleontologist Doug Erwin, an expert on the Permian extinction that may have wiped out 90% of the species on Earth, says those claiming we are in a similar situation simply do not know what a mass extinction is (see here). Erwin points out that somewhere between 0 and 1% of species have gone extinct in recent human history. Consider what he told The Atlantic, in an interview:

“So, you can ask, ‘Okay, well, how many geographically widespread, abundant, durably skeletonized marine taxa have gone extinct thus far?’ And the answer is, pretty close to zero,” Erwin pointed out. In fact, of the best-assessed groups of modern animals—like stony corals, amphibians, birds and mammals—somewhere between 0 and 1 percent of species have gone extinct in recent human history. By comparison, the hellscape of End-Permian mass extinction claimed upwards of 90 percent of all species on earth.”

The Atlantic

Daniel Botkin (UC Santa Barbara environmental scientist, bio here) has estimated that the extinction rate for animals and plants is about one per year. This is not an alarming rate and is very far from a “mass extinction” event.

“In the Danish press I pointed out that we had long been hearing figures for the extinction of the world’s species which were far too high – that we would lose about half of all species within a generation. The correct figure is closer to 0.7 percent in 50 years. This led to the Danish chairman of Greenpeace, Niels Bredsdorff, pointing out that Greenpeace had long accepted the figure of 0.7 percent.”

Lomborg, Bjørn. The Skeptical Environmentalist: Measuring the Real State of the World (p. 17).

“Extinctions are always happening. Most species that have existed on Earth have gone extinct. As I mentioned before, the average rate for animals and plants has been about one a year (although some recent scientific papers argue that the average rate has been much higher, maybe up to six per year). The number of extinctions has varied over time, including five “mega-extinction” events since the evolution of multicellular life-forms, about 550 million years ago. During each of these mega-extinctions, the majority of species appear to have gone extinct in a (geologically speaking) comparatively short time. The greatest mass extinction was the Permian-Triassic, about 250 million years ago, when an estimated 80 to 90 percent of all species went extinct.”

Botkin, Daniel B. 25 Myths That Are Destroying the Environment: What Many Environmentalists Believe and Why They Are Wrong (Kindle Locations 645-650).

The IPCC WGII AR5 report supports Lomborg and Botkin, in a bit of a back-handed way, with figure 1 below from page 43 of the Technical Summary:

Figure 1: Rates of change in distribution (km/decade) for several marine taxonomic groups for 1900 to 2000. Positive changes mean the taxa are present over a larger area, generally moving poleward.

While the IPCC AR5 report does not claim a “great extinction” is imminent they do claim that a “large” fraction of both terrestrial and freshwater species face an increased risk of extinction due to climate change. This prediction is entirely model-based and nothing like they predict has been observed. The report also acknowledges that there is very low agreement concerning the fraction of species at risk (AR5 WGII, technical summary, page 67).

The “Great” Quaternary Megafauna Extinction

After post #1, Javier included a reference to Barnosky, 2008 on the Quaternary megafauna extinction. The paper begins with the following:

Earth’s most recent major extinction episode, the Quaternary Megafauna Extinction, claimed two-thirds of mammal genera and one-half of species that weighed >44 kg between ~50,000 and 3,000 years ago.”

Barnosky, 2008

After cleverly reducing his sample size to get to two-thirds, he proclaims:

“The Quaternary Megafauna Extinction (QME) killed >178 species of the world’s largest mammals, those weighing at least 44 kg (roughly the size of sheep to elephants). More than 101 genera perished. Beginning ~50,000 years (kyr) B.P. and largely completed by 7 kyr B.P., it was Earth’s latest great extinction event.”

Barnosky, 2008

So, the “Great” Quaternary megafaunal extinction event extirpated about 178 species of the world’s largest mammals, those weighing >44kg (roughly the size of sheep to elephants). According to Mora, 2011, there are a 1.2 million catalogued species today and there may be a total of 8.7 million species alive in the world today. So, while the extinction of 178 species over ~50,000 years of rapid climate change is distressing because the creatures are so interesting, geologically it is not a significant event. It is not remotely comparable to the five great extinctions. A “Great Extinction” is defined by the American Museum of Natural History as an event where more than half of all species go extinct in a short time, from the museum’s web site:

“Around 65 million years ago, … Fossils that are abundant in earlier rock layers are simply not present in later rock layers. A wide range of animals and plants suddenly died out, from tiny marine organisms to large dinosaurs.”


“Species go extinct all the time. Scientists estimate that at least 99.9 percent of all species of plants and animals that ever lived are now extinct. So, the demise of dinosaurs like T. rex and Triceratopssome 65 million years ago wouldn’t be especially noteworthy–except for the fact that around 50 percent of all plants and animals alive at the same time also died out in what scientists call a mass extinction.”


Thus, the Quaternary megafauna extinction is about three orders of magnitude too small to be a “Great Extinction” as claimed by Barnosky.

The Quaternary megafaunal extinction event began ~50,000 years ago and was mostly complete by 3,000 years ago. This was an extinction rate of 0.004 species per year, which is much lower than the average long term extinction rate of about one species per year (Daniel Botkin, see quote above). Obviously, the extinction of sabre toothed tigers, dire wolves, mammoths, and other megafauna is not particularly significant in geological history. But, these are fascinating creatures due to their size and we value them much more than a toad or insect that goes extinct. However, this is a value judgement, not a geological event.

Barnosky notes that humans fit into the large mammal category, yet humans have survived and thrived. They also claim that the gain in human biomass largely matches the loss of large non-human megafaunal biomass until 12,000 years ago, then total megafaunal biomass crashed as many megafauna went extinct. Sounds like classic “survivor guilt” to me. 12,000 years ago, was about when human civilization began, rice was already being cultivated in China and grains in the Levant (present day Syria and Israel). The construction of the large stone monuments at Gobekli Tepe in modern day Turkey began about this time. Humans were beginning to settle down and become farmers. Humans adapted quite well both during and after the Younger Dryas, other megafauna did not.

12,000 years ago, was very near the end of the Younger Dryas period. This was a 1,000-year return to glacial conditions after a brief warm period from 15,200 years ago until 13,000 years ago. The periods are labeled in figure 2. The figure plots the GISP2 Greenland ice core air temperature record by Alley, 2004.

Figure 2, data from Alley, 2004.

At least in Greenland, and probably over the whole Northern Hemisphere, it was very cold 12,000 years ago. A more detailed time line can be downloaded here. Below is a global reconstruction, using mostly marine temperature proxies that shows pretty much the same thing, although it only goes back to 12,000 BP.

It was very cold 12,000 years ago and then the world warmed rapidly, especially in the northern hemisphere. This put a lot of stress on all species, undoubtedly some species went extinct, but the species we especially notice, in the fossil record, are the larger creatures. Some estimates suggest that air temperatures, on land, in the northern hemisphere, rose as much as 5-10°C in just a few decades (Severinghaus, et al., 1998). This extremely rapid warming could have affected many species as well. We have people concerned today because of a 0.8°C rise in 137 years, imagine a change of 5°C since 1990! This is what the world saw at the end of the Younger Dryas.

By 12,000 years ago, man had spread throughout Africa, Eurasia and the Americas. The rise of civilization and the development of new hunting tools (bows and arrows, spears, and spear throwers – all invented more than 30,000 years ago) made Upper Paleolithic hunters very formidable. We know that Upper Paleolithic humans hunted megafauna 12,000 years ago and earlier and were present in areas where megafauna went extinct. In Australia, the megafauna disappeared within a few thousand years of man’s arrival on the continent and in a time of stable climate. But, elsewhere, like in Eurasia, the extinctions occurred during periods of dramatic climate change. It is likely that hunting by Upper Paleolithic humans and climate change both played a role in the megafauna extinction event. A summary of the geological evidence for both theories can be seen in Marianne Lehnert’s 2014 essay here as well as in Barnosky, 2008. Further, it seems clear that of the megafauna present 12,000 years ago, humans were the most adaptable to the changing world. To a large degree, humans simply outlasted and out-survived their competitors, evolution at work.

Barnosky mentions that some megafauna are at risk of extinction today, many of the species have only survived in Africa. This is not a surprise, Africa sits on the equator and is less vulnerable to severe climate change. Because of their size megafauna require a lot of land to live in the wild, this will restrict them to parks, private lands, and zoos; but as man becomes more prosperous, he is more interested in preserving them and they are unlikely to die off. Upper Paleolithic humans were only interested in surviving, humans today are affluent and secure, and will expend energy and resources to help species that we value survive. It is more likely that humans today will ensure the survival of megafauna, rather than threaten them.

Barnosky speculates that our current high level of large animal “biomass” is only being sustained by fossil fuels and is dominated by human “biomass.” Strange way of putting it, but it might be true. His next prediction is that another large animal “biomass crash” is imminent because we are running out of fossil fuels, this is unlikely mainly because his prediction that we only have an 83-year supply of oil and gas is much too pessimistic. The paper states we have a 50 year supply of oil and a 200 year supply of gas, I converted the gas supply to oil by using the USGS conversion of 6 MCF of natural gas to 1 barrel of oil equivalent.

Table 1, (from here), gives a much more realistic estimate of known hydrocarbon resources that are technically recoverable, it is very conservative and does not include all known hydrocarbons. All the hydrocarbon resources in table 1 can be produced economically at prices we have seen in the last 20 years, although some may not be economic at current (2017) prices. It appears that Barnosky was only counting “proven” or “probable” conventional oil and gas deposits, when most of the oil and gas known today are classified as “unconventional” (including oil shale and oil sand deposits). While the production of unconventional oil and gas is more expensive than conventional oil and gas, it is still an order of magnitude cheaper than solar and wind. Nuclear is even cheaper than coal or natural gas, see here. The bottom line is that available energy supply is not the problem.

Table 1

While Upper Paleolithic (roughly 40,000 to 10,000 years ago) man played some role in the Quaternary megafaunal extinction event, this was a very different human than we are. They were subsistence hunters in a very tough time, this caused physiological changes as they adapted to a very cold climate. During this period, they had barely learned to farm, and even then, only in the most primitive way. When food walked by, they killed it and ate it. We have already seen that taking care of the environment is only possible when our income and security needs are taken care of (see post 1, “Do Humans harm the Environment“), figure 2. Today when GDP in PPP$ exceeds about PPP$2,000 per person, the environment, in that country, improves rapidly.

Barnosky suggests that man’s rise and other megafauna going extinct is simply a trade off in biomass, thus as man’s population grows more extinctions will occur among existing megafauna. I find this highly speculative, considering our prosperity and our interest in preserving endangered species. There is a trade off in available land, but biomass? With modern farming we can feed many more people and animals than in the past, we can also use energy to create a nearly infinite amount of clean water. Further, man has an obvious interest in preserving existing megafauna for esthetic and humanitarian reasons. They will not be able to run wild in a fenceless wilderness, but I doubt we will allow large animal species to go extinct. The best insurance for the survival of megafauna is a prosperous and secure human population.

Polar Bears

As Dr. Susan Crockford has reported in detail on her site polarbearscience.com, USFWS researchers confidently predicted that polar bears would die off to dangerously low levels if sea ice dropped below 3-5 million square kilometers on a regular basis. The first prediction was made by the International Union for the Conservation of Nature (IUCN) in 2006. A second assessment was made by the United States Fish and Wildlife Service in 2008. On the basis of these predictions (see here for the ICUN listing), polar bears were put on the vulnerable species list.

It turned out that sea-ice extent has reached 3-5 million square kilometers on a regular basis since 2007, much earlier than expected and this is long enough to assess the predictions and Dr. Crockford has done so here. The “critical” level of ice was reached many times and, yet polar bears thrived, the population stayed stable or, perhaps, grew in number. The 2015 population of polar bears has been estimated to be about 26,000 (22,000 to 31,000). It has since been suggested that a low in the polar bear population was reached between 2004 and 2006 when the sea ice was thick and extensive (figure 2). The population of bears in 2005 has been estimated to be about 22,500 (the range is 20,000 to 25,000). The population increased after the ice melted and when polar bears were spending more time on land. Generally, the accuracy of the estimates of the bear population is not great, but a slight decline in 2001 to 2005 is quite possible. The population has remained stable since 2000, which suggests all the variation in sea ice has had little effect.

The loss of sea ice since 2007 has not affected the polar bear population, in the words of Atwood, et al., 2015:

no causal link between the patterns in polar bear vital rates and increased use of terrestrial habitat

Atwood, et al., 2015

The authors speculate that if the bears spend more time on land, due to the lack of ice, it may be a problem in the future. But history has shown we should not make environmental decisions based upon speculation.

Once the lack of a link between sea ice extent and polar bear populations was established, Jeffrey Bromaghin (see Bromaghin, et al., 2015), said in an interview on the paper:

The low survival may have been caused by a combination of factors that could be difficult to unravel,” said Bromaghin, “and why survival improved at the end of the study is unknown.

Bromaghin, et al., 2015

The low point was 2004 to 2006, when the Arctic sea ice was extensive, the “survival of adults and cubs began to improve in 2007” when the Arctic sea ice declined rapidly. This is exactly the opposite of what the environmentalists predicted! The sea ice extent for the years discussed is shown in figure 4.

Figure 4, Data from JAXA, plot from Great White Con.

The polar bear story is a good example of what can go wrong when one bases policy on environmentalist’s predictions. In this case, the polar bear scientists concluded, erroneously, that polar bears needed sea ice to survive. Then they predicted if sea ice reached the 3-5 million square kilometer level or lower polar bears would suffer, this was also incorrect. Finally, they used a climate model to predict that the critical sea ice level would be reached in 2050 due to man-made climate change, also incorrect. It was reached a scant two years later and completely ignored by the bears who simply lived on land in the absence of ice. Not a single prediction was correct, but the polar bear made the “vulnerable” list anyway.

Global Warming will shut down the Gulf stream and cause a mini-ice age.

This hypothetical scenario where melting Greenland ice dilutes the Atlantic between Greenland and Norway and stops the North Atlantic thermohaline circulation (aka the “Atlantic conveyor”) causing a little ice age, such as the one 8,200 years ago, is very unlikely to happen. 8,200 years ago, an enormous fresh water lake (Lake Agassiz), in the area along the border between Canada and the U.S., broke through an ice dam, that was left over from the most recent glacial advance, and flooded the North Atlantic with fresh water. This lowered the salinity of the surface water and halted the thermohaline circulation in the North Atlantic and cooled the planet for hundreds of years (see more here by Michael Michalek). We often simply refer to one cooling, the 8,200 BP cooling period, but in reality, there were two, one was 8,490 years ago and the other from 8,340 BP to 8,180 BP. Per Lomborg’s Cool It:

“The Gulf Stream last shut down some 8,200 years ago, when the final glacial ice sheets in North America melted and a giant pool of freshwater built up around the area of the Great Lakes. One day, the ice dam broke, and an unprecedented amount of freshwater flooded the North Atlantic and disrupted the sinking salty water from the Atlantic conveyor. This pushed Europe into a little ice age for almost one thousand years. …

Yet the relevance of such a story crucially depends on the Greenland melt being on the same order of magnitude as the ancient freshwater pool—and it is not. Over the coming century, the IPCC expects Greenland to melt almost one thousand times less than what happened 8,200 years ago. A team of modelers looked at what would happen if Greenland melted at triple the rate expected by the IPCC—or, as they put it, at the “upper limit on possible melting rates.” Although they see a reduction in the Gulf Stream, they find “its overall characteristic is not changed” and that “abrupt climate change initiated by Greenland ice sheet melting is not a realistic scenario for the 21st century. …

This is also why the IPCC, in its 2007 report, is very clear about the Gulf Stream: ‘None of the current models simulates an abrupt reduction or shut-down.’ The IPCC’s models expect somewhere from no change to a Gulf Stream reduction of 50 percent over the coming century, but no models show a complete shutdown.” Lomborg, Bjorn. Cool It (Kindle Locations 1334-1394).

This idea was the inspiration for the 2004 film The Day after Tomorrow starring Dennis Quaid and directed and written by Roland Emmerich. This very imaginative film is filled with gross scientific inaccuracies, but did reasonably well at the box office. Critics panned it, as did most earth scientists I know who bothered to watch it.


Bottom line, there is no discernable trend in extinctions, up or down. But, we are certainly not in a “major extinction” event. The Gulf Stream and the world’s thermohaline circulation system are in fine shape and there is no “Lake Agassiz” waiting to spill into the North Atlantic to shut them down. Ice on Greenland cannot melt fast enough to affect the salinity to the degree necessary to repeat the 8,200 BP cold spell.

The Quaternary megafauna extinction was very sad, and both Upper Paleolithic humans and radical natural climate change played a role in those extinctions according to the data we have available. However, comparing this very minor extinction event to the five great extinctions, as Barnosky attempts to do, betrays a complete lack of proportion and an ignorance of the geological past. The true great extinctions were horrific events and the loss of 178 species of large animals is several orders of magnitude too small to qualify. For this event to be classified as a great extinction event would require the extinction of over half a million species and nothing like that is happening today or in the foreseeable future.

Dr. Susan Crockford has documented the saga of polar bears being erroneously declared “vulnerable” quite well and there are lessons to be learned from this fiasco. One cannot base public policy on unvalidated models and predictions. This recent trend of believing, without question, model results; or worse using model results as if they were data, needs to stop. At some point it will lead us off a cliff.

Published by Andy May

Petrophysicist, details available here: https://andymaypetrophysicist.com/about/

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