From ScienceDaily, Sept 2017
As it stands, according to the work, water temperatures in the tropical parts of the oceans are already nearing the upper temperature range of what many of the fish living there now can survive.
Given how rapidly temperatures are now warming, and the limits to adaptability in many fish species, it seems likely then that the tropical oceans will lose a great deal of biodiversity over the coming century. And that statement is made without even factoring in the ongoing problem of overfishing.
This wouldn’t be too surprising, as during some earlier periods of extreme climatic warming it appears that the tropical oceans became largely devoid of most large marine animals.
Notably, the new work also predicts that freshwater fish living in the higher latitudes of the Northern Hemisphere will be facing an existential crisis as well.
The press release provides more:
“The researchers compiled data from lab experiments involving nearly 500 fish species, conducted over the past 80 years by researchers around the world. These standardized experiments measure the highest temperatures fish are able to tolerate before they die. This analysis is the first time these disparate data from lab experiments have been combined and translated to predict how fish will respond in the wild…The researchers found that overall, sensitivity to temperature changes varied greatly between ocean-dwelling and freshwater fish.”
It should be noted here, before going deeper into the new research, that such work doesn’t really take into account the fact that as environmental conditions change so does genome expression. In other words, epigenetic changes accompanying rising water temperatures will no doubt result in some adaptive changes to physiology (smaller body size, etc) — though there will be sharp limits to what’s possible as far as that goes among many species.
A simpler means of adaption, of course, is simply to change the range that one lives in. This process already seems to be occurring in many parts of the world’s oceans, with some species now expanding rapidly into waters that they have not been found in historically.
“Nowhere on Earth are fish spared from having to cope with climate change,” explained senior author Julian Olden, a UW professor of aquatic and fishery sciences. “Fish have unique challenges — they either have to make rapid movements to track their temperature requirements, or they will be forced to adapt quickly.”
The press release continued:
“Using years of data — and relying on the fact that many fish species are taxonomically related and tend to share the same thermal limits — the researchers were able to predict the breaking-point temperature for close to 3,000 species. Regional patterns then emerged when those data were paired with climate-model data predicting temperature increases under climate change.
“By contrast, in freshwater streams in the far north, fish are accustomed to cooler water temperatures but have much less tolerance for warming waters. Since the effects of climate change are acutely felt in high latitudes, this doesn’t bode well for fish in those streams that have a small window for survivable temperatures.
“Fish will either migrate, adapt or die off as temperatures continue to warm, the researchers explained. Given past evolutionary rates of critical thermal limits, it’s unlikely that fish will be able to keep up with the rate at which temperatures are increasing, Olden said. The ability to move, then, is imperative for fish that live in the most critical areas identified in this analysis.”
Something that will stand in the way of this occurring, in many ways, is the ubiquitous presence of dams in many parts of the northern hemisphere. While fish ladders, or the like, could perhaps help somewhat, the approach doesn’t work well with all species. The researchers note that the restoration of vegetation along lake or river edges could perhaps help somewhat (to a limit) — by providing shade and helping to reduce water temperatures.
“Fishes across the world face mounting challenges associated with climate change,” Olden concluded. “Looking forward, continued efforts to support conservation strategies that allow species to respond to these rapid changes are needed.”
With regard to the impact on humans, the takeaway of this new research is essentially that people who live in the tropics and depend upon fish for their sustenance will have to look elsewhere more and more and the century grinds on.
In other words, even without considering overfishing, the tropical oceans are going to become much less capable of supporting the large human populations that it does now. This circumstance will be compounded by production and yield problems in other parts of the global food system.
The new findings are detailed in a paper published in the journal Nature Climate Change.
Mathematics, Mass Extinction, Climate Change, & The Threshold Of Catastrophe
September 21st, 2017 by Steve Hanley on Clean Technica
Extinctions do not take place overnight. We do not go to bed one evening and wake up to find that most plant and animal life on earth has disappeared overnight. An extinction can take place over thousands or even millions of years, depending in large measure upon how quickly a spike in carbon dioxide concentrations occurs. The more gradual the CO2 rise, the more gradual the changes occur.
Unless you are one of those people who think Charles Darwin and his theory of evolution is so much horse puckey (millions of Americans believe just that), evolution over a long enough period will allow life on earth to adapt to changes in climate and environment. But such changes take place over a very long time — often 100,000 years or more. The changes expected to take place globally before the end of this century will not allow people and other living things enough time to adapt through evolutionary changes. That’s the kind of climate change that leads to mass extinctions.
Two Components Of Carbon Dioxide Increase
The rapid pace of change today has no historic counterpart. Carbon dioxide levels going back more than 500 million years rose at a far slower pace, making it difficult to compare one to the other. That’s where Professor Rothman and his mathematical models come into play. Here is the abstract of his research as published by Science Advances.
The history of the Earth system is a story of change. Some changes are gradual and benign, but others, especially those associated with catastrophic mass extinction, are relatively abrupt and destructive. What sets one group apart from the other?
Here, I hypothesize that perturbations of Earth’s carbon cycle lead to mass extinction if they exceed either a critical rate at long time scales or a critical size at short time scales. By analyzing 31 carbon isotopic events during the past 542 million years, I identify the critical rate with a limit imposed by mass conservation.
Identification of the crossover time scale separating fast from slow events then yields the critical size. The modern critical size for the marine carbon cycle is roughly similar to the mass of carbon that human activities will likely have added to the oceans by the year 2100.
Climate Change And The Threshold Of Catastrophe
Rothman calculates that human activity will have added about 310 gigatons of carbon dioxide to the atmosphere and oceans by 2100. That’s the point at which the world will be on the “threshold of catastrophe” as it transitions into “unknown territory.” The changes that follow may take up to 10,000 years to play out, but that is still one tenth of the amount of time needed for evolutionary changes to keep pace. The result? Mass extinction Number Six.
“This is not saying that disaster occurs the next day,” Rothman says. “It’s saying that, if left unchecked, the carbon cycle would move into a realm which would be no longer stable, and would behave in a way that would be difficult to predict. In the geologic past, this type of behavior is associated with mass extinction.”
“How can you really compare these great events in the geologic past, which occur over such vast timescales, to what’s going on today, which is centuries at the longest?” Rothman says. “So I sat down one summer day and tried to think about how one might go about this systematically.” The result was a mathematical model that correlates the rate and magnitude of alterations in the carbon cycle to the timespan over which those changes occur. He hypothesized that his formula should predict mass extinctions or other global catastrophes.
Then he applied his formula to historical data. After searching hundreds of geochemistry studies, he identified 31 times in the past 542 million years in which a significant change occurred in the earth’s carbon cycle. For each event, he noted the amount of CO2 change and the time during which the change occurred. “It became evident that there was a characteristic rate of change that the system basically didn’t like to go past,” Rothman says.
His modeling identified a certain threshold of change that separated benign events from those that destabilized the environment and moved it toward catastrophic consequences. The end-Permian extinction — during which 95% of all species on earth disappeared — was the farthest over the line. “Then it became a question of figuring out what it meant,” Rothman says.
Rothman determined that a critical part of the earth’s carbon cycle involves the small amount of carbon dioxide that sinks to the bottom of the oceans, where it is sequestered in the bottom. But if the rate of carbon dioxide being added to the environment becomes too fast, that sequestration process is overwhelmed and cannot function to tamp down the effects of the extra carbon. That’s when the carbon cycle trips over into unstable territory.
The Intergovernmental Panel on Climate Change has postulated that there are four possible scenarios for future additions of carbon dioxide to the environment. The best-case scenario predicts that humans will add 300 gigatons of carbon to the oceans by 2100, a number that is right in line with the amount Rothman predicts will occur. The worst case scenario is 500 gigatons — an amount well past his threshold for catastrophe.