By Andrew Freedman From Mashable

The planet is nearing a species extinction threshold, beyond which the signal of global warming will become clearer with each passing year, a new study finds. The faster the climate changes as a result of manmade emissions of greenhouse gases, such as carbon dioxide, the greater the extinction risks to species large and small.

The study, published Thursday in the journal Science, is a comprehensive analysis of 131 peer-reviewed studies of how species around the world may fare as the world’s climate shifts, forcing range-limited species to adapt in their current habitat, move or perish.

It finds that on a current “business as usual” pathway of emissions, which assumes no major reductions in pollution, as many as one in six species are likely to go extinct or be on the road to extinction by the end of this century. This would likely amount to the highest extinction rate in all of human history. This would likely amount to the highest extinction rate in all of human history. Species are at greater risk of extinction in South America, Australia and New Zealand, where endemic species are uniquely accustomed to a narrow range of climate conditions, such as the huge numbers of species — some of which have not even been identified yet — that live in the Amazonian rainforest.

However, the study emphasizes that most of the research-to-date has focused on North America and Europe, meaning a shift in scientists’ attention to the areas most likely to see higher extinction rates may be warranted in order to help avoid such a fate if possible.

The research, by ecologist Mark C. Urban of the department of ecology and evolutionary biology at the University of Connecticut, found that current global extinction estimates vary widely, from 0 to 54%, depending on a study’s methods and the species in question. Urban conducted a “meta-analysis,” which is, essentially, an analysis of many other analyses, to compare different studies. Urban focused on the research that looked at more than one species.

Urban’s survey of the scientific literature on climate change-related extinction risks shows that the global risk of extinction for all species may rise to 7.9% by the end of the century, based on particular assumptions of greenhouse gas emissions and other factors. This figure is far higher than the current extinction risk for all species around the world, which is down near 2.8%.

However, the extinction risk varies based largely on the amount of global warming that takes place, relative to the preindustrial climate. Urban found that 5.2% of all species studied face the likelihood of extinction if global warming is limited to 3.6 degrees Fahrenheit, or 2 degrees Celsius, which is the internationally-agreed upon global warming target. However, according to many climate studies that incorporate recent emissions trends, this target is likely to be exceeded, perhaps significantly.

If we follow our current, business-as-usual-trajectory, the study finds, “climate change threatens one in six species,” or 16% of species.

“Extinction risks from climate change are expected not only to increase but to accelerate for every degree rise in global temperatures. “Extinction risks from climate change are expected not only to increase but to accelerate for every degree rise in global temperatures. The signal of climate change–induced extinctions will become increasingly apparent if we do not act now to limit future climate change,” the study states.

Also affecting the risk is whether a species is endemic to a region, and if it has a small range, such as most amphibians and reptiles do. These species face higher risks in even low-end global warming scenarios.

Species in South America, Australia and New Zealand at greater peril
Geographically, a species may fare better if it is located in North America or Europe, where the extinction risks are lowest (5% and 6%, respectively), compared to South America and Australia, where the risks were 23% and 14%. The reason for this, the study says, is because South America, Australia as well as New Zealand have many species that only call those regions home, and which have small ranges. Furthermore, the ability for species to shift to new habitat is more limited for rainforest-dependent species, for example.

Human actions that reduce the available ranges for species, such as cutting down rainforest to make way for agricultural production, or building highways and cities between areas of suitable habitat can accelerate the extinction process.

The study may actually underestimate extinction risks, however, because the research investigates the effects of increasing temperatures on species. Other factors, such as interspecies interaction and evolutionary changes, as well as habitat loss from a ballooning human population also affects a species’ extinction risks, either raising or lowering them.

Many species have already begun to move in order to avoid intolerable climates. Some, like the American pika, a squirrel-like species that lives at high altitudes in the western U.S., may soon run out of room as they migrate up mountainsides in search of colder weather conditions.

A separate study, also published in Science on Thursday, found that marine mammals are at greater risk of extinction from changing ocean conditions, such as increasingly acidic ocean waters, compared to other marine species.

risks
This means that iconic species such as whales and dolphins are at the highest risk, based on fossil records showing a 23-million-year history of marine life.

IMAGE: PAUL SOUDERS/CORBIS

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