It’s no news to scientists that our world’s plants and animals are in trouble. Species are disappearing at alarming rates, and some experts believe that Earth is on the verge of a mass extinction — the sixth one in the planet’s history, and the first one to be caused by humans.
Up to now, habitat loss and overexploitation have had the biggest hand in our planet’s rapid loss of biodiversity. But a new threat is steadily emerging: It’s global climate change, and its future impact could be bigger than we imagined.
A new study, published today in Science, predicts that climate change could threaten a whopping one in six species on Earth with extinction if humans don’t start taking measures to cut down on our greenhouse gas emissions.
Mark Urban, an associate professor of ecology and evolutionary biology at the University of Connecticut, examined 131 biodiversity studies to see how the Earth’s warming temperature would affect extinction risks worldwide. After analyzing the results of all the studies, which included a variety of different species, geographic locations and modeling techniques, he concluded that climate change-induced extinction risks are not only growing with every degree the planet warms — the rates are actually speeding up.
“I expected the risks would increase with climate change,” Urban says. “But the acceleration — the fact that at higher global temperatures those extinction rates curve upward — that was a bit of a surprise.”
Using his analysis, Urban was able to calculate extinction risks, or the percent of species on Earth facing extinction, for different warming scenarios. Currently, global leaders hope to cut carbon emissions enough to keep Earth’s temperature within 2 degrees Celsius of its pre-industrial levels — an ambitious and increasingly unlikely goal, say many experts.
According to Urban’s analysis, global extinction risk will rise from its present value of 2.8 percent to 5.2 percent of species on Earth if global temperatures increase by those 2 degrees. At 3 degrees, the extinction risk rises to 8.5 percent.
And the one-in-six prediction? That’s the risk Urban calculates if humans maintain a “business-as-usual” trajectory, failing to slash our carbon emissions and slow the current rate of global warming. In this scenario, Earth will warm by about 4.3 degrees Celsius by the end of the century, and 16 percent of all species on the planet — or one in six — will face extinction.
These are the overall risks for all species across the world. But Urban also investigated whether extinction risk will be worse for certain locations or types of organisms.
He found that different taxonomic groups — an organism’s classification, such as bird or reptile — had no significant differences in extinction risk. On the other hand, the risk did change according to region. Urban found that North America and Europe have the lowest risks, while South America, Australia and New Zealand have the highest.
There could be a few reasons for this, Urban says. Australia and New Zealand, in particular, have many endemic species, or species that are found nowhere else in the world. Since endemic species are concentrated in one area, their populations are highly susceptible to environmental disturbances. “You can’t lose much more habitat before you have a pretty small range and total population size,” Urban says.
In addition, these regions’ small land masses mean species don’t have as much room to spread out and find better habitat if their homes become unsuitable.
Urban’s analysis also raises critical uncertainties about the other biological processes that may factor into future extinction rates, according to Janneke Hille Ris Lambers, an associate professor of biology at the University of Washington.
In a comment on Urban’s study, also published today in Science, Lambers questions whether factors like a species’ adaptation strategies, its behavior or its interactions with other organisms can buffer — or magnify — the effects of climate change on its extinction risk. “These are challenging questions that biologists are only just beginning to address when considering climate change impacts on biodiversity,” she writes.
Urban feels that future research should begin to address some of these factors.
“Many of the models we have are missing what we think to be some important processes that might mediate these effects: species interactions, dispersal ability, ability to move through landscapes that have been altered by humans, trait variation among species and also evolution,” he says. “What this really suggests is we need to start building these next generation models that are going to incorporate important biological processes and try to understand how those processes might affect certain species.”
Better understanding of the combined threats to a species’ future can lead to better management decisions. “We can implement strategies to try to protect those species that are most at risk,” Urban says.
But he adds that the real goal should be preventing these extinction risks from climbing so high in the first place. By setting more aggressive carbon reduction goals and preventing the planet’s temperature from climbing too high, we can keep the climate threat to biodiversity comparatively low.
“I’m talking about predictive extinction risks,” Urban says of his analysis. “It doesn’t mean those risks need to be realized.”