Humanity can powerfully improve the survival odds of tens of thousands of species, but only if nations dramatically raise their ambitions in the fight against climate change, according to new research published on Thursday in the journal Science.
One key to salvaging plant and vertebrate habitat and protecting the world's biodiversity is to limit warming to the most challenging benchmark established under the 2015 Paris treaty—1.5 degrees Celsius of warming—not to the treaty's less stringent 2 degree guardrail, the study found.
The study assessed, in more detail than ever before, a key measure of extinction risk: the shrinking size of each species' current geographical range, or natural habitat. It projected that for an alarming number of species, their range size would shrink by at least half as temperatures rise past the Paris goals.
If nations do no more than they have pledged so far to reduce their greenhouse gas emissions—and warming consequently shoots past 3 degrees by the end of this century—6 percent of all vertebrates would be at risk. So would 44 percent of plants and a whopping 49 percent of insects.
But the dangers would be greatly reduced if warming can be limited to 1.5 degrees. That might protect the overwhelming majority of the 115,000 species assessed by the researchers. Just 4 percent of vertebrates would lose more than half of their current range. Only 8 percent of plants and 6 percent of insects would face that risk.
Keeping warming to 2 degrees is not nearly as effective, they found. The additional half degree of warming would double the impact on plants and vertebrate species, and triple the impact on insects.
First-of-Its-Kind Biodiversity Study
Conducted by researchers from the University of East Anglia in the United Kingdom and James Cook University in Australia, the study builds on their earlier work. For the first time, it examines insects and explores how effectively the extinction risks can be addressed by increasing ambition.
"If warming is limited to 1.5 degrees Celsius by 2100, then more species can keep up or even gain in range," said Rachel Warren, the study's lead researcher, "whereas if warming reached 2 degrees Celsius by 2100, many species cannot keep up and far more species lose large parts of their range."
The new research adds a compelling layer of evidence to the mounting risks of rising temperatures. The Intergovernmental Panel on Climate Change (IPCC) is currently revising a comprehensive draft report on the science behind the 1.5 degree target. This new report on endangered species was written in time to be reflected in the IPCC review, to be published in the fall.
A leaked copy of the latest IPCC draft, circulated for expert comment in the winter, noted in its summary that "local extinction (extirpation) risks are higher in a 2 degrees Celsius warmer world, compared to 1.5 degrees Celsius."
Race to Bolster Paris Treaty's Call for Action
At Paris, everyone recognized that the pledges to cut emissions would fall short of meeting the 2 degree target. Even so, the world's nations decided to shoot for 1.5 degrees, where the dangers become pronounced for small island states and other highly vulnerable people. Since then, talks about increasing ambition have made relatively little headway, and President Donald Trump has renounced the pledges of the Obama administration.
Whether the goal is 2 degrees or 1.5 degrees, scientists say it can only be met by bringing net emissions of carbon dioxide from burning fossil fuels to zero later in this century. The main difference is that with the more ambitious goal, emissions must be reduced much faster; some say it's already too late.
This urgency has been highlighted by one peer-reviewed study after another, as scientists explore the consequences of falling short. Hundreds of scientists have filed thousands of comments to the IPCC as it races to bolster the treaty's call for rapid action.
115,000 Species Studied; Insects Particularly Vulnerable
Since lost species never come back, and since many species perform vital ecosystem services, the growing risks of extinction are an especially profound aspect of climate change.
Until now, these problems have been studied in relatively few species, notably tropical coral reefs, which are already dying off under the approximately 1 degree of warming that's been observed so far. They may be partly saved if emissions are reduced aggressively enough to stay below 1.5 degrees.
This time, the researchers examined 115,000 species, including 34,000 insects and other invertebrates that previously have not been included in global studies of climate and biodiversity. (Roughly a million species of insects have been named, and there may be many more.)
Insects, it turned out, are particularly sensitive to temperature increases, and these findings are particularly alarming.
They focus attention on pollinators essential to agriculture and insects that serve as food for birds and animals. The researchers found that three groups of pollinators are especially vulnerable to climate risks—true flies, beetles, and moths and butterflies.
The study's authors concluded that meeting the most aggressive temperature target would most benefit species in Europe, Australia, the Amazon and southern Africa.
The study also looked at the ability of different species to migrate outside their normal ranges.
Birds, mammals and butterflies have better chances of relocating than other species as temperatures rise, the researchers found.