Last December, at the Paris COP21 conference, 178 nations pledged to do their part to keep global average temperatures from rising more than 2 degrees Celsius (3.6 degrees Fahrenheit) over preindustrial levels -- adding on an even more challenging, but aspirational goal of holding temperatures at 1.5 degrees Celsius (2.7 degrees Fahrenheit). To this end, each nation produced a pledge to cut it's own carbon emissions, targeting everything from the burning of fossil fuels to deforestation to agriculture.
Eight months later, a study in the journal Nature finds that those pledges are nowhere near as ambitious as they need to be to keep temperatures below 2 degrees Celsius, let alone 1.5 degrees. And in August, British scientists reported that this year's record El Niño has already pushed us perilously close to the 1.5 degree milestone. While a temperature rise of 1.5 to 2 degrees Celsius, as opposed to 2.6 to 3.1 degrees Celsius, may not sound like much in numerical terms, many scientists have pinpointed the 2 degree target as the limit beyond which the world would face dangerous climate change. Impacts would likely, many say, become catastrophic if temperatures are allowed to come anywhere near 3 degrees Celsius (5.4 degrees Fahrenheit).
Joeri Rogelj, a researcher at the Energy Program of the International Institute for Applied Systems Analysis (IIASA), said that he wasn't surprised by findings showing that current national carbon reduction pledges would blast past the 2 degree target, leading to global warming of between 2.6 degrees Celsius and 3.1 degrees Celsius. He explained "The pledges currently on the table are a first step in a continuous process of pledging, reviewing, and taking stock to what they add up. This process has been defined by the Paris Agreement, and nations are thus expected to review and adjust their pledges in light of the best science over the coming years." The Paris Agreement was structured from the bottom up, whereby national pledges would be reviewed every 5 years (beginning in 2020) in order to make sure that carbon cut targets are boosted as time goes by. Rogelj cautioned, if pledges aren't sufficiently ramped up – and followed through on – it will make achieving the 2 degrees Celsius goal "significantly more ambitious" after 2030.
For some ecosystems a 2 degree C rise in temperature is already going to be a catastrophe. Tropical ecosystems, just like Arctic ecosystems, appear to be particularly vulnerable because species there have evolved within very specific and often narrow temperature ranges. As many species face escalating temperatures, they may simply not survive.
Nor is temperature the only global warming impact to consider: extreme weather, ocean acidification, and sea level rise are all effects that are currently, and will continue to be, felt across the tropics. Mark Urban, with the University of Connecticut, in a study last year looked at extinction risks for species linked to climate change. To get the best estimate possible, Urban analyzed findings from 131 studies.
He found that currently 2.8 percent of species face extinction due to climate change -- this with a warming of around 0.9 degrees Celsius. If that warming jumps to the Paris pledged 2 degrees, extinction rates could rise to 5.2 percent of all species on the planet. And if we hit 3.1 degrees Celsius this century, as projected by Joeri Rogelj's study, which totaled up the current Paris pledges and the maximum temperature rise they could bring? Then we could lose 9 percent of the world's species due to global warming.
That's nearly one-in-ten species facing extinction from climate change -- and of course that doesn't figure in extinction from other human induced threats like habitat degradation and destruction, deforestation, pollution, over-harvesting, poaching, invasive species, or a lethal combination of any two or more of these combined with climate change.