The international effort to limit global temperature rise to 2 degrees Celsius by the end of 2100 has its origins in the 1992 United Nations Framework Convention on Climate Change. Article 2 of the document calls for the “stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.” The two-degree threshold was later set by the 2009 Copenhagen Accord, in an effort to reduce global carbon dioxide emissions and deter the worst effects of climate change.
Since that time, however, several experts have come forward to say that, not only are most nations on track to overshoot their target emissions (and well before 2100), the 2°C was never a safe limit anyway.
“There was little scientific basis for the 2°C figure that was adopted,” David Victor, professor of international relations at UC San Diego, and his coauthor, Charles Kennel, director emeritus of the Scripps Institution of Oceanography, wrote last month in Nature, “but it offered a simple focal point and was familiar from earlier discussions … At the time, the 2°C goal sounded bold and perhaps feasible.”
The scientists go on to write that the goal is both “effectively unachievable” and “impractical.”
As early as 2008, scientists called the two-degree threshold into question in a paper published in the Proceedings of the National Academy of Sciences. They lay out myriad risks to biodiversity and the environment in the 1.5°C to 2.5°C range, an increased likelihood for coral bleaching between 1°C and 3°C, the continued loss of forest biomass to mountain pine beetles in British Columbia (an effect of present-day warming), and the increases in droughts, heat waves, floods and wildfires starting at less than 1°C of additional warming above 1990 levels.
Furthermore, the scientists point out that the IPCC’s assessed “likely range” (66-90 percent) of global temperature rise by 2100 (for the lowest emissions scenario) is already 1.1°C to 2.9°C. The highest emissions scenario puts global temperature rise between 2.4°C and 6.4°C.
Yet, since 2000, “the trajectory of global emissions is above the highest SRES scenario.”
In any case, “There is no such thing as a safe rise,” Bob Watson, chair of the IPCC from 1997 to 2002, told Aljazeera. “You will see food and water insecurity, human health problems, and sea level rise even with a 2 C rise.”
“Since the start of the Industrial Revolution, in the late 19th century, we’ve had about 1 C of warming, and even with that, we’ve already seen big changes in frequency of extreme events and big societal impacts,” Radley Horton, a scientist at the NASA Goddard Institute for Space Studies and Columbia University professor, also told the paper.
“We’ve seen more frequently deadly heat wave events as temperatures rise and more frequent coastal flooding as sea levels rise. These are not just more frequent or longer lasting, but when they happen they’re more severe.”
Scientists warn that hitting the two-degree ceiling will trigger positive feedback cycles, or warming processes that will lead to more warming, such as melting ice sheets in the Arctic leading to greater heat absorption, which lead to more ice melting and more heat absorption. This is happening right now.
Even the latest IPCC reports fail to account for the full scope of warming-associated disasters, as they take years to adequately research and write, making them out of date before they’re complete.
“The cutoff date is three to four years before it’s published, meaning this report is the extent of climate science in 2010 — and a number of things have happened since then,” writes David Spratt, an Australia-based climate blogger. “We now have evidence saying if we get to 2 C we’ll pass the tipping point to irreversible changes…which policymakers simply ignore.”
In all likelihood, we will go well past the two-degree threshold. According to the 2014 carbon emissions progress report from PricewaterhouseCoopers, current emissions figures from leading nations will send the planet over its carbon budget by 2034, resulting in a 4°C increase by century’s end.
A German study published in June also supports this case, warning that global emissions are on a course to warm the planet between 3°C and 4.6°C by 2100.