Until this week, there was a broad consensus among climate scientists and policymakers that capping warming at two degrees Celsius (above preindustrial levels) was the best humanity could hope for. That level of warming might be enough to imperil millions in underdeveloped island nations; increase the severity and frequency of extreme weather; and create agricultural crises in regions throughout the world. But human civilization could still (probably) weather it. Anyway, keeping warming significantly below that figure just didn’t seem plausible.
To limit warming to the earlier goal of 1.5 degrees Celsius, humanity would need to emit no more than 245 billion tons of CO2 into the atmosphere after 2015, according to data from the the U.N.’s Intergovernmental Panel on Climate Change (IPCC). At present, we emit around 41 billion tons each year. Maybe you think our global economic system is only four to five years away from kicking its carbon habit; unfortunately, no one who has put any significant thought into this subject (or ever heard the phrase “President Trump”) would agree with you.
But a new study challenges the IPCC’s data — and suggests that limiting warming to 1.5 degrees is far more possible than previously thought. According to a team of researchers led by Richard Millar of the University of Oxford, the Earth-system models that the IPCC has been relying on have been slightly overestimating the pace of warming — while, simultaneously, slightly underestimating the amount of CO2 emissions required to produce such warming. These minor discrepancies have, thus, led the international panel to underestimate how much time humanity still has to avert dangerous levels of warming. In truth, humanity can still emit a little more than 700 billions tons of carbon dioxide without ensuring warming in excess of 1.5 degrees Celsius — or so this new study in Nature Geoscience suggests.
Unsurprisingly (and appropriately), the findings are being met with a good deal of skepticism.
“It is very hard to see how we could still have a substantial CO2 emissions budget left for 1.5 °C, given we’re already at 1 °C, thermal inertia means we’ll catch up with some more warming even without increased radiative forcing, and any CO2 emissions reductions inevitably comes with reduced aerosol load as well, the latter reduction causing some further warming,” Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany told the Washington Post. “They appear to have adjusted the budget upward based on the idea that there has been less observed warming than suggested by the climate models, but that is not actually true if you do the comparison properly.”
The study’s calculations and methodology will face plenty of scientific scrutiny in the coming months. Meanwhile, fossil-fuel interests are sure to exploit the new findings for their own purposes. But no matter whose math you accept, the prudent course for global policy remains the same: Effect a transition to a less carbon-intensive global economy as fast as practically possible.
“Even with the largest estimates of the remaining carbon budget,” Millar said at a press event Monday, “this path is extremely challenging, starting reductions immediately and then reducing emissions to zero over 40 years,”
The upshot of this new data then, shouldn’t be that we can blithely burn way more carbon than the U.N. thought, and still keep warming south of 2 degrees. Rather, the takeaway should be that we may still have an opportunity to keep warming below 1.5 degrees — and we must move with all deliberate speed to capitalize on it.