Humanity may have more time to avoid “dangerous” levels of global warming, and a 1.5°C long-term limit on average warming may still be within reach, according to a new carbon budget study published in the journal Nature Geoscience.
“But other outside researchers raised questions about the work, leaving it unclear whether the new analysis—which, if correct, would have very large implications—will stick,” the Washington Post reports.
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“What this paper means is that keeping warming to 1.5°C still remains a geophysical possibility, contrary to quite widespread belief,” said lead researcher Richard Millar of the University of Oxford.
Co-author Joeri Rogelj of Austria’s International Institute for Applied Systems Analysis explained that the recalculation was based on the observation that global warming has been somewhat less severe than models predict, even though greenhouse gas emissions have been somewhat higher.
“The most complex Earth system models that provided input to [the Intergovernmental Panel on Climate Change] tend to slightly overestimate historical warming, and at the same time underestimate compatible historical CO2 emissions,” he told the Post. “These two small discrepancies accumulate over time and lead to a slight underestimation of the remaining carbon budget. What we did in this study is to reset the uncertainties, starting from where we are today.”
The result: about 700 billion tons of additional atmospheric space, the equivalent of 20 years of present-day emissions, a suggestion that was tough to swallow for least one veteran climate scientist.
“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 1.0°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,” wrote Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research.
“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,” he added.
Oliver Geden, head of the EU Division at the German Institute for International and Security Affairs, warned that the new numbers could sow confusion.
“First, it is quite unusual that scientists say that the state of the climate is better than expected, that a recalculation of the remaining carbon budget gives us more breathing room, not less,” he told the Post in an email. “Second, it is far from clear that the authors’ method/results will form a new scientific consensus, given that some researchers are already voicing objections. A significant carbon budget recalculation should not come as a surprise, but for many policy-makers it will.”