Yet another new study finds the climate’s sensitivity to carbon pollution is on the high side. That means, absent rapid reductions in greenhouse gases, global warming is likely to be high enough to destroy a livable climate.
This is consistent with a January Nature study on climate sensitivity, which found we are headed toward a “most-likely warming of roughly 5°C [9°F] above modern [i.e. current] temperatures or 6°C [11°F] above preindustrial” temperatures this century.
This finding is also consistent with paleoclimate data (see “Last Time CO2 Levels Hit 400 Parts Per Million The Arctic Was 14°F Warmer!”). Also, this study is consistent with other recent observation-based analyses (see “Observations Support Predictions Of Extreme Warming And Worse Droughts This Century”).
And this study throws yet more cold water (hot water?) on some claims that the climate’s sensitivity is on the low side, claims that have been widely challenged and perhaps fatally undermined by the most recent studies.
As the NASA news release explains:
Global temperatures have increased at a rate of 0.22 °Fahrenheit (0.12 °Celsius) per decade since 1951. But since 1998, the rate of warming has been only 0.09°F (0.05°C) per decade — even as atmospheric carbon dioxide continues to rise at a rate similar to previous decades. Carbon dioxide is the most significant greenhouse gas generated by humans.
Some recent research, aimed at fine-tuning long-term warming projections by taking this slowdown into account, suggested Earth may be less sensitive to greenhouse gas increases than previously thought. The Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), which was issued in 2013 and was the consensus report on the state of climate change science, also reduced the lower range of Earth’s potential for global warming.
To put a number to climate change, researchers calculate what is called Earth’s “transient climate response.” This calculation determines how much global temperatures will change as atmospheric carbon dioxide continues to increase — at about 1 percent per year — until the total amount of atmospheric carbon dioxide has doubled. The estimates for transient climate response range from near 2.52°F (1.4°C) offered by recent research, to the IPCC’s estimate of 1.8°F (1.0°C). Shindell’s study estimates a transient climate response of 3.06°F (1.7°C), and determined it is unlikely values will be below 2.34°F (1.3°C).
It is worth noting that absent sharp CO2 reductions, we are headed toward a tripling of atmospheric CO2 levels this century, or even higher, which will lead to amplifying feedbacks (like carbon emissions from the defrosting permafrost) and almost unimaginable increases in temperature.
This study provides more evidence to support a 2013 New York Times piece on how the IPCC “seems to be bending over backward to be scientifically conservative” in its most recent assessment (see “Did Denier ‘Intimidation Tactics’ Move IPCC To ‘Lowball’ Sea Level Rise And Climate Sensitivity?“).
Michael Mann, one of the country’s top climatologists (who did not contribute to the paper), called the study “extremely important” and said it contains two especially key findings. First, the cooling effect of sulfate aerosols in recent decades may have been underestimated. Second, the concept of TCR may be flawed. Both findings point to the fact that the threat of future warming may have been underestimated, Mann said. “As shown in this article,” Mann said, “transient climate response doesn’t adequately distinguish between the short-term cooling effects of sulfate aerosols (which can disappear quickly) and the long-term, committed warming from carbon dioxide emissions which last in the atmosphere for centuries and beyond.”
So while we may have seen a slowdown in recent surface temperature warming — though not in ocean warming or glacial melt — future warming remains likely to be on the high side, if we stay on our current emissions pathway.
As lead author Drew Shindell, a NASA climatologist, put it:
“I wish we could take some solace from the slowdown in the rate of warming, but all the evidence now agrees that future warming is likely to be towards the high end of our estimates so it’s more clear than ever that we need large, rapid emissions reductions to avoid the worst damages from climate change.”
The science is clear. The solutions are here. It’s time for the political will to appear.