Good News, Bad News
But the bad outweighs the good ...
There have been glimmers of hope for averting climate change in recent years. But only glimmers.
The plot below, from James Hansen again, is the good news (such as it is). Overall, temperature forcing is trending in the wrong direction, but there were significant reductions in the latter part of last century - attributable mainly to methane and CFCs - shown by the narrowing of the blue and red regions respectively.
The climate forcing from methane (dark blue) decreased markedly in the 1980s and 1990s. Satellite data have shown that leakage from gas pipelines is a significant source of atmospheric methane. It’s been speculated that the collapse of fuel production in the Soviet Union following its breakup in 1991 may have been a factor. But other factors, including the drying of wetlands, are also important. Unfortunately, the contribution from methane again seems to be increasing after reaching a minimum about 15 years ago.
The warming contribution from gases under the control of the Montreal Protocol on Depletion of the Ozone Layer (red, mainly CFCs) reduced markedly over the 1990s phase out period mandated by the Protocol. As a result, although it was targeted towards solving the ozone problem, the Montreal Protocol has also done more than any other initiative to slow down the rate of climate change. (Even more so in light of the recent publication that I’ll discuss in a future post).
Without the phase-out of the old CFCs, temperatures would already be close to 1.5C above pre-industrial levels. Of course, had we not been using so much of those CFCs, their contribution would not have occurred in the first place. Their interim replacement chemicals (they’re called hydrochlorofluorocarbons, or HCFCs for short) had less effect on ozone, but stronger measures were still needed. Sadly, the newest ozone-friendly replacements (hydrofluorocarbons, or HFCs) that are currently being used instead are also potent greenhouse gases. So that red slice will soon increase unless we find new refrigerant chemicals to replace the HFCs.
So the “good” news wasn’t all that good really, was it? Though without those reductions we’d have already passed the 1.5C threshold by now.
The really bad news is that the added contribution each year from the sum of all greenhouse gases (GHGs) is still increasing, as shown in the figure below which uses data from the most recent IPCC report. It’s interesting that the temporary slowdown in emissions in the 1990s had a barely detectable effect on the upward trend in temperature. But, whatever future emissions path we take, we’ll very soon be passing the Paris Climate Accord’s aspirational 1.5C threshold. Perhaps within the next 3 years. And it’s likely that even their mandated 2.0C threshold will be surpassed by mid-century.
Thanks for reading this. Previous posts on the intersection between Ozone, UV, Climate, and Health can be found at my UV & You area at Substack. Click below to subscribe for occasional free updates.