We have long known that, even if we stop producing greenhouse gases today, the planet will continue to warm for some time. The article in the url below quantifies the extent of this causal relationship:
"Much of the international effort thus far to combat climate change has focused on cutting emissions of greenhouse gases, chief among them carbon dioxide. That is, of course, a rational approach. … But greenhouse-gas emissions do not cause an instantaneous rise in global temperatures, and neither does cutting them result in instantaneous cooling. Instead, it will take decades for today's policy efforts to result in measurable impacts on global temperature."
How many decades exactly? Researchers used hypothetical scenarios to simulate the range of possibilities:
"[The researchers] probed hypothetical futures in which emissions of nine different industrial pollutants, including carbon dioxide and methane, were either eliminated instantly or phased out at a rate of 5% each year, starting in 2020."
The results are not very encouraging:
"Running these simulations over and over again in order to get statistically reliable results suggests that cutting CO2 emissions could slow the rate of warming as early as 2033, but only if they are ended worldwide in 2020. In effect, that would mean eliminating 80% of the world's energy sources, including shutting down all fossil-fuel power stations, overnight—clearly not a realistic or desirable scenario."
More realistic scenarios understandably produced more worrying results:
"Reducing CO₂ by 5% per year, starting this year, would produce a statistically significant deviation from what temperatures would have otherwise been only in 2044. And yet, even that rate of CO2 reduction is ambitious, on a par with the 4-7% drop estimated this year as a result of the covid-19 pandemic and widespread economic shutdowns. Before this, annual emissions were creeping up. Without concerted efforts from governments, they are likely to rise again as economies reopen."
There are a number of reasons for this:
"The main reason for the delay, however, is that carbon dioxide emitted today will remain in the atmosphere for decades to centuries before it is reabsorbed by vegetation and the oceans. That is not true of other industrial emissions. Each molecule of methane warms the planet 84-87 times more, averaged over 20 years, than carbon dioxide, but it stays aloft for merely years instead of decades or centuries."
The main takeaway from this research is that atmospheric temperature may not be the best measure we have to indicate progress on combating climate change. The Paris Agreement, for example, contains the overall commitment to try and limit global warming to below 2 degrees centigrade. But, the research summarized here suggests that, even though we can (in theory) make great strides in reducing emissions, temperatures will continue to rise for many years to come. This makes temperature a misleading indicator of progress:
"Instead, direct measurements of the concentrations of greenhouse gases in the atmosphere may be better, as they will remove the confounding effect of natural variability. And without clever messaging, there could be a public backlash against seemingly ineffectual policies."
More immediately, however:
"… results like these underline that even as economies begin to decarbonise, governments and societies need to drastically step up efforts to adapt to the inevitable warming that lies ahead."
Take care
David
David Chandler
© Sage Publications, 2020
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Delayed cool
July 11, 2020
The Economist
Late Edition – Final
65
