Disclaimer: I am now retired, and am therefore no longer an expert on anything. This blog post presents only my opinions, and anything in it should not be relied on.
I continue to monitor the CO2 results measured at Mauna Loa, as pretty much the best indicator out there as to whether our recent efforts at mitigating climate change are having any effect at all, or whether the rate of growth of atmospheric CO2 continues to increase as it has for the last atmospheric growth.
I have been doing this since around 2010, and have only seen two months’ data over that time that suggested there might be some leveling of the CO2 growth rate. Of course, that is only the first step in saving the planet – the second is to start decreasing the growth rate, the third is to drive the growth rate to zero, and the final step (which is the point at which we will actually be doing something positive about climate change) is to pursue decreases in CO2 until it reaches about 280 ppm (a far harder task than boosting its level).
The first of the two data points was last May. For no obvious reason (and therefore the likeliest reason was actual effectiveness in cutting CO2 emissions) May was almost flat compared to April, although April was a normal-growth month and in all previous years since 2010 May has been significantly above April. Oh well, maybe it was a one-time event.
But then came March of this year. As I have never seen before, March has been significantly below February. It still appears likely that May will end up above 420 ppm – an important milestone, since average yearly atmospheric CO2 was around 280 ppm in the early 1800s before human-caused global warming began. Each doubling of CO2 is projected to be associated with 3-4 degrees Celsius of global warming (perhaps two-thirds of that being directly caused by CO2 itself), so reaching 420 ppm should in the long run be associated with 2-2.67 degrees of warming. In any event, reaching 420 ppm is clearly unadulterated Bad News.
However, the second downturn from trend in the last year suggests that maybe, just maybe, we are reaching the point of a level growth rate in atmospheric CO2. This is slightly supported by the fact that the last four years of CO2 growth rates have been in the 2.3-2.5 range – a period which seems to have mixed mild La Nina (inhibiting CO2 growth rates) and neutral (no effect on CO2 growth rates) weather. Since this is not too far from the typical case across history (El Nino being more of an exception than La Nina), I conclude that there are therefore three possible signs that a leveling of CO2 growth rates may have been reached.
Thoughts on Implications
I admit that I base my thinking loosely on a draft paper by James Hansen et al in which he argued that the maximum number of doublings of CO2 would be three or four (somewhere above 2240 ppm). This would be achieved, iirc, if approximately 60-70% of the fossil-fuel reserves identified at the time of writing (2013 or so) were burned. At the pace at which use was increasing at the time, the appropriate amount of fossil fuels would have been burned and its CO2 moved into the atmosphere in 50-60 years time. Thus, a continued rise in the growth rate of CO2 represents this worst-case scenario: if the last nine years continued the growth-rate rise trend, then we would have narrowed the time for avoiding the worst-case scenario to 40-50 years in the future – not to mention drastically decreasing the chances of avoiding the first and second doublings.
Therefore, I argue, what we would have achieved by leveling the growth rate of atmospheric CO2 is at least more time to avoid the worst-case scenario, and at best a major decrease in the probability of reaching the worst-case scenario. That is the sense in which I say, this is slightly less bad news. Considering that the worst-case scenario as described by Hansen involves the death of most of the human race, not to mention much of the rest of the environment – in this nightmare scenario, if you go outside in most places to work during the day during most of the year and stay out more than an hour, you will die of heat stroke – anything that reduces that likelihood is to be celebrated. But the first two doublings involve the deaths perhaps of hundreds of millions to a billion, so we should be clear-eyed about increasing toughness of the job ahead, even with this news, and recognize that those who seek to prevent us from decreasing that growth rate for their own selfish purposes may well be murderers beyond the scale of the Holocaust, or the Holodomor, or WW II.
But enough of gloom. Go enjoy the slightly less bad news, he said on his birthday.
