Guest essay by Eric Worrall
Bill McKibben sees climate change every day, and he wants you to see climate change as well. But his dramatic description of “Hiroshimas” worth of energy leaves out some important context.
How Fast Is the Climate Changing?: It’s a New World, Each and Every Day
By Bill McKibben
September 3, 2020
The struggle over climate change is necessarily political and economic and noisy—if we’re going to get anything done, we’ll have to do it in parliaments and stock exchanges, and quickly.
But, every once in a while, it’s worth stepping back and reminding ourselves what’s actually going on, silently, every hour of every day. And what’s going on is that we’re radically remaking our planet, in the course of a human lifetime. Hell, in the course of a human adolescence.
The sun, our star, pours out energy, which falls on this planet, where the atmosphere traps some of it. Because we’ve thickened that atmosphere by burning coal and gas and oil—in particular, because we’ve increased the amount of carbon dioxide and methane it contains—more of that sun’s energy is trapped around the Earth: about three-fourths of a watt of extra energy per square meter, or slightly less than, say, one of those tiny white Christmas-tree lights. But there are a lot of square meters on our planet—roughly five hundred and ten trillion of them, which is a lot of Christmas-tree lights. It’s the heat equivalent, to switch units rather dramatically, of exploding four Hiroshima-sized bombs each second.
We get a sense of what that feels like when we have a week like the one we just came through. Hurricane Laura detonated in intensity in a few hours before it made landfall—that escalation was one of the most rapid that has ever been observed in the Gulf of Mexico, and it’s because of the extra heat that’s available. …Read more: https://www.newyorker.com/news/annals-of-a-warming-planet/how-fast-is-the-climate-changing-its-a-new-world-each-and-every-day
Back in the real world, there is a weak correlation between warming and wind speed, but the correlation is not statistically significant (see the graph at the top of the page).
Bill McKibben’s talk of Hiroshima’s worth of energy is very dramatic. But that 3/4 of a watt per square meter Bill talks about has to be seen in the context of other climate phenomena, such as changes to insolation caused by Earth’s not quite circular orbit around the Sun.
In January the Earth is only 0.9833 AU from the Sun, in June the Earth is 1.017 AU from the sun (AU – astronomical unit = 93 million miles). This results in a variation of solar intensity of 1413 w/m2 in early January, when the Earth is closest to the sun, which drops to 1321 w/m2 in June.
Obviously there are other numbers you could use, such as total sunlight striking the Earth’s surface, but my point is natural annual variations in total solar intensity are at least an order of magnitude larger than any anthropogenic CO2 signal.
In the context of this and other large climate shifts such as seasons, variations in snow cover, or random changes in ocean currents and cloudiness, Bill McKibben’s 3/4 of a watt / square meter of anthropogenic warming could best be described as “noise”.
There is no substantial evidence anthropogenic CO2 is adding enough energy to the climate system to make a significant difference to storm intensity.
Correction (EW): 1.017 AU, not 1017AU (h/t Dave Yaussy)