Not a bird. Not a plane. And not superman. It’s a cloud. Banal, you might think. But as Charles Blaisdell wrote recently on Watt’s Up With That, “The earth’s cloud cover has long been an important puzzle in climate change.” To which we respond that you ain’t foolin’. Indeed a viewer recently asked us why the computer models put so much emphasis on CO2 when the most important greenhouse gas, and this point really is settled science, is dihydrogen monoxide. And part of the answer is, rather embarrassingly, that the impact of water vapour and clouds is too complex for even ineffective modelling so they don’t like to think about it. Another part, more embarrassing in our view, is that you can’t blame people for it, so they don’t like to think about it. Unless they can find a way to blame people for clouds not behaving.
Clouds are as complicated as they are pretty. Blaisdell starts by noting that “Cloud cover has many types and varies significantly from year to year. Ground records of global cloud cover over 40 years have shown a 0.41%/decade decrease in cloud cover. (A 37-year European only study found a 1.4%/decade decrease).” And if we don’t even know what they’re doing, well, we’re going to have trouble explaining why. Or not, in the wacky world of climate science.
Blaisdell outlines some key unanswered questions: “When did cloud cover start to decrease? Is it cyclic? How much of the of the observed global warming, GW, can be attributed to cloud cover reduction? What is causing it? Will the decrease stop? And, why should I care?”
Then he answers the last one first: you should care because “every 1% reduction in cloud cover could account for 1.6 W/m^2 (about 0.8’C) increase in earth’s net incoming energy flux – a significant part of all the observed GW. If this decrease started a 100 years ago and the current decrease is 0.4%/decade the total decrease over that time could be 2% or 3.2 W/m^2 (estimated 1.6’C GW) – more than the observed 2.2 W/m^2 (1.1’C GW).” In short, the whole warming that has alarmists in such a lather could be due to declining cloud cover not CO2, man-made, natural or both.
Of course in alarmist world, things look different. If clouds are declining and letting in more solar energy, it could be the fault of man-made CO2 provided that substance, or other man-made GHGs, are causing clouds to decline. Mind you another awkward theory is that human land-use changes are affecting cloud formation. As Blaisdell explains, “Cold air meeting warm humid air is the most common way clouds are formed.” And both conversion of forest to farmland and farmland to cities could be reducing the humidity of the warmer air in significant ways.
If so, you get to blame people and prosperity. But on the downside, you don’t get to blame CO2 which is going to be an embarrassing climb-down at this point.
It's an interesting theory. It’s not settled science. But since the science of cloud formation generally is not settled, and the relationship of clouds to global warming is not settled, it’s something that urgently needs attention from anyone who can look away from the CO2 dogma. Though as noted you might still get to blame humans, and human prosperity, if that consideration matters more to you than adherence to the normal scientific method of seeking truth through the testing of hypotheses rather than moralistic denunciations.