Surprise! Clouds have a cooling effect

Drawing attention to misinformed pseudoskeptical analyses of peer-reviewed climatology studies is usually counterproductive. But in this case, it's worth mentioning because the author makes such a common mistake that exploring the error might actually help shed light on the why so many people are easily led astray.

ResearchBlogging.orgThe offender is Anthony Watts, who is arguably (depending on how much weight you assign to blog popularity polls) among the most influential anti-science bloggers out there. His error was to confuse (or conflate, to use a fancier term beloved by social scientists) a direct effect with a feedback.

Most instances of this error involve the argument that because 1) there is so much more water vapor in the atmosphere than there is carbon dioxide (orders of magnitude), and 2) both are "greenhouse gases" whose presence is proportional to the amount of heat the atmosphere can trap, then logically, it is silly to worry about CO2 levels. The whole global warming scare is much abo about nothing, and there's no reason to stop pouring CO2 into the air.

Both 1 and 2 are correct. Indeed, most of the greenhouse effect is related to water vapor. But the conclusion does not follow, because water vapor is a feedback related to the amount of heat in the system. The hotter it gets, the more water evaporates and ends up in the atmosphere, where it helps trap more heat. But that vapor rapidly returns to a liquid state and falls to the surface in the water cycle. The amount of water available to the entire system is constant, and while changing the share that's in the air at any given moment can amplify the forces causing the greenhouse effect and therefore global warming, it doesn't cause the problem. It is a feedback. Water vapor's net effects only strengthen if the actual forcings strengthen. Remove the real causes and the Earth will stop warming, even though there will still be a lot more water vapor in the air than CO2.

Carbon dioxide, by comparison, is released to the atmosphere when carbon in fossil fuel deposits laid down a couple of hundred million years ago is burned. Unlike water, CO2 levels in the biosphere are changing. And changes in the amount of heat-trapping CO2 in the air changes the strength of the greenhouse effect. It is a forcing -- something that causes the problem. It is also part of a feedback loop as a warmer planet can release CO2 in the permafrost, for example, but it's CO2's role as a forcing that we can control, and why need need to stop burning so much fossil carbon. Stop burning carbon and the Earth will stop warming (eventually).

Watt's error is rooted a similar failure to appreciate the difference between what elements of a system do to the climate and how their effects on the climate can change. He applies this variety of muddled understanding to clouds, in discussing the subject.

A new paper in Meteorological Applications by Richard P. Allan of the University of Reading someone who's securely in the not-very-exclusive club of anthropogenic-climate-change-consensus supporters, by the way tweaks the effect of cloud cover on local climate conditions.

This is not all that remarkable. It's long been known that "the net effect of clouds is a cooling." You can read statements like that on old science-based blog posts like this one.

Or you can walk outside and wait for a cloud to pass in front of the sun.

Here's how the author of the blog post linked above, climatologist Bart Verheggen, explains it in a comment on Watt's blog:

I think you're confusing two issues:

- the net effect of clouds on climate

- the net feedback of clouds on a change in climate

The paper, as I read it with a first quick overview, addresses the first, whereas you interpret it as if it addresses the second.

They are two distinctly different issues. The second (clouds as feedback) is about how cloud cover and properties might change in response to a warming or cooling of the climate: Will the net cloud radiative effect become more or less negative[?]

[UPDATE: Allan has posted his own response at Watt's blog:

I was surprised that this paper was mis-interpreted as suggesting negative cloud feedback. This is a basic error by the author of the post that has been highlighted by many contributors including Roy Spencer.*]

We know what will happen with water vapor if the forcings of climate change continue to strengthen. It will create more vapor and consequently will amplify the warming. The question of what will happen with the clouds is proving harder to nail down. It's a critical question, because it is conceivable that more clouds could cool the Earth by reflecting more sunlight. But it is also conceivable that more clouds could trap more heat.

Allan's paper deals with the issues involved, but it doesn't answer the question. All it does is refine a number that climatologists use in their models all the time. (If you're interested, Allan's estimate is -21 watts per square meter). The older estimates are negative, too. Allan doesn't change the fundamental understanding of global warming science in any way whatsoever. And if Watts had any understanding of the basics of climate science he would know that.

Instead he writes a blog post trumpeting Allan's paper as support for the idea that clouds are putting the brakes on global warming. In a just universe, he would hang his head in shame and admit he just doesn't have a clue.

* Note that Roy Spencer is usually counted among those very few climatologists who don't agree with the ACC consensus.
Richard P. Allan (2011). Combining satellite data and models to estimate cloud radiative effect at the surface and in the atmosphere Meteorological Applications, 18 (3), 324-333 : 10.1002/met.285

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Actually, the role of clouds depends on so many things it is impossible to give a single number. Clouds may warm or cool depending on their distribution (nightside or dayside? High, with cold tops, or low, with warm tops?) or the albedo of the surface below them, at least. Here in Alaska in winter the effect is almost always warming at the surface. No question that clouds are one of the things hardest to handle in models, but at this point I'm not sure even of the sign of their effect. Only that the parameterizations now used are inaccurate.

You write "... it is conceivable that more clouds could cool the Earth by reflecting more sunlight. But it is also conceivable that more clouds could trap more heat."

Is it even clear that warming will lead to more clouds (of all types?) Even the sign of the change in cloud coverage in response to surface warming seems uncertain to me, though perhaps it's been covered elsewhere.

Douche boy continues his intentionally misinformed spinneret into irrelevance. Go douche boy! Go douche boy!

What a train wreck.

By Dannie douche (not verified) on 20 Sep 2011 #permalink

Watts also took the total cloud effect and compared it with just the enhanced greenhouse effect from a doubling of CO2 (and, obviously, just the direct forcing at that), so as to make the greenhouse effect appear small in comparison.

Comparing apples to apples, you'd have a total effect of +33°C from CO2 and -21°C from clouds. Watts spins this as +1.2°C from CO2 and -21°C from clouds.

"Even the sign of the change in cloud coverage in response to surface warming seems uncertain to me,"

The current consensus is that the overall effect is positive.

Since the past climate record is the result of this earth with all its clouds and so on included in that by definition also gives a range of 2-4.5C per doubling of CO2 with a best guess of 3C per doubling, and current warming indicates around 3.2C per doubling, it remains a VERY high wall for the deniers and the skeptics to jump over to show that the clouds will this time, for some reason, produce an exceptionally large cooling effect.

Gosh censoered eh. Who woulda thunk it?

By Neil Craig (not verified) on 21 Sep 2011 #permalink

Sun and Clouds instead of 3 ppm of plant food, OH MY!!???

Who coulda woulda thunk it!

By Momma Nature (not verified) on 21 Sep 2011 #permalink

I guess you just breathe on your garden to make it grow, then, momma nature. No need for watering or nitrogen fertiliser or composting or anything other than CO2, since it's all plant food.

PS maybe you can enlighten us: why are the plants on hunger strike? After all all this "plant food" is accumulating, so it MUST be because they're not eating it, right?

An edit request: for clarity, could you make "then logically..." a #3? (otherwise the brain has to figure out if it's part of #2, which you've said is correct; this distracts.)

The following statement confirms you have no idea what you're talking about:

"Or you can walk outside and wait for a cloud to pass in front of the sun."

obviously the cloud is absorbing some and reflecting the rest of the energy that otherwise would be felt as warmth.
Journalists and lawyers have no business discussing science.

"Or you can walk outside and wait for a cloud to pass in front of the sun."

And at night?

When it's a cloudy night, is it cooler than a clear night?

How about late evening or early morning? When a cloud passes in front of the sun then, do you feel cooler then?