Justin Gillis: More on the Science of Clouds and Climate

Actually a bit better attempt (at least it’s not a rank hit piece)

I always wonder about these warming worriers because they don’t ask the basic questions.

Kevin Trenberth is a respected senior scientist with NCAR/UCAR who specializes in “climate change and global warming, particularly influences on drought, precipitation, hurricanes and other storms; El Niño, weather, and climate; global water and energy cycles“.

For a couple of decades he’s been working energy transfer through the atmosphere and states that “back radiation” (greenhouse effect) totals ~330 Watts per meter squared (W/m²). As most every schoolboy is told, earth’s “natural” greenhouse effect amounts to 33°C and 330W/m²/33°C resolves to 10W/m²/1°C or 0.1°C for every W/m².

The IPCC is certainly not discrete about declaring that each doubling of atmospheric CO₂ should deliver 3.7W/m² additional forcing which resolves to +0.37°C for each doubling of CO₂ – nowhere near the absurd claims from the modeling fraternity of 6°C and anything up to 10°C.

Unremarkably Trenberth’s calculations are in perfect agreement with Idso’s eight natural experiments.

This is how the world observably behaves. What’s the problem?

Nevertheless:

In a recent article, I mentioned that scientists are trying to use historical records and data sets to get a better handle on how clouds might respond to the warming of the planet.

It’s a crucial question because clouds are the biggest single uncertainty in the effort to forecast the future climate. Some contrarian scientists, as I wrote in my piece, assert that clouds will change in a way that largely offsets the human release of greenhouse gases. Most mainstream scientists are dubious that clouds could have such a large damping effect, but they do acknowledge substantial uncertainty. They say the bulk of the evidence suggests that clouds might have a neutral effect or might enhance planetary warming.

With the earth’s already having warmed modestly, scientists say it is a vexing problem to figure out whether anything has actually happened yet to clouds.

Our best observations of clouds, from a highly capable satellite now circling the Earth, go back only a bit longer than a decade. Many types of satellite and observational records stretch back well into the 20th century, but they are increasingly spotty as you go back in time. And scientists are trying to detect trends in cloud properties that are likely to be very small on a time scale of decades, so the short duration of the records really hobbles them.

If we wait long enough, of course, we will learn how clouds respond to global warming just by watching them. But that could take decades, and scientists and policymakers want answers sooner. So, valiant attempts are being made to do as much as possible with the existing data.

Perhaps the single most interesting paper came recently from Roger Davies, the Buckley-Glavish professor of climate physics at the University of Auckland in New Zealand, and Matthew Molloy, a student. They published a global analysis of cloud measurements spanning the first decade of data from a cloud-measuring instrument flying on NASA’s Terra satellite.

The results were preliminary, but provocative nonetheless. They found that on average, the heights of clouds around the world had dropped by about 1 percent over the decade ending in 2010. Since higher clouds tend to have more of a warming effect on the climate, this drop probably had a cooling effect.

Their finding is consistent with the idea of clouds as negative feedback – that is, an intrinsic response by the earth that will tend to offset some global warming. Consistent, that is, but the paper does not constitute definitive proof.

NYT