Two weeks ago, I interviewed Dr. Roy Spencer from the University of Alabama, Huntsville. Spencer is a trained atmospheric scientist and actively publishes in peer-reviewed journals –  he is also a global warming skeptic. Given his background and contrarian views, I asked Spencer what evidence there is to suggest that a majority of the climate science community is wrong about global warming.

He explained that the IPCC climate models used to forecast drastic temperature increases assume that low level clouds, which tend to cool the climate, dissipate in response to warming from CO2 emissions. The assumption is based on the observation that warmer years tend to have less cloud cover than cooler years. 

Spencer argues that the IPCC is mixing up cause and effect; the warming could actually be caused by decreases in cloud cover. If he is correct, there are good reasons to believe that increases in cloud cover will mitigate the warming caused by CO2 emissions, and, as a result, global warming may not be the disaster many scientists anticipate.

Some readers took issue with that theory. Patrick Lockerby was so moved by the interview that he wrote a fairly lengthy rebuttal to it. Given the detailed criticism, I asked Spencer to briefly respond. 

Patrick Lockerby argues that Spencer's theory has been falsified  because regions of the earth with both the least and most amounts of cloud cover are experiencing above average warming. If both regions are warming, how can clouds mitigate global warming?

Roy Spencer:
It is well known that one can not simply look at the temperature and cloud cover of different *regions* to deduce cloud feedbacks.  Even [the] examples of regions which have experienced “higher than average warming” do not make any sense: deserts, forests, ice sheets and glaciers, the Arctic and Antarctic.  Of these, only the Arctic has obviously experienced higher than average warming.

But this is a red herring anyway.  Cloudy and clear regions are interconnected as a single system, and cannot be pointed to separately to infer much of anything about cloud feedbacks.  Generally speaking, cloudy regions are where rising air driven by latent heat release in clouds exists, and clear regions are where air sinks in response to the rising air, sometimes thousands of kilometers away. 

Determining cloud feedbacks is not a matter of comparing these cloudy regions to the clear regions, but a matter of determining how the whole system changes with warming, e.g., when averaged over the whole Earth, does average cloudiness increase or decrease with warming?  This is what I am talking about, and what researchers of the subject publish results on.
Lockerby also took issue with the assumed 50 meter ocean depth in Spencer's model. The argument being that any model making unrealistic assumptions cannot accurately explain what is really happening. An ocean depth of 50 meters is not realistic; therefore, Spencer's model has little scientific value. 

Roy Spencer:
[Patrick Lockerby's] criticism of the simple climate model I use to demonstrate basic concepts is that my assumed ocean depth for mixing of heat (50 meters) is a poor choice...[I]t is clear he has not read any of my writings on the subject since the cloud 'illusion' I am talking about exists independent of the assumed ocean depth, independent of the time scale of the forcings that cause temperature change, and independent of whether the model experiment assumes positive or negative cloud feedback.  These are all adjustable parameters in the model, which is publicly available.

In conclusion, I should point out that the handful of top climate researchers who provided the peer review of our papers on this subject do indeed understand what I am talking about.  It would behoove Mr. Lockerby to also come up to speed before he criticizes that which he does not understand.