Cloud-temperature feedback

In my three feet of global warming note, I mentioned that two processes in the climate system are a) warmer temperatures -> more moisture in the atmosphere, and b) more moisture -> more severe storms.  A commenter followed up wondering how warming could actually take place, if a) more moisture -> more clouds and  b) more clouds -> cooler temperatures.

A key word there is if.  Although warmer temperatures are observed to lead to more moisture in the atmosphere, it isn't clear that more moisture actually leads to more clouds.  Section 3.4.3 of the IPCC report gives you an overview of the literature on the topic.  Depending on which scientific paper you read, it's more cloud, less cloud, or more over one surface type and less over another.  In other words, an area of significant scientific debate.

It's also a question whether more clouds mean cooler temperatures.  If you're from a cold weather climate, you've experienced that on clear days you get a nice warm daytime temperature, but also a blistering cold nighttime.  Because of those very cold nights, cloudy days can actually average warmer than a sunny day.  The daytime isn't quite as warm, but the night time is far warmer.

Let's take a deeper look in to the relationships between clouds, in particular to look at the feedback on temperature.  You'll notice that the commenter's question is about a feedback -- we start with temperature, and processes occur which ultimately lead to an effect on temperature.  What I'd originally talked about was a straightforward chain.  One thing causes another, causes another.  But no effect on the term or process that started us off.  We'll ultimately get back to the simplest climate model, as it can help shed some light on the question as well.

Read more »