Global warming: crime scene investigation
Closely related to my recent post about the ethics of global warming, is a post at Real Climate using the analogy of the TV shows CSI and Cold Case to help explain how climate science is done. Recent studies (of the past 30 years or so) are like looking at a fresh crime scene with blood still on the walls. While older climate studies (thousands of years ago) involve looking at more circumstantial evidence such as ice cores, ocean sediments,etc. They also address some claims from climate change deniers:
The most prevalent reasonably scientific question about current climate changes is ‘how do we know that this isn’t natural variability?’. A number of versions of that question came up in the House hearing last week (a nice report from the proceedings can be found here). Some of those comments were serious, some were ridiculous, but all essentially pointed to the same issue. Kevin Trenberth and Richard Alley answered it best when they pointed out that the causes of ‘natural variability’ - whether the sun, volcanoes or ocean changes - should be detectable (but haven’t been), and that the anthropogenic ‘hypothesis’ should have consequences that are also detectable (which have). Add in the modelling studies which indicate that current conditions can’t be explained without including greenhouse gases and you have a pretty solid case that what is happening is in large part anthropogenic.
Basically what they’re saying is that those who make the claim that natural variability is the primary cause of current climate change are making claims which we can test. Good ‘ol scientific method. And what do we find? The claims don’t stack up. If there are changes in the natural course of things, those changes should have predictable effects which we can then measure. We haven’t found any such effects. Then when speaking of human-caused greenhouse gases, there are also predictable effects we can measure, which have been found.
Even further, we can model what natural variability should look like in computer models, and it doesn’t account for current climate change. Anthropogenic (that is, human caused) related activities can.
However, it’s their next comments that address more closely what I was talking about earlier:
A rather more specious comment heard often (including at this hearing) is that ‘if it was warmer before, then the current warming must be natural’ or alternatively ‘if you can’t explain all of the past changes, how can you explain anything now?’. First of all, there are many periods in Earth history that are unequivocally accepted to be warmer than the present - the Pliocene (3 million years ago), the Eocene (50 million years ago) and the mid-Cretaceous (100 million years ago) for instance. Less clearly, the Eemian interglacial period or the Early Holocene may have been slightly warmer than today. Thus, if that logic were appropriate, no-one should bother worrying about climate change until sea levels start to approach mid-Cretaceous levels (about 100m above today’s level!).
However, the logic is fatally flawed. It is akin to a defense lawyer arguing that their client can’t possibly have committed a particular murder because other murders have happened in the past that were nothing to do with them. [emphasis added]
Indeed. I’m not sure if these critics actually believe their own analogies since they fall short in so many ways. There almost seems to be a shutting down of higher brain functions when the topic of global warming comes up. Either that, or people just put their fingers in their ears, close their eyes and hum to themselves, quietly praying that it will all just go away. Because how awful it would be if they had to try to do some work and try to figure out a solution to the problem. Change is scary.
