Sound Science Bite: June 13. The May 2015 Texas Floods: Proof of Global Warming?
As was widely reported in the news, parts of Texas suffered devastating flash floods in May, 2015: floods that should statistically occur only once in about a thousand years when you consider that trees several hundred years old were washed away. A reporter asked Texas Senator Ted Cruz about the possible role of global warming, and he responded to the effect that the reporter was trying to politicize a tragedy. Although I agree the question was probably inappropriate given the circumstances, Ted Cruz and many other politicians have been busily politicizing this issue for years.
So, what is the answer? Was this flood a consequence of climate change? Well, "yes" and "no". Greenhouse gases don't in themselves change the average temperature of the earth. They redirect the flow of infrared radiation, changing the temperature distribution in the atmosphere, warming the lower levels and cooling the upper ones. But, the fact they change the temperature distribution means they change the weather and climate, because temperature differences are key to driving weather patterns.
So, "yes", the weather in central Texas would have been different during May were there less greenhouse gases in the atmosphere. But, "no", because really good weather somewhere else would also be due to the changed atmosphere. Instead of a beautiful, sunny day at some location, maybe, with pre-industrial levels of greenhouse gases, there would be an EF-5 tornado. It's only by keeping records and studying statistics that you can ascertain if there are increasingly violent weather events. Even then, you have to determine causality. Basically, atmospheric scientists compare what research and computer models say may occur with actual weather trends to indicate whether or not climate change might be responsible for an increase in extreme events. Currently, the evidence seems to be that there is an increase in extreme events due to climate change. However, the record is not long enough at this time to be sure. On the other hand, who wants to roll the dice when the consequences could be so dire?