Should really stop writing and get back to being on holiday, but thought I would just comment briefly on Watts Up With That (WUWT) recent post about Heidi Cullen’s Briefing to the United States Senate Committee on Environment. The WUWT post is called Heidi Cullen at Senate EPW: ‘73% increase in heavy downpours’ not supported by data.I didn’t actually watch her testimony, but you can download a copy of her briefing. The relevant part of the report appears to say
Heavy downpours are increasing nationally, especially over the past three to five decades. According to the National Climate Assessment (currently available in draft form 11) those events in the top 1 percentile of intensity have increased in every region of the contiguous United States since 1958 with the largest increases occurring in the Midwest
and Northeast and smallest increase occurring in the Northwest.
The report then includes the following figure. Firstly, this figure is showing the percentage increase in events that fall in the top 1% in terms of intensity. Secondly, I can’t find any mention of an increase of 73%. The closest is an increase of 74% in the Northeast. Clearly, over the whole USA, the increase is not 73%. Also, the data that WUWT uses to supposedly refute this claim is data showing the “percentage of streamgages above bankfull streamflow 1950-2012”. Heidi Cullen provides rainfall data (and there’s no evidence that there is a problem with this data) and WUWT then tries to refute something she may not have actually said by showing a plot of a completely different (although possibly related) set of data. Hmmm, not the most convincing debunking I’ve ever seen.
Heidi Cullen’s report then goes on to say something which, in my opinion, is quite important.
It is important to note that while the trend in intensity has been upward, it has not been steady. The record contains ups and downs from one decade to the next. This provides another example of the fact that human caused climate change hasn’t replaced natural climate variability: it appears on top of it.
I think this is a very important point. We will clearly continue to see variability in weather events. However, the excess energy in the climate system means that we will likely see more extreme events than would have been the case was global warming not happening.
Anyway, maybe a bit longer than I had intended but it does seem that WUWT has not only tried to refute something that Heidi Cullen didn’t actually say but also tried to do so using data that wasn’t actually suitable for refuting what Heidi Cullen was actually illustrating. As usual, happy to be corrected by those who know more than I do.