On December 11th, the US Congress Committee on Science, Space, and Technology (labeled by many the House Anti-Science Committee for the unscientific views of many of its Republican members) held a hearing on the link between climate change and extreme weather events. Unfortunately, like many such hearings, the purpose of the event appeared to be more about reinforcing preconceived notions than educating committee members. This was made clear by a simple examination of the invited witnesses.
The Republicans on the committee invited two witnesses, John Christy and Roger Pielke Jr. House Republicans regularly invite Christy to testify on climate issues, because he's one of the less than 3 percent of climate experts whose research indicates that the human contribution to global warming is relatively small. Christy also reliably provides factually inaccurate testimony at these hearings, and this time around was no exception. In fact, Christy led off his written testimony with the following myth:
"As the global temperature failed to warm over the past 15 years..."
John Christy and Roy Spencer compile satellite measurements of the temperature of the Earth's atmosphere at the University of Alabama at Huntsville (UAH). Their data set estimates the warming of the lowest layer of the Earth's atmosphere at 0.21°C over the past 15 years, so Christy's opening statement is in direct contradiction with his own data. New estimates of average global surface temperatures also put the value at about 0.21°C global surface warming over the past 15 years.
Additionally, the warming of the atmosphere only accounts for about 2 percent of the warming of the global climate, which as a whole has accumulated heat at a rate equivalent to 4 Hiroshima atomic bomb detonations per second over the past 15 years. Perhaps the House Republicans keep inviting Christy to testify because he tells them what they want to hear regardless of its factual accuracy.
Global heat accumulation from Nuccitelli et al. (2012)
Roger Pielke Jr. was more factually accurate with his testimony, but conveniently for those who favor climate inaction, he's known for downplaying the link between human-caused climate change and extreme weather events. This link is often difficult to make because our records of some types of extreme weather measurements aren't very good, and because it's difficult to tease out human contributions from natural variation. Pielke tends to focus on the links we can't yet make while downplaying or ignoring the links that we can.
For example, human-caused global warming has increased the frequency and/or intensity of heat waves, extreme storms, floods in some areas, and droughts in some areas. We know that hurricane intensity in the North Atlantic has increased, and is expected to continue increasing as global warming continues, because warmer oceans are fuel for hurricanes. New preliminary research from James Elsner suggests that US tornadoes may be becoming more intense, and a new paper led by Kevin Trenberth suggests that global warming will also make droughts more intense.
Pielke also claimed,
"The United States is currently in a remarkable stretch with no major hurricane (Category 3+) landfalls"
While Sandy was technically a Category 1 hurricane when it made landfall, it was also more energetic than Hurricane Katrina at landfall, and inflicted about $50bn in damages. People living in New Jersey and New York would likely object to the claim that Sandy was not a major hurricane.
To counter the testimony from the Republican witnesses downplaying the risks from climate-amplified extreme weather, Democrats invited retired Navy Rear Admiral David Titley, who's now the director of the Center for Solutions to Weather and Climate Risk at Penn State. As his title suggests, Titley focused on approaching the problem from a risk management perspective. In his written testimony, Titley noted,
"The Absence of Evidence is not the Evidence of Absence ... to ignore the possibility of change is the same as assuming we have high confidence there will be no change - and that is simply not true."
In other words, while we can't yet confidently link human-caused climate change to some types of extreme weather, that doesn't necessarily mean there is no link. Titley also used his military background to draw an analogy to risk management in national defense, showing the following chart.
Posted by dana1981 on Thursday, 26 December, 2013
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