COMMITTEE ON SCIENCE, SPACE, AND TECHNOLOGY
Subcommittee on Environment
RESPONSES OF ROGER PIELKE, JR. TO
Hearing Questions for the Record
The Honorable Lamar Smith
A Factual Look at the Relationship between Climate and Weather
1. Everyone from the UN Intergovernmental Panel on Climate Change to the President to the journal Nature have admitted it is very difficult to attribute specific weather events to climate change. However, Dr. Titley and Dr. James Hansen have argued that man-made climate has resulted in the deck being stacked toward more extreme weather events generally.
a. Is this characterization correct? Is there a detectable signal that these events have been made more likely over the scale of decades?
PIELKE RESPONSE: Debate over the influence of human-caused climate change on extreme events often conflates expectations for the future with observations of the past. The scientific literature, as assessed by the Intergovernmental Panel on Climate Change, does include projections for some types of extreme events to become more frequent and/or more intense. At the same time, as I summarized in my testimony, there is very limited evidence to support claims that such increases in frequency and/or intensity have been observed in most types of extremes – notably, the incidence and impacts of tropical cyclones (hurricanes), floods, drought, tornadoes and winter storms. Given a set of projections for changes in frequency/intensity of particular extreme events, it is a mathematical exercise to calculate when such changes might be detected in the observational record. As I detailed in my testimony, such detection may lie in the distant future. Consequently, that no such signal is detected today is consistent with long-term projections. That is, we should not expect to see changes in most types of extreme at the present time and this is indeed what the data shows.2. In light of the last decade and a half of global temperatures not rising, have we learned anything new about the relationship between temperature and extreme weather events?
a. In light of this “pause,” how can the President and others continue to project with medium and high confidence that certain extremes may get worse?
PIELKE RESPONSE: While the issue of the so-called “pause” in global temperature increases has attracted considerable attention, it is not of direct relevance to understanding either the historical patterns of most extreme events or long-term projections for their future evolution.3. Dr. Titley’s testimony cites a single study regarding one climate model about tropical cyclone activity in the 21st century when making that claim that “our future may include more intense, and possibly more frequent storms.”
a. How is this claim consistent with the IPCC’s recently-revised projection that there is “low confidence” in any increase in intense tropical cyclone activity through 2050?
PIELKE RESPONSE: Dr. Titley is correct to say that “our future may include more intense, and possibly more frequent storms.” However, it would also be correct to say that “our future may include less intense, and possibly less frequent storms.” Looking across studies, rather than at any single study, the IPCC concludes, “there is low confidence in region-specific projections of frequency and intensity.”4. Has man-made climate change contributed to increased intensity or frequency of wildfires is the U.S., as the President has indicated?
PIELKE RESPONSE: The IPCC AR5 does not detect or attribute a linkage between human-caused climate change and wildfire intensity or frequency. However, there is ample literature to suggest that such a connection is plausible. The many factors which influence wildfire incidence, many of which are related to human activities, make the detection and attribution of signals difficult.5. Were the recent floods in Colorado driven by man-made climate change?
PIELKE RESPONSE: Attribution of causality to human-caused climate change for single-events remains a much debated topic and of questionable scientific value. Flooding in the US Southwest, including Colorado has decreased on climate time-scales (Hirsch and Ryberg 2012).6. Is there evidence that recent historic droughts in Texas have been driven by man-made climate change?
PIELKE RESPONSE: You will find conflicting claims on Texas drought in the literature. A NOAA report does not find strong evidence for such a linkage. Another recent study is suggestive of a linkage. Attribution of causality to human-caused climate change for single-events remains a much debated topic and of questionable scientific value. Drought in the US, as I documented in my testimony, has not increased nation-wide or globally on climate timescales.7. Were there any aspects of testimony received during the hearing regarding extreme weather events and climate change that you would like to elaborate on further?
PIELKE RESPONSE: No. I am quite satisfied with the breath of information that I shared in my testimony.8. Were there any aspects of testimony received during the hearing regarding extreme weather and climate change that you disagree with? If so, please elaborate.
PIELKE RESPONSE: No.