Thursday, December 1st 2011, 2:23 PM EST
Extreme weather events have recently assumed a central role in the global warming discussion. Al Gore spent the majority of his recent “24 Hours of Reality” internet program on extreme weather. Peter Gleick last week wrote a Forbes.com column in which he asserted a disbelief in “the increasing severity of extreme weather events influenced by climate change” is what distinguishes scientific skeptics from anti-science “deniers.” According to a recently published United Nations Intergovernmental Panel on Climate Change (IPCC) report, however, there are many scientific gaps regarding asserted connections between global warming and extreme weather events.
The IPCC report, “Summary for Policymakers of the Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX),” individually addresses several of the most frequently asserted extreme weather issues. SREX co-chair Qin Dahe discusses these in a press release accompanying the report.
Dahe first addresses claims of more extreme temperature events due to global warming. According to Dahe, “There is high confidence that both maximum and minimum daily temperatures have increased on a global scale due to the increase in greenhouse gases.” In other words, there is an increase in extreme heat but a decrease in extreme cold. Accordingly, there is little or no change in the frequency of extreme temperature events as a whole.
Turning next to droughts, Dahe reports only a “medium confidence” in assertions that global warming is causing more intense and lengthy droughts. According to Dahe, there is “a lack of direct observations and a lack of agreement in the available scientific studies” regarding global warming and drought. In common terms, a lack of direct observations and a lack of agreement in scientific studies means such assertions amount to unproven speculation rather than fact.
Moving on to tropical cyclones, Dahe reports, “Confidence in any long-term trend in tropical cyclone intensity, frequency or duration is assessed to be low.”
Perhaps the most compelling evidence for an increase in extreme weather events relates to heavy precipitation situations. The report finds, “It is likely that the frequency of heavy precipitation will increase in the 21st century over many regions.” Even here, however, there are important caveats. The increase in heavy precipitation is merely “likely” (meaning at least a 66% probability) rather than “very likely” (meaning at least a 90% probability). Moreover, the “likely” increase applies to “many” region” rather than “most” regions or the planet as a whole.
Still more importantly, the report does not find strong evidence that the increase in heavy precipitation events will cause an increase in flooding. According to the report, “overall there is low confidence at the global scale regarding climate-driven changes in magnitude or frequency of river-related flooding, due to limited evidence and because the causes of regional changes are complex.”
The most instructive findings of the report relate to economic damages from extreme weather events. Total economic losses from weather-related disasters are higher in developed countries with more property and wealth at risk. Economic losses in relation to Gross Domestic Product are higher in developing nations, however.
“Economic losses from weather- and climate-related disasters have been heavily influenced by increasing exposure of people and economic assets,” concludes the report. In other words, trends regarding total economic damages from extreme weather events largely reflect trends in property values and geographical patterns of development rather than trends regarding the frequency and severity of extreme weather events.
Folks like Gore and Gleick may claim that anyone with doubts about an asserted connection between global warming and an increasing severity of extreme weather events is an anti-science “denier,” but the facts, and even the United Nations Intergovernmental Panel on Climate Change, tell a different story.