The Yale School of Forestry and Environmental Studies, which isn't exactly the Heartland Institute or the Heritage Foundation "asked eight leading climate experts whether they think there is growing evidence that human-caused global warming is contributing to an increased incidence of extreme weather." Among the answers:
Andrew Watson, professor of environmental sciences at the University of East Anglia.
My answer to this question as posed is no...."Human-caused climate change" is something that will develop over decades to a century (the time scale on which greenhouse gas concentrations are changing), and evidence for or against it needs also to be considered over such lengths of time. So if you are thinking about recent events such as Hurricane Katrina, tornadoes in Alabama or Missouri, flooding in Bangladesh, Southeast Asia or on the Mississippi, my answer is that a few such examples of extreme weather cannot, by definition, be used as evidence for, or against, climate change.
Roger A. Pielke Jr., professor of environmental studies at the University of Colorado.
The IPCC [Intergovernmental Panel on Climate Change] defines "climate change" as a change in the statistics of weather occurring over 30 years or longer and persisting for decades. Thus, the detection of a change in climate requires long-term records. To suggest that particular extreme weather events are evidence of climate change is not just wrong, but wrongheaded — every bit as much as the claims made during a particularly cold and snowy winter (or even several in a row) that such events somehow disprove climate change. Weather is not climate and short-term climate variability is not climate change....Given this context, claims that particular events can be attributed in a causal fashion to human emissions of greenhouse gases are simply unscientific if not fundamentally incoherent. It is true that overall damage from tornadoes, floods, and hurricanes has been increasing in recent decades. A recent literature review of extreme event impacts around the world found that everywhere that researchers have looked, this increase can be entirely explained by increasing value of property at risk and increasing exposures to these hazards. Human-caused climate change is real and deserves effective policies in response. The making of claims that are scientifically unsupportable will not further that effort.