As a swollen Mississippi River breached levees last week, the U.S. Climate Change Science Program released a report that warned of more heavy precipitation events and associated flooding in the coming years due to global climate change. The report, entitled "Weather and Climate Extremes in a Changing Climate," is possibly the most thorough overview yet of the changing landscape of extreme weather and climate events in North America and the policy challenges that lie ahead in order to adequately manage climate-related risk.
The report, which is part of a series of narrowly focused climate science studies published by the Bush administration, found that extreme weather and climate events have been occurring with increasing regularity and severity in recent years in North America, largely as a result of human-induced climate change.
The report details shifts in temperature and precipitation extremes, as well as extreme weather events such as hurricanes. It cites evidence that shows that precipitation is now coming in heavier doses courtesy of human emissions of greenhouse gases, with lighter precipitation occurring less frequently.
The crucial link behind this trend, the report notes, is the increased water vapor in the air due to warming (warmer air holds more water vapor). "Heavy precipitation events averaged over North America have increased over the past 50 years, consistent with the observed increases in atmospheric water vapor, which have been associated with human-induced increases in greenhouse gases," the report states.
None of this information is profoundly new, since the increasing likelihood of extreme weather and climate events has been well-known at least since the mid 1990s. What is more interesting is the finding that, in the near to mid-term at least, more frequent and severe extremes will be one of the most important manifestations of climate change in North America. "We will continue to see some of the biggest impacts of global warming coming from changes in weather and climate extremes," said report co-chair Gerry Meehl, of the National Center for Atmospheric Research in Boulder, Colo in a press release.
Adapting to these new extremes, the report notes, will not come cheaply, nor will it be easily accomplished.
For an example of a broken human management system of weather extremes, look no further than the network of levees that have tried to hold back the Mississippi River and other rivers in recent days. As the New York Times described in its Sunday edition, the Mississippi's levees come under state, local and federal jurisdiction, with no single overriding authority present to perform regular inspections and require that levees comply with construction standards. In fact, the feds don't even know where all of the levees are!
The report makes clear that numerous sectors of society have a large role to play in determining how disruptive future weather and climate extremes will be. For example, policymakers will soon need to decide whether homes and businesses should be rebuilt in Iowa flood zones, or if policies should discourage such development. The decision in this case will have ramifications for the next major flood, be it in 10 years or 50 years.
In fact, levees may not be that great anyway. The report cites the "levee effect" as a contributor to escalating losses from major flooding events. This phenomenon, the report states, is when flood control measures such as building levees encourage development in flood-prone areas because of a perceived sense of safety. This can protect people from small flood events, but may make society more susceptible to losses when a major event hits, such as the ongoing flooding.
"Moderate flood control measures on a river can stimulate development in a now "safe" floodplain," the report states, "only to see those new structures damaged when a very large flood occurs."
The flooding in the Midwest could provide an opportunity for policymakers to rethink the pattern of development and flood control in that region. However, recent experience argues against such a development, the report implies, noting the demand to rebuild vulnerable neighborhoods after Hurricane Katrina.
The report was led by Meehl and Thomas Karl, the director of the National Climatic Data Center in Asheville, North Carolina. Because Karl had conducted some of the research that was included in the report (as did Meehl), his leadership of the team was called into question last week when University of Colorado atmospheric scientist Roger Pielke Sr. accused the authors of selectively excluding information that went against their own research.
"Since this assessment is so clearly biased, it should be rejected as providing adequate climate information to policymakers," Pielke Sr. wrote on his web site. "There also should be questions raised concerning having the same individuals preparing these reports in which they are using them to promote their own perspective on the climate, and deliberately excluding peer reviewed papers that disagree with their viewpoint and research papers. This is a serious conflict of interest."
Karl and Meehl are widely cited experts on weather and climate extremes, particularly concerning precipitation extremes. However, if they did exclude peer-reviewed research that disagreed with their own conclusions, without providing adequate scientific justification for doing so, then that would indeed call into question some of the report's conclusions. It will be interesting to see if Karl and the co-authors respond to this criticism in the coming days. I will note this in the comments section of this column, and also welcome readers' thoughts on this study and its importance.