A summary of key passages from the IPCC 2007 Fourth Assessment Report and recent CCSP reports on Weather and Climate Extremes, Impacts of Climate Variability and Change on Gulf Coast Transportation Systems and Infrastructure, and Effects of Climate Change on US Energy Production and Use.

From the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (2007)

Summary for Policymakers, Report of Working Group I, The Physical Science Basis

•  About the past: “There is observational evidence for an increase of intense tropical cyclone activity in the North Atlantic since about 1970, correlated with increases of tropical sea surface temperatures. There are also suggestions of increased intense tropical cyclone activity in some other regions where concerns over data quality are greater.  Multi-decadal variability and the quality of the tropical cyclone records prior to routine satellite observations in about 1970 complicate the detection of long-term trends in tropical cyclone activity. There is no clear trend in the annual numbers of tropical cyclones.”

•  About the future: “Based on a range of models, it is likely that future tropical cyclones (typhoons and hurricanes) will become more intense, with larger peak wind speeds and more heavy precipitation associated with ongoing increases of tropical SSTs. There is less confidence in projections of a global decrease in numbers of tropical cyclones.  The apparent increase in the proportion of very intense storms since 1970 in some regions is much larger than simulated by current models for that period.”

From recent U.S. Climate Change Science Program reports

Weather and Climate Extremes in a Changing Climate. Regions of Focus: North America, Hawaii, Caribbean, and U.S. Pacific Islands.

•  Atlantic tropical cyclone (hurricane) activity, as measured by both frequency and the Power Dissipation Index (which combines storm intensity, duration, and frequency) has increased. The increases are substantial since about 1970, and are likely substantial since the 1950s and 60s, in association with warming Atlantic sea surface temperatures. There is less confidence in data prior to about 1950.
•  There have been fluctuations in the number of tropical storms and hurricanes from decade to decade, and data uncertainty is larger in the early part of the record compared to the satellite era beginning in 1965. Even taking these factors into account, it is likely that the annual numbers of tropical storms, hurricanes, and major hurricanes in the North Atlantic have increased over the past 100 years, a time in which Atlantic sea surface temperatures also increased.
•  It is very likely that the human-induced increase in greenhouse gases has contributed to the increase in sea surface temperatures in the hurricane formation regions. Over the past 50 years there has been a strong statistical connection between tropical Atlantic sea surface temperatures and Atlantic hurricane activity as measured by the Power Dissipation Index (which combines storm intensity, duration, and frequency). This evidence suggests a human contribution to recent hurricane activity. However, a confident assessment of human influence on hurricanes will require further studies using models and observations, with emphasis on distinguishing natural from human-induced changes in hurricane activity through their influence on factors such as historical sea surface temperatures, wind shear, and atmospheric vertical stability.

Impacts of Climate Variability and Change on Transportation Systems and Infrastructure—Gulf Coast Study
See our previous post:
March 13, 2008: Stealth release of major federal study of Gulf Coast climate change transportation impacts

Chapter 6 of the report says: 

•  Climate change appears to worsen the region’s vulnerability to hurricanes, as warming seas give rise to more energetic storms. The literature indicates that the intensity of major storms may increase 5 to 20 percent. This indicates that Category 3 storms and higher may return more frequently to the central Gulf Coast and thus cause more disruptions of transportation services.  The impacts of such storms need to be examined in greater detail; storms may cause even greater damage under future conditions not considered here. If the barrier islands and shorelines continue to be lost at historical rates and as relative sea level rises, the destructive potential of tropical storms is likely to increase.
•  While further study is needed to examine in more detail the impacts on specific transportation facilities, such as individual airports or rail terminals, this preliminary assessment finds that the potential impacts on infrastructure are so important that transportation decision makers should begin immediately to assess them in the development of transportation investment strategies.

Effects of Climate Change on Energy Production and Use in the United States

Climate change may cause significant shifts in current weather patterns and increase the severity and possibly the frequency of major storms (NRC 2002). As witnessed in 2005, hurricanes can have a debilitating impact on energy infrastructure. Direct losses to the energy industry in 2005 are estimated at $15 billion (Marketwatch.com 2006), with millions more in restoration and recovery costs. Future energy projects located in storm prone areas will face increased capital costs of hardening their assets due to both legislative and insurance pressures. For example, the Yscloskey Gas Processing Plant was forced to close for 6 months following Hurricane Katrina, resulting in both lost revenues to the plant’s owners and higher prices to consumers as alternative gas sources had to be procured. In general, the incapacitation of energy infrastructure – especially of refineries, gas processing plants and petroleum product terminals – is widely credited with driving a price spike in fuel prices across the country, which then in turn has national consequences….

Off-shore production is particularly susceptible to extreme weather events. Hurricane Ivan (2004) destroyed seven GOM platforms, significantly damaged 24 platforms, and damaged 102 pipelines (MMS 2006).

See our previous posts on earlier Bush administration political interference with communication about hurricanes and climate change. For example:
September 27, 2006: Why the administration buried NOAA scientists’ statement on hurricanes and climate
July 5, 2006: Hurricanes and global warming: A credibility challenge for the Climate Change Science Program
June 4, 2006: NOAA, global warming, and hurricanes: CSW director interview