NOAA has released a well-manicured and comprehensive report on observed and conjectured changes in North American weather and climate extremes.
The Final Report of CCSP 2008 provides and up-to-date scientific collation of many peer-review studies along with a consensus interpretation like the UN IPCC AR4 reports. Some of the main findings are summarized in the handy “brochure” provided on the website:
I quote here from the NOAA press release
* Abnormally hot days and nights, along with heat waves, are very likely to become more common. Cold nights are very likely to become less common.
* Sea ice extent is expected to continue to decrease and may even disappear in the Arctic Ocean in summer in coming decades.
* Precipitation, on average, is likely to be less frequent but more intense.
* Droughts are likely to become more frequent and severe in some regions.
* Hurricanes will likely have increased precipitation and wind.
* The strongest cold-season storms in the Atlantic and Pacific are likely to produce stronger winds and higher extreme wave heights.
Along with attribution of the above observed changes to human activity, the report provides a likelihood estimate of future changes. Based upon model projections and expert judgment, it goes without saying that it is “very likely” that the extremes will continue into the future.
From the press release on the NOAA website, report co-chair Tom Karl of NCDC explains the motives of this report and goes on to answer the age-old question: is this flood or rain shower or hurricane caused by global warming? It is usually said as a matter-of-fact statement that one individual weather event cannot be attributed to global warming per se. However, it is likely that with global warming, we will see more of these events. Karl says as much,
This report addresses one of the most frequently asked questions about global warming: what will happen to weather and climate extremes? This synthesis and assessment product examines this question across North America and concludes that we are now witnessing and will increasingly experience more extreme weather and climate events.
This is a landmark document coming from NOAA, which has been lambasted in the past for allegedly censoring or silencing its scientists. Yet, it is an amalgamation of differing viewpoints on such issues as hurricanes and climate change, the obvious hot-button concern going forward into the 2008 Atlantic hurricane season. With the terrible Midwest/Iowa flooding (not seen since 1993) ongoing, the report will get plenty of publicity in the same way that Emanuel’s 2005 Nature paper received after Hurricane Katrina. However, before attributing all observed phenomena to unnatural climate changes, we must not forget that natural climate variations exist and generate extremes all the time including plenty of weather systems. For instance, the tornado numbers as well as the Midwest flooding were largely expected from the record La Nina conditions seen in late 2007 to early 2008. With the continued negative values of the Pacific Decadal Oscillation (PDO) and large uncertainty in future ENSO conditions, natural climate variations are providing plenty of climate extremes all on their own.