Regional Patterns of Climate Change

1. Regional Patterns of Climate Change Kenneth Hunu & Bali White EESC W4400 Dynamics of Climate Variability and Climate Change December 5, 2006

2. Evidence and trend • Regional patterns in climate change are evident. Recent warming has been greatest over the mid­latitude continents in winter and spring, with a few areas of cooling, such as the North Atlantic ocean. Precipitation has also increased over land in high latitudes of the Northern Hemisphere, especially during the cold season (IPCC) • There has been an increase of temperature across the US amounting to nearly 0.5 C since the turn of the certury (Karl et al. 1996). • Precipitation changes over the US during the 20th C have increased significantly over most of the contiguous US in all seasons except winter The trends range from 7% to 15% per century during the summer and transition seasons • Natural forcings are unlikely to cause the global average temperature to vary by more than about 0.5 K around its multidecadal average which indicates that these changes are due to man’s activities. (Mann et al. 1999).

3. Main Point #1(what are models saying about temperature changes) • There is a notable warming in the northern regions of North America, and northern and central Asia, which exceeds global mean warming in each model by more than 40%. In contrast, the warming is less than the global mean change in south and southeast Asia in summer and in southern South America in winter (IPCC, TAR) • Most models show weakening of the ocean thermohaline circulation which leads to a reduction of the heat transport into high latitudes of the Northern Hemisphere. The northern hemisphere is however projected to warm up due to greenhouse gases.

4. Main Point #2(what are the models saying about precipitation changes) • There has been about 5 to 10% increase in Northern hemisphere, mid-to-high latitude precipitation since 1900 with much of it due to heavy/extreme events. Widespread significant increases in water vapor in the Northern hemisphere has also been observed from 1925 to 1995. • By the second half of the 21st century, it is likely that precipitation will have increased over northern mid- to high latitudes and Antarctica in winter. At low latitudes there are both regional increases and decreases over land areas. Larger year to year variations in precipitation are very likely over most areas where an increase in mean precipitation is projected.

5. Main Point #3(Uncertainties) • Significant uncertainties remain in the science underlying regional climate changes and their impacts. Large uncertainties still remain in the prediction of local details of climate change especially in the water vapor feedback, cloud and precipitation efficiency.

6. References • Patz J.A, Campbell-Lendrum D, Holloway T, Folay J.A (2005). “Impact of regional climate change on human health” nature pages 310-318. • Groisman, PY and co-authors, 2004. Contemporary changes of the hydrological cycle over the contiguous United States: Trends derived from in situ observations. Journal of Hydrometeorology, 5 (1): 64-85. • Groisman, PY, WE Knight and TR Karl, 2001. Heavy precipitation and high streamflow in the contiguous United States: Trends in the twentieth century. Journal of Climate, 82 (2): 219-246. • MacCracken, MC and co-authors, 2003. Climate change scenarios for the US National Assessment. Bulletin of the American Meteorological Society, 84 (12): 1711-+. • The IPCC third report.