Wednesday, September 29, 2010

Paper: Northeast US Had Strong Warming Trends 1893-1950, Cooling Since

A paper published today in the Journal of Climate finds that in "one of the most variable [disrupted?] climates of the world" - the Northeastern US - "Although maximum temperatures indices showed strong warming trends over the period 1893 – 1950, subsequent trends show little change and cooling."

Journal of Climate 2010 ; e-View doi: 10.1175/2010JCLI3363.1 

Changes in extreme climate indices for the northeastern U.S., 1870 – 2005. 

Paula J. Brown*, Raymond S. Bradley, Frank T. Keimig

Climate System Research Center, Department of Geosciences, University of Massachusetts, Amherst, Massachusetts

Abstract: The northeastern U.S. is one of the most variable climates in the world, and how climate extremes are changing is critical to populations, industries and the environment in this region. A long-term (1870 – 2005) temperature and precipitation dataset was compiled for the northeast U.S. to assess how the climate has changed. Adjustments were made to daily temperatures to account for changes in mean, variance and skewness resulting from inhomogeneities, but precipitation data were not adjusted. Trends in 17 temperature and 10 precipitation indices at 40 stations were evaluated over three time periods: 1893 – 2005, 1893 – 1950 and 1951 – 2005, and over 1870 – 2005 for a subset of longer term stations. Temperature indices indicate strong warming with increases in the frequency of warm events (e.g. warm nights and warm summer days) and decreases in the frequency of cold events (e.g. ice days, frost days and the cold spell duration indicator). The strongest warming is exhibited in the decrease in frost days and the increase in growing season length. Although maximum temperatures indices showed strong warming trends over the period 1893 – 1950, subsequent trends show little change and cooling. Few significant trends were present in the precipitation indices; however, they displayed a tendency toward wetter conditions. A stepwise multiple linear regression analysis indicated some of the variability the 27 indices from 1951 – 2002 was explained by the [naturally occuring] North Atlantic Oscillation, Pacific Decadal Oscillation and Pacific North American pattern. However, teleconnection patterns showed little influence on the 27 indices over a 103-year period.

More evidence of natural variability/disruption also published today in the Journal of Climate:

The Influence of El Niño – Southern Oscillation and the Atlantic Multi-decadal Oscillation on Caribbean Tropical Cyclone Activity

Philip J. Klotzbach

Abstract: Caribbean basin tropical cyclone activity shows significant variability on inter-annual as well as multi-decadal timescales. Comprehensive statistics for Caribbean hurricane activity are tabulated, and then large-scale climate features are examined for their impacts on this activity. The primary inter-annual driver of variability is found to be El Niño–Southern Oscillation, which alters levels of activity due to changes in levels of vertical wind shear as well as through column stability. Much more activity occurs in the Caribbean with La Niña conditions than with El Niño conditions. On the multi-decadal timescale, the Atlantic Multi-decadal Oscillation is shown to play a significant role in Caribbean hurricane activity, likely linked to its close relationship with multi-decadal alterations in the size of the Atlantic Warm Pool and the phase of the Atlantic Meridional Mode. When El Niño – Southern Oscillation and the Atlantic Multi-decadal Oscillation are examined in combination, even stronger relationships are found due to a combination of either favorable or unfavorable dynamic and thermodynamic factors. For example, 29 hurricanes tracked into the Caribbean in the ten strongest La Niña years in a positive Atlantic Multi-decadal Oscillation period compared with only two hurricanes tracking through the Caribbean in the ten strongest El Niño years in a negative Atlantic Multi-decadal Oscillation period.

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