Although scientists often caution not to ascribe the cause of a singular weather event to climate change, recent trends conform to projections of global warming consequences. The following three reports exemplify the kinds of observations of weather extremes and phenological shifts that meet scientific expectations of changes under global warming.

A report issued by NOAA describes April as a month of historic climate extremes in numerous places across the United States. Flooding, record-breaking outbreaks of tornadoes and wildfires punctuated a month when the country’s average temperature was nearly a full degree Fahrenheit warmer than the long-term average. Although severe drought persisted in the South Plains and South Rockies, the national average precipitation was 0.7 inches above normal.

A paper published in the American Meteorological Society (subscription required) presents evidence of a pattern of consistent warming in Vermont over the past 50 years. The author used freeze dates, the length of the growing season, the frozen period of small lakes, and the onset of spring as determined by the first

Photo: Dusan Smetana

leafing of lilacs to demonstrate the trend toward a warmer climate.

Observations of monthly snow water equivalent and temperature data were used to identify how warming affects North American mountain snowpack. In a paper published in Climate Dynamics (subscription required), the authors show that snowpack loss occurs in mid- to late-season through decreased accumulation and increased snow melt, the author concludes recent changes in snowpack are the result of regional-scale warming and cautions the earlier onset of snowmelt is to be expected in the future.