Winter Warming Indicated by Recent Temperature and Precipitation Anomalies

Abstract

Analysis of daily maximum and minimum temperatures and precipitation observations for the 1932-1999 period at 74 weather stations in the United States, Europe, Asia, and Australia suggests that an abrupt climate change occurred in the 1980s. Five variables are considered, namely the daily maximum, minimum, and mean temperatures, precipitation, and the diurnal temperature range. Daily departures (anomalies) of five observed variables relative to an early base period (1932-1950) are calculated for each station for the test period (1951-1999), and a 74-station daily average made for each variable. Based on these global averages, five main results are presented: (1) Since 1985, there is a significant increase in positive anomalies of winter temperatures during the season approximately defined by the Northern Hemisphere winter solstice and spring equinox; positive anomalies range from 2° to 8°C for individual Northern Hemisphere stations. Seasonal warming during the Northern Hemisphere winter also occurs in the Southern Hemisphere, but to a lesser degree. (2) Beginning about 1990, positive temperature anomalies at nearly all stations are synchronized (having positive anomalies on the same day) during the winter-warming season. There is an inexplicable similarity in the seasonal patterns of temperature departures and the fraction of synchronized stations. (3) Temperature and precipitation anomalies since at least 1951 have been increasing at approximately the same rate during the winter season. The positive precipitation anomalies since the mid-1990s are strongly correlated (r = 0.9) with the minimum temperature anomalies. (4) Both precipitation anomalies during the Northern Hemisphere winter season and mean temperature anomalies during the Southern Hemisphere summer season are bimodal and appear to be physically linked. (5) When the mean daily temperature anomalies are segregated into separate categories using the diurnal temperature range and precipitation anomalies, there is an abrupt and consistent rise in cumulative positive temperature anomalies after 1985, suggesting a positive feedback fueled by atmospheric water vapor. The impact of warmer winters include effects on hydroelectric generation, energy consumption, water supplies, glaciers, agriculture, ocean salinity, fisheries, and ski resorts.