Search Results

You are looking at 1 - 3 of 3 items for

  • Author or Editor: Peter Whetton x
  • All content x
Clear All Modify Search
Wenju Cai, Peter H. Whetton, and David J. Karoly


Recent results from greenhouse warming experiments, most of which follow the Intergovernmental Panel on Climate Change (IPCC) IS92a scenario, have shown that under increasing atmospheric CO2 concentration, the Antarctic Oscillation (AAO) exhibits a positive trend. However, its response during the subsequent CO2 stabilization period has not been explored. In this study, it is shown that the upward trend of the AAO reverses during such a stabilization period. This evolution of an upward trend and a subsequent reversal is present in each ensemble of three greenhouse simulations using three versions of the CSIRO Mark 2 coupled climate model. The evolution is shown to be linked with that of surface temperature, which also displays a corresponding trend and reversal, incorporating the well-known feature of interhemispheric warming asymmetry with smaller warming in the Southern Hemisphere (smaller as latitude increases) than that in the Northern Hemisphere during the transient period, and vice versa during the stabilization period. These results indicate that once CO2 concentration stabilizes, reversal of the AAO trend established during the transient period is likely to be a robust feature, as it is underpinned by the likelihood that latitudinal warming differences will reduce or disappear. The implication is that climatic impacts associated with the AAO trend during the transient period may be reversible if CO2 stabilization is achieved.

Full access
Gerald A. Meehl, Francis Zwiers, Jenni Evans, Thomas Knutson, Linda Mearns, and Peter Whetton

Projections of statistical aspects of weather and climate extremes can be derived from climate models representing possible future climate states. Some of the recent models have reproduced results previously reported in the Intergovernmental Panel on Climate Change (IPCC) Second Assessment Report, such as a greater frequency of extreme warm days and lower frequency of extreme cold days associated with a warmer mean climate, a decrease in diurnal temperature range associated with higher nighttime temperatures, increased precipitation intensity, midcontinent summer drying, decreasing daily variability of surface temperature in winter, and increasing variability of northern midlatitude summer surface temperatures. This reconfirmation of previous results gives an increased confidence in the credibility of the models, though agreement among models does not guarantee those changes will occur. New results since the IPCC Second Assessment Report indicate a possible increase of extreme heat stress events in a warmer climate, an increase of cooling degree days and decrease in heating degree days, an increase of precipitation extremes such that there is a decrease in return periods for 20-yr extreme precipitation events, and more detailed analyses of possible changes in 20-yr return values for extreme maximum and minimum temperatures. Additionally, recent studies are now addressing interannual and synoptic time and space scale processes that affect weather and climate extremes, such as tropical cyclones, El Niño effects, and extratropical storms. However, current climate models are not yet in agreement with respect to possible future changes in such features.

Full access
Gerald A. Meehl, Thomas Karl, David R. Easterling, Stanley Changnon, Roger Pielke Jr., David Changnon, Jenni Evans, Pavel Ya. Groisman, Thomas R. Knutson, Kenneth E. Kunkel, Linda O. Mearns, Camille Parmesan, Roger Pulwarty, Terry Root, Richard T. Sylves, Peter Whetton, and Francis Zwiers

Weather and climatic extremes can have serious and damaging effects on human society and infrastructure as well as on ecosystems and wildlife. Thus, they are usually the main focus of attention of the news media in reports on climate. There are some indications from observations concerning how climatic extremes may have changed in the past. Climate models show how they could change in the future either due to natural climate fluctuations or under conditions of greenhouse gas-induced warming. These observed and modeled changes relate directly to the understanding of socioeconomic and ecological impacts related to extremes.

Full access