Trends in Extreme Weather and Climate Events: Issues Related to Modeling Extremes in Projections of Future Climate Change^*

Abstract

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 Nino effects, and extratropical storms. However, current climate models are not yet in agreement with respect to possible future changes in such features. This is the third of five papers in the "Understanding Changes in Weather and Climate Extremes" series.

Implications of Anthropogenic Climate Change for Tropical Cyclone Activity: A Case Study with the NCAR CCM2.

“…One of the features of spatial variation is a local maximum in the eastern equatorial Pacific especially in January, which is similar to the spatial pattern of SST anomalies during a warm event of El Niñ o/Southern Oscillation (ENSO). However, the east-west gradient of the SST anomalies is not very large compared to typical El Niñ o-like responses simulated by other climate models (Meehl et al 2000a). In the subtropics, positive SST anomalies are relatively small, and there are some differences between the Pacific and Atlantic; in July anomalies, the meridional variations are most evident in the Pacific while the anomalies display less spatial variability in the Atlantic.…”

“…The SST anomalies are similar to the spatial patterns during El Niñ o, and associated changes in large-scale circulations are consistent with the regional TC changes. However, confident projections of future El Niñ o conditions are an area of uncertainty for current climate models, as reviewed by Meehl et al (2000b). Taking account of this uncertainty, as well as the relatively large interannual variability of TCs, the simulated regional tendencies in response to the CO 2 -induced warming are considered only as just one of the possibilities of the future change.…”

“…As reviewed by Meehl et al (2000b), most of the studies regarding TC intensities suggest an increase of intensities due to greenhouse gas-induced warming. Such studies include the experiments using a nested high-resolution regional model by Knutson et al (1998), and theoretical analyses of potential intensity of TCs by Emanuel (1987).…”

Yield Variability and Agricultural Trade

“…Yield variability is largely a function of weather and may be exacerbated by widespread adoption of common high-yielding varieties and uniform agronomic practices (Anderson and Hazell 1987). Recent research shows that global climate change may increase yield variability since it will likely increase the probability of extreme heat stress events, precipitation extremes, El Niño like events, and other climate phenomena (Meehl and Washington 1993, Meehl et al 2000, Reilly et al 2002, Intergovernmental Panel on Climate Change 2007. While there is much uncertainty surrounding these predictions, the implication is that yield variability could rise.…”

Adaptation of Water Resources Management to Changing Climate: The Role of Intensity-Duration-Frequency Curves

“…An important use for this science is the assessment of the frequency of occurrence for relatively uncommon events. [21]. With the increase in anthropogenically warmed climate, extreme precipitation events are projected to become more common.…”