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Duffy P.B.,Lawrence Livermore National Laboratory | Duffy P.B.,Climate Central Inc. | Tebaldi C.,U.S. National Center for Atmospheric Research
Climatic Change | Year: 2012

Human-caused climate change can affect weather and climate extremes, as well as mean climate properties. Analysis of observations and climate model results shows that previously rare (5th percentile) summertime average temperatures are presently occurring with greatly increased frequency in some regions of the 48 contiguous United States. Broad agreement between observations and a mean of results based upon 16 global climate models suggests that this result is more consistent with the consequences of increasing greenhouse gas concentrations than with the effects of natural climate variability. This conclusion is further supported by a statistical analysis based on resampling of observations and model output. The same climate models project that the prevalence of previously extreme summer temperatures will continue to increase, occurring in well over 50% of summers by mid-century. © 2012 Springer Science+Business Media B.V. Source

Thrasher B.,Climate Analytics Group | Thrasher B.,Climate Central Inc. | Maurer E.P.,Santa Clara University | McKellar C.,San Jose State University | Duffy P.B.,Lawrence Livermore National Laboratory
Hydrology and Earth System Sciences | Year: 2012

When applying a quantile mapping-based bias correction to daily temperature extremes simulated by a global climate model (GCM), the transformed values of maximum and minimum temperatures are changed, and the diurnal temperature range (DTR) can become physically unrealistic. While causes are not thoroughly explored, there is a strong relationship between GCM biases in snow albedo feedback during snowmelt and bias correction resulting in unrealistic DTR values. We propose a technique to bias correct DTR, based on comparing observations and GCM historic simulations, and combine that with either bias correcting daily maximum temperatures and calculating daily minimum temperatures or vice versa. By basing the bias correction on a base period of 1961-1980 and validating it during a test period of 1981-1999, we show that bias correcting DTR and maximum daily temperature can produce more accurate estimations of daily temperature extremes while avoiding the pathological cases of unrealistic DTR values. © Author(s) 2012. Source

Mastrandrea M.D.,Stanford University | Tebaldi C.,Climate Central Inc. | Snyder C.W.,Stanford University | Schneider S.H.,Stanford University
Climatic Change | Year: 2011

In the next few decades, it is likely that California must face the challenge of coping with increased impacts from extreme events such as heat waves, wildfires, droughts, and floods. This study presents new projections of changes in the frequency and intensity of extreme events in the future across climate models, emissions scenarios, and downscaling methods, and for each California county. Consistent with other projections, this study finds significant increases in the frequency and magnitude of both high maximum and high minimum temperature extremes in many areas. For example, the frequency of extreme temperatures currently estimated to occur once every 100 years is projected to increase by at least ten-fold in many regions of California, even under a moderate emissions scenario. Under a higher emissions scenario, these temperatures are projected to occur close to annually in most regions. Also, consistent with other projections, analyses of precipitation extremes fail to detect a significant signal of change, with inconsistent behavior when comparing simulations across different GCMs and different downscaling methods. © 2011 Springer Science+Business Media B.V. Source

Wehner M.F.,Lawrence Berkeley National Laboratory | Smith R.L.,University of North Carolina at Chapel Hill | Bala G.,Indian Institute of Science | Duffy P.,Climate Central Inc.
Climate Dynamics | Year: 2010

We investigate the ability of a global atmospheric general circulation model (AGCM) to reproduce observed 20 year return values of the annual maximum daily precipitation totals over the continental United States as a function of horizontal resolution. We find that at the high resolutions enabled by contemporary supercomputers, the AGCM can produce values of comparable magnitude to high quality observations. However, at the resolutions typical of the coupled general circulation models used in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, the precipitation return values are severely underestimated. © The Author(s) 2009. Source

Mastrandrea M.D.,Stanford University | Heller N.E.,Climate Central Inc. | Root T.L.,Stanford University | Schneider S.H.,Stanford University
Climatic Change | Year: 2010

A critical challenge in supporting climate change adaptation is improving the linkage between climate-impacts and vulnerability research and public and private planning and management decisions. We highlight the need for bottom-up/top-down vulnerability assessment, bringing together bottom-up knowledge of existing vulnerabilities with top-down climate-impact projections, as a transparent basis for informing decisions intended to reduce vulnerability. This approach can be used to evaluate the likelihood of crossing identified thresholds of exposure, and to evaluate alternative adaptation strategies based on their ability to reduce sensitivity to projected changes in exposure and their robustness across uncertainty in future outcomes. By identifying thresholds for which adaptive capacity is limited in particular systems, adaptation and mitigation become complements where the magnitudes of climate change at which such thresholds cluster can help to define mitigation targets. © Springer Science+Business Media B.V. 2010. Source

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