North American Climate in CMIP5 Experiments: Part III: Assessment of Twenty-First-Century Projections*

Abstract

In part III of a three-part study on North American climate in phase 5 of the Coupled Model Intercomparison Project (CMIP5) models, the authors examine projections of twenty-first-century climate in the representative concentration pathway 8.5 (RCP8.5) emission experiments. This paper summarizes and synthesizes results from several coordinated studies by the authors. Aspects of North American climate change that are examined include changes in continental-scale temperature and the hydrologic cycle, extremes events, and storm tracks, as well as regional manifestations of these climate variables. The authors also examine changes in the eastern North Pacific and North Atlantic tropical cyclone activity and North American intraseasonal to decadal variability, including changes in teleconnections to other regions of the globe. Projected changes are generally consistent with those previously published for CMIP3, although CMIP5 model projections differ importantly from those of CMIP3 in some aspects, including CMIP5 model agreement on increased central California precipitation. The paper also highlights uncertainties and limitations based on current results as priorities for further research. Although many projected changes in North American climate are consistent across CMIP5 models, substantial intermodel disagreement exists in other aspects. Areas of disagreement include projections of changes in snow water equivalent on a regional basis, summer Arctic sea ice extent, the magnitude and sign of regional precipitation changes, extreme heat events across the northern United States, and Atlantic and east Pacific tropical cyclone activity.

Projected changes in US rainfall erosivity

“…Although barely significant (see the limited extent of the stippling), there is general drying in Mexico and Texas, extending into the southwest US, and more positive anomalies in the eastern gulf and Florida. The pattern of yearly anomalies shown here is consistent with the expectations reported in the literature for both CMIP3 and CMIP5 models (see for example Seager et al, 2007Seager et al, , 2014Biasutti et al, 2011;Christensen et al, 2013;Maloney et al, 2014). It can be interpreted as the sum of a weak US-wide summertime drying and the wintertime pattern of increase in rainfall north of 40 • N and decrease in precipitation in the southwest and Texas.…”

“…Areas close to the wintertime zeroanomaly line are areas where the climate signal is projected to be small compared to natural variability, and model disagreement is not problematic. But in other areas, such as northern California and Texas, model disagreement is indicative of true uncertainty in the response (Maloney et al, 2014).…”

“…The pattern can be interpreted as the superposition of the general (thermodynamic) tendency for more intense rainfall in a moister atmosphere (O'Gorman and Schneider, 2009), dampened in the middle of the continent by circulation-driven dry anomalies in summertime (Maloney et al, 2014). Where these two effects are of comparable magnitude in the multi-model mean, the changes in intensity are less robust.…”

Whither the 100th Meridian? The Once and Future Physical and Human Geography of America’s Arid–Humid Divide. Part I: The Story So Far

“…Inevitably, as climate changes over North America due to rising greenhouse gases (Maloney et al 2014), the AI will change. This is analyzed in Part II, where we show that models project a general increase in aridity and an eastward movement of the climatically defined 100th meridian (i.e., the longitude where AI ' 1).…”

Whither the 100th Meridian? The Once and Future Physical and Human Geography of America’s Arid–Humid Divide. Part II: The Meridian Moves East

“…Based on the most recent climate model projections from phase 5 of the Coupled Model Intercomparison Project (CMIP5) and analyzed by the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5), many workers have reported that North America will see, over the coming decades, a marked transition in hydroclimate. Precipitation is expected to decline in southwestern North America but increase in the northeast, and temperature will rise everywhere (Seager et al 2013;Maloney et al 2014;Seager et al 2014). Cook et al (2015) used the CMIP5 model ensemble to show that these changes combine to cause a quite alarming increase in aridity in the plains as measured either by the Palmer drought severity index (utilizing the Penman-Monteith formulation for potential evapotranspiration) or in the actual modeled soil moisture.…”