2001: Climates of the twentieth and twenty-first centuries simulated by the NCAR climate system model

• Main Authors: Aiguo Dai, T. M. L. Wigley, B. A. Boville, J. T. Kiehl, L. E. Buja
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: North Atlantic; North Atlantic oscillation
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.530.4607; http://www.cgd.ucar.edu/cas/adai/papers/CSM-JC-01-Paper.pdf

The Climate System Model, a coupled global climate model without ‘‘flux adjustments’ ’ recently developed at the National Center for Atmospheric Research, was used to simulate the twentieth-century climate using historical greenhouse gas and sulfate aerosol forcing. This simulation was extended through the twenty-first century under two newly developed scenarios, a business-as-usual case (ACACIA-BAU, CO2 ø 710 ppmv in 2100) and a CO2 stabilization case (STA550, CO2 ø 540 ppmv in 2100). Here we compare the simulated and observed twentieth-century climate, and then describe the simulated climates for the twenty-first century. The model simulates the spatial and temporal variations of the twentieth-century climate reasonably well. These include the rapid rise in global and zonal mean surface temperatures since the late 1970s, the precipitation increases over northern mid- and high-latitude land areas, ENSO-induced precipitation anomalies, and Pole– midlatitude oscillations (such as the North Atlantic oscillation) in sea level pressure fields. The model has a cold bias (28–68C) in surface air temperature over land, overestimates of cloudiness (by 10%–30%) over land, and underestimates of marine stratus clouds to the west of North and South America and Africa. The projected global surface warming from the 1990s to the 2090s is;1.98C under the BAU scenario and;1.58C under the STA550 scenario. In both cases, the midstratosphere cools due to the increase in CO 2, whereas the lower stratosphere warms in response to recovery of the ozone layer. As in other coupled models, the surface