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=10.1.1.431.8303; 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, CO 2 � 710 ppmv in 2100) and a CO2 stabilization case (STA550, CO2 � 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 (2�–6�C) 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 �1.9�C under the BAU scenario and �1.5�C under the STA550 scenario. In both cases, the midstratosphere cools due to the increase in CO 2, whereas