Anthropogenic and Natural Influences in the Evolution of Lower Stratospheric Cooling
V. Ramaswamy,1
M. D. Schwarzkopf,1
W. J. Randel,2
B. D. Santer,3
B. J. Soden,4
G. L. Stenchikov5
Observations reveal that the substantial cooling of the global
lower stratosphere over 1979–2003 occurred in two pronounced
steplike transitions. These arose in the aftermath of two major
volcanic eruptions, with each cooling transition being followed
by a period of relatively steady temperatures. Climate model
simulations indicate that the space-time structure of the observed
cooling is largely attributable to the combined effect of changes
in both anthropogenic factors (ozone depletion and increases
in well-mixed greenhouse gases) and natural factors (solar irradiance
variation and volcanic aerosols). The anthropogenic factors
drove the overall cooling during the period, and the natural
ones modulated the evolution of the cooling.
2 National Center for Atmospheric Research, Boulder, CO 80303, USA.
3 Program for Climate Model Diagnosis and Intercomparison, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.
4 Rosentiel School for Marine and Atmospheric Science, University of Miami, Miami, FL 33149, USA.
5 Department of Environmental Sciences, Rutgers University, New Brunswick, NJ 08901, USA.
