Forecasting Climate and Ozone Changes on Multi Decadal Time Scales

Forecasting Climate and Ozone Changes on Multi Decadal Time Scales
Judith L. Lean [[email protected]], Naval Research Laboratory, Washington DC
Growing empirical evidence attests to the Sun’s role in altering the Earth’s climate and
atmosphere, including the ozone layer, in ways that can mitigate or exacerbate anthropogenic
effects on time scales of decades. Furthermore, solar and anthropogenic influences occur
simultaneously with natural variability driven by dynamical motions within the global
system. A multiple regression analysis is used to identify and characterize the specific mix
of natural and anthropogenic components that influences the Earth’s surface temperature and
ozone layer, respectively. Changes in surface temperature and ozone are forecast during
future decades using scenarios for upcoming 11-year cycles in total and UV irradiance,
projections of greenhouse gases including chloroflurocarbons, and propagation of internal
variability cycles. The forecasts suggest that during the next three to four years, global
surface temperature will increase at a faster rate than is attributable to greenhouse gases
alone, as a result of increasing solar irradiance during the ascending phase of solar cycle 24.
The occurrence of a significant El Niño or volcanic event notably impacts the scenarios for
decadal climate change in the near future. Forecasts of future ozone levels suggest that total
global ozone has already reached its minimum level and may recover to 1980 levels as soon
as 2025. This recovery precedes the return of CFCs to 1980 levels, after which total ozone
will continue to increase due to greenhouse gas cooling. By 2050 total ozone levels may
exceed those of the past century.