Frontiers of Science Lectures, Irvine, June 8-10, 2000

Global climate models, past, present and future

The Earth’s Climate system and reconstruction of past climates

Martin Stute

(1) Barnard College, Columbia University
3009 Broadway
New York, NY 10027
(2) Lamont-Doherty Earth Observatory, Columbia University
61 rte 9W
Palisades, NY 10964
martins@ldeo.columbia.edu
The Earth's climate system consists of the atmosphere, cryosphere (ice), hydrosphere (oceans), lithosphere (land), and biosphere (life). Global climate is a result of complex interactions between these components. The incoming radiation, and the concentrations of atmospheric greenhouse gases such as water vapor, CO2, and CH4 control the average temperature and precipitation on Earth. Energy is transported across latitudes as sensible and latent heat by winds and ocean currents. Climate change occurs over periods ranging from hundreds of millions of years to a few years. The mechanisms that trigger and control the magnitude of many of these natural fluctuations are still poorly understood. Climate reconstructions using ice cores, ocean and lake sediments, tree rings, corals, cave deposits, and ground water as archives have provided fairly detailed pictures of past states of the Earth's climate, in particular for the past 100,000 years including the last ice age. These studies clearly demonstrate the spatial variability, non-linearity and extreme abruptness of climate change.
Numerical models of the Earth's climate, now including ocean and atmosphere as coupled systems, have been developed over the past 25 years and are being tested against current and paleoclimate data sets. Despite these major improvements, uncertainties remain in our understanding of how the climate system functions, in particular in the area of feedback mechanisms involving atmospheric moisture. It remains a major challenge to researchers in this field to predict future natural and anthropogenic climate change, in particular on the regional level.
For relevant links and the projections shown in the 'Global climate models' section see: http://www.ldeo.columbia.edu/~martins/irvine/