Understanding the Earth's Climate System

The Earth’s climate system is an important influence on the social and economic well-being of our societies, affecting water resources, ecosystems, and temperature patterns that enable — and in some cases restrain — a diverse array of activities. Fluctuations in climate occur naturally over time scales ranging from seasons to centuries and beyond. There is emerging evidence that humans may be influencing the climate by increasing the concentration of greenhouse gases in the atmosphere.

    As evidenced by the 1997-1998 El Niño-Southern Oscillation event, climatic variations can seriously disrupt the world's socioeconomic activity, resulting in the loss of human lives and billions of dollars worldwide. However, these same fluctuations in climate can provide opportunities in some areas by, for example, bringing increased rainfall to a semi-arid region, resulting in an increase in agricultural productivity. The key to mitigating the damage and taking advantage of the opportunities presented by climate variability lies in large part in achieving a predictive understanding of the climate system as a whole, including its multiple modes of variability across timescales and its interaction with human systems. Unraveling the complexities of the climate system offers opportunities to make optimal use of this knowledge in the pursuit of economic development and social benefits in the coming century.

 


Figure 1. La Niña experimental climate forecast: Global temperature forecast for January - March 1999.
(see Appendix E for additional information)

    This holistic approach will be advanced through unprecedented levels of interagency collaboration in a combination of modeling, observations, and process studies that will be conducted within the framework of the international Program on Climate Variability and Predictability (CLIVAR). The program’s emphasis on both intellectual and interagency integration will lead to an improved predictive understanding of the climate system across virtually all timescales.

Key research challenges include:
1. ENSO: Maintaining and improving the capability to make El Niño-Southern Oscillation predictions.
2. Global Monsoon: Defining global seasonal to interannual variability, especially that affecting the global monsoon system, and understanding the extent to which it is predictable.
3. Land Surface Exchanges: Understanding the roles of land-surface energy and water exchanges and their correct representation in models for seasonal to interannual prediction.
4. Downscaling: Improving the ability to interpret the effects of large-scale climate variability on a local scale.
5. Impacts on Weather: Understanding how seasonal to interannual climate variability is manifested in storms, floods, and other extreme weather events.
6. Natural Climate Patterns:

– Improving knowledge of decadal to century-scale natural climate patterns, including their distributions in time and space.
– Improving the optimal characterization of climate patterns, their mechanistic controls, and feedbacks.
– Improving knowledge of the sensitivities of climate patterns to changes in forcing, including their interactions with, and responses to, anthropogenic forcing.
7. Climate System Components: Addressing those issues whose resolution will most efficiently and significantly advance our understanding of decadal to century-scale climate variability for specific components of the climate system.
8. Anthropogenic Perturbations: Improving understanding of the long-term responses of the climate system to the anthropogenic addition of radiatively active constituents to the atmosphere, and devising methods of detecting anthropogenic influences against the background of natural climate variability.

Focus for FY 2000:

The USGCRP will develop and publish a summary that synthesizes the state of knowledge of the relationship between El Niño cycles and longer-term anthropogenic climate change. This summary will provide input to the international assessment of climate change being conducted by the Intergovernmental Panel on Climate Change for its Third Assessment Report, to be completed in 2001.

The USGCRP will develop improved El Niño/La Ni–a forecasts based on models that incorporate other important multiple-time scale phenomena, particularly: 1) the longer-term anthropogenic component of the climate system; 2) the decadal variability within the ENSO cycle; and 3) the influence of subseasonal phenomena such as the Madden- Julian Oscillation on the development of ENSO events. Forecasts will improve both in terms of accuracy and in terms of regional specificity.

The USGCRP will produce a Land Data Assimilation System that incorporates both atmospheric and land surface data (e.g., soil moisture), to provide analyzed fields for future climate studies. The program will develop at least one land surface module that contains a full suite of cold season processes (e.g., snow distribution, snow melt, and frozen ground) and will integrate it into operational models to improve the land surface exchange component of seasonal to interannual prediction.

The USGCRP will analyze and model how climate variability associated with the ENSO phenomenon is manifested in localized extreme weather events, such as storms and floods.

The USGCRP will document quantitative and qualitative savings/gains resulting from the use of integrated regional weather and climate forecasts.