USGCRP
Program Elements

Atmospheric Composition

Ecosystems

Global Carbon Cycle

Decision-Support Resources Development and Related Research on Human Contributions and Responses

Climate Variability and Change

The Global
Water Cycle

Observing and Monitoring the Climate System

Communications

International Research and Cooperation

The following are some of the USGCRP's major accomplishments related to Understanding the Earth's Climate System during Fiscal Year 2000.

New research findings have identified declines in the extent of Arctic sea ice and its thickness over the past several decades. The average thickness from the ice surface to the bottom of the ice pack has declined by about 40 percent. A related study used climate models to estimate that the probability that the observed trends could be caused entirely by natural variability is less than 2 percent. This research suggests that human activities are very likely contributing to the loss of Arctic sea ice.

Scientists have showed that sea-surface temperature changes associated with the Pacific Decadal Oscillation (PDO) have a significant effect on the steering of ocean storms across the North Pacific Ocean, thereby influencing North American weather. There is evidence that reversals in the PDO phase occurred around 1925, 1947, and 1977. Because the PDO tends to persist in one phase or the other for multi-year periods, being able to account for its phase in the future is potentially important in increasing the accuracy of seasonal to interannual forecasts.

Research results demonstrate increases in the seasonal predictability of U.S. precipitation and surface air temperature when the combined impacts of ENSO, the PDO, and the Arctic Oscillation (AO) are all taken into account. Considering ENSO and the PDO together enhance predictive accuracy for precipitation, primarily across the southern states; adding the AO adds significantly to the predictive accuracy over the eastern states.

Observations and models have demonstrated a link between decadal variations in the production of Labrador Sea water and large-scale surface temperature anomalies in the tropical Atlantic Ocean. This finding suggests that there is a link between climate variability at high and low latitudes and that the deep ocean may influence climate variability on decadal timescales.