National Assessment: The U.S. National Assessment of the Potential Consequences of Climate Variability and Change was initiated in 1997 to define potential vulnerabilities and coping strategies for the United States in the context of future climate variability and change. The USGCRP coordinates the assessment, which involves geographical regions, socioeconomic and natural resource sectors, and a national synthesis. The Global Change Research Act of 1990 requires an assessment, and it has been used to emphasize broad stakeholder participation that extends beyond the research community.

    In early 1998, the USGCRP appointed a National Assessment Synthesis Team, with members broadly representing the public and private sectors, to provide intellectual leadership to the National Assessment and to manage the overall synthesis of regional and sectoral information. Twelve additional regional scoping workshops took place in 1998, bringing the total number held in 1997-1998 to 19. Many of the regions initiated their analyses of key issues and preparation of reports in a common format, and continued stakeholder engagement. In addition, the Synthesis Team selected five sectors – agriculture, coastal areas and marine resources, forests, human health, and water resources – for assessment. For each sector, the Synthesis Team appointed a team that is conducting an assessment of key issues and vulnerabilities, with reports to be published in a common format.

    El Niño-Southern Oscillation (ENSO) forecasting: Substantial improvements in the field of short-term climate prediction and the application of these developing capabilities to problems of social and economic consequence continued in 1998. Over the last year, USGCRP-supported scientists developed new products and methodologies based on insights generated by the 1997-1998 ENSO event, including climate information tailored for regions such as the Pacific Northwest and California, and the implementation of a series of regional Climate Outlook Fora throughout the world. In addition, scientists anticipated the current La Niña conditions in mid-1998.

    Global temperature record: Based on observations of global average surface temperature, scientists from both NASA’s Goddard Institute of Space Studies and NOAA’s National Climatic Data Center found that 1998 was, by a good margin, the warmest year on record since widespread instrumental measurements began in the 1860s. The record warming also showed up in the microwave satellite temperature record of tropospheric temperatures compiled by NASA’s Marshall Space Flight Center. This continues the recent pattern of very warm conditions during the 1980s and 1990s.

    Warmest period in at least 1000 years: Paleoclimatic reconstructions of pre-instrumental temperatures in the Northern Hemisphere indicate that the late 20th century is the warmest period in at least the last 1000 years. While the Medieval Warm Period in Europe was somewhat warmer for that region, that warming, unlike the current one, did not affect the entire hemisphere. These reconstructions also show that the cold period of the 16th to 18th centuries that is often labeled the Little Ice Age was also mainly a regional climatic cooling covering the North Atlantic region and did not involve the whole Northern Hemisphere. The key implication of these findings is that the very warm, hemispheric conditions during the latter part of the 20th century are even less likely than previously believed to be due to a natural fluctuation and are more likely to be significantly affected by anthropogenic influences.

    North America carbon sink: Analyses of the gradients and fluxes of carbon dioxide concentrations over North America during a recent five-year period indicate that the forests, soils, and sediments of North America may be sequestering surprisingly large amounts of carbon, thereby somewhat limiting the rise being caused by the increasing use of fossil fuels. While the regrowth of forests in the Northeast may be one contributor to the uptake (and so may become limited as forests mature), other processes, such as changes in land use and agricultural practices, also may be contributing to the uptake. Although a number of studies suggest that North America is a carbon sink, the findings on the size of the sink vary. Further research is needed to better understand the location and mechanisms of sources and sinks and to narrow the uncertainty of the estimates.

    Greenhouse gas increase and ozone depletion: The rise in the atmospheric concentration of greenhouse gases that causes warming at the surface tends to cause cooling in the lower stratosphere, and may affect the propagation of waves and transport of trace substances from the troposphere to the stratosphere. Any cooling of the stratosphere is likely to enhance ozone depletion, potentially delaying the recovery of the ozone layer that is expected due to the reduction in stratospheric halogen concentrations resulting from emission reductions associated with the Montreal Protocol on Substances that Deplete the Ozone Layer.

    Assessment of Ozone Depletion: USGCRP results were prominent in the Scientific Assessment of Ozone Depletion, released in June by the United Nations Environmental Programme and the World Meteorological Organization. The total combined abundance of ozone-depleting compounds in the lower atmosphere peaked in about 1994 and is now slowly declining. In the stratosphere, combined abundance of chlorine is expected to peak before the year 2000, but direct evidence for the recovery of the ozone layer still lies well into the future. Detailed analysis has provided conclusive evidence of statistically significant reductions of ozone over northern mid-latitudes for the time period 1980-1996. This depletion is largest in the lower and upper stratosphere (~7.5%/decade) and smallest in the middle stratosphere (~2%/decade near 30 km).

    Long-range transport of air pollution: Data from ground- and space-based instruments have shown clear evidence for long-range transport of pollutants over relatively unpolluted areas. In some cases, plumes of polluted air originally from South and East Asia have been shown to reach the West Coast of the United States; transport of mineral desert dust from Africa to the southeastern U.S. and of smoke and ash from Mexican forest fires into the northeastern U.S. also has been demonstrated.

    Ocean analysis:The Joint Global Ocean Flux Studies (JGOFS) program, in cooperation with the World Ocean Circulation Experiment (WOCE), has logged a decade of observations of the surface waters at two mid-ocean subtropical sites off Hawaii and Bermuda. The suite of data gathered on ocean climate, nutrient cycling, biological production, ecological community composition, particulate sedimentation, and carbon dioxide from ships and moored buoys is unique in the history of oceanography. These data are providing invaluable insights into the biocomplexity of the central ocean. Time series observations have shown that nitrogen fixation plays a major role in supporting new production. A comparison of the two sites indicates very different nutrient and primary production dynamics.

    Tropical Rainfall Measuring Mission (TRMM): One year after its successful launch, TRMM has proven to be valuable for both scientific research and development of new weather forecasting capabilities. The scientific understanding resulting from this mission will greatly enhance our knowledge of how storms and hurricanes form and dissipate.

    Radarsat:The U.S.-Canadian Radarsat provided the first detailed radar map of Antarctica. Nearly 70 percent of the Earth’s fresh water is contained in the Antarctic region, and changes in this reservoir directly influence world sea levels and climate.

    Fire monitoring: In an effort to improve the monitoring of the fires in Central America and Mexico, the NASA Earth Science Enterprise worked with NOAA to develop a new Internet site to provide information to study fires. Other fires worldwide have been monitored, including those in Indonesia and Russia, and the results are available via the Internet.

    SeaWiFS:One year after its successful launch, the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) is providing important data on coastal upwelling in the U.S. Northwest, Argentina, and South Africa. Upwelling fosters dramatic plankton blooms, a critical food source for fish. These SeaWiFS data are used to understand the role of oceans in removing carbon dioxide from the atmosphere, and the ocean’s productivity. The spacecraft is also providing valuable images of the land.