television and radio presentations, and establishment of educational programs have all enhanced the access and connection to IPY activities.

In conclusion, this was the first International Polar Year to address Arctic health issues, and first results are still emerging. By establishing the infrastructure, connectivity, and dissemination products and prioritizing them around user needs, a system has been in place to provide support for this research mission and user interface for years to come. This is an important new direction in science that is a distinct and important legacy of IPY.

CONCLUSIONS

Scientific discoveries during IPY used observations from some of the most remote regions of the Earth for a new understanding that benefits all humanity. Clear attribution that current warming of the planet is due to human activity came during IPY from at least three totally different research areas, the paleoclimatology, space physics, and modeling communities. Lake sediment sequences, ice cores, and tree ring records from the circumarctic show that recent warming has reversed the cooling trend of the last 2,000 years. Warming and freshening of the Arctic Basin is increasing, having a large impact on both sea ice reduction and basin stratification. The changes are having significant impacts at all trophic levels of the marine environment—from microorganisms to top predators in both polar regions. Terrestrial research show that land warming, sea ice decline, and greening of the Arctic are linked; this observation of modern processes is supported by paleoclimate findings on terrestrial systems. A new realization emerged that the total belowground carbon pool in permafrost is more than double the atmospheric carbon pool and three times larger than the total global forest biomass; this potentially provides an additional positive feedback parameter in the global system.

Discoveries involving the mechanisms of ice sheet flow associated with internal hydrological and subglacial conditions and interaction of ice shelves with the warming ocean enabled new understanding of ice sheet stability. The West Antarctic ice sheet became unstable and collapsed repeatedly, significantly raising sea level, during the interglacials of the past 3.5M years, which were warmer than today. Paleoclimate data show repeated intervals in the past when the Greenland ice sheet may have been much smaller than today and sea ice reduced. The IPY years spawned the realization that the impacts of warming on the Greenland ice sheet and the West Antarctic ice sheet will likely raise sea level faster than current models now can predict. Remotely sensed and direct measurements of accumulation across the East Antarctic ice sheet showed that current climate models have overestimated accumulation due to snowfall. Cutting-edge radar measurements of the bottom of the East Antarctic ice sheet yield insight on ice sheet origins.

From the polar regions looking into space, IPY allowed for some of the most comprehensive synoptic measurements of the geospace environment ever taken, including new nets for observing and understanding the impacts of space weather on global communications.

Engagement with the inhabitants of the Arctic has led to new capacities for learning about the social processes and health of the people who live in the polar regions.



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