Antonio J. Busalacchi
Earth System Science Interdisciplinary Center
University of Maryland
College Park, Maryland, U.S.A

From July 10-13, 2001, the three Global Environmental Change Programs, i.e., International Geosphere Biosphere Programme (IGBP), Intenational Human Dimensions Programme on Global Environmental Change (IHDP), and the World Climate Research Programme (WCRP), hosted the Global Change Open Science Conference: Challenges of a Changing Earth in Amsterdam, The Netherlands. This major conference was attended by 1700 participants from 94 countries. The scientific program for the meeting encompassed the range of global change topics including terrestrial and marine productivity, air quality, the global carbon cycle, the global water cycle, global biogeochemistry, land-ocean interactions, climate variability and change, land-use change, biodiversity, the role of technology, and global sustainability. As one might expect from such a broad sweep of topics, the time scales of interest ranged from seasonal to millennial. As it pertains to decadal variability, this time scale was discussed to be at the upper end of the time scale for political systems (order 4 years), but at the lower end of the time scale of human choice (decades to centuries). Decadal variability and social response is at the nexus of the time scale for present Global Change Programmes (order 15 years), major infrastructural changes (e.g., power, roads, dams, of order 15 years), and the restoration time of regional environmental quality (10-50 years).

In the future, it is anticipated that decadal variability of the coupled climate system will result in ever increasing interaction and feedbacks with social systems as it pertains to water quality/availability and the global carbon cycle. One example of which is the decadal droughts that hit the Nordeste, Brazil. Brazilian literature, going back over 100 hundred years, has frequent references to the drought cycles that hit this region of subsistence farming and a present population of nearly 30 million. During times of particularly severe droughts, there are major emigrations from the region. Those displaced from the Nordeste, often end up in one of two areas, either the major cities and the favelas in Sao Paulo and Rio de Janeiro, or in Amazonia. Many of the new farmers and loggers involved in the deforestation of the Amazon come from the Nordeste and are merely trying to eke out a living in this frontier. Thus there is an interesting interplay between natural climate variability and social systems such that cyclical droughts induce population migration from one region to another, this results in major changes in land use and land cover, which in the end may come full circle and also feed back to the coupled climate system on the regional, if not, global scale. Another example, is that of the Bantu tribe in Africa. Lake Naivasha in Kenya also undergoes decadal drought cycles. In the distant past, the Bantu people would migrate to southern Africa when drought hit the region. This was part of their normal adaptation response. However, with the "Balkanization" of countries in the region such population migration has been severely restricted. Their loss of freedom of movement has limited the Bantus’ ability to respond to climate variability in the region. In summary, the interaction between decadal variability and social systems is likely to take on an ever increasing importance in view of the action and response times involved.