Latin America has the expertise needed for the study of climate, climate variability, and climate change-as is apparent from the relatively ample bibliography of research by local authors. This expertise is important because recent observations have shown that the Southern Hemisphere, where the largest portion of the region lies, is warming more than the Northern Hemisphere. The very heavily-populated land masses in the north produce more atmospheric pollution (in particular, sulfate aerosols and particulates), which dampens the heating capacity of solar radiation on the Earth. This situation is quite different from that in the oceanic Southern Hemisphere, where the distribution and density of air pollutants are remarkably lower. As a result, the absorption and reflection of incoming solar radiation do not counteract the background release of GHGs to the extent that they do in the north.
Other characteristics further differentiate the two hemispheres. The geographical features of the Southern Hemisphere (and Latin America in particular) consist mainly of a solid continent on the South Pole (the Antarctic); a very large oceanic mass with a well-known thermal moderating capacity; a subcontinent (South America) extending to the southernmost latitudes; and a vertebral mountain chain (the Cordillerra de los Andes) running from north to south over the entire subcontinent-all sandwiched between the two largest oceans of the world. Another important difference affecting the middle atmosphere over this region is the seasonal and regional formation of the Antarctic ozone hole. This remarkable stratospheric ozone depletion, combined with dynamic changes in middle atmospheric circulation, has the double impact of creating a window for infrared radiation-which globally compensates about 25% of GHG warming effects-and increasing the amount of ultraviolet-B (UV-B) radiation that reaches the ground, with direct effects on the region's terrestrial and marine ecosystems.
Thus, there is room not only for improving mathematical models to encompass hemispheric peculiarities (as is being done in Australasia) but also for developing appropriate regional climate models that should have the capacity, inter alia, to provide appropriate climate scenarios for running hydrological models for the region's river basins.
This analysis once again underscores the fact that the region suffers from insufficiently dense and reliable observation networks and that other basic information-biological, economic, and social-necessary to build up complete and coherent regional scenarios is missing. Last but not least, appropriate coordination with the Australasian countries, as well as with the United States and Canada, is becoming more and more critical because of common factors affecting climate variability (e.g., the ENSO phenomenon) and climate change over these regions.
In summary, the situation in Latin America calls for specific research initiatives; comprehensive ecological and socioeconomic databases; appropriate data validation techniques; proxy data capture, particularly regarding the neighboring Antarctic continent (which began keeping regional records only after the 1958 geophysical year); and appropriate training of personnel, particularly regarding integrated assessments and development of appropriate adaptation option methodologies. More fundamental research on ecosystem functioning, hydrographic systems, and interactions between land use and technological approaches by different communities is indispensable for the region to thoroughly undertake integrated assessments of potential impacts of climate change and develop appropriate adaptation and mitigation alternatives. Therefore, combined actions with countries in neighboring regions, such as those already implemented through joint activities with the USCSP, and the organization of activities within the Valdivia Group-which associates Latin American countries in the temperate Southern Hemisphere with activities of common interest in Australia, New Zealand, and South Africa-are in order. The participation of grassroots organizations and NGOs also is essential for achieving sustainable development in the region vis-�-vis climate change.
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