Today the Intergovernmental Panel on Climate Change (IPCC) released the first part of its long-awaited Fourth Assessment Report. This is a major event, because the Report strengthens the scientific consensus about the threat from global warming if we don't curb greenhouse gas emissions. The Report projects sea-level rise of 0.2 - 0.6 meters by 2100 but, citing uncertainty in the scientific literature, it simply excludes the possibility of future rapid changes in the Greenland and West Antarctic ice sheets. This conservative posture reflects the IPCC's insistence on scientific consensus. However, according to press accounts from the IPCC's Paris meetings, the experts continued arguing about Greenland and West Antarctica until their publication deadline arrived. In the case of Greenland, at least, no one believes that its ice cap will survive sustained temperatures in the range that the IPCC projects. Ultimately it will disappear, adding 7 meters to sea level. The argument is about timing, not results: No one expects complete disintegration in the 21st century, but there are worrisome signs that the process has begun. Eventual disintegration of the West Antarctic ice sheet remains controversial; if it happens, it will add another 7 meters to sea level.
The stakes in this debate are critical for the people of coastal developing nations. Before joining the Center for Global Development in December, I worked with a World Bank research team that used the latest digital maps to study the implications of sea-level rise. Our results were sobering: Of the world's 300 million people who live less than 5 meters above sea level, 80% are in developing countries: 200 million in Asia (90 million in China alone); 17 million in the Middle East and North Africa; 11 million in Sub-Saharan Africa, and 8 million in Latin America and the Caribbean. Rapid sea-level rise will threaten millions with inundation, as well as more severe flooding from storm surges and abnormally high tides.
How imminent is the threat? The IPCC's conservative projection of sea-level rise reflects scientific estimates through early 2005, but upward revisions have been suggested by a recent raft of publications in Science, Nature, and other scientific journals. One recent paper, published in Science in December, finds that a 1.4-meter rise by 2100 is plausible if current trends continue. Another paper, published in Science yesterday, shows that past IPCC projections have significantly underestimated sea-level rise. Other papers document signs of unexpectedly rapid change in the Greenland and West Antarctic ice sheets, and the possibility of a 3-meter sea-level rise in this century is no longer beyond the bounds of informed discussion in the literature.
To see what this means for developing countries, consider the situation in the fertile delta regions that feed Egypt and Vietnam. A 3-meter sea-level rise will drown Egypt's Nile Delta, and a 1-meter rise will inundate much of its fertile land. In Vietnam, the high-risk "red zone", less than 5 meters above sea level, holds 38% of the country's population, 36% of its GDP, and 87% of its wetlands. As the sea rises, progressive inundation, high tides and storm surges will take an increasing toll. And, of course, many low-lying island nations and coastal areas of other countries will also go under.
Overall, the scientific message is clear and daunting: If we don't curb greenhouse gas emissions, there is a significant risk that global warming will raise the sea level by 1-3 meters in this century. According to our World Bank study, even a 1-meter rise will force 60 million people to become environmental refugees in developing countries.
The IPCC Report leaves little doubt about the source of this problem: a century of uncontrolled emissions, particularly from the United States. We confront a stark reality here: Millions of the poor will be displaced by sea-level rise that has been caused by the affluent West, and the piper will ultimately be paid. When this happens, current international turbulence may seem placid by comparison.
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