The 1990s was the warmest decade on record in the Northern Hemisphere, and this decade is likely to be even warmer.
That is also the forecast for the next several centuries - an ever warmer climate that brings flooding in some regions, drought elsewhere and the extinction of hundreds of species of animals and plants. Even if industrial pollution stays at today's levels, the warming would continue for the indefinite future, according to a report released yesterday by an authoritative group of scientists reporting to the United Nations.
The scientists' findings are contained in "Climate Change 2001," a 1,000-page report issued by the Intergovernmental Panel on Climate Change, representing the work of more than 1,000 experts who have been studying global warming for more than a decade. Their report might help end debate on whether warming has taken place.
The warming, the panel concludes, is a fact.
Scientists forecast that it will bring a rise in deaths in the Northern Hemisphere from malaria and other tropical diseases, submerge Africa's coastal cities, flood parts of Asia by melting glaciers in the Himalayas and reduce crop yields throughout Latin and Central America.
In the Chesapeake Bay region, where waters are rising about a half-inch a year, many miles of oceanfront and bay shoreline will be in danger of being submerged by rising seas. Some commercially important bay creatures might not be able to survive in the warmer waters and might disappear from the region.
Excerpts from the report follow:
The globe is warming
The global average surface temperature (the average of near surface air temperature over land, and sea surface temperature) has increased since 1861. Over the 20th century the increase has been 0.6 degrees Centigrade (plus or minus 0.2 degrees). ... The record shows a great deal of variability; for example, most of the warming occurred during the 20th century, during two periods, 1910 to 1945 and 1976 to 2000.
Globally, it is very likely that the 1990s was the warmest decade and 1998 the warmest year in the instrumental record, since 1861.
Satellite data show that there are very likely to have been decreases of about 10 percent in the extent of snow cover since the late 1960s, and ground-based observations show that there is very likely to have been a reduction of about two weeks in the annual duration of lake and river ice cover in the mid- and high latitudes of the Northern Hemisphere, over the 20th century.
Northern Hemisphere spring and summer sea-ice extent has decreased by about 10 percent to 15 percent since the 1950s. It is likely that there has been about a 40 percent decline in Arctic sea-ice thickness during late summer to early autumn in recent decades and a considerably slower decline in winter sea-ice thickness.
Tide gauge data show that global average sea level rose between 0.1 and 0.2 meters during the 20th century.
Some areas remain cold
A few areas of the globe have not warmed in recent decades, mainly over some parts of the Southern Hemisphere oceans and parts of Antarctica. No significant trends of Antarctic sea-ice extent are apparent since 1978, the period of reliable satellite measurements.
The atmospheric concentration of carbon dioxide has increased by 31 percent since 1750. The present concentration has not been exceeded during the past 420,000 years and likely not during the past 20 million years. The current rate of increase is unprecedented during at least the past 20,000 years.
The atmospheric concentration of methane has increased by 151 percent since 1750 and continues to increase. The present methane concentration has not been exceeded during the past 420,000 years. The annual growth in methane concentration slowed and became more variable in the 1990s, compared to the 1980s.
Slightly more than half of current methane emissions are anthropogenic (e.g., use of fossil fuels, cattle, rice agriculture and landfills). In addition, carbon monoxide emissions have recently been identified as a cause of increasing methane concentration.
The atmospheric concentration of nitrous oxide has increased by 17 percent since 1750 and continues to increase. The present nitrous oxide concentration has not been exceeded during at least the past thousand years.
In light of new evidence and taking into account the remaining uncertainties, most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations.
The globally averaged surface temperature is projected to increase by 1.4 to 5.8 degrees C over the period 1990 to 2100.
The projected rate of warming is much larger than the observed changes during the 20th century and is very likely to be without precedent during at least the last 10,000 years, based on palaeoclimate data.