WHAT THE SKEPTICS SAY: There is no consensus that human-caused warming is creating a disastrous rise in global temperatures. The causes of 20th-century warming are in sharp dispute among scientists, as is the amount of warming expected in the future.

THE RESPONSE: Science is rarely final, and it always has its skeptics. Hypotheses are tested and retested as more data are collected and examined, and disagreements among researchers play a vital role in moving scientific understanding forward.

But the vast majority of scientists who study the climate agree on the essential points: that the Earth is getting warmer and that most of the warming in recent decades has been caused by carbon-dioxide emissions from human activities. As CO2 concentrations increase, the rate of warming will accelerate.

This view, summarized by the Intergovernmental Panel on Climate Change, is endorsed by the world's leading scientific organizations, including the national academies of science in a score of countries and, in the U.S., the American Association for the Advancement of Science, the American Geophysical Union and the American Meteorological Society.

In a recent survey of more than 3,000 Earth scientists, 82% agreed that human activity is a "significant contributing factor" in changing global temperatures. Specialists were in greater agreement: 75 of the 77 climate scientists who actively publish in the field—about 97%—agreed with the statement.