Global warming

The global warming controversy is about claims that the rise of average atmospheric and ocean temperatures of the last several decades is largely (or mostly) man-made. The term "global warming" thus has two comman meanings. One refers to this political issue. The other refers to any period in which global temperature is higher than average or is rising (see climate cycles).

Climate change has been a natural phenomenon that has occurred hundreds of times through geologic time, but the term "global warming" is common used to refer to warming since the end of the Little Ice Age in the mid-1800s. Many people also use the term "global warming" as an abbreviaton for "anthropogenic global warming", both because it is shorter and because the term anthropogenic is used chiefly by specialist.

Many people consider the Modern Warm Period to be mostly attributable to human activity, with registered US voters split evenly on the issue (73% of Republicans say it's natural, 75% of Democrats say it's man-made). "Anthropogenic climate change" is also sometimes used to refer how humans are impacting the climate.

The causes of the Modern Warming Period have been strongly debated in the last decades, but in the last few years, many scientists, journalists, and politicians have reported an strong consensus on the anthropogenic origin of this warming. This view is advanced, prominently, by the reports of the United Nations' International Panel on Climate Change. See "The consensus about anthropogenic global warming," below.

Based on the belief that most recent warming is man-made, several steps have been taken to mitigate global warming, such as the Kyoto Protocol, an international treaty intended to reduce greenhouse gas emissions. Further policy changes are widely, but not universally, recommended. See "The politics of global warming," below.

Claims of a "consensus" about anthropogenic global warming

Politicians and other partisans who urge "action" to "combat" global warming have asserted that there is a "scientific" consensus about AGW. They cite organization positions, statements signed by groups of scientists, polls, and a literature search.

Others say that "the science is not settled" and that far from there being a scientific consensus, most scientists either disagree with AGW or are undecided: i.e., that support for AGW is decidedly in the minority.

The politics of global warming

The origin of global warming, and the extent of the consensus about it, have been subject to considerable political fighting, primarily because an anthropogenic origin is widely thought to require policy changes, such as the adoption of the Kyoto Protocol, necessary. Most Democrats and Greens assert that most scientists have reached a consensus on its anthropogenic origin. Some Republicans, notably the conservative Jim Inhofe, U.S. state climatologists, and several prominent individual scientists remain skeptical.