Scientific Consensus On Global Warming

Scientific Consensus On Global Warming

The scientific opinion on climate change is that the Earth's climate system is unequivocally warming, and it is more than 90% certain that humans are causing most of it through activities that increase concentrations of greenhouse gases in the atmosphere, such as deforestation and burning fossil fuels. In addition, it is likely that some potential further greenhouse gas warming has been offset by increased aerosols. This scientific consensus is expressed in synthesis reports, by scientific bodies of national or international standing, and by surveys of opinion among climate scientists. Individual scientists, universities, and laboratories contribute to the overall scientific opinion via their peer-reviewed publications, and the areas of collective agreement and relative certainty are summarised in these high level reports and surveys.

National and international science academies and scientific societies have assessed the current scientific opinion, in particular on recent global warming. These assessments have largely followed or endorsed the Intergovernmental Panel on Climate Change (IPCC) position of January 2001 which states:

An increasing body of observations gives a collective picture of a warming world and other changes in the climate system... There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.

The main conclusions of the IPCC Working Group I on global warming were the following:

1. The global average surface temperature has risen 0.6 ± 0.2 °C since the late 19th century, and 0.17 °C per decade in the last 30 years.
2. "There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities", in particular emissions of the greenhouse gases carbon dioxide and methane.
3. If greenhouse gas emissions continue the warming will also continue, with temperatures projected to increase by 1.4 °C to 5.8 °C between 1990 and 2100. Accompanying this temperature increase will be increases in some types of extreme weather and a projected sea level rise. From IPCC Working Group II: On balance the impacts of global warming will be significantly negative, especially for larger values of warming.

No scientific body of national or international standing maintains a formal opinion dissenting from any of these three main points; the last was the American Association of Petroleum Geologists, which in 2007 updated its 1999 statement rejecting the likelihood of human influence on recent climate with its current non-committal position. Some other organizations, primarily those focusing on geology, also hold non-committal positions.