It is now widely accepted that the world's climate is undergoing some profound and long-standing changes. One of the most authoritative sources of information about global climate change is the Intergovernmental Panel on Climate Change (IPCC). In its most recent report, the Fourth Assessment Report, the IPCC confirmed that the Earth's climate is getting warmer and is projected to increase in temperature. It concluded that the Earth has warmed by 0.74 degrees Celsius in the last 100 years and that, furthermore, that “[t]he rate of warming averaged over the last 50 years (0.13°C ± 0.03°C per decade) is nearly twice that for the last 100 years.” It devises six different scenarios. According to these six scenarios the likely increase in temperature ranges from 1.1°C to 6.4°C and the likely increase in sea-level ranges from 0.18 metres to 0.59 metres. The IPCC's reports reflect the research of hundreds of climate scientists and represent the most comprehensive and thorough account of the causes and impacts of climate change as well as what mitigation and adaptation is necessary. It does bear noting, however, that some distinguished climate scientists predict more dramatic changes to the Earth. Stefan Rahmstorf, to give one example, argues that sea levels may rise by more than the IPCC's projections. He argues that by 2100 they may have increased by between 0.5 to 1.4 metres compared to 1990 levels. James Hansen similarly has long drawn attention to the possibility of more serious climate scenarios.