Previous Year Question

The long-term increase in the Earth's Global Average Surface Temperature is known as Global Warming. According to NASA's 2010 assessment, the Earth's average temperature had increased by approximately 0.8 degrees Celsius (°C) since 1880. Global Warming is primarily associated with increasing concentrations of Greenhouse Gases in the atmosphere.

Global temperature increases are studied by NASA's Goddard Institute for Space Studies (GISS) and other scientific institutions. These assessments analyse temperature records from land-based weather stations and the oceans. According to NASA's 2010 assessment, approximately two-thirds of the recorded 0.8°C warming since 1880 had occurred after 1975. During this period, the rate of warming was approximately 0.15–0.20°C per decade.

According to the 2007 Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC), the linear trend in Global Average Surface Temperature showed an increase of approximately 0.74 ± 0.18°C during 1906–2005. The same report estimated an increase of approximately 0.76 ± 0.19°C when comparing the average periods 1850–1899 and 2001–2005, which rounds to approximately 0.8°C to the nearest tenth. Earlier, the IPCC's 2001 Third Assessment Report had recorded warming of approximately 0.6 ± 0.2°C during 1901–2000. These estimates differ because of variations in the study periods and calculation methods.

The major human causes of Global Warming include fossil fuel combustion, deforestation, and the increase in gases such as Carbon Dioxide (CO₂), Methane (CH₄), and Nitrous Oxide (N₂O) from industrial and agricultural activities. These gases absorb Infrared Radiation emitted by the Earth and intensify the Greenhouse Effect. Major consequences include glacier melting, sea-level rise, and changes in the risks associated with extreme weather events. The figure of 0.8°C in the question refers to a historical assessment rather than the present magnitude of global warming.