Global Warming

Global warming is the observed and projected increase in the average temperature of Earth's atmosphere and oceans that became apparent by the latter half of the 20th century. The Earth's average near-surface atmospheric temperature rose 0.6 ± 0.2 o Celsius (1.1 ± 0.4 o Fahrenheit) in the 20th century.[1]

The scientific consensus on global warming has been summarized by the IPCC: "In the light of new evidence and taking into account the remaining uncertainties, most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations".[2]. Only a small minority of climate scientists disagree that humanity's actions have played a major role in recent warming.

The largest contributing source of greenhouse gas is burning of fossil fuels by humans.[2] Greenhouse gases are those that contribute to the greenhouse effect.

Increasing global temperatures are expected to cause a broad range of changes. Sea levels are expected to rise by about 0.5m by 2100, due to thermal expansion of the ocean, in addition to melting of land ice. Changes in temperature and precipitation patterns are likely to increase the frequency, duration, and intensity of other extreme weather events, such as floods, droughts, heat waves, and tornadoes. The total annual power of hurricanes has already increased markedly--since the mid-1970's--because their average intensity and average duration have increased (in addition, hurricane power was observed to be highly correlated with tropical sea-surface temperature)[3]. Other consequences may include altered agricultural yields, further glacial retreat, reduced summer stream flows, species extinctions and increases in the ranges of disease vectors. Although warming is expected to affect the number and magnitude of these events, it is difficult to connect specific events to global warming.

World net carbon-emission rates would need to be reduced approximately 60%-80% by 2050 to keep global temperatures within 1oC (1.8oF) above present[4]. A 1oC rise would likely raise sea levels by no more than approximately 5 meters (16 feet) over the next 200 to 1000 years[5]. A projection of current trends--as represented by IPCC scenarios A1B or A2--gives temperatures 3oC above present by the year 2100 or soon afterwards[6]. Although most studies focus on the period up to 2100, warming is expected to continue