| None like it hot
|Lies, talking points, manufactroversies|
|—Katharine Hayhoe, climatologist and evangelical Christian|
Global warming, also known as anthropogenic (or human-caused) global warming, is the rising average temperature of Earth's atmosphere and oceans and its related effects. In the last 100 years, Earth's average surface temperature increased by about 0.8 °C (1.4 °F) with about two thirds of the increase occurring over just the last three decades. As a result, anthropogenic global warming has recently become a major concern for humanity. Such concerns are supported worldwide by the wide majority of climatologists.
Global warming is an increase in temperature in addition to the natural greenhouse effect. The greenhouse effect interacts with other planet-wide influences such as the Milankovitch cycles in order to produce long term climate movements. Many gases contribute to the greenhouse effect, some of the most important being water vapor, methane and carbon dioxide.
 What's so bad about global warming?
Global warming is bad for a number of reasons.
- A dramatic rise in sea level. Global warming will cause a continuing sea level rise of an uncertain amount. The IPCC reports a range of 9 – 88 cm (3.5 – 34.6 inches) up to 2100, but further contributions are possible from glacier and ice sheet discharge from Greenland and Antarctica. Even this small rise would cause significant disruption to coastal communities. If the whole Greenland ice sheet melted this would lead to a global rise of 7 m (23 ft).
- More active weather systems. More energy in the atmosphere will lead to more active weather systems, with more frequent and more violent storms.
- Disturbed rainfall patterns. Rainfall patterns will be significantly disrupted, with floods in some places and droughts in others.
- Acidification of the oceans. Carbon dioxide dissolves in water by reacting to make H2CO3 (carbonic acid), causing great damage to fish stocks and coral reefs. Note this is not a consequence of warming: it is a consequence of the forcing agent, CO2. To make matters worse, this acidification appears to have been an important factor in the Permian-Triassic Extinction Event — the most severe extinction Earth has ever known — and possibly every extinction other than the Cretaceous.
- Tipping points/feedback loops. Multiple possibilities here. As glaciers disappear, the planet will not reflect as much solar radiation back into space, leading to more warming. When northern permafrost melts, the organic material will decompose and release methane, again leading to more warming. As the oceans warm, their ability to dissolve carbon dioxide decreases, and if ever reach a certain temperature, the methane stored under pressure on the seafloor will vaporize, leading to (you guessed it) more warming.
- Spread of tropical diseases. As northern latitudes become warmer, vectors that spread tropical diseases (such as mosquitoes or other organisms) will begin to encroach into new areas.
- Disruption of ocean currents. For example, the disruption of ocean currents could reduce the strength of the North Atlantic Drift that keeps Europe relatively warm for its latitude.
- Habitat loss or change faster than plants or animals can adapt. Mechanism such as species migration or changes in ecosystem boundaries often are slow, and in some cases could be slower than the speed of climate change. Some habitats may disappear completely: the loss of polar habitats will leave animals such as polar bears with no place to go. (Bad example: Polar bears are actually breeding with other local bear species. We do not have to worry about those horny troopers!)
- Loss of mountain glaciers and snowpack exacerbating summer droughts. Glaciers and snowpack act as natural reservoirs, for example releasing water that had fallen as snow several months later when summer arrives and snow melts. The loss of this natural storage mechanism will lead to floods in winter and droughts in the summer.
Not all of these consequences are certain, and some may be mitigated. For example, whilst global warming might tend to promote the spread of tropical diseases, advances in medicine or control measures (insect spraying, swamp draining) could well counteract this, as has already happened during the industrial era for a number of previously common diseases.
Equally though, there will probably be many unanticipated additional — probably negative — consequences.
If climate change doesn't sound so bad, consider that we've spent the past few hundred years building cities in places that don't flood and farms in places with enough water and ice hotels in places with ice. There is an awful lot of money and human endeavor relying on the weather staying just the way it is.
 What's the limit?
While projections of the potential (maximum) temperature rise have ranged from 2 – 6°C, there's broad agreement that anything above 2°C will mean we are beyond recovery. The International Energy Agency suggests that the window to prevent this from occurring will close by 2020, a view shared by the OECD. So let's get cracking.
 A reminder on comparing apples to apples
When comparing sources of greenhouse gases, be sure to note whether the figure lists the number of tons of carbon released, or the number of tons of carbon dioxide released. One ton of carbon dioxide contains only a little over a quarter ton of carbon.
 See also
- Global warming denialism
- Global warming conspiracy theory
- Kyoto Protocol
- The global warming wager
- Gore's Law
- What climate scientists should talk about: their personal stories, Andrew Dressler
- By all means question climate policies. But facts are facts, The Economist
- Four Ways to Look at Global Carbon Footprints, National Geographic
- ↑ Missionary from Toronto winning converts — on climate change, University of Toronto
- ↑ Ward, Peter F. Under a Green Sky
- ↑ Limiting Global Warming to 2°C: Can Europe and the United States Keep the Climate Window Open?, German Marshall Fund
- ↑ The climate challenge: Achieving zero emissions, OECD