| Global warming is the Process that increased | | | | warming. Although global warming and ozone |
| the average temperature of the Earth, | | | | depletion often are linked in the media, the |
| near-surface air and oceans. The term global | | | | relationship between the two is not strong. |
| warming is a specific example of the broader | | | | Scientists have stated with 66-90% confidence |
| term climate change, which can also refer to | | | | that the effects of volcanic and human-caused |
| global cooling. In principle, global warming | | | | aerosols have offset some of global warming, |
| is neutral as to the period or causes, but in | | | | and that greenhouse gases would have resulted |
| both common and scientific usage the term | | | | in more warming than observed if not for this |
| generally refers to recent warming and | | | | effect. Many estimates of aggregate net |
| implies a human influence. The climate system | | | | economic costs of damages from climate change |
| varies through natural, internal processes | | | | across the globe, the social cost of carbon |
| and in response to variations in external | | | | (SCC), expressed in terms of future net |
| "forcing" factors including solar activity, | | | | benefits and costs that are discounted to the |
| volcanic emissions, variations in the earth's | | | | present, are now available. Peer-reviewed |
| orbit In the past 200 years human industrial | | | | estimates of the SCC for 2005 have an average |
| activity has injected carbon dioxide and | | | | value of US$43 per tonne Rising global |
| other greenhouse gases into the atmosphere, | | | | temperature might cause forest fires to occur |
| and recently global average temperatures have | | | | on larger scale, and more regularly. This |
| been increasing. The predicted effects for | | | | releases more stored carbon into the |
| the environment and for human life are | | | | atmosphere than the carbon cycle can |
| numerous and varied. The main effect is an | | | | naturally re-absorb, as well as reducing the |
| increasing global average temperature. | | | | overall forest area on the planet, creating a |
| | | | positive feedback loop Projected climate |
| The scientific consensus is that these | | | | changes due to global warming have the |
| greenhouse gases have been responsible for | | | | potential to lead to future large-scale and |
| most of the present warming trend. That | | | | possibly irreversible changes in our climate |
| consensus is not unanimous. The earth has | | | | resulting in impacts at continental and |
| experienced natural global warming and | | | | global scales. With increasing average global |
| cooling many times in the past. The recent | | | | temperature, the water in the oceans expands |
| Antarctic EPICA ice core spans 800,000 years, | | | | in volume, and additional water enters them |
| including eight glacial cycles with | | | | which had previously been locked up on land |
| interglacial warming periods much hotter than | | | | in glaciers, for example, the Greenland and |
| current temperatures.the time of the last | | | | the Antarctic ice sheets. The sea level has |
| glacial maximum about 20,000 years ago. | | | | risen more than 120 metres since the peak of |
| Scientists have studied global warming with | | | | the last ice age about 18,000 years ago. For |
| computer models of the climate. These models | | | | some time it was hoped that a positive effect |
| are based on physical principles of fluid | | | | of global warming would be increased |
| dynamics, radiative transfer, and other | | | | agricultural yields, because of the role of |
| processes, with some simplifications being | | | | carbon dioxide in photosynthesis, especially |
| necessary because of limitations in computer | | | | in preventing photorespiration While local |
| power. Some effects on both the natural | | | | benefits may be felt in some regions (such as |
| environment and human life are, at least in | | | | Siberia), recent evidence is that global |
| part, already being attributed to global | | | | yields will be negatively affected. |