Globalwarming awareness2007

Scientists have studied global warming with computer models of the climate (see below). Before the scientific community accepts a climate model, it has to be validated against observed climate variations. As of 2006, sufficiently high-resolution models successfully simulate summer/winter differences, the North Atlantic Oscillation, and El Niño. All validated current models predict that the net effect of adding greenhouse gases will be a warmer climate in the future. However, the amount of predicted warming varies by model, and there still remains a considerable range of climate sensitivity predicted by the models which survive these tests; one of the most important sources of this uncertainty is believed to be different ways of handling clouds. Part of the technical summary of the IPCC TAR includes a recognition of the need to quantify this uncertainty: “In climate research and modeling, we should recognize that we are dealing with a coupled non-linear system, and therefore that the prediction of a specific future climate is not possible. Rather the focus must be on the probability distribution of the system’s possible future states by the generation of ensembles of model solutions.” An example of a study which aims to do this is the Climateprediction.net project; their methodology is to investigate the range of climate sensitivities predicted for the 21st century by those models which are first shown to give a reasonable simulation of late 20th century climate change.

As noted above, climate models have been used by the IPCC to anticipate a warming of 1.4 °C to 5.8 °C (2.5 °F–10.4 °F) between 1990 and 2100. They have also been used to help investigate the causes of recent climate change by comparing the observed changes to those that the models predict from various natural and human derived forcing factors. In addition to having their own characteristic climate sensitivity, models have also been used to derive independent assessments of climate sensitivity.

Climate models can produce a good match to observations of global temperature changes over the last century. These models do not unambiguously attribute the warming that occurred from approximately 1910 to 1945 to either natural variation or human effects; however, they suggest that the warming since 1975 is dominated by man-made greenhouse gas emissions. Adding simulation of the carbon cycle to the models generally shows a positive feedback, though this response is uncertain (under the A2 SRES scenario, responses vary between an extra 20 and 200 ppm of CO₂). Some observational studies also show a positive feedback.

Uncertainties in the representation of clouds are a dominant source of uncertainty in existing models, despite clear progress in modeling of clouds. There is also an ongoing discussion as to whether climate models are neglecting important indirect and feedback effects of solar variability. Further, all such models are limited by available computational power, so that they may overlook changes related to small-scale processes and weather (e.g. storm systems, hurricanes). However, despite these and other limitations, the IPCC considered climate models “to be suitable tools to provide useful projections of future climates”.

In December, 2005 Bellouin et al. suggested in Nature that the reflectivity effect of airborne pollutants was about double that previously expected, and that therefore some global warming was being masked. If supported by further studies, this would imply that existing models under-predict future global warming.

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The likelihood that global temperatures will continue to significantly increase has led to proposals to mitigate global warming. Mitigation covers all actions aimed at reducing the negative effects or the likelihood of global warming.

There are five categories of actions that can be taken to mitigate global warming:

1. Reduction of energy use (conservation)
2. Shifting from carbon-based fossil fuels to alternative energy sources
3. Carbon capture and storage
4. Carbon sequestration
5. Planetary engineering to cool the earth, including screening out sunlight and increasing the reflectivity of the earth.

Strategies for mitigation of global warming include development of new technologies; carbon offsets; renewable energy such as biodiesel, wind power, and solar power; nuclear power; electric or hybrid automobiles; fuel cells; energy conservation; carbon taxes; enhancing natural carbon dioxide sinks; increased use of sulfate aerosols, which exhibit a cooling effect on the Earth; population control; and carbon capture and storage. Many environmental groups encourage individual action against global warming, often aimed at the consumer, and there has been business action on climate change.

The world’s primary international agreement on combating climate change is the Kyoto Protocol. The Kyoto Protocol is an amendment to the United Nations Framework Convention on Climate Change (UNFCCC). Countries that ratify this protocol commit to reduce their emissions of carbon dioxide and five other greenhouse gases, or engage in emissions trading if they maintain or increase emissions of these gases.

Although the governments of 163 countries ratified the Kyoto Protocol, (notably excluding the United States and Australia), there is a growing debate about how effective the Kyoto protocol has been. Some politicians, including President of the United States George W. Bush and Prime Minister of Australia John Howard have argued that the cost of mitigating global warming via the Kyoto protocol is too large to be practical. This view may be proving correct, as the signatories of the Kyoto protocol, including Europe and Japan, are currently struggling to meet their targets.[14] After only five years, Canada has given up entirely. Also, of the 163 countries that have signed and ratified Kyoto, only 31 are actually required to lower greenhouse emissions. Notable among those countries that have signed and ratified Kyoto but are not required to reduce greenhouse gas emissions are China and India with their huge populations and rapidly growing economies.

Some segments of the business community have accepted global warming and its attribution to anthropogenic causes as valid, as well as a need for actions such as carbon emissions trading and carbon taxes.

Adaptation strategies accept some warming as a foregone conclusion and focus on preventing or reducing undesirable consequences. Examples of such strategies include defense against rising sea levels or ensuring food security.

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Mitigation of global warming involves taking actions aimed at reducing the extent or likelihood of global warming. This is in contrast to Adaptation to global warming which involves taking action to take advantage of the positive effects of global warming while preventing or minimizing the negative effects.

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