Earth already committed to 2.4-dgree C rise from climate change

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Earth already committed to 2.4-dgree C rise from climate change
Jeremy Hance, mongabay.com
September 15, 2008

Air pollution masking full impact of global warming

As of 2005 the Earth was already committed to rise of global mean temperatures by 2.4°C (4.3°F), concludes a new study published in the journal Proceedings of the National Academy of Sciences (PNAS). The conclusion is significant because the Intergovernmental Panel on Climate Change (IPCC) has warned that a rise in global temperature by 1 to 3°C will lead to catastrophic consequences, including “widespread loss of biodiversity, widespread deglaciation of the Greenland Ice Sheet, and a major reduction of area and volume of Hindu-Kush-Himalaya-Tibetan glaciers, which provide the head-waters for most major river systems of Asia.” These glaciers, predicted to shrink considerably in the next few decades, provide food and water to over two billion people.

Glaciers in the Bhutan-Himalaya. Glacial lakes have been rapidly forming on the surface of the debris-covered glaciers in this region during the last few decades. Image courtesy of Jeffrey Kargel, USGS/NASA JPL/AGU

V. Ramanathan and Y. Feng of the Scripps Institution of Oceanography at the University of California at San Diego argue that due to unique conditions in the Arctic, mean global temperature must be doubled to accurately reflect changes there. With a committed raise of nearly 5°C (9°F), the already diminishing sea-ice will continue to abate at alarming rates and the Greenland Ice Sheet may begin to crumble under climatic pressures. The researchers estimate the long-term exposure (thousands of years) of the Greenland Ice Sheet to a minimum warming between 1.9–4.6°C will lead to a complete melt of Greenland. Such a melt would raise sea levels by seven meters (23 feet).

Given the dire projections, Ramanathan and Feng warn that time is running out. Unless tough mitigation policies on greenhouse gases are put in place, the authors say the Earth will be locked into a rise of 3°C by 2030. They write that “CO2 mitigation polices are extremely critical if we want to limit further increases in the committed warming.”

Air pollution masking climate change

Ramanathan and Feng also explore a question often raised by skeptics: "Why hasn't the planet yet felt the full force of climate change?" So far, the planet has experienced a mean warming of 0.76°C since the late 1800s.

The scientists conclude that a variety of factors are masking the full effect of climate change; one of the most significant of which is air pollution. Some types of air pollution send aerosols that reflect light like a mirror, brightening the planet and thereby cooling it. The pollutants ability to mask rising temperatures has been estimated at 47 percent. However, as nations clean up their skies, the masking effects of such pollutants disappear causing the Earth to undergo sudden warming. The researchers state that this relationship between dwindling air pollutants and higher temperatures can already be seen in Europe.

Considering the many negative aspects for health and environment of air pollution, the researchers do not recommend that nations should forgo policies that clean-up air pollution. But they say countries and international organizations should be aware of the potential rise in temperature due to such actions.

The authors suggest better models are needed to provide nations with more accurate predications of the relationship between air pollutants and greenhouse gases. “This is not easy and the costs may be substantial for developing such models and the associated observing systems, but,” the scientists conclude, “we do not have much choice.”

V. Ramanathan and Y. Feng (2008). On avoiding dangerous anthropogenic interference withthe climate system: Formidable challenges ahead. PNAS Online Early Edition for the week of September 15-19, 2008.

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