GREENHOUSE GASES

Greenhouse effect schematic showing energy flows between space, the atmosphere, and earth's surface. Energy exchanges are expressed in watts per square meter (W/m²).

EXTERNAL FORCINGS

External forcing refers to processes external to the climate system (though not necessarily external to Earth) that influence climate. Climate responds to several types of external forcing, such as radiative forcing due to changes in atmospheric composition (mainly greenhouse gas concentrations), changes in solar luminosity, volcanic eruptions, and variations in Earth's orbit around the Sun. Attribution of recent climate change focuses on the first three types of forcing. Orbital cycles vary slowly over tens of thousands of years and thus are too gradual to have caused the temperature changes observed in the past century.

TEMPERATURE CHANGES

Two millennia of mean surface temperatures according to different reconstructions, each smoothed on a decadal scale. The instrumental record and the unsmoothed annual value for 2004 are shown in black.

Evidence for warming of the climate system includes observed increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level. The most common measure of global warming is the trend in globally averaged temperature near the Earth's surface. Expressed as a linear trend, this temperature rose by 0.74 ± 0.18 °C over the period 1906–2005. The rate of warming over the last half of that period was almost doubles that for the period as a whole (0.13 ± 0.03 °C per decade, versus 0.07 °C ± 0.02 °C per decade). The urban heat island effect is estimated to account for about 0.002 °C of warming per decade since 1900. Temperatures in the lower troposphere have increased between 0.13 and 0.22 °C (0.22 and 0.4 °F) per decade since 1979, according to satellite temperature measurements. Temperature is believed to have been relatively stable over the one or two thousand years before 1850, with regionally varying fluctuations such as the Medieval Warm Period and the Little Ice Age.

Estimates by NASA's Goddard Institute for Space Studies (GISS) and the National Climatic Data Center show that 2005 was the warmest year since reliable, widespread instrumental measurements became available in the late 1800s, exceeding the previous record set in 1998 by a few hundredths of a degree. Estimates prepared by the World Meteorological Organization and the Climatic Research Unit show 2005 as the second warmest year, behind 1998. Temperatures in 1998 were unusually warm because the strongest El Niño in the past century occurred during that year. Global temperature is subject to short-term fluctuations that overlay long term trends and can temporarily mask them. The relative stability in temperature from 2002 to 2009 is consistent with such an episode.

Temperature changes vary over the globe. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C per decade against 0.13 °C per decade). Ocean temperatures increase more slowly than land temperatures because of the larger effective heat capacity of the oceans and because the ocean loses more heat by evaporation. The Northern Hemisphere warms faster than the Southern Hemisphere because it has more land and because it has extensive areas of seasonal snow and sea-ice cover subject to ice-albedo feedback. Although more greenhouse gases are emitted in the Northern than Southern Hemisphere this does not contribute to the difference in warming because the major greenhouse gases persist long enough to mix between hemispheres.

The thermal inertia of the oceans and slow responses of other indirect effects mean that climate can take centuries or longer to adjust to changes in forcing. Climate commitment studies indicate that even if greenhouse gases were stabilized at 2000 levels, a further warming of about 0.5 °C (0.9 °F) would still occur. 

GLOBAL WARMING- INTRO

Global warming is the increase in the average temperature of Earth's near-surface air and oceans since the mid-20th century and its projected continuation. According to the 2007 Fourth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC), global surface temperature increased 0.74 ± 0.18 °C(1.33 ± 0.32 °F) during the 20th century. Most of the observed temperature increase since the middle of the 20th century was caused by increasing concentrations of greenhouse gases, which results from human activity such as fossil fuel burning and deforestation.

Climate model projections summarized in the latest IPCC report indicate that the global surface temperature is likely to rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F) during the 21st century. The uncertainty in this estimate arises from the use of models with differing sensitivity to greenhouse gas concentrations and the use of differing estimates of future greenhouse gas emissions. An increase in global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, probably including expansion of subtropical deserts. Warming is expected to be strongest in the Arctic and would be associated with continuing retreat of glaciers, permafrost and sea ice. Other likely effects include changes in the frequency and intensity of extreme weather events, species extinctions, and changes in agricultural yields. Warming and related changes will vary from region to region around the globe, though the nature of these regional variations is uncertain.

The scientific consensus is that anthropogenic global warming is occurring. Nevertheless, political and public debate continues. The Kyoto Protocol is aimed at stabilizing greenhouse gas concentration to prevent a "dangerous anthropogenic interference". As of November 2009, 187 states have signed and ratified the protocol. 

WORLD CLASSICAL TAMIL CONFERENCE, COIMBATORE 2010

World Classical Tamil Conference would be held in Coimbatore from 23rd Jun’10 to 27th Jun’10. 

‘CODISIA’ has been selected and announced as the venue of the world classical Tamil conference on 09th Nov’09. Tamil Internet Conference also is organized along the Tamil conference.
The chairman of the conference is Tamil Nadu CM.

The conference is organized by Tamil Nadu Govt. TN government spends crores of rupees for infrastructure development of Coimbatore. Tamil people from all over world are going to participate in the event. 

About Tamil
Tamil is spoken by Tamil people of India and SriLanka. It has official Status in Tamil Nadu, Pudhuchery, Srilanka and Malasiya. It is the first Indian language to be declared as classical language by Govt of India in 2004. 

For more details,
http://www.ulakathamizhchemmozhi.org

Tamil University - www.tamiluniversity.ac.in
Tamil Virtual University - www.tamilvu.org
INFITT - www.infitt.org
Association of Tamil computing - www. kanithamizh.in

For more details, visit http://www.ulakathamizhchemmozhi.org

TUNDRA THAWING

Climate scientists also worry that permafrost in the Arctic tundra will thaw, releasing enormous amounts of CO₂ and methane gas into the atmosphere. According to Field, the most critical, short-term concern is the release of CO₂ from decaying organic matter that has been frozen for millennia. "The new estimate of the total amount of carbon that's frozen in permafrost soils is on the order of 1,000 billion tons," he said. "By comparison, the total amount of CO₂ that's been released in fossil fuel combustion since the beginning of the Industrial Revolution is around 350 billion tons. So the amount of carbon that's stored in these frozen soils is truly vast."

Much of the carbon is locked up in frozen plants that were buried under very cold conditions and have remained in deep freeze for 25,000 to 50,000 years, he added. "We know that the Arctic is warming faster than anyplace else," he said. "And there is clear evidence that these frozen plants are very susceptible to decomposition when the tundra thaws. So melting of permafrost is poised to be an even stronger foot on the accelerator pedal of atmospheric CO_2, with every increment of warming causing an increment of permafrost-melting that shoots an increment of CO₂ into the atmosphere, which in turn increases warming.

"There's a vicious-cycle component to both the tundra-thawing and the tropical forest feedbacks, but the IPCC fourth assessment didn't consider either of them in detail. That's basically because they weren't well understood at the time."

For the fifth assessment report, Field said that he and his IPCC colleagues will have access to new research that will allow them to do a better job of assessing the full range of possible climate outcomes. "What have we learned since the fourth assessment? We now know that, without effective action, climate change is going to be larger and more difficult to deal with than we thought. If you look at the set of things that we can do as a society, taking aggressive action on climate seems like one that has the best possibility of a win-win. It can stimulate the economy, allow us to address critical environmental problems, and insure that we leave a sustainable world for our children and grandchildren. Somehow we have to find a way to kick the process into high gear. We really have very little time."

FOREST-CARBON FEEDBACK

Of particular concern is the impact of global warming on the tropics. "Tropical forests are essentially inflammable," Field said. "You couldn't get a fire to burn there if you tried. But if they dry out just a little bit, the result can be very large and destructive wildfires."

According to several recent climate models, loss of tropical forests to wildfires, deforestation and other causes could increase atmospheric CO₂ concentrations from 10 to 100 parts per million by the end of the century. This would be a significant increase, given that the total concentration of CO₂ in the atmosphere is currently about 380 parts per million, the highest in 650,000 years.

"It is increasingly clear that as you produce a warmer world, lots of forested areas that had been acting as carbon sinks could be converted to carbon sources," Field said. "Essentially we could see a forest-carbon feedback that acts like a foot on the accelerator pedal for atmospheric CO₂. We don't exactly know how strong the feedback could be, but it's pretty clear that the warmer it gets, the more likely it is that degradation of tropical forests will increase the atmospheric CO₂."

The ocean is another vital reservoir for carbon storage. Recent studies show that global warming has altered wind patterns in the Southern Ocean, which in turn has reduced the ocean's capacity to soak up excess atmospheric CO₂. "As the Earth warms, it generates faster winds over the oceans surrounding Antarctica," Field explained. "These winds essentially blow the surface water out of the way, allowing water with higher concentrations of CO₂ to rise to the surface. This higher-CO₂water is closer to CO₂-saturated, so it takes up less carbon dioxide from the atmosphere."

NOBEL PRIZE

Established by the United Nations in 1988, the IPCC brings together hundreds of experts from around the world to assess the science and policy implications of climate change. In 2007, the IPCC and Al Gore were awarded the Nobel Peace Prize. Field was among 25 IPCC scientists who attended the award ceremony in Oslo, Norway.

Since 1990, the IPCC has published four comprehensive assessment reports on human-induced climate change. Field was a coordinating lead author of the fourth assessment, Climate Change 2007, which concluded that the Earth's temperature is likely to increase 2 to 11.5 degrees Fahrenheit (1.1 to 6.4 degrees Celsius) by 2100, depending on how many tons of greenhouse gases are released into the atmosphere in coming decades.

But recent climate studies suggest that the fourth assessment report underestimated the potential severity of global warming over the next 100 years. "We now have data showing that from 2000 to 2007, greenhouse gas emissions increased far more rapidly than we expected, primarily because developing countries, like China and India, saw a huge upsurge in electric power generation, almost all of it based on coal," Field said.

This trend is likely to continue, he added, if more developing countries turn to coal and other carbon-intensive fuels to meet their energy needs. "If we're going to continue re-carbonizing the energy system, we're going to have big CO₂ emissions in the future," he said. "As a result, the impacts of climate change will probably be more serious and diverse than those described in the fourth assessment."

IPCC assessment reports are organized into three working groups. In September 2008, Field was elected co-chair of Working Group 2, which is charged with assessing the impacts of climate change on social, economic and natural systems. One of his major responsibilities is to oversee the writing and editing of the "Working Group 2 Report" for the IPCC fifth assessment, which will be published in 2014.

"In the fourth assessment, we looked at a very conservative range of climate outcomes," Field said. "The fifth assessment should include futures with a lot more warming."

CLIMATE CHANGE LIKELY TO BE MORE DEVASTATING THAN EXPERTS PREDICTED, WARNS TOP IPCC SCIENTIST

Without decisive action, global warming in the 21st century is likely to accelerate at a much faster pace and cause more environmental damage than predicted, according to a leading member of the Nobel Prize-winning Intergovernmental Panel on Climate Change.

IPCC scientist Chris Field of Stanford University and the Carnegie Institution for Science points to recent studies showing that, in a business-as-usual world, higher temperatures could ignite tropical forests and melt the Arctic tundra, releasing billions of tons of greenhouse gas that could raise global temperatures even more—a vicious cycle that could spiral out of control by the end of the century.

"There is a real risk that human-caused climate change will accelerate the release of carbon dioxide from forest and tundra ecosystems, which have been storing a lot of carbon for thousands of years," said Field, a professor of biology and of environmental Earth system science at Stanford, and a senior fellow at Stanford's Woods Institute for the Environment. "We don't want to cross a critical threshold where this massive release of carbon starts to run on autopilot."

Field will present his findings Feb. 14, at the annual meeting of the American Association for the Advancement of Science (AAAS) in Chicago during a symposium titled, "What Is New and Surprising since the IPCC Fourth Assessment?"