Countires across the globe celebrate World Environment Day on June 5. And the theme this year is 'Melting Ice � a Hot Topic.'

The World Environment Day theme for 2007 is 'Melting Ice - a Hot Topic? In support of the International Polar Year 2007-08, the theme focuses on the effects that climate change has on polar ecosystems and communities, and the ensuing consequences around the world.

The main international function is being held in the city of Tromse, Norway. Global outlook for Ice & Snow, is also being launched around the world to provide an up-to-date account of the state of the environment and the trend in ice and snow regions.

Greenhouse Gases
The Earth has warmed by approximately 0.75 degree Celsius since pre-industrial times. Eleven of the warmest years in the past 125 years occurred since 1990, with 2005 the warmest on record. There is overwhelming consensus that this is due to the emission of greenhouse gases, such as carbon dioxide from burning fossil fuels.

In 1863, it was John Tyndall, the English Physicist, who recognized the power of carbon dioxide and water vapour to change the earth's climate. Greenhouse gas emissions from human activities are causing our world to get warmer.

Concentrations of carbon dioxide in the atmosphere are higher than at anytime for the past 0.6 million years, and the rate of increase is accelerating. Between 1960 and 2002, annual anthropogenic global emissions of carbon dioxide, approximately trippled. It rose by about 33 per cent since 1987 alone.

Danger to Polar Regions
The most dramatic evidence of climatic change is in the polar regions. The Arctic is warming twice as fast as the global average. The extent and thickness of permanent Arctic sea ice is diminishing; areas of permafrost, frozen for centuries, are thawing; and ice-caps in Greenland and Antarctic are melting faster than anyone anticipated.

Scientists are increasingly concerned about the possibility of abrupt climatic change, including reduction in ocean currents, such as the Gulf Stream, which warms Europe, and changed pattern of rainfall, such as the monsoon seasons, which would affect food security for billions of people.

Imminent Sea-level rise
As sea level rise, inhabitants of low-lying islands and coastal cities throughout the world face inundation. In December 2005, a small community living in the Pacific Island chain of Vanuatu became perhaps the first to formally move as a result of climatic change.

Climatic change also threatens marine habitats and the livelihood of people who depend on them. The oceans have absorbed approximately half of the carbon dioxide produced in the past 200 years, producing carbonic acid and lowering the pH of surface seawater. This could affect the process of calcification by which animals such as corals and mulluscs make their shells from calcium carbonate.

Continued global warming is expected to cause shifts in the geographic range i.e., latitude and longitude, and seasonality of certain infectious diseases such as malaria and dengue fever, and food-borne infections, such as salmonellosis, which peak in the warmer months.

Retreating Glaciers
The Earth's crysophere - its frozen regions - is melting fast. According to the 2007 report of the Intergovernmental Panel on climate change, 30 mountain glaciers around the world lost more than half a metre of thickness in 2005, resulting from a temperature rise of 0.60 C over the 20th century.

Most scientists agree that this is largely due to greenhouse gas emissions. Side effects from the melting itself may now be accelerating the process; when permafrost thaws, for example, it releases methane, a long lasting greenhouse gas, from the soil, and melting Arctic sea ice also means loss of its reflective qualities, as water absorbs more of the sun's energy than ice and snow. In Himalayas, Mount Everest's glaciers have shrunk by 2 to 5 km in the last five decades, flooding glacier lakes and nearby communities.

Sixty seven percent of the glaciers in the Himalayas are retreating at a startling rate and the major casual factor has been identified as climatic change. The Gangotri glacier between Kashmir and Nepal is another good example of an accelerated glacier retreat.

As glaciers retreat, governments are causing an increasingly anxious eye at future water supplies. And for the one-third of the World's population living in dry lands, changing weather patterns linked to climate change threaten to exacerbate desertification, drought and food insecurity.

The polar regions are natural 'sinks' for toxic chemicals which are produced around the world. In the Arctic persistent organic pollutants are transported by air and ocean currents. They accumulate in organisms at the top of the food chains, such as marine mammals and sea birds, presenting a threat to the animals themselves, the ecosystems they inhibit and to humans who use them as food.

Stress on Energy Efficiency
Society's dependence on fossil fuels is jeopardizing social and economic progress and our future security. Fortunately, there are many policy and technological options available to avert the impending crisis, but we need increased political will to use them.

Developed countries in particular can do more to reduce greenhouse gas emissions and increase energy efficiency. They can also support clean development in fast growing economies such as Brazil, China and India, as well as adaptation measures in those countries that face the greatest hardships from climate change.

Other options available to avoid catastrophic climate change are worldwide improvements in energy efficiency and a shift to low carbon and renewable resources such as solar and wind power, bio-energy and geothermal energy. There is also potential for capturing and storing CO2 , while a number of analyst consider that nuclear power could play a significant role.

In 1995, installed global wind power capacity was 4,800 megawatts of electricity. At the end of 2005, the figure had increased twelve-fold to more than 59,000 megawatts. The Global Wind Energy Council estimates that over a third of the World's electricity could be generated by wind by 2050.

Energy Alternatives
A low-greenhouse gas future will also need to include social changes. Millions of households now use the sun to heat water, with an increasing number also harnessing solar energy for electricity. In Ice Land, abundant hydropower and geothermal energy is being channeled into developing hydrogen from water as a major energy source to replace fossil fuels. In Brazil, ethanol made from sugarcane has replaced about 40% of the country's need for petrol.

As a part of the UNEP's 'Plant for the Planet: Billion Tree Campaign', people are banding together to plant trees. Trees can slow climate change by absorbing CO2 , help to reduce pollution, keep cities cool, protect water catchments and reduce soil erosion.

The author is former assistant director, NEERI, Nagpur and technical expert on water quality, World Bank Project.