Global warming: Natural or human induced?Examination of ice cores shows that there is more CO2 in the atmosphere than at any time in the past 600,000 years. Between 1960 and 2002, annual anthropogenic global emissions of CO2 approximately tripled.

They rose by about 33 per cent since 1987 alone. At the same time we find 11 of the most warm years in the past one and a quarter century since 1990, with 2005 the warmest on record. From the period of industrialisation people are using more and more energy than ever especially from the fossil fuels. Fossil fuel produce CO2 upon burning which directly increases the amount of CO2 in the ambient air. At the same time mankind destroyed huge area of forests to create more living space for them. Till now, natural forests are being cleared all over the world. Plants absorb CO2 to prepare their food and ultimately maintain the balance of CO2 in atmosphere. So shrinking of forest cover means higher concentration of CO2 in the ambient air. So, it is very easily understood that the global warming is more human induced than natural resulting in increased thawing of permafrost, and melting of polar ice masses, with profound world-wide environmental, economic, social, cultural and political implications.

Sea level rise accelerated: In the past 100 years, global sea level rose between 1 and 2 millimeters a year. Since 1992 the rate has increased to about 3 millimeters a year, primarily through thermal expansion of warming oceans and then by freshwater flowing into the oceans from melting ice. Melting ice is responsible for a significant portion of the observed sea level rise, with the Greenland and Antarctic ice sheets the largest contributors. The Greenland ice sheet is melting faster than new ice is being formed. In the Antarctic, three large sections of ice shelves in the peninsula have collapsed over the past 11 years, followed by a marked acceleration in thinning of glaciers that were held back by the shelves.

Adverse effects on Arctic and Antarctic: Arctic and Antarctic zones are considered as the last frontiers of global unaltered natural ecosystems. Polar environments are among the most extreme on the planet, with limited sunlight, extreme temperatures, short growing seasons, sea ice, snow cover, glaciers, tundra and permafrost. Global climate models indicate that global warming induced by the greenhouse effect will be most acute in Polar regions. Parts of the Polar regions are already warming at a rate of two to three times of the global average. Most of these areas are in the Arctic but the Antarctic peninsula is also warming. Each summer has been shrinking the area of the ice covered Arctic Ocean and the remaining ice is becoming less thick.

Keystone species in arctic, polar bears hunt seals on floating ice and use ice corridors to move from one area to another. Pregnant females build winter dens in areas with thick snow cover. They need good spring sea-ice conditions for their own and their cubs' survival. During the past two decades, the body weight of adult polar bears in the Hudson Bay area in Canada has declined between 15 and 26 per cent. The number of cubs born is also declined between 1981 and 1998.

Precursor of grim global disaster: Melting ice in the Polar regions and glaciers will drive changes elsewhere on the planet. The process of melting ice will lead to sea level rise about 3 millimeter annually. By the year 2050 sea level will be raised by about 13 cm. Intergovernmental Panel on Climate Change (IPCC) projections for the years 2050 and 2100 establish that the small island states (AOSIS), less developed countries (LDCs), the arctic region and low lying coastal states will be more vulnerable to the inundation process. Low lying countries will be inundated making a huge number of people refugees. In December 2005, a small community living in the Pacific island chain of Vanuatu became perhaps the first to be formally moved as a result of climate change.

Continued global warming is expected to cause shifts in the geographic range and seasonality of certain infectious diseases. These include vector-borne infections including malaria and dengue fever, and food-borne infections, like salmonellas, which peak in the warmer months. Human health all over the world will be affected also by global warming. The rise in temperature will favour pathogenic activities and human health will be at higher risk, increased risk of Dengu, Malaria and Diarrhea etc.

The Munich Re Foundation estimated weather-linked economic losses due to disaster like tropical storms and forest fires at more than US$ 200 billion, with insured losses at more than US$ 70 billion in 2005.

Remedial measures: There are various options available to avoid catastrophic climate change. These include worldwide improvement in energy efficiency and a shift to renewable resources. Popularising the use of renewable energy sources such as solar and wind power, bio-energy and geothermal energy can reduce green house has emission considerably. Trees can slow climate change by absorbing carbon dioxide as they grow. Deforestation must be stopped and more trees planted to slow down the process. A number of analysts consider that nuclear power could play a significant role by meeting electricity demand without emitting CO2. But a low greenhouse gas future will also need to include social changes. Without massive campaign it is not possible to make people aware of the imminent disaster.

Conclusion: It is now crystal clear to all that polar ice sheets are melting due to global warming. The ongoing global process will bring about very harmful effects not only upon the biota of polar region or people near the Arctic or Antarctica, the melting of polar ice berg is precursor of a great disaster that victimises the whole mankind. Each and every body of this planet has his/her role to play for tackling the disaster. The motto should be "Think globally, act locally."

Md. Mahfujur Rahman is studying Environmental Sciences at Jahangirnagar University.