Greenhouse Effect
Prior to the advent of the industrial age, the concentration of CO2 in the atmosphere was about 280 ppm (parts per million). Today it's over 360 ppm. That's an increase by about 30 percent in less than 300 years. For the earth, this is an unprecedented rate of change, about 10,000 years' change compressed into 100 years. Carbon dioxide is critical to controlling the earth's heat balance because it absorbs infrared radiation (IR), basically heat. Heat coming to earth from the sun, visible radiation passes through the clear atmosphere and hits the earth and portion of it is absorbed and re-radiated back to space as IR. CO2 traps this IR and reflects it back to the earth's surface, causing further warming. This is called the greenhouse effect. Without it, water would freeze on earth. But with too much greenhouse effect, water would evaporate leaving the surface of earth.

Rising Ocean
Global sea level rise is caused by two factors. One is the delivery of water to the ocean as land ice melts, such as mountain glaciers and polar icecaps. Current evidence of global warming includes the widespread retreat of glaciers on five continents. For example: The ice cap on Mount Kilimanjaro may be gone in 20 years. About 1/3 of Kilimanjaro's ice field has disappeared in the last 12 years and 82 percent of it has vanished since it was first mapped in 1912. Next evidence is that sea ice in the Arctic Ocean is thinning. Massive Antarctic ice sheets have collapsed into the sea with alarming rapidity. The second factor is the thermal expansion of water within the oceans. As the temperature of water rises and the seas become less dense, they will spread, occupying more surface area on the planet. Increased temperature will accelerate the rate of sea level rise.

Impact Region Wise
Asia: Glacier melt in the Himalayas is projected to increase flooding, rock avalanches from destabilised slopes, and affect water resources within the next two to three decades. This will be followed by decreased river flows as the glaciers recede. Freshwater availability in Central, South, East and Southeast Asia particularly in large river basins is projected to decrease due to climate change which, along with population growth and increasing demand arising from higher standards of living, could adversely affect more than a billion people by the 2050s.

The endemic morbidity and mortality due to diarrhoeal disease primarily associated with floods and droughts are expected to rise in East, South and Southeast Asia due to projected changes in hydrological cycle associated with global warming. Increases in coastal water temperature would exacerbate the abundance and/or toxicity of cholera in South Asia. A 1 meter rise in sea level would inundate half of Bangladesh's rice land. Bangladeshis would be forced to migrate by the millions. Other rice growing lowlands which would be flooded include those of Viet Nam, China, India and Thailand. Millions of climate refugees could be created by sea level rise in the Philippines, Indonesia and Egypt.

Africa:? By 2020, between 75 and 250 million people are projected to be exposed to an increase of water stress due to climate change. If coupled with increased demand, this will adversely affect livelihoods and exacerbate water-related problems. Agricultural production, including access to food, in many African countries and regions is projected to be severely compromised by climate variability and change. This would further adversely affect food security and exacerbate malnutrition in the continent. In some countries, yields from rain-fed agriculture could be reduced by up to 50 percent by 2020. The cost of adaptation could amount to at least 5-10 percent of GDP.

Australia and New Zealand: As a result of reduced precipitation and increased evaporation, water security problems are projected to intensify by 2030 in southern and eastern Australia and in New Zealand, in Northland and some eastern regions. Production from agriculture and forestry by 2030 is projected to decline over much of southern and eastern Australia, and over parts of eastern New Zealand, due to increased drought and fire.

Europe: Negative impacts will include increased risk of inland flash floods, and more frequent coastal flooding and increased erosion (due to storminess and sea level rise). Mountainous areas will face glacier retreat, reduced snow cover and winter tourism, and extensive species losses (in some areas up to 60% under high emission scenarios by 2080). In Southern Europe, there will be reduced water availability, hydropower potential, summer tourism, and in general, crop productivity. It is also projected to increase health risks due to heat waves and the frequency of wildfires. In Central and Eastern Europe, summer precipitation is projected to decrease, causing higher water stress. Health risks due to heat waves are projected to increase.

Latin America: By mid-century, increases in temperature and associated decreases in soil water are projected to lead to gradual replacement of tropical forest by savanna in eastern Amazonia. Semi-arid vegetation will tend to be replaced by arid-land vegetation. There is a risk of significant biodiversity loss through species extinction in many areas of tropical Latin America. In drier areas, climate change is expected to lead to salinisation and desertification of agricultural land. Productivity of some important crops are projected to decrease and livestock productivity to decline, with adverse consequences for food security.

North America: Major challenges are projected for crops that are near the warm end of their suitable range or depend on highly utilised water resources. Warming in western mountains is projected to cause decreased snow pack, more winter flooding, and reduced summer flows, exacerbating competition for over-allocated water resources.

Conclusion
Very less heard about before 80s, Global Warming has now turned into an issue which no more remains a hypothesis but advancing in a pace more than predicted. It is an outcome of the lavish and indiscriminate exploitation of the nature by the developed countries but the burden is to be borne more by the developing and underdeveloped countries. If the issue is not rightly and timely addressed, a disaster is imminent. What it needs, is a real concern and commitment by the national and global political bodies and a global awareness to bring to an end to arbitrary abuse of the nature, and to reverse the damage that has already been done.

Dr. Zulfiquer Ahmed Amin is a freelance contributor.