Effects of global warming

Global warming means increase in the average temperature of the atmosphere, oceans, and landmasses of the earth. The planet has warmed (and cooled) many times during the 4.65 billion years of its history. At present, earth appears to be facing a rapid warming, which most scientists believe results, at least in part, from human activities.
The chief cause of this warming is thought to be the burning of fossil fuels, such as coal, oil, and natural gas, which releases carbon dioxide and other substances known as greenhouse gases into the atmosphere. As the atmosphere becomes richer in these gases, it becomes a better insulator, retaining more of the heat provided to the planet by the sun.
Scientists use elaborate computer models of temperature, precipitation patterns, and atmosphere circulation to study global warming. Based on these models, they have made several predictions about how global warming will affect weather, sea levels, coastlines, agriculture, wildlife, and human health.
Weather
Some experts predict that an increase in global warming will result in unpredictable weather patterns, including storm surges in which the wind piles up water in low-lying areas. The curved arms of the New Waterway Storm Surge Barrier in the Netherlands protect Rotterdam and other inland cities from flooding during large storms in the North Sea.
Normally, the large, curved arms are retracted to allow ships from the North Sea to travel to ports along the New Waterway. When a dangerous storm is anticipated, the arms are swung out to block off the waterway and prevent large waves from pushing floodwaters inland.
Scientists predict that during global warming, the northern regions of the Northern Hemisphere will heat up more than other areas of the planet, northern and mountain glaciers will shrink, and less ice will float on northern oceans. Regions that now experience light winter snows may receive no snow at all.
In temperate mountains, snowlines will be higher and snow-packs will melt earlier. Growing seasons will be longer in some areas. Winter and nighttime temperatures will tend to rise more than summer and daytime ones.
The warmed world will be generally more humid as a result of more water evaporating from the oceans. Scientists are not sure whether a more humid atmosphere will encourage or discourage further warming. On the one hand, water vapour is a greenhouse gas, and its increased presence should add to the insulating effect. On the other hand, more vapour in the atmosphere will produce more clouds, which reflect sunlight back into space, which should slow the warming process (see Water Cycle).
Greater humidity will increase rainfall, on average, about 1% for each Fahrenheit degree of warming. (Rainfall over the continents has already increased by about 1% in the last 100 years.) Storms are expected to be more frequent and more intense. However, water will also evaporate more rapidly from the soil, causing it to dry out faster between rains.
Some regions might actually become drier than before. Winds will blow harder and perhaps in different patterns. Hurricanes, which gain their force from the evaporation of water, are likely to be more severe. Against the background of warming, some very cold periods will still occur. Weather patterns are expected to be less predictable and more extreme.
Sea levels
An increase in global warming will likely result in a rise in sea levels, which could threaten many coastal areas around the world. Experts predict that parts of Bangladesh may become completely submerged if sea levels rise.
As the atmosphere warms, the surface layer of the ocean warms as well, expanding in volume and thus raising sea level. Warming will also melt much of the glacier ice, especially around Greenland, further swelling the sea. Sea levels worldwide rose 10 to 25 cm (4 to 10 in) during the 20th century, and IPCC scientists predict a further rise of 9 to 88 cm (4 to 35 in) in the 21st century.
Sea-level changes will complicate life in many coastal regions. A 100-cm (40-in) rise could submerge 6% of the Netherlands, 17.5% of Bangladesh, and most or all of many islands. Erosion of cliffs, beaches, and dunes will increase. Storm surges, in which winds locally pile up water and raise the sea, will become more frequent and damaging. As the sea invades the mouths of rivers, flooding from runoff will also increase upstream.
Wealthier countries will spend huge amounts of money to protect their shorelines, while poor countries may simply evacuate low-lying coastal regions.
Even a modest rise in sea level will greatly change coastal ecosystems. A 50-cm (20-in) rise will submerge about half of the present coastal wetlands of the United States. New marshes will form in many places, but not where urban areas and developed landscapes block the way. This sea-level rise will cover much of the Florida Everglades.
Agriculture
A warmed globe will probably produce as much food as before, but not necessarily in the same places. Southern Canada, for example, may benefit from more rainfall and a longer growing season. At the same time, the semiarid tropical farmlands in some parts of Africa may become further impoverished.
Desert farm regions that bring in irrigation water from distant mountains may suffer if the winter snow-pack, which functions as a natural reservoir, melts before the peak growing months. Crops and woodlands may also be afflicted with more insects and plant diseases.
Animals and plants
Animals and plants will find it difficult to escape from or adjust to the effects of warming because humans occupy so much land. Under global warming, animals will tend to migrate toward the poles and up mountainsides toward higher elevations, and plants will shift their ranges, seeking new areas as old habitats grow too warm.
In many places, however, human development will prevent this shift. Species that find cities or farmlands blocking their way north or south may die out. Some types of forests, unable to propagate toward the poles fast enough, may disappear.
Human health
In a warmer world, scientists predict that more people will get sick or die from heat stress, due less to hotter days than to warmer nights (giving the sufferers less relief). Diseases now found in the tropics, transmitted by mosquitoes and other animal hosts, will widen their range as these animal hosts move into regions formerly too cold for them.
Today, 45% of the world's people live where a mosquito carrying the parasite that causes malaria might bite them; that percentage may increase to 60% if temperatures rise. Other tropical diseases may spread similarly, including dengue fever, yellow fever, and encephalitis. Scientists also predict rising incidence of allergies and respiratory diseases as warmer air grows more charged with pollutants, mold spores, and pollens.
Md. Badsha Mia writes from the Dept. of Environmental Science and Resource Management, Mawlana Bhashani Science and Technology University, Santosh, Tangail.