THE increase in temperature of the atmosphere, seas, oceans and land masses is due to global warming. The global warming is caused by burning of fossil fuels (coal, oil and natural gas) which is released into the atmosphere.

Greenhouse gas occurs naturally in the environment but human beings increase it when they burn fossil fuels, wood products to heat buildings, drive vehicles and generate electricity.

By far the most abundant greenhouse gas is water vapour which reaches the atmosphere through evaporation of water from oceans, seas, lakes and rivers.

The second most abundant greenhouse gas is CO2 which flows into the atmosphere from natural processes such as volcano eruptions, respiration by life forms which breathe in O2 and exhale CO2 and by the decomposition of organic matter.

Carbon dioxide (CO2) leaves the atmosphere when it is absorbed by the process of photosynthesis. Photosynthesis breaks up CO2, releasing O2 into the atmosphere and fixing up the carbon (C) into aquatic and terrestrial plants.

The excess of CO2 goes back into the atmosphere. Methane (CH4), another greenhouse gas, is emitted during the production of coal, natural gas and oil and is also released from ruminant animals as a byproduct of digestion, nitrons oxide (N2O) another greenhouse gas is released by burning fossil fuels and plugging of farm field soils.

The water vapour in the atmosphere traps CO2, CH4 and N2O and acts as insulator trapping 20 times more heat than does the CO2.

In 1750 there was about 281 molecules of CO2 per million molecules (pmm) of air and today CO2 concentration is 368 pmm.

It is apprehended that it may reach up to 970 pmm by the middle of 21st centuary if the burning of fossil fuels is continued by the burgeoning population. Anthropogenic activities have caused greenhouse gas to be released to the atmosphere at a much faster rate than at which earth's natural processes can cycle the gases.

The widespread replacement of human labour by machines that began in Europe in 1850 has spread to the USA and other countries.

The global warming is causing climate change. The climate change is causing erratic torrential rain at some places and drought at other place.

The Himalayan glacier may melt at a faster rate in the near future. It may then cause heavy runoff of water causing flood in the Indus basin. The flood may break banks of big dams and rivers and submerge low lying areas.

Planet earth has warmed and cooled many times during the 4.65 billion years of its history and plants, animals and human beings have perished in large numbers and some have become extinct.

In order to remain extant, we have to adapt to the change in climatic condition. For this we need to build small dams all over Pakistan for storing water — the most precious natural resource.

Water sustains crop plants, livestock and humans. It is a wake-up call for developing and preserving drought-tolerant plants.

In this regard soil-borne beneficial micro-organisms, which increase the uptake of nutrients and withstand drought, should be given special attention for enhancing agricultural productivity. We are facing a shortage of food and edible oil. Agriculture, the most ancient culture of mankind, stands in dire need of resuscitation for our substance.

Food security is the best guarantee for our survival. Who lives if plants die and who dies if plants live.

DR M. JALALUDDIN

Department of Agriculture

University of Karachi