What is the greenhouse effect?
The sun is our only external source of heat and energy. The earthъs temperature is maintained by а balance between heating from the sunrays and cooling caused by energy escaping to space from the earth’s warm surface and atmosphere. This natural balance between incoming and outgoing energy is essential to life on earth.
On а clear day, most of the energy arriving from the sun in а form of short wave length radiation passes through the atmosphere to warm the earth’s surface. This energy must be got rid of to maintain the earth’s energy balance. It escapes in the form of longer wavelength infrared radiation. But if the infrared radiation could escape directly to space, then the earth’s surface would be 30 degrees colder than it is today. It would be uninhabitable.
Fortunately, much of this infrared radiation is absorbed in the atmosphere by the so-called greenhouse gases making the world much warmer than it would be without them. These gases act rather like the glass in а greenhouse, which allows sunlight to enter, provides shelter from the wind and prevents most of the infrared energy from escaping, keeping the temperature warm.
So, the greenhouse effect is not а manmade phenomenon. In fact, it is perfectly natural.
It influences to the benefit of all our ecosystems by stabilizing atmospheric temperatures at levels conducive to plant, animal and human life. But for this kind of life to survive on earth, it is essential that the right balance be maintained between incoming and outgoing energy. By increasing greenhouse gas emissions we are disturbing this age-old balance.
Many of us think of greenhouse gases as being only the dirty emissions from car exhausts and industrial smokestacks. But in fact, there are six important greenhouse gases occurring randomly in the atmosphere in small quantities. These gases are:
- Water Vapor
- Carbon Dioxide
- Nitrous Oxide
- And, more recently, Chloroflourcarbons or Cfcs. Apart from Cfcs, all of these gases occur naturally.
But human activity is increasing their concentrations. This increase is causing the enhanced greenhouse effect - а manmade and potentially dangerous phenomenon.
CO2 is by far the most significant of the manmade greenhouse gases. Although it occurs naturally, it is also the one we produce in the greatest quantity. Industrialization has meant а greater use of fuels extracted from the ground such as coal, gas and oil. These are known as fossil fuels. And when burned they produce large amounts of CO2. Transport and generating of electricity alone account for about 45 % of fossil fuel CO2 emissions.
It is estimated that during the last 200 years, the concentration of CO2 in the atmosphere has risen by 26%. Levels have never been this high since humans inhabited the planet. Carbon dioxide now accounts for about 55% of the enhanced greenhouse effect.
Ice core samples have provided accurate data on the atmosphere going back thousands of years. This data, together with modern observation, shows а clear rise not only in carbon dioxide levels but also in those of methane (CH4) and other greenhouse gases. The rising levels of methane are at least in part due to increased rice production, waste disposal, mining, cattle ranching and large scale extraction and transportation of natural gas. All of them produce significant quantities of methane and all of them are on the increase.
Ozone (O3) is familiar to us all by now. It is the substance that protects us from the sun’s harmful ultraviolet rays. The highest concentrations exist in the upper atmosphere and form what is known as the ozone layer. It is damage to this protective layer that has caused so much concern in recent years. But ozone also plays а significant role as а greenhouse gas. Due to а complex chemical reaction in the lower atmosphere, а number of substances, most of them manmade, come together and ozone is formed. The amount of ozone produced depends largely on weather conditions and sunlight but it is on the increase.
Natural vegetation emits large amounts of nitrous oxide (N2O) but the increased concentrations of this gas are thought to come mainly from agriculture and the burning of biomass, such as wood and other vegetation.
Cfcs are the only greenhouse gases to be exclusively manmade. They are non-toxic and inert, which makes them safe and useful as aerosol propellants, refrigerants and insulators. They are also used in the manufacture of foam rubber and for cleaning of electronic components. Cfcs are well known to most of us as the gases blamed for the depletion of the ozone layer. But they are also а powerful greenhouse agent contributing to the enhanced greenhouse effect. They are particularly significant because they absorb infrared radiation not absorbed by the other gases.
Water vapor (H2O) is undoubtedly the most important greenhouse gas, but it is also, perhaps, the least understood. It occurs naturally, it is invisible, and is not directly affected by human activity, however it is affected indirectly through an important feedback mechanism. Warming brought about by the other greenhouse gases increases evaporation and allows the atmosphere to hold more water vapor. This may, in turn, enhance the warming
* * *
Some gases are more stable in the atmosphere than others. So it is not just the amount we pump out that is important. The quantity of any gas in the atmosphere is determined by а balance between its emissions and the size and strength of its available sinks.
Sinks are processes, which remove substances from the atmosphere by absorbing. In the case of carbon dioxide, for example, the main natural sinks are absorption by the oceans and photosynthesis occurring both on land and at sea. The sun’s rays strike green plants, driving а process in which carbon from the atmosphere is captured and fixed in the plant itself while oxygen is emitted. But often even this carbon is not removed from the atmosphere for long. Only plant or marine life, which dies and becomes fixed in the earth or seabed to eventually fossilize, removes carbon permanently from the climate’s system. if it not subsequently burned as fuel!
Although we increase CO2 levels by burning ever-greater quantities of fossile fuels, the effect of the increasing is also due to the further reducing size of the world’s natural sinks, such as forest cover. In fact, deforestation usually adds to both sides of the equations.
The world’s climate is а complex system governed by an interaction between the atmosphere, the ocean, man, ice caps, glaciers and sea ice. These elements form а carefully balanced equilibrium, into which we have introduced а new and potentially destabilizing element.
The excess energy trapped by manmade greenhouse gases will cause our planet to change, although we don’t know exactly how. The social and political consequences of climate change will be especially acute for people whose lives depend most critically on the present climate patterns. Human poverty and hunger are already on the increase. If food supplies fade, migrants from degraded areas in search of arable land and fresh water will aggravate social and political harmony.
Details are often disputed. But the fundamental problem is plain - our current rates of greenhouse gas emissions amount to nothing less than а worldwide uncontrolled and potentially catastrophic experiment with the earth’s climate.