A giant asteroid could hit the earth!Something else could happen!The global temperature could rise! Wake up!
The last several decades have been a time of international soul-searchingabout the environment. What are we doing to our planet? More and more, weare realizing that the Industrial Revolution has changed forever the relationshipbetween humanity and nature. There is real concern that by the middle or theend of the 21st century human activities will have changed the basicconditions that have allowed life to thrive on earth.The 1992
United Nations Framework Convention on Climate Change
isone of a series of recent agreements through which countries around the worldare banding together to meet this challenge. Other treaties deal with suchmatters as pollution of the oceans, dryland degradation, damage to the ozonelayer, and the rapid extinction of plant and animal species. The ClimateChange Convention focuses on something particularly disturbing: we arechanging the way energy from the sun interacts with and escapes from ourplanet's atmosphere. By doing that, we risk altering the global climate. Amongthe expected consequences are an increase in the average temperature of theearth's surface and shifts in world-wide weather patterns. Other unforeseeneffects cannot be ruled out.
We have a few problems to face up to.
In the long term, the earth must shed energy into space at the same rate atwhich it absorbs energy from the sun. Solar energy arrives in the form of short-wavelength radiation. Some of this radiation is reflected away by the earth'ssurface and atmosphere. Most of it, however, passes straight through theatmosphere to warm the earth's surface. The earth gets rid of this energy(sends it back out into space) in the form of long wavelength, infra-redradiation.Most of the infra-red radiation emitted upwards by the earth's surface isabsorbed in the atmosphere by water vapour, carbon dioxide, and the othernaturally occurring "greenhouse gases". These gases prevent energy frompassing directly from the surface out into space. Instead, many interactingprocesses (including radiation, air currents, evaporation, cloud-formation, andrainfall) transport the energy high into the atmosphere. From there it canradiate into space. This slower, more indirect process is fortunate for us,because if the surface of the earth could radiate energy into space unhindered,the earth would be a cold, lifeless place - a bleak and barren planet rather likeMars.By increasing the atmosphere's ability to absorb infra-red energy, ourgreenhouse gas emissions are disturbing the way the climate maintains thisbalance between incoming and outgoing energy. A doubling of theconcentration of long-lived greenhouse gases (which is projected to occurearly in the 21 century) would, if nothing else changed, reduce the rate atwhich the planet can shed energy into space by about 2 per cent. Energycannot simply accumulate. The climate somehow will have to adjust to get ridof the extra energy - and while 2 per cent may not sound like much, over theentire earth that amounts to trapping the energy content of some 3 million tonsof oil every minute.Scientists point out that we are altering the energy "engine" that drives theclimate system. Something has to change to absorb the shock.