In the long term, the earth must shed energy into space at the same rate at which 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’s surface and atmosphere. Most of it, however, passes straight through the atmosphere 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-red radiation.

Most of the infra-red radiation emitted upwards by the earth’s surface is absorbed in the atmosphere by water vapour, carbon dioxide, and the other naturally occurring "greenhouse gases". These gases prevent energy from passing directly from the surface out into space. Instead, many interacting processes (including radiation, air currents, evaporation, cloud-formation, and rainfall) transport the energy high into the atmosphere. From there it can radiate 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 like Mars.

By increasing the atmosphere’s ability to absorb infra-red energy, our greenhouse gas emissions are disturbing the way the climate maintains this balance between incoming and outgoing energy. A doubling of the concentration of long-lived greenhouse gases (which is projected to occur early in the 21stcentury) would, if nothing else changed, reduce the rate at which the planet can shed energy into space by about 2 per cent. Energy cannot simply accumulate. The climate somehow will have to adjust to get rid of the extra energy - and while 2 per cent may not sound like much, over the entire earth that amounts to trapping the energy content of some 3 million tons of oil every minute.

Scientists point out that we are altering the energy "engine" that drives the climate system. Something has to change to absorb the shock.

The last several decades have been a time of international soul-searching about the environment. What are we doing to our planet? More and more, we are realizing that the Industrial Revolution has changed forever the relationship between humanity and nature. There is real concern that by the middle or the end of the 21st century human activities will have changed the basic conditions that have allowed life to thrive on earth.

The 1992 United Nations Framework Convention on Climate Change is one of a series of recent agreements through which countries around the world are banding together to meet this challenge. Other treaties deal with such matters as pollution of the oceans, dryland degradation, damage to the ozone layer, and the rapid extinction of plant and animal species. The Climate Change Convention focuses on something particularly disturbing: we are changing the way energy from the sun interacts with and escapes from our planet’s atmosphere. By doing that, we risk altering the global climate. Among the expected consequences are an increase in the average temperature of the earth’s surface and shifts in world-wide weather patterns. Other unforeseen effects cannot be ruled out.

We have a few problems to face up to.