This describes how carbon dioxide causes the earth to heat up.
The greenhouse effect is caused mainly by two gases – water vapour and carbon dioxide. Other gases are known to be greenhouse gases but their concentrations are smaller and so they have less effect.
The total quantity of water vapour in the air can vary but remains fairly constant with vast areas of ocean being able to supply water vapour. The concentration of carbon dioxide is not as well regulated and is increased by burnig of oil, petrol, coal, trees and so on.
The greenhouse gases keep the earth warmer. Fortunately nitrogen and oxygen, which are the main constituents of the atmosphere, are not greenhouse gases or we would heat up too much. It has been estimated that we would be roughly 40 degrees Celsius colder were it not for the greenhouse effect of water vapour and carbon dioxide.
It might be noted that in the desert where there is little water vapour to keep the heat in things become cold quickly after the sun has set.
If water vapour and carbon dioxide keep heat in why don’t they keep the heat from the sun out? The answer lies in the very different temperatures of the earth and sun. The sun is very hot and emits radiation mainly of a shorter wavelength. The cooler earth emits radiation of a longer wavelength. Now the water vapour and carbon dioxide will let the shorter wavelength radiation in, but when it hits the cooler earth it warms the earth, but the earth is still a lot cooler than the sun and therefore emits radiation of a lower frequency. Now this lower frequency radiation is absorbed by the water vapour and carbon dioxide, so the radiant heat energy is transferred to the atmosphere rather than going off into space. This has a warming effect on the earth.
Obvious disadvantages of a significant increase in temperature in a short time are changes in sea levels that are hard to cope with, disruptive changes in the distribution of life on earth – animals being found where they would not normally be, others dying. Might there be tropical forests at the South Pole and malaria bearing mosquitoes all over the earth, or deserts without much life?
But if carbon dioxide levels are rising would plants not be able to grow more easily? This is one of the advantages suggested by optimists. With faster growing plants more carbon dioxide will be absorbed every second and there would be some compensation.
There is controversy as to how much the earth will be able to adjust (if at all) with some believing mechanisms will come into play allowing the earth to compensate, but the rate at which temperature is changing makes for very disruptive times.