How do greenhouse gases affect global climates?
Greenhouse gases like
This traps heat in the earth's atmosphere and cause what is called global warming.
Picture credit Astrocamp.school.com.
As the diagram shows solar radiation passes through the atmosphere and heats the Earth's surface which in turn radiates energy at a longer wavelength (infrared and near infrared). The longer wavelengths cannot freely exit the atmosphere due to the action of greenhouse gases. These gases work like windows in that they allow light in and do not freely allow heat to escape. Hence "greenhouse" gases.
How does this affect global climates?
Climate is the weather we expect, like cold dry winters in the prairies, but it does not change day by day like weather. In the terms of the greenhouse effect we are looking at general heat of the atmosphere which doesn't have a huge effect on day to day weather but can greatly impact climate.
For example, one aspect of climate would be humidity. Well warmer air would be able to hold more humidity before condensation occurs. Therefore in some areas we are likely to see droughts occur because the air is holding onto a lot more moisture before it actually rains.
On the chart above, the red line shows the number of grams of water a kilogram of atmosphere can hold at a given temperature. So if and area is normally 25 degrees and has precipitation it has about 20 g of water per kg of air in the atmosphere. If that same area was 5 degrees warmer with the exact same amount of water, the air can almost hold 30 g of water. The relative humidity goes from 100% to about 70% without changing the amount of water.
There are other aspects of climate that can get changed due to greenhouse gases, but this answer is already getting too long. If you would like to know more you can either ask another question or message me.