There are a variety of ways that the climate can be affected but it is mostly tied to the content of our atmosphere.
Things like Sulfur reflect the sun's light and can contribute to colder periods, like theorized the cause of the "little ice age" that killed a great amount of people in Europe. Could very well have been cause by volcanic eruptions across the planet that emitted vast quantities of sulfur in the air. We've seen first hand the impact of sulfur in the atmosphere, whether changes have been recorded due to the volcanic clouds that circle the Earth after eruptions. Sulfur has a period of about 5 years in which it will stay in our atmosphere until it comes down in the form of acid rain. We have seen acid rain as a result of volcanic activity but we have also caused it ourselves from the burning of coal that contains high levels of sulfur.
Carbon dioxide, the gas that human's produce a substantial amount of, takes 50 years to exit our atmosphere. Our influence on the atmosphere can be measured by taking our output over the last 50 years. The greenhouse effect can also be measured and we know how much carbon dioxide has an effect on global temperature.
Methane is multiple times more potent as a greenhouse gas but it's atmospheric life is only 20 years(?). Our influence on introducing carbon dioxide and methane gas is having a direct impact on the global temperature. This could lead to a shift in our air and ocean currents dramatically altering our planets climates. Areas that were once tropical could find themselves receiving much less precipitation, and the opposite for arid regions. The polar caps are the portion of our planet that will not shift due to the temperature increase and will continue to shrink because of it. Some areas may very well be colder than normal, but that all depends on the shifting of the currents. Europe for example, relies on the warmth of the gulf stream. Without it, it would be as cold as Canada.
Though climate shifting might not necessarily be that threatening, if it effects our method of growing food or access of water, dramatic steps will need to be taken to let ourselves adjust. We could reverse the changes if we feel we would be better off at our current climate, but to do so would take many years after the effects occur. Outside forces such as solar ray activity could affect climate change as well, but human introduction of greenhouse gasses are edging our planet closer to the point in which climate will change. So while our climate might not change from a sudden shift in solar activity, if we are on the edge, it could certainly tip the scale.
Before the PS3 everyone was nice to me :(
