what are major things that impact climat change?

Answer 1

The natural impacts are usually divided up into two groups, external climate forcings and internal climate variation:
* Changes in radiative forcings - the sun spot cycle known as solar variation - plays some role. While the changes in Total Solar Irradiance are not large, some scientists are speculating about a possible "solar amplification."
http://en.wikipedia.org/wiki/Solar_variation
* Changes in the level of cosmic rays which are responsible for creating low-level clouds that shade and cool the surface
* Changes from volcanic activity - when a volcano erupts, it causes sudden cooling that may last for a year or up to five years depending on the size of the eruption.
* Changes from oceanic oscillations - the most important longer term one is the Pacific Decadal Oscillation. The most significant shorter term one is El Nino Southern Oscillation. When they are both in the warm phase, as in 1998 and 2006, it can be quite warm.
http://en.wikipedia.org/wiki/Pacific_decadal_oscillation
* Other ocean-atmospheric interactions - these are complex interactions the climate models do not model well because they are so poorly understood. If the oceans burp, the climate changes.
http://www.giss.nasa.gov/research/briefs/schmidt_02/

Man-made climate changes
* The most discussed one is increasing levels of atmospheric CO2 from the burning of fossil fuels, mainly coal-powered electric plants and cars.
* Changes in land use/ land cover. Sprawling suburbs and cities, growing agriculture, etc lead to warming. The most prolific and respected climatologist, Roger Pielke, claims this one is more significant that CO2.
http://climatesci.colorado.edu/2007/09/02/summary-conclusions-of-climate-science/

Answer 2

Water vapor