The sun just like on every other planet. Duh.
A common denier rant is the climate has always changed, for once this is actually true, of course denier are less happy to admit that many of those changes are in fact linked to long term changes in Co2 levels, they try to pretend it's linked to other things like the Sun, they will talk about pauses of ~800 years before Co2 rose in the Milankovitch cycles. This is a common denier tactic, they take some real science, which is in fact where the pause theory comes from, but they leave out the rest of that same theory that has Co2 rising latter and also adding to global average temperature.
Of course in a geologic sense the current glacial cycle is a fairly recent event, only happening for about the last 2.5 million years, go back further and there are many case of higher Co2 levels linked to both a warmer planet and periods (with very high levels) when the Oceans lost most of their life due to acidification. Of course while denier rant about cavemen with hummers and similar nonsense past Co2 levels can and did rise due to much more active volcanic activity, that needed neither cavemen or hummers. In an actual historic sense Co2 levels should be falling as we descend back into the next glacial on it's roughly 120 thousand year cycle, but at the moment we have a quite low volcanic activity and a Co2 level at a level that is the highest in the last 800,000 years, we are the only possible cause of that and in fact research has proved that by looking at the isotope structure of the extra Co2 and it is not of volcanic origin.
Co2 has always been a major driver of climate change, past variation of Co2 was natural, but what is happening now is caused by us, scientists no longer have any real doubt about that.
http://climate.nasa.gov/key_indicators#c...
As referred many variables influence climate, topography, cloud cover, axis of the Earth, orbit, sun activity, greenhouse gas concentrations, volcanoes etc. etc.
In answer to James regarding ice cores having higher carbon after global warming would this be because the carbon is in the atmosphere during the warming and for cooling to happen carbon is removed from the atmosphere (trapped in ice samples, the oceans, sinks etc.). This would be my guess without having researched the topic much.
Well mainly Earths rotation in relation to the sun. And we go sometimes wibbly wobbly on the revolution and get further or closer to the sun causing things like ice ages or hotter seasons. There are many other factors that you can look into as well. Such as things that effect precipitation and life.
The sun (solar cycles) orbital changes (milankovitch cycles) volcanoes, forest fires, deforestation, industry, human habitation (building and blacktop roads causing changes in albedo, also called the urban heat effect) and to a minor extent greenhouse gases like CO2 and CH4
There is no man-made Climate Change.
Top climate scientists say there is no man-made Global Warming.
The Great Global Warming Swindle
