Global warming causes
The climate system varies both through natural, “internal” processes as well as in response to variations in external “forcing” from both human and non-human causes, including solar activity, volcanic emissions, and greenhouse gases. Climatologists agree that the earth has warmed recently. The detailed causes of this change remain an active field of research, but the scientific consensus identifies greenhouse gases as the primary cause of the recent warming. Outside of the scientific community, however, this conclusion can be controversial.
Adding carbon dioxide (CO2) or methane (CH4) to Earth’s atmosphere, with no other changes, will make the planet’s surface warmer; greenhouse gases create a natural greenhouse effect without which temperatures on Earth would be an estimated 30 °C (54 °F) lower, and the Earth uninhabitable. It is therefore not correct to say that there is a debate between those who “believe in” and “oppose” the theory that adding carbon dioxide or methane to the Earth’s atmosphere will, absent any mitigating actions or effects, result in warmer surface temperatures on Earth. Rather, the debate is about what the net effect of the addition of carbon dioxide and methane will be, when allowing for compounding or mitigating factors.
One example of an important feedback process is ice-albedo feedback. The increased CO2 in the atmosphere warms the Earth’s surface and leads to melting of ice near the poles. As the ice melts, land or open water takes its place. Both land and open water are on average less reflective than ice, and thus absorb more solar radiation. This causes more warming, which in turn causes more melting, and the cycle continues.
Due to the thermal inertia of the earth’s oceans and slow responses of other indirect effects, the Earth’s current climate is not in equilibrium with the forcing imposed by increased greenhouse gases. Climate commitment studies indicate that, even if greenhouse gases were stabilized at present day levels, a further warming of perhaps 0.5 °C to 1.0 °C (0.9–1.8 °F) would still occur.