Why the Earth is warming
The Earth is warming because there is more energy coming in than going out, like switching on a very slow kettle. Atmospheric greenhouse gases such as CO2 act like a blanket, keeping the Earth warm. By increasing atmospheric CO2 by a third, mankind has increased the effectiveness of that blanket, causing what scientists call an ‘energy imbalance’.
Climate scientists say we have perhaps less than a decade before planetary self-reinforcing feedback processes take the situation completely out of our control. Some are saying they are now terrified by the accelerating, worsening conditions they observe. How long have we got before tipping points become irreversible? We don’t know with any useful accuracy. But uncertainty justifies action, not inaction.
For much more detail see this presentation from Paul Beckwith, climate scientist at the University of Ottawa: