Guardian: As humans put more and more heat-trapping gases into the atmosphere, the Earth's climate changes; we all know that. Some of the trickier questions are, how fast is it changing, what can we expect in the future, what are the costs of slowing emissions (compared to the costs of doing nothing), and what changes are we already observing that give us such confidence in our predictions?
Perhaps the poster child of climate change is in the Arctic, where sea ice has been declining at an astonishing rate....