Scientific American - Arctic Sea Ice: What, Why, and What Next

[Speck Tater]

2. Something I didn't realize...

In June, the Arctic ice cap covers around 2% of the Earth’s surface – around 11 million square kilometers of Arctic ice cap out of a total of 510 million square kilometers of Earth’s land and oceans. And that 2% of the Earth’s surface, for a period of roughly two months, receives more solar energy per day than even the sunniest areas on the equator.

Analyzing this, Peter Wadhams of the Global Oceans Physics Program at Cambridge calculates that the loss of the Arctic ice throughout the summer would have a warming effect roughly equivalent to all human activity to date. That is to say, with the ice gone in summer, the planet would, have an additional heating effect, just as large as the heating effect of all human CO2 and other greenhouse gasses to date.

(My emphasis)

On edit: The punchline:

In other words, the complete meltdown of the Arctic could roughly double the rate of warming of the planet as a whole.