It's all so confusing: If the Earth's temperature is 59 F and "just right" is 72 F, why should we panic at the thought of a few degrees of warming?

And if we're admitting that liquid water is so important to life, why should we get all worked up over the prospect of mile-thick ice sheets becoming a little thinner some day?

Habitable Zone For Planets Redefined, Shifting Ranks Of Exoplanets In 'Goldilocks' Range

The habitable zone defines the region where a planet might be able to retain liquid water on its surface. Any closer to the star and water would vaporize away; any farther, and it would freeze to ice. But water in its liquid state is what scientists are after, since that is thought to be a prerequisite for life.

Flashback: A Possible Second Home for Humanity Found, but the Commute's Brutal | PBS NewsHour | Dec. 7, 2011 | PBS

Scientists have discovered a so-called "Goldilocks" planet with a temperature that is not too hot, not too cold, but maybe just right to support life.
...scientists say the temperature averages about 72 degrees

Global Warming : Feature Articles

If there were no greenhouse effect, the Earth’s average surface temperature would be a very chilly -18°C (0°F) instead of the comfortable 15°C (59°F) that it is today.