Why would a minor temperature increase caused by global warming pose a threat to Earth?

Two degrees Celsius of warming doesn't seem very much, however if the earth warms by two degrees:
  • The glaciers will disappear from Greenland
  • Polar bears will struggle to survive as so much ice has melted
  • Insects move with the climate. Pine bark beetles will move north and kill off the white bark forests in the USA that provide the grizzly bear with food
  • New forests will spring up in the melting tundra of Canada and all the methane released will add to the greenhouse gases and to the warming.
  • Pacific islands like Tuvalu are underwater
  • Most of the world's tropical coral reefs will be lost.

Coral reefs are like the canary in the coal mine, warning us of danger to ocean life.