At the Paris Conference of the Parties - COP21 - almost 200 nations agreed to reduce greenhouse gases to levels yielding no more than 1.5 to 2.0 degrees of warming.
Scientists are convinced that anything above the 2 degree mark locks in changes to the planetary climate beyond civilization's adaptive capacity.
For some climate activists, like Gary Cranston, the accord was an exercise in empty, feel-good promise making. For example, a group of climate scientists recently submitted a letter to The Independent calling the agreement "false hope" and full of "deadly flaws." They cited the fact that the CO2 reduction commitments in the agreement don't kick in until 2020. By that time, the scientists argue, so much more CO2 will have been pumped into the atmosphere that we may already be locked into warming, pushing us above the 2 degree line.