How much climate change? That will be determined by how our emissions continue and also exactly how our climate system responds to those emissions. Despite increasing awareness of climate change, our emissions of greenhouse gases continue on a relentless rise. In 2013, the daily level of carbon dioxide in the atmosphere surpassed 400 parts per million for the first time in human history. The last time levels were that high was about three to five million years ago, during the Pliocene era.
Because we are already committed to some level of climate change, responding to climate change involves a two-pronged approach:
1. Reducing emissions of and stabilizing the levels of heat-trapping greenhouse gases in the atmosphere (“mitigation”);
2. Adapting to the climate change already in the pipeline (“adaptation”).