Arctic sea ice retreat, increases in heavy rainfall and flooding, permafrost melt, loss of glaciers and snowpack with attendant changes in water supply, increased intensity of hurricanes, etc.

OMG

climate change that takes place due to increases in carbon dioxide concentration is largely irreversible for 1,000 years after emissions stop.

http://www.pnas.org/content/early/2009/01/28/0812721106.full.pdf+html