Global warming isn't a prediction. It is happening.

The last time the world was three degrees warmer than today-which is what we expect later this century-sea levels were 25m higher. So that is what we can look forward to if we don't act soon.

I have been described as the grandfather of climate change. In fact, I am just a grandfather and I do not want my grandchildren to say that grandpa understood what was happening but didn't make it clear.

Injection of environmental and political perspectives in midstream of the science discussion cannot help the process of inquiry. I believe that persons with relevant scientific expertise should concentrate, with pride, on cool objective analysis, providing information to the public and decision-makers when it is found, but leaving the moral implications for later common consideration, or at most for summary inferential discussion.

We have at most ten years—not ten years to decide upon action, but ten years to alter fundamentally the trajectory of global greenhouse emissions.

Adding CO2 to the air is like throwing another blanket on the bed.

...chief executives of large fossil fuel companies to [should] be put on trial for high crimes against humanity and nature; [Hansen] accusing them of actively spreading doubt about global warming in the same way that tobacco companies blurred the links between smoking and cancer.