We are on the precipice of climate system tipping points beyond which there is no redemption.

If humanity wishes to preserve a planet similar to that on which civilisation developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO₂ will need to be reduced from its current 385 ppm [parts per million] to at most 350 ppm... If the present overshoot of this target CO₂ is not brief, there is a possibility of seeding irreversible catastrophic effects.

Our analysis shows that, for the extreme hot weather of the recent past, there is virtually no explanation other than climate change. The deadly European heat wave of 2003, the fiery Russian heat wave of 2010 and catastrophic droughts in Texas and Oklahoma last year [2011] can each be attributed to climate change. The odds that natural variability created these extremes are minuscule, vanishingly small. To count on those odds would be like quitting your job and playing the lottery every morning to pay the bills.

The trains carrying coal to power plants are death trains. Coal-fired power plants are factories of death.

Several times in Earth's history, rapid global warming occurred, apparently spurred by amplifying feedbacks. In each case, more than half of plant and animal species became extinct. New species came into being over tens and hundreds of thousands of years. But these are time scales and generations that we cannot imagine.

As you get more global warming, you should see an increase in the extremes of the hydrological cycle - droughts and floods and heavy precipitation.

The question is not whether to close the parks, but how to accomplish this goal.