A level of no more than 350 ppm is still feasible, with the help of reforestation and improved agricultural practices, but just barely - time is running out.

I was lucky to grow up at a time when it was not difficult for the child of a tenant farmer to make his way to the state university.

What has become clear from the science is that we cannot burn all of the fossil fuels without creating a very different planet.

The climate dice are now loaded. Some seasons still will be cooler than the long-term average, but the perceptive person should notice that the frequency of unusually warm extremes is increasing. It is the extremes that have the most impact on people and other life on the planet.

The evidence for human-made climate change is overwhelming.

Coral reefs, the rain forest of the ocean, are home for one-third of the species of the sea. Coral reefs are under stress for several reasons, including warming of the ocean, but especially because of ocean acidification, a direct effect of added carbon dioxide. Ocean life dependent on carbonate shells and skeletons is threatened by dissolution as the ocean becomes more acid.

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