We all know the leopard can't change his stripes.

Third world nations are producing too many children too fast...it is time to ignore the controversy over family planning and cut out-of-control population growth.

To use a Southern euphemism, our space program has been snake-bit.

Political will is a renewable resource, and everyone can have it in abundance if they so choose.

There's an old African proverb that says "If you want to go quickly, go alone. If you want to go far, go together." We have to go far - quickly. And that means we have to quickly find a way to change the world's consciousness about exactly what we're facing, and why we have to work to solve it.

Where solar energy is concerned - and wind energy and battery storage and electric vehicles and efficiency technologies - that is what we are now seeing. So, yes, I'm very optimistic, but anyone who works on the climate crisis has an internal struggle between hope and despair. I won't deny that, but hope has always prevailed in my outlook.

Today we're dumping 70 million tons of global-warming pollution into the environment, and tomorrow we will dump more, and there is no effective worldwide response. Until we start sharply reducing global-warming pollution, I will feel that I have failed.