The consensus is that climate change ranks along with nuclear warfare as the top two risks facing human civilization.

The sun is the source of all energy on planet Earth and we cannot experiment with our only energy source.

We have to remove the CO2 that the industrial economy has already emitted, which otherwise will remain in the atmosphere for hundreds of years and alter the Earth's climate irreversibly. It is possible to do this.

We know little of the consequences of the geoengineering process, such as spraying particles into the atmosphere that shade the planet from the sun's rays and could decrease its temperature. But this process is how dinosaurs disappeared from the Earth about 60 million years ago, by particles spewed by a volcano or a giant meteorite impact, and our species could follow suit.

We have used the majority of our carbon budget and we are already at dangerous levels of CO2 concentrations, about 400 parts per million. The levels were 250 before industrialization. So the problem is what we have done already and, therefore, what must be undone.

We need a transformation of the world economy and of how we use and share the Earth's resources. We are running out of time. We are truly at the point of no return.

If nuclear warfare is believed to be somewhat controlled, then climate change is now the greatest threat.