Even if we planted a tree on every square yard available in the planet by the end of the century we would only capture at most 10 percent of the CO2 we need to reduce. This does not mean that we should not plant trees; we should, for biodiversity's sake, and for our long-term future together with the other species.

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.

Geoengineering means changing the Earth's fundamental large-scale processes.

As difficult as it is to eliminate the risk of nuclear warfare, it requires fewer changes to the global economy than does averting or reversing climate change.

Changing the world's oceans to increase their uptake of CO2, as other geoengineering solutions propose, is equally dangerous, as the increased resulting acidity of the oceans kills tiny crustaceans, such as krill, that are the basis of the pyramid of life on the planet as we know it.

Political parties often take advantage of denial and fear in a moment of change. This is a well understood phenomenon that often leads to scapegoat-ism: blaming outsiders, such as immigrants, or racial and religious minorities. The phenomenon is behind Brexit and the violence in the political cycles in the US and EU.

Technology is a many-headed monster and perhaps it would be better to regress to a safer past and avoid technological change; it is tempting to think like that.