Mr. President [Obama], I find it encouraging that you are proposing an initiative for reducing air pollution. Accepting the urgency, it seems clear to me also that climate change is a problem which can no longer be left to a future generation.

By the time we see that climate change is really bad, your ability to fix it is extremely limited... The carbon gets up there, but the heating effect is delayed. And then the effect of that heat on the species and ecosystem is delayed. That means that even when you turn virtuous, things are actually going to get worse for quite a while.

A lot of challenges we face today are also entirely global - so fighting climate change or ending terrorism, or ending pandemics or when a civil war in one country leads to a refugee crisis across different continents.

We must not place the burden on the next generations to take on the problems caused by the previous ones. Instead, we should give them the opportunity to remember our generation as the one that renewed and acted on - with honest, responsible and courageous awareness - the fundamental need to collaborate in order to preserve and cultivate our common home. May we offer the next generation concrete reasons to hope and work for a good and dignified future!

In other words, by mid-century, climate change could be just as deadly as COVID-19, and by 2100 it could be five times as deadly.

There are two numbers you need to know about climate change. The first is 51 billion. The other is zero. Fifty-one billion is how many tons of greenhouse gases the world typically adds to the atmosphere every year.