Bill Gates on the climate crisis: ‘I can't deny being a rich guy with an opinion’

In an exclusive extract from his new book, the Microsoft founder explains why we need to cut carbon emissions to zero - even if he is an imperfect messenger'

There are two numbers you need to know about climate change. The first is 51bn. The other is zero.

Fifty-one billion is how many tons of greenhouse gases the world typically adds to the atmosphere every year. Zero is what we need to aim for. To stop the warming and avoid the worst effects of climate change, humans need to stop adding greenhouse gases to the atmosphere. The climate is like a bathtub that's slowly filling up with water. Even if we slow the flow of water to a trickle, the tub will eventually overflow. Setting a goal to reduce our emissions won't do it. The only sensible goal is zero.