HENRY SHUE - Author of “The Pivotal Generation” - Snr. Research Fellow, Centre for International Studies, Oxford

“Well, it's because of the situation we face. We can tell from the science that we have to reach zero carbon emissions by 2050. And common sense tells you that bringing them down for the second 50% is going to be harder than the first 50%. So we have to take care of the first 50% by about 2030, and it's 2023 already. We literally must - if we're going to keep climate change from becoming even more dangerous than it is - is to do a very great deal in the next seven or eight years. And a huge amount between now and 2050. So it's not that this problem is the most important of all possible problems. There are other problems like preventing nuclear war, but this is a problem that either we get a grip on it now, or there's a real possibility that it will escape from our control."