They knew.
This is from page 1 of Michael Mann's book The New Climate War.
The original source is Inside Climate News.
Michael Mann's book is excellent, and I heartily recommend it. He dissects the information war that has been going on for decades now, waged by the fossil fuel industry. But he also gives it to those who are all doom-and-gloom, the "Deep Adaptation" people who think all that's left is for us to prepare for the collapse of society. Mann's position is that we can still cut emissions enough by 2030 to prevent serious problems, with enough activism and political will, and that's his message in the book and in the talks he's giving seemingly everywhere.
I wish I were that optimistic but I can't say I am. I just can't see the world getting it together, primarily because of corruption driven by the multi-trillion dollar fossil fuel industry. (Just today I saw a tweet by Senator Elizabeth Warren about an army of Exxon lobbyists on Capitol Hill.) There's far too much money to be made for them to go quietly, or to transition into energy companies that produce renewable energy. They're making token efforts at best:
But who cares about me--a lot of young people aren't very optimistic either:
which is incredibly sad. And infuriating. OK, I worried a lot about global nuclear war when I was younger, between about 25 to 35, and would occasionally jolt upright in the middle of the night yelling from a dream, scaring the hell out of girlfriends in the process. Maybe my subconscious thought humanity was "doomed," but I outgrew it (but am rather surprised there hasn't been a global nuclear war in my lifetime--I would have bet there would have been. There's still time for one, of course. but I no longer wake up screaming at night.). But climate change seems a different order of disaster, because it looks inevitable. No attempts at a solution have done anything to modify the exponential Keeling curve--not Kyoto, not Copenhagen, not the Paris Agreement--and it's difficult to believe it will happen now at COP26.
Though there is just a touch of room for hope, as 2019's CO2 emissions were flat compared to 2018's. (2020's were much lower than 2019's, but that was due to the pandemic.) But through June 2021, global carbon emissions were 7% higher than June 2019's.
So why be optimistic? I don't see it yet. Does anyone?