I know this is an old comment, but I hope you see this all the same--or at least came to realize what I did.
At first I, too, thought that it was some nihilistic art piece about how we're just generally fucked. I had been in the green as far as Metric tonnage goes, and with CO2 PPM, but I was still in the red with the total anomaly temp! But I found that if I kept planting more trees, eventually I gained enough of a weighted ratio that the anomaly started to decrease in temperature, finally. The problem is, an hour and a half isn't enough time to get a real feel for the game. I had to restart after I messed up pretty badly and had hit a point of no return (so of course I ruined my chances to get to game over quickly and see what the bad ending looked like lol) and began the new game in earnest. I logged abooout three hours or so from start to "all green", and I was playing pretty quickly. It was 2071 when I started decreasing PPM and tonnage, but it wasn't until ~2130 that I started decreasing in global temp/anomaly.
Patience is a virtue. :) Hope you went on to find success!