I was reading this book today and had a revelation - I suddenly realized why we're here. (Heavy.) The earth tended to be cold, even once freezing right down to equator. Life appeared about 4 billion years ago, when a great cloud of methane was gradually replaced by oxygen, and then carbon dioxide came into the mix because of the algae and bacteria and changed the atmosphere and warmed the planet. Gaia, (as the self-regulating mother earth is known,) has nurtured creatures who nurture her. About 8000 years ago, humans began increasing carbon dioxide. That allowed the weather to remain warmish all these millenia, and for the great diversity of life that we now have to flourish. (We did that. We're amazing!) When plagues hit, such as the black plague of medieval times, "the epidemics were global in their reach and killed so many people that forests were able to grow back on deserted farmland. In the process, they absorbed CO2, lowering atmospheric concentrations by 5 to 10 parts per million. Global temperatures then fell, and periods of relative cold ensued in places such as Europe."
Wow. I've been thinking that we're nothing to Gaia, that we're behaving like parasites, killing our host, but now I realize that she wanted us here. We've just overdone it. Will we be able to step back from our carbon dioxide production ourselves, or will she have to regulate us with another plague?
Just to put the whole CO2 thing in perspective - the atmosphere of Venus is 98% CO2, and its surface temperature is 891 degrees F.
8000 years ago, the CO2 was 160 parts per million (ppm). Earth's pre-industrial high in 1800 was 280 ppm. We're now up to around 385 ppm. When we reach 500 ppm, it's all over but the burning up, all life as we know it dies, and Gaia either starts over, or, unable to cool herself (old lady that she is), she could well become a hot, dead rock, like Mars.
But we won't let that happen, will we? Will we?