On CO-2 and long range climate change, and the role of humanity as a key element of Gaia

I've posted several comments deriving from the rambling little book by James Lovelock I read recently, A Rough Ride to the Future. I haven't read all of his books on his Gaia hypothesis, so I am assuming some of what he says in this book is recycled.

Be that as it may, he makes an interesting point about the Earth Self-Regulatory (Feedback) System ("Gaia") and CO-2. For the past million years or so, the Earth has been in a glaciation state about 80% of the time. Apart from the present anthropogenic climate change, we are in the midst of what would otherwise almost certainly have been a relatively brief interglacial. (Warmer period, usually only 15-20% of the duration of glaciations, during which most of the ice melts, sea levels rise, and the Earth's average temperature rises; currently about 16° C).

According to Lovelock, this pattern of repeated glaciation, although partly known to be caused by changes in the earth's orbit and precession, is also part of the long term feedback system. "Gaia" is (was) keeping the World colder because, counterintuitively, cooler tropical waters, in particular, allow a cooler world to maximize biomass and biodiversity. Even in the (geographically shifted) more temperate areas, there is more forest and more robust life overall during glaciations. One major factor is that during glacial maxima, the sea level worldwide is nearly 100m (!) lower, which means there were huge areas, almost an entire additional continent, of land that's now submerged.

In fact, during such maxima, the Self Regulatory System keeps CO-2 levels very close to the lowest possible. At the height of recent glaciations, it was about 180 ppm, which is the LOWEST it has EVER been, at least since the inception of an oxygen rich atmosphere, and before that it was probably MUCH higher anyway.

What this means is that until recently the Earth was keeping CO-2 as low as possible in order to keep the world cool. This is in part to counterbalance the slow-exponential rise in the brightness of the Sun. A billion and a half years or more ago, the amount of sunlight striking the surface of the Earth's atmosphere (the "Solar Constant") was about 1 kW/m^2, yet the greenhouse gases in the atmosphere, principally water vapor and methane, usually kept the surface temperatures higher than they are today (although there were periods of intensive glacial activity scattered in time). Today, it's about 1.35 kW/m^2. The lower CO-2, low methane levels, and low humidity worldwide on average, keep the Earth cooler. In as little as 100 million years, the Solar Constant will be about 1.5 kW/m^2. At that point (or somewhat later, but the exact date isn't the point), in order to keep the oceans from getting so warm that water vapor will induce a runaway greenhouse and turn the Earth into a Venus, the Earth's Self-Regulatory System will have to lower CO-2 levels to zero. But at zero, plants cannot live in the atmosphere, so macroscopic life on land will disappear.

This may seem arcane, but what it means is that the Earth has been fighting global warming, caused by the SUN, for epochs, and it will start losing the battle in a much shorter time than the time in which complex life, much less simpler life, has existed on Earth. The Earth is likely doomed to a runaway heat death, no matter what its self-regulatory systems do. The wildcard being humans, who may, by space engineering, be able to do something about all this (Lovelock scarcely mentions space engineering, but I see it as virtually inevitable).

Lovelock is optimistic, and sees human beings as an essential element of Gaia, and its future ability to regulate climate and other factors to keep the Earth habitable. Sounds right to me, but I think our role as the only Earth life capable of acting in the wider Solar System, not just on Earth, will be key. For those inclined to a teleological view of the nature and role of humanity in the Universe, that is probably it: we are here to broaden Gaia's game so life can persevere more than a short span in the scheme of things into the future, and, I'll throw in, probably equally importantly (Lovelock ignores this completely), we are here to be the Earth's gonads, or flowers, if you prefer: to replicate Earthian biospheres elsewhere, by transporting the seeds of life to other suitable locations, either in the Solar System, or beyond (or both). (This idea was promoted by the late Timothy Leary, who, despite addling his brain a bit with LSD, was quite the visionary thinker).