First off, his Gaia hypothesis is a largely a load of crap, because he anthropomorphizes the interaction. The idea of superorganisms is not a load of crap and there are plent of examples (e.g. a colony of ants vs. a single ant). Human beings and in the greater context all life on earth can be considered to be a large superorganism, because of the all the complex interactions and dependencies. All levels of organisms are undergoing evolution. Some of it is directed by what we call "intelligent processes" i.e. our own human derived "logical" decisions. The reality is the decisions we make en masse are more statistical than logical (e.g. the marketplace). While an individual may pride himself on logical decisions, the "mass mind" works more like the neural nets of our brains.

Anyway, it is pretty clear that the high order self evolution is going pretty rapidly these days (AI, genetic engineering) and it is extremely hard to predict how that evolution will proceed in eras of much less than geologic time (i.e. 1000's of years). In fact it is hard to predict even 100 to 200 years in the future with the rapid technological advances occuring with literally billions of minds able to draw upon a common knowledge base.

There are so many presumptions necessary to be so pessimistic as to say "we are doomed" it is laughable. There will always be those predicting armagaddon, and I have to say so far they have all been wrong. Frankly, I see no reason to not be optimistic.

I can make the same kind of sweeping statements James Lovelock makes from an optimistic point of view and I defy anyone to show that my statments are less credible. I believe we will have space elevators and relatively cheap access to space by the end of this century. I believe we will invent and perfect new power sources so that our power need will continue to be met. We will go outword and colonize the solar system and eventually there will be trillions of human beings not just billions. Self replicating robots will build massive structures in space to house those trillions. Human beings will not so much be destroyed as replaced by what we self evolve to. That will be some combination of AI and biological. Keeping the earth's climate stable will become as easy as setting a thermostat in a room, as we can literally control the amount of sunlight that hits the earth and reflects from it.

Currently, we inhabit a relatively microscopically thin skin of the earth. We certainly may with virtually unlimited power from the planetary core utilize much more than the surface of the earth and be able to support many more people just on planet earth if we desire. The efficiencies necessary to handle yet more billions must of course increase many fold, but nanotechnologies and utilizations of in situ materials will open vast new resources at the same time as containing and converting the waste of their use.

If we so desire, we will seed the stars with yet more of our life form. It is unknown whether the superorganism to which we evolve will care to do so, as it may be able to transcend this dimension, or just want to create its own virtual reality universes.

Anyway, my point is that we can all speculate wildly, but to have any sort of certainty with the rapid change that is occuring and is possible is absurd.