So can any one tell me where the whole tipping point is ? When will we reach the point of no return ?
Two things:
1) There is for the most part only one way in which it makes sense to talk about points of no return. And not just for the trivial reason (arrow of time), but because a fundamental, widespread assumption seems to be that the life on earth and the various non-living external and internal dynamics which are a part of or affect this planet, are generally stable. Or even that humans have disrupted some delicate balance, and that if we haven't already "unbalanced" it already so much that at best we can only hope to lessen the inevitable doom, we will reach that point soon. Regardless of the very real (and numerous) ways in which humans have polluted, harmed, altered, and so on ecological systems, the climate, and even individual species, there was never a balance, there isn't now, and the only way there will be one is probably because the sun exploded.
2) That said, this planet is itself a dynamical system, and within it a innumerable other such systems. By "dyanamical" I mean what is usually called "chaotic" (thanks largely to the popularity of Gleick's book on "Chaos" theory). In general, although these systems show varying degrees of randomness and unpredictability, they also tend to stay within a range of variation. Another defining property, though, is their sensitivity to changes in parameters which goven the system. Simple population models are often the best way to explain this.
Imagine a simple ecosystem in which we have plants, an kind of animal which eats the plants, and a predator which eats that animal. The more food which grows, the more herbivore has to eat, which means there will tend to be more. However, as the number of these herbivores grows, two things happen: 1) more plants get eaten and 2) the carnivores have more food. Which means that there will be less food for this increased herbivore population, and the additional food will tend to increase the number of carnivores.
What happens next? It could be that the carnivores and the lack of food for the herbivores results in a decline in their numbers, accompanied by a decline in carnivores, and the plants start increasing again.
In other words, even in this incredibly simplistic model, there isn't any "balance" per se, only a range in which all three groups will continue to increase and decrease. However, it is possible the system to go outside of that range. For example, it could be that an increase in plant food leads to an increase in herbivores and then carnivores, but by the time the carnivores have eaten enough herbivore for the plants to begin to increase again, there are too many carnivores. So although the carnivores don't have enough food to continue to increase, their population is so great that the increase in plant food and in herbivores isn't fast enough to compared to the decrease in carnivores. And the carnivores kill off all of their food supply, die, and we have only plants.
The climate system is one of the most complicated systems around, filled with incredibly complex internal and external subsystems which alter its dynamics. Which means that there are a constant number of "tipping points" which are constantly being reached. It also means that looking for a specific "tipping point" in terms of the effect of anthropogenic co2 emissions isn't exactly meaningful. Not just because we don't know what it might be, but because it doesn't exist. That is, there are certainly points at which these emissions will alter some number of other systems in a way that ends up changing the way they "evolve" outside some previous "normal" range, and there are certainly points at which we can safely say we've caused problems for a vast number of ecosystems, species, and ourseleves. However, there isn't really any point at which we know the effects will be
y given
x amount of atmospheric anthropogenic carbon.
