Essentially, yes. What we're doing is accelerating natural global cycles, and in this we have a problem. Earth's cycles exist because they create feedback loops with each other. You see the same in the example of a small lake.
Small lake - has lots of creatures in it, from bacteria, to algae, to ducks, to fish, to otters. So, normally, these populations are stable, with a little fluctuation here and there. More algae means more smaller fish, which allows more larger fish, increasing the otters food supply and population. Now, algae will then start to decline as the predators increase, which will cause a ripple effect throughout the food chain, and populations will decrease. Cool. Natural cycles, right?
Now, a problem occurs when algae suddenly bloom. If the algae get nutrients and increase in population at a very high rate, they inundate the lake, and choke out any other life, creating anoxic conditions. Basically, by giving the cycle a sudden sharp shock, the natural 'checks and balances' in population control fail, and algae extinguish all other life, and eventually die themselves due to lack of nutrients.
Thats what scientists are frightened of. Never has our Earth seen such sudden and radical changes in its climate, and we could be setting ourselves up for a massive global disaster. The signs of this are already present and we're not going to feel the real effects for a few years, but by then, it might already be too late.
