Luboš' answer here is a good one to the question as posed, but as the question is in response to something I said, I think I should explain a bit at what I was actually getting at.
Microclimate (also known as weather) is often taken as a prime example for chaotic systems and that in turn as the reason behind our inability to accurately make forecasts beyond a certain point in time.
However, looking at temperature records on the scale of 100,000s of years (let's call this macroclimate), we do not see chaos, but a sequence of cold and warm intervals with a period of about 100k years despite a lot of seemingly random noise (spectral analysis of ice core data confirms significant spikes at periods 111kyr, 41kyr, 23kyr).
At the scale of 10.000 years, we're still near the peak of a warm period following the end of the last glacial one. Our best estimate on global temperature shows at an (again, highly scientific) eyeball analysis a periodic overlay over a slight downward trend.
Now, Luboš' claim that triggered my comment was that the human-induced global warming (according to the Berkeley Earth analysis of land-surface temperature data, $1.5K$ over the past 250 years, of which about $0.9K$ happened during the last 50 years) is too small to affect anything.
But as far as I can see, that's not really the case. As I described in the second to last paragraph, we've been in a sort of meta-stable state, and on that scale, the temperature increase is significant:
It disrupts the 'natural' cycle that emerged from the various positive and negative feedback mechanism (ice albedo, water vapour, cloud cover, ocean dynamics, ...) and external forcing factors (solar activity, planetary orbit).
Going by heuristics alone and not detailed modelling (last I looked at global warming with more than a cursory glance was in 2007 or so), I do not find it too far fetched that the recent introduction of a new forcing mechanism ($CO_2$ emission) of the observed magnitude could move a rather complex and messy dynamical system with peridoc forcing, noise, chaotic subsystems away from it's current meta-stable state.
In fact, such things are even possible for actual chaotic systems. Take the Lorenz system: If you're lucky (as humans possibly have been for the last 10kyr - which is, perhaps not incidentally, also the timescale on which human civilization really got going), you can stay orbiting around a given fixed point for a significant amount of time - but a seemingly slight perturbation will prematurely force you into an effectively random (as far as predictability goes) domain.
I can imagine (temporarily) runaway solutions in either direction due to passing some critical point after an inconsequential temperature change, but as I'm a non-expert, that's somewhat idle speculation, and was just one of the three claims I made in that particular comment: The more moderate claim was about the accumulated effect of inconsequential changes on the ecosystem after a sufficiently long timespan under the assumption non-chaotic behaviour.
Feel free to correct any gross mistakes in my heuristic arguments.