Apparently, the most likely theory of the cause of the younger dryas involves a comet impact. The Younger Dryas is a rapid cooling event of about 13K years ago, going against the trend of moving into the current interglacial period. The reckoning is that a comet caused a catastrophic melt event which rapidly sent fresh water into the northern polar region: This caused a severe disruption of the thermo-haline current, plunging the Northern hemisphere back into ice age temperatures. Extra snow and ice cover caused an albedo effect which somewhat affected the temperature of the whole Earth somewhat, giving a thousand year pause to the interglacial warming, which even more suddenly corrected globally to a warm temperature consistent with the interglacial.
Climate scientists are almost unanimous in stating that a similarly triggered iceage could not happen due to the ice melt in greenland etc. due to global warming. The two prongs of this argument are 1) that the melting is too slow to give enough fresh water to similarly disrupt the currents, and 2) the base climatic conditions are too different - ie. there are less chance that there would be enough snow/ice cover to affect the albedo enough.
Most of the fearmongering however is that the icemelt and northern polar warming is going to be much more than had been calculated just a few short years ago, and quicker than anything since the younger dryas. That, to me, means that if Europe has a sudden cooling event (whithin the next 40 years), climate scientists could still claim that they were correct.