Chicxulub crater caused global cooling, proof:

Originally posted by sonhouse
http://phys.org/news/2014-05-proof-global-cooling-chicxulub-asteroid.html

The global cooling could also have been caused by a large volcanic eruption pouring ash into the sky and it could have left the large crator also. So I don't see that this is solid proof that it must have been caused by an asteroid strike.

Most recently, the 1991 explosion of Mount Pinatubo, a stratovolcano in the Philippines, cooled global temperatures for about 2–3 years.

http://en.wikipedia.org/wiki/Volcanic_winter

Is Catastrophic Global Cooling Dead Ahead?

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