It is thought that the eruption caused a global drop in temperature of greater than 1 °C, but the best source I could find indicated a drop closer to 0.5 °C. (theinconvenientskeptic.com)
On the other, our sudden drop in temperature over the last week (40 + degrees) has left me ready for Fall cooking and baking. (101cookbooks.com)
Previously, other scientists found evidence of a dramatic drop in temperature caused by dust from the impact. (sciencedaily.com)