all we need to do is turn the sun down a few degrees is all. the hard part is finding the thermostat;-)
A $2,500 billion sun umbrella?
http://blogs.zdnet.com/emergingtech/?p=400
Feasibility of cooling the Earth with a cloud of small spacecraft near the inner Lagrange point (L1)
http://www.pnas.org/cgi/content/abstract/0608163103v1