NEW YORK (AP) -- New research suggests that global warming increases the chances of heat waves in Texas, like the one that hit the state last year.

The government also confirmed Tuesday that 2011 was among the 15 warmest years on record.

Texas had record heat and drought last year. Part of the problem was a weather pattern called La Nina, which contributed to drought across the South. Scientists in Oregon and England used computer simulations to estimate how much more likely such Texas heat waves are because of global warming. Their preliminary answer: In years with a La Nina, about 20 times more likely than in the 1960s.

Other researchers calculated that in central England, a warm November like last year's is now about 62 times more likely than in the 1960s.