Last Decade Was Warmest on Record, 2009 One of Warmest Years, NASA Research Finds

"The contiguous 48 states cover only 1.5 percent of the world area, so the United States' temperature does not affect the global temperature much," Hansen said."

Global warming skeptics (especially those with political bias) are quick to remark on how cool the past year was in the United States. As indicated by the quote, though, the US represents a small fraction of the temperature values in the world. Here is what the article says about the cooler than normal temps in the US:

"High air pressures from the Arctic decreased the east-west flow of the jet stream, while increasing its tendency to blow from north to south. The result was an unusual effect that caused frigid air from the Arctic to rush into North America and warmer mid-latitude air to shift toward the north. This left North America cooler than normal, while the Arctic was warmer than normal."

At the risk of oversimplifying, I suppose it's possible that warming in the arctic is responsible for cooler temps in the US given that high air pressures can result from fair weather. I find climate science fascinating in the same way that all science fascinates me: the more we know, it seems the less we know. Each answer to a question poses a multitude of other questions. It can be mind numbing to the general public, especially when politicians attempt to make policy using science (I find politicians as a group to be some of the most scientifically illiterate and ignorant).

When I talk to my students about climate change, I advice them that the scientific consensus is clear: global warming is a real phenomena. However, the long-term effects of global warming are essentially unknown. Science can make predictions. It can't tell the future. Most of our climate predictions are based upon computer modeling and right now computer models don't deal with clouds very well. If we can't model clouds, we can't reliably model climate.