What's with all the wacky 2011 weather?

It's been quite the year of wild weather across the country.

It's also been the deadliest year for tornadoes in the United States since 1936, with tornadoes killing hundreds from Tuscaloosa to Missouri. And Mississippi River floods were among the largest and most damaging.

The summer brought record droughts and wildfires in the South and West, followed by deadly hurricanes such as Irene. Finally, this October, we saw rare snow in the northeast.

What does all this wild weather mean? M. Sanjayan, lead scientist of The Nature Conservancy, the largest conservation organization in the world, says there are probably two things going on: "The first is it's a la Nina year, which means the Pacific is cold in terms of the ocean, and that changes the air path around the continental United States. The second thing (it) probably is (is) the effects of climate change making the storms more intense and more frequent."

Will that continue?

"On the climate change side, absolutely, it's going to continue. So we are going to be in for more wacky weather, if you'd like. On the la Nina front, we are not sure. We think there is another la Nina year, this year. I, for one, I'm buying my ski passes already!" he said.

It's strange seeing this unusual snowfall total in many parts of the Northeast, in some cases, more than two feet thid past weekend. Is Sanjayan expecting a lot of snow this season? Can that be predicted?

"Well, la Nina years tend to bring snow, particularly to the north part of the country. And particularly the northwest part of the country. But any one event is very difficult to predict," Sanjayan said. "See, scientists are really good at thinking about climate, but they are not so good about thinking about weather, which is what most people ultimately care about -- what you are going to dress your kids up in when they go out trick or treating tonight>"

Sanjayan points out that climate and weather are two different things. How do you distinguish between the two?

"One is 'What are you going to do tomorrow?' And the other is 'What part of the country do you live in if you want to go skiing?"' he explained. "Climate is a long-term phenomenon and sets the expectation ... and weather is what happens on a daily, weekly basis. How it impacts specific weather events, it's hard to say."

When was the last time we saw la Nina this significant?

"Probably about five years ago. What is going to happen this year, which is sort of unusual with la Nina, it might be a back-to-back year of la Nina, and that back-to-back sort of sends that extra signal out there," he said.

Other than carrying around snow boots and gloves, is there anything else people can do to be more prepared?

"Look, we always talk about these 100 year events, but they are happening more and more frequently now. Be prepared and don't be caught off-guard," he said. "Beyond that, groups are working to help communities prepare for unusual events and the best preparation, frankly, over the long term is dealing with creating natural infrastructure. Sea grass beds (and other natural areas) can buffer us against extreme weather events. Natural infrastructure longer and ultimately cheaper than any kind of engineering that we can do."