Joplin, Missouri Tornado: What's Causing the Rise in Deadly Storms?

May 23, 2011 -- The carnage in Joplin, Missouri, has only added to an already-horrific year for tornadoes in the U.S. Sunday evening's tornado in Joplin has caused the highest death toll from a single tornado in more than 50 years.

ABC News spoke with lead forecaster Greg Carbin of the National Weather Service's National Severe Storm Laboratory and asked him why the 2011 tornado season has been so extraordinarily devastating.

Is the death toll in 2011 significantly higher than previous years?
Short Answer: Yes. The average death toll is normally 60 to 70.

Meteorologist Greg Carbin: "In the past decade the average annual death toll from tornadoes has been around 60 to 70 people. The average killer tornado claims about two lives and so what's going on this year is something well above that. ... We're now approaching about 500 fatalities for the year to date, just under that. That is something we have not experienced in this country in over 35 years and it still looks like we're still around the number nine as far as the deadliest year on record. So there have been many years in the past over the past couple of generations in which we've exceeded 500 fatalities in a year, it's just that they haven't occurred recently."

Have there been more tornadoes in 2011 than previous years?
Short Answer: No, the tornadoes are just hitting populated areas.

Carbin: "There is no indication of an upward trend in either intensity or numbers. We've had a lot more reports of tornadoes, but most of those tornadoes are actually the weak tornadoes, the F-0. When you take out the F-0 tornadoes from the long-term record, there is very little increase in the total number of tornadoes, and we don't see any increase in the number of violent tornadoes. It's just that these things are coming, and they're very rare and extreme, and they happen to be hitting populated areas. So right now, no indication of an upward trend in the strong to violent tornadoes that we're seeing."

Are strong tornadoes a result of global warming?
Short Answer: Unknown. There is evidence that suggests both yes and no.

Carbin: "With respect to a connection to climate change ... it's an unanswered question, essentially. We know that there are ingredients that thunderstorms need that could increase in a warmer world, but we also know there are ingredients that may decrease, so the connections if any are very tenuous and the scientific discoveries on this have yet to be made."

Are more tornadoes on the way?
Short Answer: The number of tornadoes is expected to decrease as summer begins.

Carbin: "In the summer months we often see a lot of thunderstorms in many areas of the country, but we also tend to lose the wind shear that's necessary for organized severe weather. ... So we'll see a lot of thunderstorms as we go through the summer months and they'll be scattered across the entire nation, but, again, as we move towards summer we lose the dynamics and the wind shear that's produced tornadoes and tornadic thunderstorms."