"Is this global warming?" "Is climate change to blame?" "Is the weather getting worse?" These are big -- almost existential -- questions. I suspect they are a polite way of asking, "Is this our fault?"
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My phone tends to ring a lot more when the weather is bad. I often get calls from reporters and producers who usually ask me the same question a bunch of different ways. "Is this global warming?" "Is climate change to blame?" "Is the weather getting worse?"

These are big -- almost existential -- questions. I suspect they are a polite way of asking, "Is this our fault?"

Climate scientists approach the question a little differently. We want to test how global warming shifts the odds of a severe weather event. Just like medical researchers do with cigarette smoking and lung cancer. In fact, this line of climate research comes straight out of epidemiology. In essence, we're doing autopsies on extreme weather events to find out what made them so bad-ass.

Depending on the type of extreme weather event, my answer can be short or long, straightforward or complicated. Keep in mind, all weather is now born into an environment that is warmer and moister because of man-made greenhouse gas pollution. But we don't always know what influences (man-made or natural) will win out on any given day.

Events like droughts, wildfires, heat waves and heavy downpours get my short answer. We know they are going to become more frequent, more intense, and last longer. In fact, we can already see this playing out in historical data. (For a complete overview, check out the "Global Climate Change Impacts in the US", as well as some newly published research summarized here.)

Tornadoes get the long answer. Will they become more frequent, more intense? Will Tornado Alley get bigger? Will the season last longer? Jeff Masters and Andrew Freedman have both done a great job laying out the state of the research.

The bottom line is that two of the key ingredients that go into making a tornado are expected to change as a result of global warming -- water vapor (moisture in the atmosphere) and wind shear (changing wind speed and direction with height). Thanks in part to warmer oceans, water vapor has already increased about 4% and it will continue to increase as the planet warms -- providing more fuel for storms. But wind shear may decrease and that could mean fewer tornadoes. So which influence wins out -- increasing water vapor or decreasing wind shear? We don't know yet.

But even though we don't have all the answers -- and maybe never will -- we do know enough to act. And that is really the bigger point, the one I try to bring home when the phone rings. The recent National Research Council's "America's Climate Choices" report advised Congress that we know enough to get started on preparing for climate change and preventing the most severe consequences, and we need to get started right away. Almost anything we do to protect ourselves in the future from this hotter world we're creating, will also protect us right now from many of the extremes Mother Nature throws at us. We can't afford to wait.

Yet, despite this recent report, and despite all we do know about climate change, the topic has become the C-word in Washington, D.C. Just as the term "global warming" fell out of favor, the term "climate change" is now one that few in our nation's capital dare bring up in conversation, much less in legislation. Budgets for climate research have been threatened and now a nominee for Commerce Secretary is garnering opposition in large part because of his stance on environmental issues, including global climate change.

As the people of Joplin, Missouri begin the slow, painful process of rebuilding their lives -- a new wave of extremes is making headlines. A state of emergency was declared in Massachusetts on Wednesday after rare and powerful tornadoes ripped through the city of Springfield and smaller towns nearby. At the same time, long-standing temperature records fell as a wall of heat blanketed the eastern half of the country -- Washington, D.C. set a new daily record high of 98°F -- busting the old record that dated back to 1895. Hurricane season also started this week and forecasters expect it to be busier than usual. And I'm here ready for the phone to ring again, so that I can tell you one more time that if we do nothing to adapt and reduce our greenhouse gas pollution, things will only get worse... and yes, it will be our fault.

Heidi Cullen is a climate scientist at Climate Central (www.climatecentral.org) -- an independent, non-profit journalism and research organization. She is also a Visiting Lecturer at Princeton University and the author of The Weather of the Future.

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