Climate Change and the Floods

By Tom Yulsman | May 1, 2014 10:37 pm

An infrared image from the GOES-13 weather satellite shows a massive system of thunderstorms over the Gulf Coast of Alabama and Florida on April 29. Click for an animation showing the evolution of the storm. Be patient — it’s a huge animated gif and the loading time may be slow. (Source: Cooperative Institute for Meteorological Satellite Studies.)

Much has been made in the past couple of days about the possible role of climate change in the extreme rainfall and subsequent flooding in Alabama and Florida. Here, for example, is a particularly overwrought headline from Future Tense, hosted by Slate:


There certainly was a calamity. As Jeff Masters of reports:

Torrential rains on Tuesday night in Pensacola, Florida brought an all-time calendar-day record of 15.55” of rain to the city. The old calendar day record of 15.29″ in October 1934 was due to a tropical storm that made landfall just to the west of the city.

But claiming that a “calamitous climate” was “responsible” for this disaster goes well beyond what climate science can actually say at this point.

To be fair, the author of the piece, Eric Holthaus, actually says something more conservative:

It probably wouldn’t be correct to say that climate change caused Pensacola’s floods, but it surely made them more likely. Climate change is playing a role in extreme rainfall events like the one on Tuesday.

Well, I am sorry to say that even this more conservative statement misses the mark.

Yes, it is true. The atmosphere is warmer, so it holds more water vapor. And that means there’s more water available to fall to land in storms and thereby cause flooding.

In fact, as Kevin Trenberth of the National Center for Atmospheric Research has said, the effect of increased greenhouse gases in the atmosphere is now part of the climate system’s background state. So it plays some role in every event.

But the important questions are what role specifically, and just how much? For this event, we don’t know yet. Period. It’s possible that climate change had a significant impact, through a variety of mechanisms. But it’s also possible that in this particular event, the impact was relatively modest.

Scientists won’t have an answer unless and until they do a formal “attribution” study. This is a painstaking process that has in the past taken months or more for a single event. The process “involves big demands on computing power, sophisticated statistical methods, and a crystal-clear definition of ‘extreme’ for the event at hand,” according to the National Center for Atmospheric Research.

Myles Allen, a pioneer of attribution research, has in the past criticized none other than Al Gore for saying something similar to the Future Tense headline above — that there is proof that climate change is directly causing extreme storms and droughts. When Gore said that back in 2011, “my heart sank,” Allen wrote in a column in The Guardian. That’s because “human influence on climate is making some events more likely, and some less likely, and it is a challenging scientific question to work out which are which.”

By itself, the fact that the atmosphere carries more water vapor now than before — a point that Holthaus and other journalists emphasized in their coverage — doesn’t really tell us everything we need to know to assess what happened here. Why?

Consider this: Research shows that the most intense precipitation events are likely to produce between five and ten percent more rain than in the past. That’s because for every 1 degree F rise in temperature the atmosphere holds about  4 percent more water vapor. Now let’s put that in context. Total precipitable water over Pensacola during the storms (meaning the amount of water vapor in the atmosphere available to fall as rain) was more than 200 percent above normal.

Clearly, more water vapor in the atmosphere from climate change wasn’t responsible for all of that.

Even so, attribution research has shown that some extreme weather events were made more likely by climate change. For example, such research showed that climate change significantly raised the risk of damaging flooding that occurred in England and Wales in 2000. The scientists ran thousands of climate model simulations of the weather, some without the estimated influence of climate-altering greenhouse gases, and others with that influence added in.

In a paper in the journal Nature, here’s what the researchers concluded:

The precise magnitude of the anthropogenic contribution remains uncertain, but in nine out of ten cases our model results indicate that twentieth-century anthropogenic greenhouse gas emissions increased the risk of floods occurring in England and Wales in autumn 2000 by more than 20%, and in two out of three cases by more than 90%.

But just because human-caused changes to the climate system increased the risks substantially in that case, does not automatically mean that they did so in the South this week — let alone that “the calamitous climate” was “responsible” for what happened there.

I honestly don’t know why publications and journalists are so eager to make connections like this in the aftermath of every extreme weather event. If you have to say anything, it should be enough to point out, as the latest IPCC report did, that there “are likely more land regions where the number of heavy precipitation events has increased than where it has decreased.” And that the “frequency or intensity of heavy precipitation events has likely increased in North America and Europe.”

To that, maybe you can add that the long-term risk appears to be rising because of increased water vapor in the atmosphere, as long as you quantify how much of an effect that is estimated to have had already. It would certainly be legitimate also to provide readers with estimates of how much the risks might rise in the future if greenhouse gas emissions continue unabated.

And if your audience would be interested to know what’s going on at the cutting edge of science, by all means, go ahead and discuss the role that climate change may be having on meteorological blocking patterns like the one that was in place earlier this week. Andrew Freedman did just that at Mashable — responsibly, in my opinion, because he emphasized scientists are divided on this particular question and therefore there’s no definitive answer just yet.

But for goodness sakes, while alliterative and dramatic headlines like Future Tense’s may get you thousands of page views, in the long run they do a disservice to climate change communication.

  • windy2

    I had written a full thoughtful response Tom but then I remembered the Climategate emails I read and how climate scientists discussed using climate journalists as useful idiots to promote their agenda. Then I remembered the JournoList scandal that had pretty much killed any respect or trust in the journalism industry. I then deleted my original post.

    The problem that I have is that I am not a part of your industry, I have a low opinion of your industry and I could care less as to why climate journalism became so bad. I have better options available such as Science 2.0 and other science/physics sites where I can exchange with scientists directly. I couldn’t care less anymore what a Chris Mooney or Eric Holthaus report as they aren’t educated enough or objective enough to merit my interest.

    Over the last few years many climate science writers have been dropped by major news organizations and my view is that the industry is reaping what they sewed. I hope you figure out why climate science journalism lost its way but it has been in a tail spin for quite some time IMO.

    • Tom Yulsman

      Windy2: Just so you know, Eric Holthaus (who, btw, wrote the story but may not have written that egregious headline) is a meteorologist.

      • windy2

        I know he is I just don’t think he’s very good.

    • disqus_atlq8Zmtsd

      It may not merit your interest in terms of content, but I think we should all certainly care what climate journalists have to say. They are the mouthpieces that relay the information that many people are using to formulate their stances on these issues.

      It is important that those above blind political ideology have a reliable source.

      • windy2

        I am fortunate to have climate scientists in my family and community. I derive no benefit from journalists who for the most part I find prone to confirmation bias and emotional attachment to a predetermined POV. Do you think journalists ever go back and determine the accuracy of their previous reporting as a method of quality control?
        I wrote to Bryan Walsh a few years back when he wrote an ill-informed piece on snow in DC that wasn’t supported by scientific data on precipitable water vapor in the atmosphere. Now the IPCC has confirmed that his article was based on incorrect information. They don’t care about accuracy as that isn’t the goal. Sensationalism to seduce emotionally driven readers to drive circulation is their goal.
        There are exceptions like Keith Kloor and Andy Revkin and I do read their blogs.

        • Tom Yulsman

          You are painting with a rather broad brush. There are very good journalists who work very hard to get things right — many more than simply Keith and Andy (who, btw, are friends).

          • windy2

            Tom you my be correct but they aren’t working for the AP, Time NYT WAPO (except Brad Plummer) LA Times, Chicago Tribune, etc. Name the journalists who challenged the methane bomb nonsense from Sharkova a few years back? I sifted through her data points the day she released her study and found huge holes. No journalist that I am aware of looked at her data and challenged her. What reporter challenged Steig’s Antarctic math extrapolation fantasy a few years back or Mann’s hockey stick which selectively excluded 20 of 22 tree proxies? Which journalist challenged John Holdren’s recent White House blog post suggesting that a warming Arctic was causing the colder US winter? Even after Cliff Mass ripped Holdren’s position to shreds journalist just kept repeating the nonsense from Holdren and Obama and let them accuse any dissenters like Cliff Mass as “deniers”. Cliff Mass is a denier? Yikes!
            Journalists are pretty much useless as far as I can tell Tom and like Juliet Eilperin reminded me today in WAPO, they are mostly biased or outright shills for climate scientists or politicians. If you have a specific journalist in mind that you think is smart honest and independent I would be happy to check him/her out. Thanks.

  • disqus_atlq8Zmtsd

    Sigh. If it rains… CLIMATE CHANGE! Drought? CLIMATE CHANGE! Unusually cold? CLIMATE CHANGE! Unusually hot? CLIMATE CHANGE!

    A period of time in which there are no extreme weather events could itself be considered an extreme weather event…. they are part of the background.

    That kind of headline is just as irresponsible as Donald Trump tweeting about how a cold snap during the winter disproves global warming.

    Thank you for holding people to a standard of intellectual rigor, Tom.

    • Tom Yulsman

      You’re welcome! And thank you very much for continuing to participate in the discussions here.

      For the record: In my own reporting and writing I’ve tried to move away from ever saying that this or that event is “consistent” with climate change. As my colleague here, Roger Pielke, Jr., has pointed out to me, because we humans have changed the background state of the climate system, in some sense EVERYTHING is consistent with climate change. There was an extreme weather event? Yup, consistent with climate change. Nothing happened today? Still consistent. Sunny? Cloudy? Hot? Windy? Flooding? Drought? All of it is consistent… The point is meaningless — in produces no insight — which is what I think you were saying above.

      Realizing this, I’ve tried to stick to reporting on what the observations show robustly about trends occurring on climate-relevant timescales; what attribution research has to say about specific events like the flooding in England and Wales in 2000, etc.; and what the best research shows about the future while including a reasonable description of the gaps in knowledge and the degrees of uncertainty.

      All of this said, this stuff is really down in the weeds — in the sense that we have more than enough information to justify taking significant steps to reduce our emissions of greenhouse gases. Whether or not the flooding down south was caused by climate change makes no difference. We’ve known enough for a long time to say that reducing emissions makes sense in the same way that taking out insurance on your home makes sense. And that if we went about it in the right way we could reap additional benefits.

      That’s my opinion, of course, and I realize others disagree. But we disagree not because of a lack of science to resolve the dispute. That’s asking science to do too much. We disagree because of differences in values and ways of looking at the world. If all people of good will could at least agree on that, I think we could make progress on a host of issues we’re all but ignoring right now. Unfortunately, aided and abetted by a hopelessly corrupt corporate media and the forces of plutocracy behind it, most of us prefer to scream at each other than to think in this way. (What better way to accrue unbridled power than to keep the citizenry screaming at each other. Divide and conquer… )

      And now you’ve heard much more of my opinions than you bargained for!

      • disqus_atlq8Zmtsd

        Agreeing to the need to lower emissions doesn’t even require agreement on the climate issue. Pollution is bad, yo.

        One of my favorite things about Breaking Bad was that Jesse Pinkman was often the source penetrating insight. When others overcomplicated things, he would often state the obvious and shut everyone up.

        Maybe we just need the Jesse Pinkman roundtable hour on Sunday mornings to set things straight.

        • Tom Yulsman

          This I would love to see!

      • Buddy199

        “Unfortunately, aided and abetted by a hopelessly corrupt corporate media and the forces of plutocracy behind it”

        You lost me at that point. The media has a largely liberal ideological bent, as do the plutocrats behind it. There are a couple of discordant notes in the otherwise mellifluous chorus – Fox, talk radio – but, seriously, the media plutocrats who wield the most influence on the general public – Oprah, the CEO’s of the networks, NYT, Wash Post, Arianna – are hardly right wing capitalist caricatures. And if there’s screaming, it’s not all one sided; much comes from the left shouting down any point of view or voice they don’t agree with – see Condi Rice being disinvited by Rutgers (although Hillary who voted to invade Iraq would surely be welcome) or the L.A. Times which refuses to print any dissenting opinion on climate change.

        That’s just a beef I have. I don’t like censorship, either the obvious hard kind or the more pernicious soft kind – ignoring or distorting ideologically “unapproved” view points.



ImaGeo is a visual blog focusing on the intersection of imagery, imagination and Earth. It focuses on spectacular visuals related to the science of our planet, with an emphasis (although not an exclusive one) on the unfolding Anthropocene Epoch.

About Tom Yulsman

Tom Yulsman is Director of the Center for Environmental Journalism and a Professor of Journalism at the University of Colorado, Boulder. He also continues to work as a science and environmental journalist with more than 30 years of experience producing content for major publications. His work has appeared in the New York Times, Washington Post, Audubon, Climate Central, Columbia Journalism Review, Discover, Nieman Reports, and many other publications. He has held a variety of editorial positions over the years, including a stint as editor-in-chief of Earth magazine. Yulsman has written one book: Origins: the Quest for Our Cosmic Roots, published by the Institute of Physics in 2003.


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