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Extreme climate-linked events are virtually certain to increase, according to exhaustive government report

We are now in the warmest period in modern civilization. That’s according to an extensive report -- authored by 13 federal agencies, experts and scientists -- that directly contradicts the Trump administration’s position on climate change. Hari Sreenivasan speaks with Radley Horton of Columbia University about the dire assessment of the state of the climate and its impact on the U.S.

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  • Judy Woodruff:

    Every four years, the federal government releases the National Climate Assessment. It is an exhaustive report undertaken by 13 different agencies, with the help of hundreds of scientists and experts.

    It is generally considered the most definitive state of climate science by the U.S. government.

    The latest one contained some unusually dire warnings about what's happening to the climate, how it's already impacting parts of the U.S., and where we may be headed.

    Back to Hari now, who has more from our New York studios.

  • Hari Sreenivasan:

    The report finds that we're now in the warmest period in modern civilization.

    It says — quote — "It's extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of observed warning since the mid-20th century."

    That directly contradicts what President Trump, EPA Administrator Scott Pruitt, Interior Secretary Ryan Zinke and others in the administration have all said.

    Scientists also write the frequency and intensity of extreme high-temperature events are virtually certain to increase, and extreme precipitation is very likely to increase as well.

    There's much more.

    Radley Horton is one of the authors and climate scientist at Columbia University.

    Let's start with the phrase extremely likely. There's not much room for doubt here. How do we get to that?

  • Radley Horton:

    That's right.

    Well, you have got to think that this is really an incremental advance. We have had several such national assessments. Now, with this latest report, it's more years of data, better physical understanding and improved models.

    So we pushed the science forward. We feel more confident than ever that extreme heat waves are going to be much more common, more heavy rain events, more frequent coastal flooding.

  • Hari Sreenivasan:

    I know there's a difference between weather and climate, but what are the types of data points that you're looking at to help make this case, to help understand the type of changes that are coming?

  • Radley Horton:


    We're really looking at extreme weather events. These are the things that impact people on the ground and impact our society, where we're so vulnerable. What we have seen, for example, is twice as many record-breaking extreme heat events as record-breaking extreme cold events so far this century, when we look across a large number of weather stations.

    That's with just about one degree Fahrenheit or a little bit more of warming. So, already a small shift in average means much more frequent extremes. Some coastal cities are seeing five times as frequent coastal flooding as they did two generations ago just with something on order of less than a food of sea level rise.

  • Hari Sreenivasan:

    So, by the end of this century, it's likely to get worse?

  • Radley Horton:

    We're basically locked in to a lot of additional warming and sea level rise.

    Fortunately, though, if we rapidly reduce our emissions, we're still going to get some more warming, but we can avoid those worst-case trajectories and we can minimize the risk of what we call surprises, which are a big focus of this report.

    The possibility of changes, such as tipping points, compounding effects of extreme events that could lead to outcomes that are even worse than what the climate models have been telling us, if we reduce emissions, we reduce the risk of those kind of surprises.

  • Hari Sreenivasan:

    So, if we're extremely likely to cause this, we can also be a part of the solution.

    So, what role does government play here in this?

  • Radley Horton:

    Well, I think the first thing to highlight is that this is largely a government report. Out of about 30 lead authors, the vast majority resided in federal agencies, from NOAA, to NASA, the Department of Energy.

    So this really — this report really does represent federal science in action. Furthermore, if you think about the supporting data, the satellite products, the high-tech computing, the latest in computing advances, a lot of this science resides in government. So it really is a government report that underwent several rounds of review by government agencies, in addition to the public and other groups.

  • Hari Sreenivasan:

    Next week, we have got another U.N. conversation on climate change. This is at a time when the United States says it is going to withdraw from the Paris accords.

    We have got the head of the EPA, the head of the DOE, a number of different Cabinet agencies who really still doubt the words that you're writing in this report, that the government agencies are coming up with in this report.

  • Radley Horton:


    So, I mean, again, sort of highlighting the role of on-the-ground folks in these agencies contributing to the report. Clearly, whether we're talking about some of the signals we're seeing from government or some of the really disturbing aspects of the climate science, there is a lot of reason to be pessimistic.

    It does seem like climate change is happening faster than we thought in some ways. It seems, societally, that maybe we're more vulnerable than we thought, agriculture, for example, being affected by heat waves worse than we thought.

    But I think we can hold out hope and have a little bit of optimism that maybe we have also underestimated our ability as society to quickly reduce greenhouse gas emissions. We're seeing some signs. I don't want to be too sanguine here, but we're seeing some evidence of the leveling of carbon dioxide emissions the last couple years, even as we're seeing economic growth.

    We're seeing the prices of a lot of renewables dropping dramatically, potentially sending a price signal to companies and investors more and more demanding that corporations ask the climate question. How vulnerable are they to climate change, and how much are they emitting, and how much could they be held liable potentially in the future?

  • Hari Sreenivasan:

    All right, Radley Horton of Columbia University, thanks so much.

  • Radley Horton:

    Thank you.

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