Michael Slate Interview with Scientist Michael Mann:
The Links Between Climate Change and More Destructive Storms, Worse Droughts and Floods, and Other Extreme Weather

September 25, 2017 | Revolution Newspaper | revcom.us


The following is an edited transcript from a September 22, 2017 interview on The Michael Slate Show on KPFK radio, with Michael Mann, professor of atmospheric science and the director of the Earth Systems Science Center at Penn State University. He coauthored, with the Washington Post cartoonist Tom Toles, The Madhouse Effect: How Climate Change Denial is Threatening Our Planet, Destroying Our Politics and Driving Us Crazy.

The Michael Slate Show airs every week at 10 am Pacific Time on KPFK, 90.7 FM, a Pacifica Network station in Los Angeles. The show can also be streamed live and people can listen to or download archived shows.

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Michael Slate: It’s always good to talk with you. Let’s start off with the big question. How do things stand right now? How bad is it?

Michael Mann: As I’ve often said recently, the impacts of climate change are no longer subtle. We are seeing them play out in real time. Here on the East Coast, of course, we have seen two unprecedented storms: Harvey, which was the most flood-producing hurricane on record here in the United States. And of course, Irma, which devastated the Caribbean islands, Key West, Florida, led to massive flooding along the Florida coast. It was the strongest storm as measured by peak wind speeds ever in the open Atlantic. So let’s take stock. Over the last two years or so, when global sea surface temperatures have been at an all-time high, the warmest on record, we have seen the strongest hurricane globally, Patricia in the Pacific a couple years ago. We have seen the strongest hurricane in both the northern and the southern hemispheres. In the southern hemisphere we had Winston, which struck Fiji, the strongest hurricane ever observed in the southern hemisphere, the strongest hurricane in the Pacific, and now with Irma, the strongest hurricane ever in the open Atlantic.

As we continue to warm surface temperatures, this is one of the easiest things to predict. Because it’s basically just the laws of thermodynamics. And they tell us that as you warm the ocean’s surface, you’re going to get stronger storms, stronger hurricanes. The strongest hurricanes will get stronger, and you will see more flooding because there’s more moisture in the air when the air is warmer. And we saw that. That’s what contributed to the record flooding in Harvey.

So, we long predicted that this would be the case, and now we’re seeing it. And as we here in the East Coast are dealing with these devastating storms—and there’s another one brewing, as your listeners might know, Maria, which is now about to strike several of the Leeward Islands. The same islands that suffered through Irma are now going to get hit again by a hurricane that is intensifying very quickly. And the warmer the ocean temperatures, the faster these storms intensify, and we’re seeing it once again.

While all of this is happening here in the East, of course you folks out west have been suffering through record heat and a record wildfire season. Let me say it again. The impacts of climate change are no longer subtle. We are now seeing them. They are making extreme events even more extreme. And whether we’re talking about hurricanes, or droughts, or floods, or wildfires, we’re now seeing this stuff.

Michael Slate: You once said that climate change has changed the fabric within which all weather now occurs. Let’s talk about that.

Michael Mann: Yeah. The atmosphere on average, the surface of the earth, the lower atmosphere, is more than a degree Fahrenheit warmer than it was a century ago, in fact, roughly a degree Celsius, almost a degree and a half Fahrenheit warmer than it was. Basic thermodynamics tells us that that means there’s probably somewhere between 5, 6, 7 percent more moisture in the atmosphere. And that means there is more moisture available to be turned into record precipitation, whether it’s rainfall, flooding rains in these hurricanes, and the many thousand-year rainfall events we’ve seen around the country over the last couple of years, events that shouldn’t happen on their own, due to chance alone, more than once in a thousand years. And we’re seeing lots of these events, because we’re literally loading the random dice of weather towards more of these events. It’s very basic physics. It’s basic thermodynamics that tells us that a warmer atmosphere has more moisture. That means you get more floods, and there’s more energy in the atmosphere to intensify tropical storms, or to give us these record Nor’easters we’ve seen on the East Coast.

Seemingly paradoxical, but it’s not, is the fact that warmer winters, where it’s still cold enough to snow, and on the East Coast of the U.S., Washington, DC, through New England, it’s still going to be cold enough to snow in the winter, and because the winters are warmer there’s more moisture in the atmosphere. That moisture can feed these massive storms known as Nor’easters that form along the Northeast Coast and themselves have very damaging winds associated with them, but they produce record snowfalls as well. So yes, record snowfall doesn’t disprove climate change. It’s actually consistent with what we expect. We expect a shorter season where the ground is covered with snow, but individual snowfall events, we expect them to become more intense. And these Nor’easters, like hurricanes, we expect them to become more intense because there’s more warmth, there’s more moisture in the atmosphere, and that moisture is what provides the energy to intensify those storms.

Michael Slate: Is that the whole story about why these storms today seem to grow much bigger and much stronger than people have ever seen?

Michael Mann: Yeah. It’s actually not rocket science. Warmer temperatures, more moisture in the atmosphere mean more fuel for strengthening these storms. And we’re seeing it. In fact, there’s an article that appeared in Nature a few years ago that estimated from observation—this isn’t theoretical, this is actually from the observations—we can see an increase of about 10 miles per hour in the peak wind speeds of the strongest hurricanes with each degree Fahrenheit of warming. That amounts to roughly a seven percent increase in wind speeds. That might not sound so bad, but guess what? The destructive potential of a hurricane is proportional to the third power of the wind. So that seven percent increase in wind speed leads to a 20 percent increase in destructive potential. That’s not subtle. That sort of increase, you can see it happening. And we are seeing it happening.

Michael Slate: Now, you’ve also said that almost all of the strongest hurricanes on record have occurred over the past two years. What is it about the past two years that actually seems to have concentrated a lot of this?

Michael Mann: We’ve seen record global temperatures for the past few years. There was a period of time during which the contrarians, the climate change deniers, made a lot of hay out of this supposed hiatus or pause. There wasn’t a pause in global warming, but we had a sustained period of El Niños and La Niñas—these are natural climate events that impact weather around the world. And an El Niño year tends to be warmer than average. A La Niña year tends to be colder than average. And we had a number of La Niña years in a row. We sort of had a decade-long period where we were in La Niña conditions much of the time, and that actually combined with some small natural factors, volcanic activity, small variations in the output of the sun—all these natural factors sort of conspired to offset some of global warming, over the period of the better part of a decade. But those natural factors swing one direction at one time, and then they swing in the other direction at another time, and they’re temporary. It was a temporary reprieve from the ongoing warming of the climate. And now that those natural factors have subsided, we’re now seeing that we’re still, as we always were, very much on this course of a rate of warming right now that is about two degrees Celsius, more than three degrees Fahrenheit, warming per century. That is the trajectory that we are on right now.

Michael Slate: Let’s look at the sea level rise and how it’s threatening human society and the planet.

Michael Mann: Absolutely. That’s another one of those factors. People can debate the details of the various processes involved in the intensification of these tropical storms, and which of those processes might have been impacted by climate change, but here’s something that we can’t debate, the fact that global sea level has risen more than half a foot over the past century. In some areas like New York City, it’s close to a foot. We’ve seen the veritable tip of the iceberg. We’re starting to see global sea levels bend upward and we know there’s a lot more to come as we start to melt the major ice sheets, which are going to be the major contributors to ongoing sea level rise.

So regardless of what else might have been impacted by climate change, Superstorm Sandy, one foot of that 13-foot storm surge was due to global sea level rise. That added a foot to the size of that storm surge that struck Battery Park, New York, that struck the Jersey coastline. I grew up going to the Jersey coast with my grandparents. And that may sound like a small amount of sea level rise, one foot. Actually it meant 25 more square miles of coastal flooding and billions of dollars of additional damage that was done. And that’s just one foot.

Now, if we continue on the course that we’re on, the science is now fairly clear on this. By the end of this century, we’re probably talking about six feet, six feet of global sea level rise at least. If we continue, again, with business as usual and we don’t abate ongoing burning of fossil fuels, then you can see what one foot has already done. We’re seeing the inundation of low-lying island nations. Bangladesh has suffered through record flooding. It’s impacted both by sea level rise and potentially more rainfall that now comes with the monsoons, because that atmosphere is warmer and holds more moisture.

And of course, with Harvey, now the Gulf Coast, with sea level rise, in that region sea level rise has been a little less. It’s been about a half a foot. But that means that storm surge associated with Harvey was at least half a foot higher than it otherwise would have been. And that led, once again, to a lot more flooding. Now, if we truly stay on the course we’re on, and we have six feet plus of sea level rise by the end of the century, then we’re starting to talk about literally retreating from the major coastal cities of the world. It would be a massive upheaval. You can imagine the conflict that would come as we have to relocate 25 percent of the world’s population over a timescale of just decades. So in a worst-case scenario we’re talking about calamitous changes, calamitous impacts. The good news is that we still have time to choose a different path.

Michael Slate: We’re talking about how the storms today have grown much bigger and much stronger and you use the phrase, “Global warming is juicing storms.” And the effect that global warming has on extreme weather, making storms like Irma and Harvey even more dangerous and more likely than it ever would have been in other times.”

Michael Mann: Yeah, absolutely. Warmer temperatures mean more energy to strengthen these storms. Warmer temperatures in the summer when you don’t have rainfall in subtropical regions, in mid-latitude regions that see relatively little rainfall, and where you can have sinking dry air in the summer, well those warmer temperatures evaporate what moisture you do have in the soil even faster, and you get worsened droughts. California suffered through what we have reason to believe now was their worst drought in at least 1,200 years. So it’s making the droughts worse. You have more heat extremes, more drought so drier soils. That comes together and you get the sort of record wildfires that we’re seeing this season. This is the worst fire season out West on record. Not a mystery. Why? It’s been drier, and it’s getting hotter. And the forests are weakened, ironically, by pests like pine bark beetles that can live through the increasingly warm winters. So the forests had been weakened by these pests that in part have prospered as winters have warmed up and that creates much more fuel for these fires when they do happen in the summer.

Michael Slate: What about the situation where Hurricane Harvey actually was stalled over Texas with 50 inches of rain, causing all kinds of disastrous flooding?

Michael Mann: That’s an important thing to understand about Harvey. A substantial part of why we saw that record flooding, more than four feet in some parts of Houston, was because of the stalled nature of that weather system. It just stayed in place. And when weather systems stay in place, that’s when you start to get extremes. You get extreme droughts when the same location is being baked by the sun day after day. You get extreme heat waves under those circumstances. You get extreme flooding when storms stay parked over the same place day after day. And this is where the connections become a little more tenuous. There is an emerging body of research, and we’ve published on this ourselves, that suggests that as we warm the planet, and in particular, the Arctic warms even faster, because as the ice melts, the earth’s surface, the Arctic Ocean, can absorb more of the incoming sunlight when there isn’t ice on top of it, so it warms even faster. This in part leads to what’s known as “Arctic amplification,” where warming is even greater as you go north towards the Arctic.

As you change that pattern of how temperatures vary from the tropics to the polar regions, it turns out that that pattern of variations is actually what controls the jet stream. The jet stream owes its existence to changes in temperature with latitude, and changes in temperature with height in the atmosphere. So as you start to change those temperature patterns, you can change the jet stream. And as you weaken the contrast between the equator and pole, which is what happens when you warm the poles a lot more than the tropics, you decrease the contrast, you decrease the difference in temperature between the warm tropics and the cold polar region. And as you reduce that contrast, that tends to weaken the jet stream.

What’s also true is that climate change tends to shift the jet stream poleward. So, for example with Harvey, we had this very large, blocking high pressure, this ridge over the southern United States. The jet stream had been pushed way up to the north. That is consistent with what climate model projection says that we’re going to tend to see the jet stream in the summer pushed further north. And there weren’t these troughs associated with the jet stream there to come through and sort of take Harvey away and take it east toward the Atlantic Ocean.

So we can’t say with certainty that those mechanisms were responsible for the specific behavior of Harvey. But we can say that climate change is creating conditions in terms of the behavior of the jet stream and the weakened nature of the jet stream and the poleward migration of the jet stream, is favoring the sorts of conditions that we saw with Harvey, where these systems can stay stalled.

We saw that with Irene, back in 2011. It was a devastating hurricane that produced record flooding in Pennsylvania and up through New England. It was only a tropical storm when it struck the New Jersey coast. But sea surface temperatures off the East Coast were unusually high at that time. That meant there was more moisture in the air and there was more moisture to turn into record flooding. So we see this theme repeating itself over and over again.

Michael Slate: What is the role of human-induced climate change in all the events we’ve been talking about, in terms of both these things happening and in terms of the worsening of it all?

Michael Mann: Yeah, absolutely. There are certain things that are iron-clad. You don’t even have to talk about them probabilistically, statistically. We can just say, sea level rise means that these storm surges are bigger. Full stop. That’s a very direct causal connection. More moisture in the atmosphere, greater intensity because of warmer sea surface temperatures. Those are statistical relationships. On average we expect storms to be stronger and for there to be more moisture because ocean temperatures are warmer. In any one case, of course, the vagaries of weather come into play, and just how any one weather event evolves depends on a number of factors, some of which are random. But the way to think about this, once again, is like dice. We’re loading the dice so that the sixes are coming up much more often than they should. The “sixes” can take the form of unprecedented superstorms, unprecedented droughts, floods, heat waves. These things are happening significantly more often than we would expect in the absence of our warming of the planet, and the change in climate that we are causing.

In the same sense that the tobacco industry was found guilty of hiding health impacts of their product—their product was killing people. We can’t prove that any one person who smoked cigarettes for 20 years and died of lung cancer—we can’t prove that they wouldn’t have died of lung cancer anyway. That’s possible. But we can step back and look at the fact that 10 times as many died than should have and that smoking cigarettes increased the likelihood of you getting lung cancer by a factor of more than ten.

We say that smoking cigarettes causes lung cancer. We’re comfortable saying that, even though it’s a statistical linkage. We should be equally comfortable in saying that warming the planet with greenhouse gases leads to more destructive storms, worse droughts, worse floods, and that’s exactly what we’re seeing.



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