University Place  Steve Vavrus Is Global Warming Causing Weather Weirding?  November 28, 2012 UP812   cc >> Welcome, everyone, to Wednesday Nite at the Lab. I'm Tom Zinnen. I work here at the UW Madison Biotechnology Center. I also work for UW Extension Cooperative Extension, and on behalf of those folks and our other sponsors, Wisconsin Public Television, the Wisconsin Alumni Association, and the UW Madison Science Alliance, thanks for coming to Wednesday Nite at the Lab. We do this every Wednesday night, 50 times a year. Tonight, it's my pleasure to introduce to you Dr. Steven Vavrus. He's a senior scientist in the Center for Climatic Research at the Nelson Institute here at UW Madison. After undergraduate training in meteorology at Purdue University, Steve earned both his Master's and PhD degrees in atmospheric sciences here at UW Madison. He uses computer climate models and weather records to understand how Earth's climate is changing. Extreme weather events, such as heat waves, droughts, floods, and cold-air outbreaks, are an important theme of his research, especially how they might be affected by global climate change. 

Much of this work relates directly to local and regional conditions in Wisconsin and across the Great Lakes region. He is also exploring how the rapidly warming Arctic area may be affecting global weather and climate patterns. Please join me in welcoming Steve tonight as he gives his talk on "Going to Extremes: Is Global Warming Causing Weather Weirding?" [APPLAUSE]  >> Well, before I get started, can you hear me okay? Is the mic working? Okay, great. Well, thank you. That's the first time I've ever been in the same sentence with Chris Christie. [LAUGHTER] But there's always a first. Thank you all for coming tonight. I'm surprised that so many of you decided to watch me instead of the Badgers' basketball team, but I'll assume you didn't get tickets and that's why you're here instead. But I'll try to make it worth your while. I'm going to be talking about two things that I'm especially interested in, both personally and professionally. 

One is climate change, and the other, perhaps related, is extreme weather. And, hence, the title of my talk. Now, let's start with the easier one because we know that there's been a spate of extreme weather lately in the last two or three years, the past decade even, but how does this relate to climate change generally? So, this figure is showing proof, really, there's lots of evidence, but this is showing one strong piece of evidence that the Earth is indeed warming and that it has been warming for at least the last century. This is a compilation of global temperature records from the surface of the Earth going back to 1880. Combined land and ocean. The blue years are cooler than normal, cooler than the long-term average, and the red years, which we've had so many of lately, are in red, the warm years. And you can see that not only has there been a warming trend, especially the last 20 or 30 years, but that warming trend since the 1970s has been so consistent. If you look carefully, we've not had a cooler than normal year since the mid-1970s. And not only that, but we've not even had a cooler than normal month since 1985. That's how consistent the warming has been. 

We've had some dips depending on whether there's a volcano or something, but even then, the relatively cool years lately are still warmer than the warmest years in the distant past. But you may say, well, climate's long-term, what about going back further? Maybe the past century is an anomaly. And we can look at that. We can put that into perspective by looking at a longer period of record, an estimate from ice cores and tree rings and lake records that go back to 1000 AD to the present. And these temperatures that you see here, these are anomalies relative to, I think, the 1990 average, the reference point. And it's showing that there were fluctuations in the past, but where we are today, even when this figure was made in the early 2000s, is warmer, probably, than we've been any time in the last thousand years, and what's more dramatic, of course, is where we're expected to head in the future. So this is projecting out to the end of this century, 2100. And the various climate models are estimating that the roughly one-degree Celsius warming that we've seen so far in the past century or so will be dwarfed by about a two-and-a-half-times that kind of warming in the next century. And you don't really need to remember the numbers so much, but just look at, if these climate models are right, just look at where we're supposed to be in less than a hundred years compared to anything that we've seen in the last thousand. So, the feeling is that we're really headed toward a very different state than anything we've seen in the recent climate past. 

And the very likely reason for this is the increase in heat trapping gasses. Carbon dioxide being the most important of these. And for carbon dioxide, we can go back very reliably hundreds of thousands of years because we have ice core records and we can look at the air that's trapped in those ice cores. They're essentially like a time machine. The deeper you go into the Antarctic ice core, the further back in time you go and the older the air you extract, and you can look and actually measure what the carbon dioxide concentration was 400,000 years ago, for example. And these records are very useful for us as climatologists because we can see that, naturally, before there was the industrial era that we typically didn't get above 300 parts per million of carbon dioxide in the atmosphere. And since then, we've certainly exceeded that. Right now we're very close to 400 parts per million, as I speak, and that's even small compared to where we're likely to be in another 50 or 100 years. This is a low-end estimate and a high-end estimate for the year 2100, and that's considerably higher than where we are now, around 400, and it's drastically higher than anything we've seen in nearly a million years and most likely many millions of years. So we've fundamentally changed the composition of the atmosphere regardless of climate change in a very short amount of time. 

Now, you don't really have to be a climatologist to figure if you're pumping in that many heat absorbing gasses into the atmosphere, it's probably going to lead to a warming trend in the climate. And indeed it has. This is showing a bit shorter record than what I showed earlier going back to 1950, but it shows the distribution of the heating over the planet. And it's indicating, in the yellows and oranges and reds, places that have warmed since 1950, and then places in white, not much change, and then a few places in the world, in the light green and blue, indicating slight cooling. But you can see that for the most part, most places, especially on land, have shown a warming trend, some places more than others, and particularly the Arctic. But it's very consistent from what we would expect from the increase in greenhouse gasses. Now, changes in average climate, which is what this is showing, may not be the most important in terms of impacts. We might be able to adapt relatively well to increases in temperature, if they're gradual enough, but it's the extremes where we really feel things regardless of climate change, but if they're exacerbated by climate change, they become a bigger problem. And I'm showing here just some examples. You're all familiar with how different ways extreme weather is important. 

But these are some of the topics that I'm doing research on here at the university. One of them is ecosystems. It turns out that birds are sensitive to extreme heat, extreme drought, and also springtime cold snaps during their breeding season. So, if there are changes in those events, that could have implications for bird populations. Agriculture. We're an agricultural state. It's no surprise 2012 drought and heat wave were tremendously impactful in the Midwest and much of the country. We saw lots of scenes like this throughout the Midwest and Wisconsin. Human health. We often think of humans' health being directly impacted by extreme heat, which it is, but also heavy rainfalls can increase waterborne diseases and also lead to health problems, gastrointestinal illnesses, or, in the case of Hurricane Katrina, mold problems exacerbated by the heat. 

Another example with heavy rainfall is important topic for stormwater managers deciding on bridge heights and stormwater pipes. A more subtle effect which we saw a good example of this year is weather variability of extremes. By that, the example I'm going to give is we had an extremely warm March, and I'll talk more about that later, but we then had that followed by a cold snap in April, freezing nights, and that was extremely harmful for apples. They don't handle cold well, and they blossomed too early, they budded too early, and then when we had that freeze in April, which wasn't terribly unusual, that combination, that one-two punch, did in the apple crop in large part this year. And then, of course, if the rainfall gets heavy enough, we have problems with infrastructure as evidenced by the 2008 floods around here, which I'll describe a little bit more right here. Probably most of you in the audience were here somewhere around southern Wisconsin four years ago when, instead of the drought problems we're having this year, we were having too much water. And these examples, pictures showing Lake Delton blowing its gasket here, knocking homes into the lake, blowing out a road here. Just tremendous amounts of damage. And scenes like this were all too common throughout southern Wisconsin, and indeed much of the Midwest, not only here. 2012, though, we've seen even more examples of weather disasters. 

This is one that I just got off the press today showing billion dollar weather disasters across the country just in this year. There's 11 such disasters. The biggest one, by far, is Hurricane Sandy, Superstorm Sandy. It's estimated the damage from that will be $30 billion-plus, maybe $50 billion. Along with over nearly 200 deaths. Not too far behind, although slower and not as dramatic, was the heat wave and drought this summer in the Midwest. That's estimated to be at least $20 billion. And then a distant third through eleventh but still very costly, some tornadoes and severe weather in different parts of the country. And then this big windstorm, this derecho, which hadn't really made the household lexicon until this summer, but that was terribly damaging, causing widespread wind damage and power outages sometimes for weeks in the east and the Midwest and causing almost $4 billion in damage. So, this is just an example of this one year, 11 such billion-dollar weather disasters, and we're not quite finished with 2012. 

And 2011, it turns out, was even worse. This is a figure put together by NOAA, the federal agency that the National Weather Service is in. And they've compiled records going back to 1980 of billion-dollar weather disasters in other years. The blue bars represent the number of events regardless of the total cost, and then the lines represent the total cost adjusted for inflation. And those cost haven't been figured yet for 2011 and 2012 yet, but presumably, they'll be very high was well. This peak here in the early 2000s was the big Florida hurricane year when four big storms struck. So even though there weren't many events, they were very costly. And so you can see from this figure that at least in the last 30 years, 2012 and 2011 are number one and two in terms of the number of billion dollar weather disasters in this country. And, of course, recently we've seen other examples from different parts of the world. So, it's really been, it's not just your imagination. 

It really leads to the question, the logical one, are weather extremes becoming more common and/or more intense? And, if the answer is yes, is climate change, the warming climate, becoming more humid, is that related to this trend? And that's what I'll be dealing with the rest of the talk. Now, one of the difficult things with answering that question is that there's not accepted definition of what constitutes and extreme event. What's an extreme event to me as a meteorologist may be very different from you as a farmer, for example, or a stormwater engineer. We have different interests. But one way to try to standardize this definition is NOAA's attempt to create this climate extremes index. So this is a measure of the total amount of the area in the country that's affected by extreme weather at a given time. And the variables they consider are the ones that we typically think of as extreme. Hot weather, cold weather, drought, and heavy rainfall. And what's nice about this is that it's a pretty long record. It goes back about a century. 

And so we can look to see whether it's our imagination that things have been changing lately or at least get a historical perspective of how these extremes have varied over time. So this figure is showing the year to year values of this extremes index going back 1910, cutting off at 2011. We don't have the very latest data for 2012 yet, but I'll show the running total in a minute. And the way it's constructed is that it's assumed that the way they come up with a threshold for these types of extremes is that in a typical year, 20% of the country would be experiencing this extreme weather. So, if it's less than 20%, it means that there wasn't much extreme weather that year. If it's more than 20%, that means a lot of the country, more than expected, was afflicted by these weather extremes. And you can see from these red bars, each one representing a different year, that there's lots of year to year variability. It varies from one year to the next, it varies from one decade to the next, but what's noticeable, what I want to draw you attention to is this green line. This is the smooth running average over this graph. So it kind of smooths out the year to year fluctuations by taking a nine-year block at a time and running through the graph. 

And when you look at it that way, you see more clearly this increase in the last 10 or 15 years, this preponderance of extremes that we've had since the late 1990s, which is more than we had sustained any time in the entire record. And if I can extend this to 2012, at least through October as far as the records go, we see that 2012 right now is the leader. It's the record-breaker at this stage. Although, we still have November and December to count, but it was even bigger than 2011. And so, again, even January through October you see this increasing trend in weather extremes according to this index. Now, the other thing that's nice about this index is because it's comprised of four different terms, extreme heat, extreme cold, drought, floods, we can break it down and see, okay, so there's this increasing trend in extremes, what's causing it? Is it all those factors or just one or two? So, the first one is trends in daytime temperatures. So, say, three o'clock in the afternoon is extremely hot, is extremely cool, and we can come up with the same, this index can be used to answer that question whether daytime temperatures are becoming more extreme, especially extreme heat. And on this curve, now we see red bars representing the amount of the country that's experiencing hot extremes for daytime temperatures, and blue are places, the amount of the country experiencing exceptionally cool daytime temperatures. So, red is indicative of a lot of heat, which we see here in the 1930s during the Dust Bowl. That stands out well. 

But even more clearly, this persistent trend in the '90s and 2000s of increases in high daytime temperatures. So the fact that we have lots of red bars above this 10% of the area of the country threshold means that we've had an unusual amount of hot daytime temperatures across the country in recent years; whereas we've had very little exceptional cool daytime temperatures. And if we look at the same sort of graph but now for nighttime temperatures, low temperatures, the trend is even more striking. So now we see lots of red, large red bars, and this green running average is consistently over the 10% area that we would expect in a typical year. And lately we've had almost none of the country experiencing exceptionally cold nighttime temperatures. So that is something that stands out in this record. Climate models are projecting that as the climate warms and becomes more humid we'll see more heavy rainfalls. And that trend is showing up at least in the last 50 to 100 years in this graph. So this is the same sort of figure but now the trend in heavy rainfalls, daily, one-day rainfalls, and we see that, again, since the 1990s, over the past 20 years or so, we've had an exceptional amount of the country afflicted by heavy rainfall, like the 2008 floods. And then, finally, on our minds this summer with all the drought is the trend in soil moisture. 

So, green in this case represents an area of the country that's exceptionally moist soil conditions, good for growing except if it gets too wet. And then the brown represents the percent of the country that's exceptionally dry. Now, notice that this record only goes through 2011. Once 2012's numbers are in, there's going to be a big brown bar at 2012, quite high. And, yet, you can pick out things like the Dust Bowl of the 1930s, exceptional. 1950s, a mini-Dust Bowl in parts of the plains. And then in recent years too, we've seen, when you look at this running average, we've had a greater amount of the country than expected experiencing dry conditions while, at the same time, a larger percentage experiencing wet conditions. So this suggestion that there's more variability in recent years. Now, what about around here? These are national averages that I showed you. What about in Wisconsin? Well, Chris Kucharik here on campus, and agronomy professor, has looked at weather records from cooperative stations across the state and computed the trends in climate, generally and also extremes, over that roughly 60-year period. 

And this figure is showing the trends in extreme cold. So this is nights per year below zero. Most of us would consider that to be a pretty cold night. And the trend, the colors here are showing whether that's a downward trend or an upward trend over that period. So the blue shading represents the number of days fewer that we've had nights below zero in 2006 compared to 1950, and you can see that the entire state, virtually, has experienced fewer very cold nights over that period, especially in the northwest. That's consistent with the warming overall climate. And so you might think, well, when I show you the hot days, say over 90, that we're going to see something similar. But, in fact, we don't. It's interesting. Here you'd be hard-pressed to say whether there is a trend, in Wisconsin at least, in extreme heat or extreme cold. 

Some places are showing a decline in the number of 90-degree days and other places somewhat of an increase. And, overall, it's really kind of a wash. And we see the absence of a warming trend in the hot days, or an increasing trend in the hot days here in Madison. This is a record from the Wisconsin State Climatology Office that Hopkins provided me. It's showing the number of days above 90 at the Dane County Airport. On average, we get about 13 per year going back to 1940. And I know this summer was extremely hot. We had 39 such days.  That was nearly a record. The record is 40. 

So we've sweltered this summer. It was really exceptional. And yet, if you look at the longer term trend, you see that it's actually been downward. This black line is the running average over time, and we've had some years, 2004 we didn't have any, 2008 we had one, and so 2012, fortunately, was an outlier. And yet, we don't know if this is a harbinger of what's to come or whether it was just a fluke, but certainly, around here for whatever reason, we have not experienced the increasing trend toward hot weather that much of the country and much of the world has experienced. And so that raises a question, sort of an example of how much variability, how much randomness there seems to be in this record. So, from one year to the next, things can change dramatically. And that has led to an analogy of dice rolling. And let me explain that. Dr. Jim Hansen, who's a very famous climatologist, even made it on 60 Minutes one night, you may have seen him, came up with this nice analogy years ago, before climate change was even in vogue, describing how to think about how climate change affects the likelihood of, say, a hot summer or a cold winter or a wet spring and so on. 

The analogy he uses is, like at the beginning of the season, it's as if you were rolling a die and if you roll a one or a two, it means you're going to have a cool summer. If you roll a three or a four, it's going to be about average. And if you roll a five or a six, it means you'll have a hot summer. Okay? So in a typical climate, a normal climate, that's about what we would expect. A one-third chance of being exceptionally cool, one-third near normal, one-third hot. What happens with a climate change? Now we're loading the dice. So now what it means is that you're still rolling the same die but now it's weighted to give you a certain probability of a certain type of summer. So now, for instance, if we roll a one, we have a cool summer. Before, if we rolled a one or a two, we'd have a cool summer. In a warmer climate, now if you roll a two, you have a near normal summer. 

Before, you could roll a three or a four and get that. And in a warmer climate, now there's four chances out of six that it'll be hot. Either moderately hot, very hot, or extremely hot, the kind we had this past summer. And yet, the point is that you can still, even in a warming climate, you still might be lucky or unlucky and roll a cool summer. Even 50 years from now we might have a cool summer, but you're much more likely to tilt the odds so that now we're much more likely to have a hot, very hot, or extremely hot weather. And Hansen took this idea and applied it to the weather records for the northern hemisphere going back to 1900, and he was interested in these extremes, sort of the very hot and extremely hot cases. And so, what he did was he and his co-authors in a recent paper, they set a temperature threshold for the summer and said, okay, at this temperature threshold in the long-term record it means that about a third of the country is going to be as hot or hotter. That's represented by this yellow curve. And then you can raise that temperature threshold and say, boy, for an even hotter temperature, only about 2%-3% of the country ought to be experiencing that in a typical year. And then raise that temperature even higher and say that only about half a percent of the nation ought to be that hot or hotter. 

And when you do that and you look at the records going back to 1900, you see that distribution holds pretty well until about 1980. So, some years had more heat than you'd expect and some years less, but typically, say, it was around the percentages that you would expect. But ever since 1980 we've seen this spike. We've seen this big increase in the amount of the country experiencing either hot conditions, now that's lately been up to 80% compared to a third, what you'd expect, very hot up to about a third compared to 2%-3% expected, and then up to about 10% of extremely hot, like 2012, compared to only a half a percent that you would expect. So, this is an example showing that the extremes, at least in the summer in his case, have really been going up with commensurate impacts on energy usage, air conditioning, and heat stress. And what's surprising about this, at least to me, is that if you look at the trend in the average summertime temperature, not looking at these extremes, it doesn't look that dramatic. So this is the summer temperature trend since 1980 when we started to have that big spike in the extremes for the same season, June, July, August, and the yellows and oranges and reds indicate a warming, and that's true. Most of the country, including the northern hemisphere, which is what he studied, is showing a warming trend over the past 30 years, but it's not all that dramatic. For instance, in most of North America, it's showing about a half a degree to one-degree Celsius warming, or over the whole northern hemisphere, about a one-degree summer warming in the past 30 years which is tolerable. You might not even notice it that much, but, yet, even that small change in the average can translate into this big of a change in the extremes. 

So, why is that? This is when we start to get into something that is useful in climate, a temperature distribution. This is the familiar bell curve which was popularized years ago, and it's useful for a lot of records. For instance, if we took the height of everybody in this room and plotted it on a graph, we'd see a bell curve, probably, with most people's heights clustering around average. This is the probability of occurrence on the Y axis. And then some people are exceptionally tall, so you get a few here at the right tail. And then probably about an equal number just happen to be short, so they're way down here. And you can do the same sort of thing with temperatures. If we were to plot all the summertime temperatures, for example, on record in Madison, we'd see something like this. That most of them were around the average, but then there's been some hot years, like this past one, and then some cold years, especially in the distant past, and then we can see what the probability of occurrence is of each of those types of temperature. And so this first curve on the left represents the recent climate, say. 

The climate we've become accustomed to. And if we get a warming, one possibility is that this entire distribution of temperatures just shifts warmer, like this arrow to the right. And in that case, we have a modest increase in the average around the peak of the bell curve, but now, even that relatively small change in the mean can translate into a lot more hot weather because now the fatter part of the temperature distribution is occupying a bigger space. And now you can even have some record heat that you never had before in your old climate, just never could get that hot. So that's one possibility of what could happen in a climate change. Another possibility is that the average temperature doesn't change at all but the variability increases. Now we get more heat waves and we get more cold snaps, but the average temperature doesn't change. So that could happen too as climate changes. But, what's most likely to happen, according to climate models, is that we're supposed to get a combination of this, for instance in summer. That is, the average temperature will climb, so the temperature distribution will shift warmer, but at the same time, we're expected to get more extreme conditions, more heat waves, even perhaps extra cool weather relative to the new average, and that will produce much more hot weather. 

So it's kind of a double whammy in terms of the heat in the summer. If you get an increase in variability, it promotes it; if you get an increase in the average temperature, it promotes it. And we've seen recent examples of this. In the last 10 years, the famous European heat wave in 2003 was really a record-breaker. There were tens of thousands of deaths. France was hit especially hard. The numbers, the estimates vary. Around 70,000 is likely the number of deaths, largely because they didn't have air conditioning. They don't usually need it in the summer. It's the hottest summer on record, going back about 500 years, almost 600 years. 

European weather records are longer than we have in this country so that's probably pretty reliable. But then, just seven years later, there was a comparable heat wave in eastern Europe this time. Moscow reached 100 degrees for the first time on record. Estimates are that it may have been the worst heat wave in a thousand years, and 10,000 deaths occurred in Moscow alone. So this was a dramatic example. And if we look at the European heat wave in 2003 and put it in perspective, again with this bell curve as an example, we can get an appreciation for just how extreme it was. So this is showing the temperatures during summer for Switzerland, going back, I think it's at least 150 years if not longer, and each year, like the summer of 1909, is plotted on here, and that was an exceptionally cool summer. 1947 was an exceptionally warm summer, and most of the years cluster around the peak of the bell curve, as you would expect. And here is 2003. So, it's just amazing. 

It looks like it couldn't even happen. It looks like it's not even part of the same climate as in the past. And if we put 2003 into a time machine and move it forward and compare it to climate model expectations for the end of this century for a new distribution, we see here now a warmer average. So this peak from the recent past shifts to the right, becomes warmer, and also an increase in variability around that new warmer average. But anyway, here's 2003 in perspective of the late 21st century, and what's alarming is that even though it would still be a warm summer, it wouldn't be exceptional. Now it wouldn't even be at the far right tail of that distribution. So the climate model predicts that we'll have even warmer summers than that within not even a hundred years. So that's a little bit concerning considering how many heat wave deaths occurred in Europe during those heat waves. And we had an example of that around here about 15 years ago, the Midwestern heat wave of 1995. That was the day Madison hit 101. 

That was the hottest temperature on record, sorry, not the hottest temperature on record, but the hottest until this summer. So we hadn't had a 100-degree temperature since 1995 until this year. And what really made it awful was the extremely high humidity. If you were all here, if you remember it, it was like being in a sauna. It was just unbearable. And it was unbearable for a lot of people. In Chicago, those who didn't have air conditioning or didn't use it resulted in hundreds of heat related deaths there as well as other cities, but Chicago was hit hardest. But what's important about this is that it was not an equal opportunity killer. It really targeted certain demographic groups, particularly the elderly, the poor, minorities, and socially isolated people were hit especially hard. And now we can compare that to the 2012 heat wave which was comparable, meteorologically, compared to 1995. 

They both occupied a large part of the Midwest. In 2012, Madison got even hotter. We got up to 104 degrees one day, and we had three straight 100-degree days, both in Madison and in Chicago. So, in terms of the temperature, it was actually worse than 1995, although it wasn't as humid. And, yet, guess how many heat wave deaths there were in Chicago this year? Eighteen. It, of course, could be a little bit more, a little bit less, but the point is it's drastically, it's an order of magnitude less than 1995. That's great news. Part of that was luck because it wasn't as humid, of course, but I think at least perhaps a bigger part of it was the adaptation that we've utilized since 1995. In Chicago, mostly precipitated by the heat wave of 1995 and other cities across the country, municipalities have implemented heat wave action plans. And these, mostly in large cities but some small cities across the US too, and they consist of specific actions that city employees take when heat waves are forecasted. 

So, cities differ which ones they do, but a typical one is to publicize heat wave warnings issued by the National Weather Service. Heat waves nowadays can be forecast days in advance with great accuracy. We should never be surprised by a heat wave that just comes out of the blue. So that can be done. Setting up air conditioned public cooling centers, like Madison did this year, is a great way to save lives. And reaching out to the most vulnerable populations. We know who they are, and sometimes this can be as simple as encouraging people to just check up on your neighbors. Your elderly neighbors, your socially isolated neighbors, mentally ill neighbors, those are the people who tend to be hit the hardest by heat during the summer. But all of these actions have a similar goal, and that is to make the public aware that hot weather is a deadly serious health risk. Chicago didn't appreciate that 15 years ago, and as a result, so many people died. 

And it's not just Chicago, but across the country people recognize hot weather as a serious health risk. It's similar to how we've changed our perception about concussions. Not very long ago, we used to joke about football players getting their bell rung, and now it's not a joke. We really take it much more seriously, and it's the same thing with hot weather. We recognize it's a serious health risk. Now, the success of these heat wave action plans is still being evaluated, but there are lots of positive signs. The example I gave you for Chicago, Philadelphia has documented some big success stories, Milwaukee as well. And it's an example of how societal adaptation can reduce our vulnerability to extreme weather. We can't stop extreme weather, with or without climate change, and if climate change produces more extreme weather, then we're going to have to do something to adapt, and this is one way to do so. Another way to do so has to do with improved weather forecasts, and weather forecasts have definitely improved in the last 10-20 years especially. 

And Hurricane Sandy was a great example of that. For as devastating as it was, it was very well forecasted. Here's an example of the forecasted track coming out of the Caribbean into the east coast. This is the actual track that it took. A really remarkable weather forecast from the European computer model. Six days ahead predicted that it would be this amazing storm and strike a little bit north of New Jersey where it actually made landfall, but comparable strength and in a very similar location. So, because the forecasts have improved that much and because people believe the forecasts, who knows how many billions of dollars and lives were saved because of better preparation. Now, Sandy is one example of something I want to get to now of an example of detection and attribution of extreme weather events. And these are two different things. So, detection is kind of how do we define an extreme event, how do we put it in perspective, and then attribution is what is its cause? Meteorological or is it related to climate change? So, let me give an example of that by something that's been repeated, for me, in the last couple of years. 

I'm sitting in my office, and I get a phone call Dr. Vavrus, we'd like your opinion on whether the extreme event of the day was caused by global warming. That's almost always the kind of question it is. And my reaction is usually something like, uh... [LAUGHTER] And the reason is it's an ill-posed question. What they want is a yes/no answer, and I can't give them a yes/no answer. Nobody can. And so the reason is, and it relates to this detection and attribution issue, we can look at things, for example detection of an extreme event, and put it in perspective. So, here's a case where we might be able to partially answer the question. So, if we look at this bell curve distribution, like I showed before, and again, 2003 is a huge outlier, there are statistical rules, mathematical rules, that define the likelihood of an event or a location, let's say, a temperature, a summer temperature, based on how far it is from the peak of the curve. And that's statistical term. 

The standard deviation. So the more standard deviations you are away from the peak, the more unusual that event was. So, based on raw statistical terms, we can say that the probability of a summer as hot as 2003, under recent climatic conditions, meaning this kind of temperature distribution, is only one in millions. So, it's almost like it couldn't have happened. That's five standard deviation warmer than normal, if you're keeping score and if that means anything to you. Now, that's based on the entire record which includes a lot of cool summers. If you just focus on the warmer recent years, say since 1990, your likelihood increases, but it's still one in almost 50,000. So it's still very, very unlikely. And so it suggests that summers like 2003 may represent a different, meaning a warmer, climate. Something that isn't even a part of this sample group. 

So that's one example of detection. Another more recent example around here was the phenomenally warm March we had. If you remember back, it wasn't just an early spring, it was a crazy spring. These are the statewide ranks of how warm March 2012 was in the 118 years of record-keeping, kept by NOAA. 118 means it was the warmest March on record out of those 118 years. And you can see, it wasn't just Wisconsin, but half the states had the record warm temperature of all time in March during this year. And, so the question is, what caused that? And I can give one answer, a simpler answer, and that is that we know that the weather pattern was extremely odd. The jet stream dipped way south, all the way into Texas, and then buckled and went way north, all the way into Canada, which kept the cold polar air north of that and set up this consistent southerly flow off of the Gulf and Texas. And we just kept getting more warm air, that warm air kept snow cover from occurring, and so this is a very recognizable weather pattern that would lead to a warm March, not necessarily as warm as we got but a very warm one nonetheless. But the real question, in terms of attribution, that people want to know is, is this weather pattern, for example, related to climate change? The short answer is we don't know yet. 

Although, I'm doing some research with a colleague at Rutgers suggesting that the likelihood of this kind of a wavy pattern is more likely to occur in the future, related to a warming Arctic. But still, the jury's out on that one, and a lot more research needs to be done, but it's at least a possibility. So, attribution, what we mean is what is the underlying cause of the event, which can be twofold. The immediate one, like the circulation pattern I just showed, but what people really want to know is climate change, is it related to climate change. Now, detecting and extreme event is easier than attributing an underlying cause because with detection we can just say, well, it's a one in a million chance without expressing why it may have occurred. But both detection and attribution are complicated by the fact that we have limited data, we'd like to have a million years of records, not just a few hundred years, and a changing climate. So, is it even possible to relate extreme weather events to climate change? And the answer is yes and no. No in the sense that we can never prove that a certain weather event occurred because the climate is changing. That gets to the phone conversation I gave earlier. But yes in the sense that we can hopefully determine how much climate change has loaded the dice, to use that analogy of Jim Hansen. 

That's probably the best we can do. And, just to show an example of some recent work that's been done to advance that cause, this is some work by Rahmstorf and Coumou a couple years ago using this concept of, it's called fraction of attributable risk or FAR. This is an idea that was borrowed from epidemiology, it turns out, where they try to attribute the cause of a disease outbreak, for example. In this case, it's the likelihood that a changing climate is responsible for a particular extreme weather event And the way it's defined is the probability of an event occurring with a climate change minus that probability of it occurring without climate change divided by the probability with climate change. So let me give you an example. That Russian heat wave of 2010 that we talked about earlier. The authors estimated that the number of heat records in the past decade in a warming climate based on computer simulations or observational records was 0.5. Without any sort of a climate change, they expected, it would have been .1 such weather records, heat records. So based on this formula, you get .8, or 80% is the fraction of attributable risk. And so they conclude that there was an 80% probability that the record heat wave in Russia in 2010 is due to the warming climate. 

Okay? So it's not a yes/no even then. 80% is pretty likely, but it's still a 20% chance that it wasn't. And so this is really the best we're going to be able to do is to get to more precise estimates like these of a certain event, like Hurricane Sandy or the 2012 heat wave, whether it's related to climate change or whether it isn't. So, up to now I've been talking mostly about the past climate change that we've had, but what about the future because that's where the warming signal is supposed to be the greatest. Here's an average, showing the average of many different climate models for what's projected by the end of this century compared to the late 20th century climate. These are temperatures in degrees Celsius. They probably don't mean much to you, but the point is, everywhere in the world is expected to warm by the end of this century. Some places, like the Arctic, a lot, most places on land, moderately, but everywhere is expected to have some sort of warming in the next century. Contrast that with projected precipitation changes. So as the climate warms, it could get wetter, or it could get drier, or it might not change at all. 

And the climate models suggest that some places, like higher latitudes, will get wetter, and deep tropics as well, but other places, largely the subtropics, are expected to become drier. Wisconsin is expected to become a bit wetter, especially in the colder months. But anything in green and blue represents a wetter climate and anything in yellow and orange a drier climate, and the dots represent places where the climate models are in good agreement with one another. So we have more confidence in those projections. So, contrast this, this mixed pattern of some places wetter, some places drier, with the projected change in the intensity of precipitation. So that means that whenever it does rain, how hard does it rain or snow? And here we see a lot more consistent pattern. The models are projecting that almost the vast majority of the land is expected to have heavier precipitation when it does fall. Again, the yellows and oranges and reds being exceptions, and there aren't many of them. Around here and most of the world is expected to see heavier precipitation regardless of the total amount that falls in a given year. And we have a pretty good idea why that is, and it's an important result because heavy rainfall can be very harmful to health, for example. 

And that is that in a warmer climate there's more moisture in the atmosphere, on average, and so when we get the right meteorological conditions, like a strong storm or a stalled weather front, then we can ring out more moisture. So, even if it would have rained hard in a different past climate, it can rain a lot harder now if it's a lot warmer and moister. Now, it's important to consider what type of weather extreme we're talking about. I hear a lot of folks say, well, the weather is going to become more extreme in the future. Well, it depends. One of the most common results from climate models is that we'll see fewer cold days and night, and, in fact, we are already seeing that trend. It's very likely that trend has been occurring in the past, and it's virtually certain that will continue in the future. But more hot days and nights, very likely in the past, virtually certain in the future. Increases in heavy precipitation, like I just mentioned, very likely to occur in the future. But also, at the same time, areas affected by drought increasing. 

That's a likely result for the future. But all of that is sort of the global picture. Now, what about closer to home here in Wisconsin? One of the projects I'm involved in is called the Wisconsin Initiative on Climate Change Impacts, or WICCI, and this is a partnership that's several years old now between the university's Nelson Institute for Environmental Studies, which I'm in, and the Wisconsin DNR as well as other state groups. And this has brought together stakeholders and scientists in a lot of different areas, but our goal is to assess and anticipate climate change impacts, so it's primarily about impacts rather than meteorological causes, and develop and recommend adaptation strategies. And, very briefly, WICCI consists of a slough of working groups that cover different topics related to climate change impacts. And I'm involved in the climate change one, primarily, but you can see from these different topics, and they're largely topics of convenience just based on the group members' interests, that they cover a lot of ground of what we would be concerned with when it comes to extreme weather. For instance, human health, stormwater, wildlife plants and natural communities, agriculture and so on. So, what WICCI is doing is very much part and parcel with this discussion tonight about extreme weather. And one of the activities that we've done as part of WICCI is to try to come up with some very detailed spatial estimates of extremes right here in Wisconsin. So, for example, heat waves. 

More heat is on the way. These are mid-century climate change projections just for Wisconsin now for the change in the number of 90-degree days per year by mid-century compared to, say, the 1980s. And the graph or the map is showing increases everywhere in the state. Now greens and yellows are all showing more hot days in the future by mid-century. And the amount is 24 for Dane County, just for example. And around Madison we average about 13 such days per year, so that means that a typical summer by the middle 21st century, according to this study, would be about 37, and we had 39 this year so it's right on the mark. Hundred degree days we rarely have here, fortunately, but by mid-century the models are suggesting that we'll have typically about three per summer. Well, we had four this year. So that means that 2012 is a pretty good example of the type of summer that may become the norm by the 2050s. So 40 years or so. 

Not very far in the future. That's probably tolerable, but if the models are right, by the end of this century we're really looking at some hot weather very different from anything we've seen in Wisconsin recently. The number of 90-degree days is expected to increase by more than two months or to have more than two months over 90 and to have about two weeks per summer over a hundred degrees. So even this hot summer we only had four such days, and, according to this, we'll be seeing more like two weeks worth in a typical summer. But, at the same time, the tradeoff is less bitter cold. Some people would like that. This is expected to show a pretty dramatic decline by mid-century. We have about 21 such nights falling below zero in Madison in today's climate. That's expected to drop by about 12 to 15 nights by mid-century, and by late century we'd probably only have about a handful of nights in winter below zero. So that would be a very noticeable change, a welcomed change for many people. 

It certainly would have impacts on our heating bills. Also a lot of ecosystem impacts, some positive, some negative depending on the species. But it would definitely have an effect on the world that we live in around here. Touching on drought, the expectations for drought are not as certain as that for heat or cold, in part because drought depends both on precipitation changes but also evaporation which is temperature dependent. So, typically, the warmer the ground, the more evaporates. In a warmer climate you'd expect more evaporation, like we had so much of this summer. And so it becomes a dicier estimate, but it's believed most climate models suggest that we'll see more drought. And you don't need to focus so much on the numbers here, I don't think they're all that certain, but the yellows and the reds and the oranges represent places where drought is expected to become more frequent and the greens less frequent. And then, finally, I'll close with this one on more heavy rainfall. So it's a bit of a paradox, more frequent drought expected, but also more heavy rainfalls. 

And that's true in Wisconsin as well based on the climate models. This time I'm showing the maps, projected changes in precipitation for the end of the century. So this is centered around 2090, year 2090. Of the total precipitation throughout the year, the changes are shown here in green and blue, indicate a wetter climate. So Wisconsin as a whole is expected to become wetter, annually, by about 8% here in Madison, but when you look at the heavier events, those go up by more. One-inch rainfalls, close to 20%, with everywhere in the state showing an increase. Two-inch rainfalls per day going up by about 30%. And the three-inch rainfalls, the kind we had in 2008 that caused all the flooding problems, going up by almost 50%. Hard to say where exactly in the state it will happen. It's sort of spotty, but we do feel, based on the climate models and meteorological theory, that we will see increases in heavy precipitation in Wisconsin and much of the world in the future. 

Okay, so, I've thrown a lot at you tonight, but I want to now end with some take-home points to try to distill everything. One point that I want to emphasize is that changes in extreme weather are occurring. It's not just our imagination, and it's in association with a warming climate. Cause and effect isn't certain yet. Most of the extreme trends in extreme weather are consistent with expectations when you look at the big picture. More heat waves, less cold weather for example. On balance, extreme weather is expected to become more common and become more intense, but, of course, there is an exception of cold weather. The impacts of extreme weather are disproportionately large, meaning that even though we don't get these events very often, they cause tremendous amounts of damage, as we've seen in 2012 and 2011. Billions and billions of dollars of damage can occur from a single extreme event. Attributing a cause, such as global warming, climate change, to extreme events is difficult but not impossible, and that, again, gets to that issue of probability. 

We probably will be able to say that there's a certain likelihood that an event was enhanced or attributable to climate change, but we'll never be able to say that, say, Hurricane Sandy wouldn't have occurred if it hadn't been for climate change. You just can't make a statement like that. The impacts of extreme weather are not just meteorological. Societal factors can matter even more. So there's reason for hope. Regardless of climate change, we can take steps with these heat wave action plans and proof weather forecasts, for example, societal adaptation can matter and can help to overcome the stresses, economic and health-wise, that otherwise would prevail. And then, finally, extreme weather may change more dramatically than average climate conditions, and that's related to that bell curve that I showed that even a little shift in one direction can translate into some large changes in the extremes. So, I will end with that and be happy to take any questions or comments you have. Thank you. [APPLAUSE]