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The role of climate in heat, fire & floods

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Extreme weather is on the rise. But to what extent are these record-breaking events directly related to climate change? The emerging science of climate attribution is revolutionizing scientists’ understanding of the relationships between various extreme weather events and climate change.

Our August 13 panel discussed the latest findings in climate attribution science and provided tips for reporters on how to communicate accurately about these complex relationships.

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RICK WEISS: Hello everybody, and welcome to the SciLine media briefing on extreme weather and attribution, with an additional focus on wildfire science and what is known about the links between wildfires and climate. I am Rick Weiss, director of SciLine.

For those who have not worked with us before, we are a philanthropically funded editorially independent free service for reporters, covering stories about science, health and the environment. We are based at the nonprofit American Association for the Advancement of Science in Washington DC. Our funders care about really just one thing, getting more solid, reliable, methodically derived scientific evidence into news stories. We help do that primarily in three ways.


First, when you are working on a science related story and you are having trouble finding just the right expert to help explain something to you or provide some evidence-based context, we have a large database of knowledgeable, articulate experts to whom we can connect to. There is a small form on the website that will get you there. Second, we produce fact sheets on various science related topics in the news. Fact sheets that are especially designed to be useful to reporters, who are insane on deadlines and just need the essentials fast without a lot of blah blah. We research and produce them in house, and then they are vetted by multiple outside experts before we post them. So, you can count on them being accurate. Finally, and third, we host media briefings, like this one today to get reporters up to speed on topics in the news, around which there seems to be some misinformation or confusion.

Today’s topic certainly fits that category. There has been a huge amount written lately about extreme weather and about wildfires. There has been a growing amount written about the media’s failure to appropriately explain the links between these events and climate change, with some stories focusing solely on the events and not even mentioning climate change, and others over generalizing and seeming to suggest that every fire and flood these days can be blamed at least in part on climate change. The truth is, it is a little complicated, but it is not that complicated. You can without very many words, squeeze the actual facts into your stories without understating well established connections or overstating weaker connections.

To help you do that, we have three extremely knowledgeable people with us today. Their bios are on the landing page that you came to. So, we are not going to take time to go through their credentials right now, but we will hear first from Marshall Shepherd of the University of Georgia, who will get us through some basics about extreme weather and climate, and then from Stephanie Herring from the National Oceanic and Atmospheric Administration, who will take us a little deeper into some extreme weather events specifics. Finally, from Tim Brown of the Desert Research Institute to talk about wildfires. After their presentations, will open it up to questions for the rest of the hour. So, without further delay,

Marshall, please go ahead and get things started.


Extreme Weather and Climate Attribution


MARSHALL SHEPHERD: Thank you. I want to just start off by thanking all of you for joining. This is an important topic. It is often a misinformed topic. It is often a topic that gets lost in the milieu of the social media tennis matches that I often see going around, where you will have an extreme event and you will have someone saying, oh here they go, saying everything is caused by climate change. Then you have the other side saying, well of course this is related to climate change. So, I think today’s SciLine effort is really important, and I am glad to see so many media involved.

I am going to start off with the bottom line up front, in terms of extreme weather and climate change. I served as one of several authors on a National Academy study on extreme weather attribution to climate change. That report is available at the National Academy. Also, AAAS and SciLine have provided some very good fact sheets.

Let us start here, a definition of weather and climate. I want to start there first. Weather is sort of our day-to-day atmospheric conditions, where as climate is really the statistics of the atmosphere. So, I start that off because, how many of us have heard on a snowy or cold day, oh so much for climate change, I have 20 inches of global warming in my yard. Well, we know that person that says that does not necessarily understand the difference between weather and climate. So, when we talk about extreme weather and climate, we have to then broaden our understanding and discussion to make note of the fact that, yes, every extreme weather event that we experience here on the planet, whether it is a hurricane, a heat wave or a flood have happened irrespective of climate change.

The key point to note is that even with a naturally varying process, we can have a human amplification on top of it, in the same way that a home run hitter in the major leagues can hit home runs naturally, but in the steroid era, they were hitting longer and more of them. So, this notion that it is either/or is flawed. It is either we have extreme events because of natural variability or we have extreme events because of human contribute to climate change. That is a flawed narrative. It is both. Grass grows naturally, yes. If we fertilize the soil, it grows differently and that is how we have to think about that.


So, now let me–if I can get my first slide, which is the bottom line up front. This was one of the most robust studies done today on extreme weather and climate change attribution. From that National Academy study, the bottom line right up front is that we found that it is indeed possible to estimate the influence of climate change on specific extreme events. The ones that had the strongest signal, in terms of our ability to understand the physical processes, our ability to have ample observations and the ability for climate models to represent them in the models. Those are the three pillars that we use to establish our confidence in these. The three or four that came to the top were heat waves, cold, the lack of cold events, drought and heavy precipitation increases.

So, this is very important, heat waves and heavy precipitation to what we are going to be talking about later with wildfires. I am sure Tim Brown will talk all about this. The notion that we have had extreme rainfall in California, and we have had extreme drought. Both of those are factors, perhaps in the extreme fires that we have been seeing in the past several months. It is the notion that the extremes will become more extreme. That is what the scientific literature always hinted at, and so that is what has manifested.

So, we get more extreme rainfall perhaps, you get more vegetation and fuel load, and then you have a drying period, and then the drought and all of those things conspire to lead to perhaps wildfire intensity. I will let Tim talk more about that. I want to make sure that media is asking the right questions. The way attribution questions are posed influences how they are answered.


So, if we can go to my next slide, this is also a very important finding of that National Academy study. We have to move away from this notion of was that event caused by climate change. That is an ill posed question. Better questions are, are the events of this severity becoming more or less likely because of climate change or to what extent is it more or less intense because of climate change. I think that gives us a better framing.

I often talk about baking cookies. If you bake a cookie, depending on how much sugar, flour or chocolate chips you place in your recipe, you are going to get a slightly different cookie, but it is going to come out looking like a cookie. In terms of our climate system, we are always going to have the naturally evolving weather processes that we are all used to, but with the backdrop of this baked in climate change from human caused emissions, in part and also land cover changes and some other things that I know some of my colleagues would also want me to talk about as well. We get this sort of different cookie. It looks like a cookie, but it is amplified in a different way.

So, it is important to understand and ask the right questions when you as media are coming to us as experts about how to frame the question.


My final slide really gives you a look at sort of the synthesis of the results of the National Academy of Science’s study. So, we found that the lack of cold events is a very strongly attributable signal to climate change. Did you guys notice last winter, this past winter, it was the news. We had winter. We had Nor’easters. So, there was all of this news about it because we have had so many winters that were not relatively cold or did not have the winter storms we talked about.

So, I actually found it quite amusing that we actually had a winter this year, and it was being covered in such a way and used by certain groups to say, see climate change– we just had winter. So, the fact that we have such a rare occurrence of these sort of extreme cold events now, that was really lead to findings of that report.

The report also said that many of the extreme heat waves that we are seeing around the globe have a very strong attribution signal to climate change, a drought, extreme rainfall event as well, also kind of ranked higher on the list of certainty and our ability to understand their linkage to climate change.


Now, I want to explain some of these that look like they fall lower on the scale. For example, you might see fire down there on that scale. I think Tim will talk about this and others as well. It is not that we do not believe there is some, perhaps linkage to climate change and wildfire activity, but there are many other sorts of factors involved in both fire and flooding, which you do not see on this list as well that were related to human management, decision making and other things that are not necessarily related to the evolving atmosphere.

So, when you see something like tropical cyclones or fire down lower on that list, that does not necessarily mean there is no link to climate change. It means based on those three factors, understanding, reproduction in models and observations that we have going back a certain amount of time, they rank lower at this time, based on the peer reviewed literature.

So, hopefully, that gives you a backdrop of some of this extreme weather and climate attribution. Attribution is a new area study within climate. Get used to it. You are going to hear more about it going forward and that is why I appreciate what SciLine is doing today by having this forum. I will stop there.

RICK WEISS: Thank you, Marshall. Stephanie?

How Climate Attribution Works


STEPHANIE HERRING: Thanks Rick, and thanks to Marshall for providing some of that context.

Sometimes attribution results–there is a real desire I think to be able to communicate them in this binary, yes climate change played an influence or no it did not. I think that when you see that plot that Marshall showed in his last slide and the three pillars that he mentioned. Really those are important because what we are trying to get at here, is not just this binary yes or no answer, but really an inability to drive towards the classification of that impact and to be able to communicate what level of competence we have and what we think the change and risk of an event might be.

So, the three pillars an example, I will dive a little more deeply into it. So, for heat and cold, one of the reasons they are so high up there, of course is we have a great observational record for heat in particular in North America, but that may not be true in other parts of the world. So, when we look at even heat attribution statements, say for the United States versus perhaps other areas like Sub Saharan Africa or South America, where the observational record is not as strong, as we have it here in North America. The ability for us to have competence and where events might actually fall on that plot that Marshall showed, there is not only an event type, but event location as well. So, that is another important piece of context to remember.


Other examples I like to point out often is the example of tornados, which is not even on the plot that Marshall showed. That is because of course, we have a very poor observational record from a climate context, certainly of a weather event. In particular now, we have good records of tornado intensities and tracks. That was not always the case. So, relative to an event like heat, the observational record is very short. It models a very poor job of replicating microevents like tornadoes. We actually have very little understanding of how we expect climate change to impact tornado intensity or frequency going forward because of all of the different drivers that go into a tornado event.

So, it is particular important to remember that when we are talking about different events that it is not just again, this sort of yes or no answer, but with what level and what degree of confidence or certainty can we make these statements about how much the risk has changed. That is really where attribution science is headed and where our focus has been.

The BAMS Explaining Extreme Events Report, which I help edit is focused on that. We do not ask the authors for a simple yes or no answer. We ask the authors to really focus on what is the change in risk that you would expect and what the level of competence that you have in that statement.


So, for example, we have looked events like Hurricane Sandy, where we saw the storm surge, not the hurricane itself, but the storm surge from the hurricane was found to have been made more intense and larger because of human influences on the climate, in particular related to sea level rise. Again, the precipitation associated with Hurricane Harvey, several studies now come out to show that the–now again, the storm itself, but the intensity of precipitation was made more intense because of climate change.

So, here are two examples where because of the event type that we are looking at. Again, not the hurricane, but either the precipitation or the storm surge associated with it. They were able to go in and look at that, and not only say yes it was impacted by climate change but come up with estimates of how much more intense or how much larger the storm surge was because of climate change and what that would mean for the future. Those are the results that then can be used by decision makers looking at–okay, what is my likelihood of having Harvey-like precipitation in the future or a Sandy-like storm surge in the future, and those decision makers now have better information to go forward and think about what is it that they want to do related to adaptation or resilience and other variables, much more the real values of attribution science. There are always of course, studies that do not find a role for climate change.

So, for example I am speaking of snowstorms. Our 2016 snowstorm Jonas, which caused over one billion dollars in damage. The authors did not find a link a to climate change in their work on that.


Now, what does that actually mean? As Marshall said, when we saw things on the lower left-hand quadrant down there, it did not mean that climate is not playing a role but given the strength of the pillars that we have today for events like snowstorms in this particular location, the research team could not make a conclusive statement that climate change played a role. Does it mean that it did not? It could have possibly, but there are also factors such as perhaps as those pillars get stronger over time, that we will actually be able to see a climate change signal in the future.

So, as a tool that we have as a research community, if it is stronger, the observational record gets better. The models get better. Our understanding of the physical processes gets better. These events that were previously found not to be impacted by climate change, a retrospective study may find something else. That is an important context to remember, when you hear about an event and one particular group may have one result, and then you hear something else from another group. The results may not necessarily be conflicting. They perhaps took a different methodological approach. If they were in different time periods, perhaps different groups had different tools to work with. So, that element of how attribution studies should be interpreted, it is important to remember that different methodological approaches may or may not yield different results.

Finally, in 2016, we had something kind of interesting happen, which is we had three events that were found to “be not possible” without climate change. So, there is a lot discussion about what does this mean? With a statistical approach what they found and that using models of a world that we live in with climate change, and then a model of a world in which theoretically human cause being how fast emissions have not been occurring. Climate change as we know it has not happened. By comparing the two, they literally could not replicate the event in a world in which human cause being how fast the emissions had not occurred. So that is what–from a scientific perspective, “not possible” means.


So, how do we explain that? Really what we are seeing is that we think climate change is now pushing events beyond thresholds that natural variability alone could not have pushed them. So, this is the question of was an event “caused by climate change.” I would still hesitate to say that because natural variability still played a role in these events. It still likely would have been a very warm year in 2016, regardless whether climate change was a factor or not, but could it have been as warm as it was without climate change? The research is pointing to the fact that perhaps it could not have been. We would not have crossed that threshold without human caused climate change.

So, there is a sense that we are now approaching new weather regimens because we have created a new climate on this planet. I will also say that climate change, still again, I want to reiterate this very importantly does not act alone, as Marshall said. Natural variability is still a player in all of these extreme events. The question we are trying to look at is–what role is climate change playing? How large is that role? So, where does that leave us?


Again, I am trying to communicate the results of attribution research. There is probably a reason that this has been a challenging area for the media. It is in part because, as Marshall said, it is important to focus on the right question. I think that is sometimes difficult to tease out from some of these complicated scientific studies.

That is where areas–people like SciLine and what Rick is doing is so important is because they do try and distill down some of this complicated research and to understandable messages. The crux of this issue is the right questions is a very, very important one. Also understanding how the extreme events did just fine. So, what type of events are you looking at and where the events occur, will impact, what confidence we have in the results. So, something to just keep in mind as you are thinking about how to talk about these events.

Finally, I think it is really important to be prepared for change. So, what I mean by that–if we had been giving this briefing, I would say a little over one year ago, we would not have been talking about these events, where they were not possible without climate change. Up until then for over a decade, scientists have been saying every event could have happened in a preindustrial climate. Now, we are actually questioning whether or not that is true. Of course, there are just three studies that we saw in 2016.

So, there is still a lot more work to be done but would seem that we may have passed some type of threshold, where perhaps these events were not possible in a preindustrial climate. So, that has been a major change in our understanding of how we communicate attribution science.

Again, if you would have asked us perhaps even 10 or 15 years ago, you would have had people on this panel potentially saying that this field of research is impossible. This is a rapidly changing area of research. Looking ahead for instance, one of the things that we are seeing is how quickly people are willing to come out with attribution statements. Germany, for instance is now working on coming with real time attribution statements shortly after an event. For instance, they are talking about potentially using social media to put out initial communication, and then following up with some kind of attribution study, in little as one week or two.


So, that again, is a huge change in the field. No one would have thought we would be here five years ago. People were thinking about it and talking about real time attribution, but it still seemed quite a way off. So, the fact that Germany is embarking on this is something that will be interesting to watch. Finally, I think that looking ahead, as Marshall mentioned, and something I will most certainly be saying today–this idea that there is natural variability that kind of lets an event happen, all is a player. There is no kind of clear line. Over that threshold is where climate change pushes events.

I think as research continues, we are going to find that potentially some of these factors that are natural variability–like the ENSO cycle for instance, which we still put in the natural variability category. I still put it in the natural variability category. Research is emerging that perhaps even these natural cycles are being impacted by climate change.


So, in that in the future, are we going to be able to draw this clear line between saying this is the natural component, and this is the climate change component. That clear line is going to start to get grayer and grayer, as we find that some of these natural variabilities, the natural drivers of these meteorological events are themselves being affected by climate change. That is research that has yet to be done, but I do think that in my personal opinion.

I do not want to speak for anybody else or my co-editors on the BAMS Report. I do think that an area that we are going to need to keep our eyes out for in the next, certainly five to ten years. So, there has been a lot of change to date, and I certainly expect to see more change in the future. I do not think they have stabilized yet as a field of research and that is very exciting. I hope that as a media community, you stick with us and wait to see what we discover. I think there is a lot of important discoveries to be had.

Thanks Rick.

RICK WEISS: Great. Thank you, Stephanie. Very interesting. Tim, let us talk about wildfires a little bit.

Wildfires and Climate


TIMOTHY BROWN: Thank you, Rick. Good day everyone.

Yes, a wildfire is in the news, not just in US, but globally as well. Will follow up on a few points to those things that Marshall and Stephanie talked about the attribution and weather and climate differences, and that helps set this up a little bit. Maybe some definitions just to be clear on those.

A wildfire for example, that refers to the uncontrolled vegetation fire. It really is the best term to talk about fire on the landscape in general. Sometimes you will hear forest fire. That term is used, but that really should be reserved explicitly for fire in forests, such as a grassland fire is say for a fire in the prairie regions. Another common term is prescribed fire, which is any fire intentionally ignited by management actions, in accordance with applicable laws, policies and regulations to meet specific objectives.


So, then a wildland fire is any non-structure fire that occurs in vegetation or natural fuels. It actually includes both prescribed fire and wildfire. An area burned is another common metric that is used describe the special extent of a wildland fire.

Notice there, I said wildland fire because I am talking about both prescribed and wildland, but by itself, it says nothing about the actual impact. Its usage related to wildfire often implies a destructive nature, but this is not always the case. In various ecosystems, it can have these different levels of high severity or low severity, but yet would get counted as a total area burned. A little bit just on climate versus weather.

I like to think a climate as enabling fire and weather as driving fire behavior. Climate is certainly an important factor in establishing the vegetation types on landscape. It describes the accumulation of weather within monthly, seasonal and longer time scales. Marshall mentioned this–for example seasonal, there are now more longer periods and reduce field moisture allowing for increased ignition potential, but wet periods allow for vegetation growth and accumulation.


So, thus climate is an important factor in the cycle of fire. The Napa Valley fires were a good example of this, where extreme precipitation in the winter and spring allowed for extensive fuel growth and then when that dried later in the fall, it became very flammable and susceptible to ignition. The shorter-term weather, temperature, atmospheric moisture (we usually think of that as relative humidity) and wind are then the drivers of fire on the local landscape.

Another term I have been seeing a lot of reference to is fire season length. When I see that, it is almost never to find, and there can be numerous definitions. I prefer to think of it as the period dominated by high fire danger and likely to have the most rapid increases and fire spread. So, it is a really and weather and climate dominated definition.


So, where are these fires coming from? If we could put that first figure, figure 1. This will show from a recent research paper. The distribution of percentage human ignitions across the US. Basically, 80% a little more than that of wildfires are human started. They also represent about 60% of the land area where ignitions occur. The reddish areas of course also highlight high population areas. The blue areas there in the west, representing the anterior west are fewer human ignitions, but they will be higher lightening ignitions. We can see that in the next figure, which shows the distribution of lightening caused fire by season. The different colors indicate that.

Not surprisingly, most of the lighting caused fires occur during the summer months, June, July and August. In the west, the human caused fires also occur a lot in June, July and August. Of course, this is largely due to recreation activities. People out camping and Disney Parks and that sort of thing. So, there is high correlation between where people live and are active and human caused ignitions.


So, another question that comes up is–is this season the worst season? How does it compare to past years? This is worthy of, actually for further assessments because for example, we really do not have a simple real time kind of index to make that comparison. For example, the number of fires, do not really use that as a comparison, while the summer does vary annually across the country at around 70,000 a year. If anything, that number has actually been on a decline, given effective fire prevention programs and increased public awareness about the risks of fire. Area burned, which I mentioned before is the most common metric for comparison, but by itself it is not a good measure of the overall impact.

A better way to get to that is fire severity, which is the degree to which the site has been altered or disrupted by fire. Loosely, we think of it as the product of fire intensity and the residence time. So, the strength of fire, in terms of its energy and how long it has been in that place. The extent of fire severity may be and as often documented at a post-fire local level, but that may take a while to actually get that information, in terms to make any kind of historical comparison. There is for large fires, greater than 1,000 acres a national data status severity that is derived from satellite observations. Those results have appeared in a number of science papers.


There is a trend, especially in the west for increased area burned for large fires, but because of this data set, we can also look at fire severity. So, there is a weak increasing trend, given the official definition of what fire severity is. Home destruction is an increasing metric related to wildfire. This is largely due to human expansion areas that are historically fire prone. For example, in California, six of the state’s most destructive wildfires occurred last year, and here in 2018 combined.

So, an objective measure is difficult because human factors are so closely tied to fire. There is one other indicator that the fire management agency used is a called a preparedness level. It is on a scale of 1 to 5, and each level describes a needed amount of firefighting resources that are being utilized or will potentially be needed. Nationally, it has been at level 5, the highest level for quite a while now, and probably even started maybe a little earlier than usual. So, for California where so much of the news has been coming from, it is actually at 4 at the moment. So, despite everything that is going on, this level is not at its maximum point of where it could be.

So, let us talk about climate change a little bit.


Marshall mentioned this, very nicely, he stated climate change has caused a single fire is not really accurate because it ignores the other factors that allow for fire, certainly warming temperatures and related drying, in terms of increased fuel aridity is a major component in a fire. So are land management practices and the public desires of what we want on the landscape. Historical aggressive suppression in many places is allowing more intense fires to burn now, instead of historically low intensity and forest regenerating natural fires. As I said before, people have increasingly moved into natural fire prone areas and without building a landscape, codes, having fire mitigation makes these places more susceptible to the damaging effects of wildfire.

So, I think that where we are at today, as a convergence, climate, people and fuels. They are all very closely tied together. As one example of that, people are warming the planet and that enables more fire. People are responsible for starting most of the fires that cause most of the damage. So, it is a full circle.

So, where are we at, in terms of predictions and what we think we know about relationship between climate and fires? Certainly, hotter days and warmer nights lead to drier fuels, so that is a factor. Once fires happen, a disturbance, there is very much a potential role of invasive species, including insects, flammable grasses and even monocultures that a single species moving in and minimizing the diversity of a landscape. It is possible there might be more convective storms, meaning more lightening. I would say this is low confidence at the moment, but more scientific studies should be looked into for this because it is a possibility.


A lot of times, you will hear about snow pack leading to more fire, but this is not actually so clear of a relationship because wildfires also start under the influence by what happens from the weather between the snow melt season and when fire occurs. So, for now, climate change is really manifesting itself primarily through changes in the character of fire, rather than the frequency. Around one half the increase in area burned in the western forest fires, and I explicitly am referring to forest fires, in recent decades can be attributed to long-term warming trends. So, that is one of the very few, maybe direct attribution studies that have come out in relation to climate change and wildfire.

Vegetation of all types is becoming more flammable. This also means if you have more high-intensity burning, you will get more smoke and the potential for human health impact. What does this mean for fire management? Well, they are having to change tactics for these larger and more destructive fires by focusing on more point protection, that is the homes and structures and also trying to guide the fire to places where it might be more directly controllable. Suppression expenditures are very much on the rise.


I think it is important to keep in mind that the wildfire problem is not really a scientific or technical dilemma, it is really more of a political and societal challenge. Limiting the severity of the wildfires, even as climate warms, should be a primary overarching goal. There is little capability in predicting when and where a fire will happen. There are short term forecasts. Most of the seasonal outlets of fire potential are largely successful in indicating places where fires may be problematic, giving firefighter agents an early warning. Fire spread models are largely statistical based. They are widely used, but we really need a lot more research and development to advance the physics modeling of the wildfire spread aspect.

So, just to summarize, I think we should all be careful about throwing around terms like the worst fire season without really defining what that means. We want to try and relay–we should try and relay a specific connection of climate to fire activity being described, rather than just generally saying climate caused it. As I mentioned, the best documented climate change attribution we have at the moment is warming and its relation to fuel aridity. It is also important not to overstate this data knowledge or modeling activities and remind the audience that most fires are human caused. So, there is a role there that we can also increase prevention. All right. Thank you.


What is the point of attributing certain weather events to climate change?


RICK WEISS: Great. Thank you, Tim. Again, to remind folks if you have questions, you can type them into the Q&A box and will pick them up and give them to the speakers. I want to also note that if it was not clear from the beginning, this entire briefing is of course, on the record. In fact, the entire video and a timestamped transcript should be up within the next day or so for people to read.

While people submit their questions, I just want to throw one out to maybe Marshall or Stephanie. As it becomes clearer that we can move away from this general association, saying climate change is leading to an increase generally in heavy rain and heatwaves. We know that those are a little bit more attributable that maybe other things like fires and towards being able to specifically attribute this particular event was 300% or 400% more likely because of climate change or maybe even could not have happened if not for climate change.

Maybe one or both of you quickly address the question of–why we want to know? If the Germans are going to providing almost a weather report, but as an attribution report saying, yeah, this storm that just happened that was 3x as likely to happen because of climate change. What is the point, other than finger pointing? There is a reason why we want to know this, right?

MARSHALL SHEPHERD: I will defer to Stephanie.


STEPHANIE HERRING: Sure. So, I think that, as I mentioned, one of the main focuses of the BAMS Explaining Extremes Report and why those originally started, actually was to really advance the methodology. One of the main focuses was how do we quantify the change in risk and improve our certainty around those quantifications. So, I will give an example from the 2016 report–of this area that is emerging now, which we are calling impact attribution. I think this is for me, personally one of the more important values in having that quantification is that, as I mentioned in my previous comment the relationship–attribution sciences are great but there is finger pointing, but what do you do about it?

What kind of adaptation and resilience activities can be taken? The climate science community we are not in that decision-making position, but ideally science is a seat at the table for the decision makers, so we can provide them with information that does–within Hurricane Harvey and as you start to rebuild, this is a likelihood of this event happening again. Certainly, there will have to be things, such as how much is it going to cost to rebuild? How much does it cost to rebuild to a new standard, where they have to go into that decision, but without having some sense of this is the likelihood of that happening again in the future? It is difficult to simply take these binary yes or no answers and do anything about it.

If someone tells you it is going to rain tomorrow, does that mean it is going to rain a little bit? I do not need to bring an umbrella or am I going to have a flash flood warning? Those are two very different pieces of information that as an individual you might take some kind of action against or not take action against. So, it is really the ability to provide an understanding to decisions, per community as to–here is how we think your risk is actually due to climate. They can then layer that into all of the other variables that go into any other type of adaptation or resilience decision. It is another piece of information that they can be using.


MARSHALL SHEPHERD: I wanted to follow up on that quickly because another piece that we briefed congressional leaders on after the National Academy’s report is that from attribution activities, there is a goal perhaps to provide predictive or probabilistic forecasts of future extreme events at lead times of days, to seasons or longer. So, the more we understand about how some of these extreme weather events are emerging within the backdrop of this sort of elevated sort of climate forcing, if you will–that actually can perhaps provide guidance on future predictive capabilities at scales longer than seven to ten days, which is the typical weather forecasting scale.

Is it true that half of the increase in Western forest fires can be attributed to long-term warming?


RICK WEISS: Cool. Here is a question from Benjamin Stillman, Reno Gazette Journal. He is saying Dr Brown, you said half of increase in western forest fires can be attributed to long-term warming. Can you please elaborate on that point? Tim, you might be on mute.


TIMOTHY BROWN: Sorry. Yes, this is referring to a paper that was in the proceedings of the National Academy of Sciences in 2016. It is referenced in the fact sheet that was sent out. Basically, that paper describes warming in the Western US and its relation to area burned in forests and the fact that temperature is strongly related to atmospheric moisture, which is related to fuel moisture. So, they looked at eight different indicators of drying for fuel aridity and showed through that, that the warming in relation to the drying of the fuels was responsible for an increase of half the area burned in these western forests in recent years.

Is there a good source of how many severe wildfires there have been?


RICK WEISS: Great. The fact sheet that Tim just referred to is the SciLine fact sheet on wildfires, which is available at our website, We have a question here from Doyle Rice at USA Today. Is there a good source of how many severe wildfires there have been year to date similar to the National Interagency Fire Center’s running total of acres burned and number of fires? Since severity, you have mentioned is a better metric.


TIMOTHY BROWN: Yes. Not really, not one that is very easily or publicly accessible. It is that satellite derived data set that goes back to the early 1980s and is more less up-to-date. So, no we do not have a good readily available index for the public, in terms of severity at this time.

Which contributes more to the increase in forest fires, precipitation or temperature?


RICK WEISS: Question from Seth Bernstein of The AP. Which is more important, with regard to the increase or the status of forest fires going on, wildfires going on, precipitation versus temperature? That is to say, I think lack of precipitation or drought versus temperature increase. Is it possible to rank those?


TIMOTHY BROWN: Possibly. I know some climate scientists work in fire would say that temperature is more important because, again, the warming leads to drying of the fuels. This would be particularly so up in northern environments, a boreal forest. So, if we are thinking of this globally. Also, I think given that proceedings paper and the work that was done there leading to the fuel aridity, temperature would rank very high. Again, precipitation, if you go into drought situations that allows for fire potential, but also as was mentioned, if you have very wet periods, this increases the fuel growth and amount of fuel available.


MARSHALL SHEPHERD: I wanted to just kind of quickly follow up on that to Seth as well. I think one of the things, for me, jumps out about this is that it is both ends of the extremes that play a role. One of the things that is crystal clear to us, as climate changes is that the intensity and perhaps frequency of the extreme aspects of the hydroclimate, meaning rainfall and drought, will increase in intensity and frequency. So, if you think about these distribution curves, these curves, these Gaussians and these probability distributions. If you are shifting those curves towards the likelihood of more extreme drought and rainfall, then that really suggests that will lead to some of these sort aridity and fuel loading scenarios that we are seeing.

I try to give–Seth and others that know me that talk to me–I try to give very clear sort of human examples. If you are adding one foot to the basketball court, even I, at 48 years old can now dunk a ten-foot basketball. I might not be able to at ten feet, but if I add a foot to the floor, I bet I can get it. So, if we are continuing to add to those extremes, given what we know in the literature, that suggests this is something we are going to be dealing with.

How has the risk of wildfires changed due to climate change?


RICK WEISS: Great. This is a question also from Seth, but for Stephanie. I am not sure if this something you can get Stephanie or whether you punt to Tim, but he is asking–since you mentioned you cannot quantify the increased risk for this specific fire season due to climate change; can you give us some kind of qualitative sense of how risk has changed due to climate, again risk on wildfire?


STEPHANIE HERRING: I think Tim started to answer that question in his previous–I will punt back to him. I will also say there have been attribution studies done on particular fire seasons. Tim was talking about a more comprehensive, sort of longer time scale attribution study and the proceedings in the National Academy of Science’s paper.

For instance, in 2014, Alaska had a particularly bad fire season. There were some attentive quantifications for that particular fire season, a 34% to 60% increase in risk. So, again, there have been some efforts to do that. I will also say that the region, and again, this is where the question matters–the region in particular for these fire season matters quite a bit. Because in my experience and what I have seen individual attribution studies done for a particular fire season or a particular fire and different location. Because of all of the different variables Tim talked about that go into a fire, different areas use different models to understand their fire risk. So, the papers in Alaska, for instance were using something called a build up index.
Papers about fire risk in California tend to look more at drought, using a drought precipitation metric. I have also seen papers from out of Australia that use a different type of modeling approach that tries to account for that local influence of that particular region, where the fire happened.

Tim, I do not know if you have anything you want to add to that?


TIMOTHY BROWN: Thanks Stephanie. Yeah, that was good too, to bring those up. Maybe what this does remind me of though is that in the past, back in the 1900s, in particularly say in the 1930s, when we had a lot of fire, a lot of large area burned. The conditions–those were big drought periods, warm temperatures. So, we know that the warmer it gets and the drier it gets, the more susceptibility to fire there is. So, in some ways what we are seeing now with these large area burns. If we use that as a metric in trying to compare that from what we know from earlier years; we are really coming back to a period of very large fires, more extreme fires because of where people are involved and home destruction. The fact that it is very likely that this is a trend now that will continue and strengthen as we go forward.

Can we say that the intensity or the number of fires happening now could not have happened without climate change?


RICK WEISS: We have a dual question here from Benjamin Stillman in Reno. Actually, one of them is asking Stephanie to actually list the three events from 2016 that have been now said to have not been possible or likely never would have happened without climate change. I can just tell you, Benjamin those are listed on the fact sheet, the SciLine fact sheet here. So, it might be simplest just to see them on the sheet there.

The second half of the question asks whether that kind of statement has been made yet about anything having to do with fires. Can we say that the intensity or the number of fires happening now, perhaps could not have happened without climate change? My understanding, from what I am hearing Tim and others say, is that climate–because fires are so influenced by other factors like forest management practices, it is a lot harder to get a firm grasp on whether a fire would have happened or not. Tim or Stephanie, do you want to pick up that question of whether we can say at this point that there are either some fires or the number of fires or the intensity of fires simply would not have happened according to models if not for climate change?

STEPHANIE HERRING: Well, I have certainly never seen any research that makes that statement, but Tim knows the literature better than I do, I am sure–so.

TIMOTHY BROWN: No, I have not seen anything specific to that either.


MARSHALL SHEPHERD: Yeah, and I would add that is why fires did fall lower on that graphic that I showed earlier from the academy study. There are just various factors beyond those three pillars that we talked about earlier. I think that is important. I think that is what maybe the public and maybe even sometimes our colleagues, perhaps are trying to convey to the public. It is a tough problem because we are not sitting here saying that climate change is not a part of these of fires or may not be related to these fires, but it would be disingenuous, I believe, and I think my colleagues would agree to say that a particular fire this season is absolutely because of climate change. Cannot say that, but we clearly know climate change is happening.

We clearly know there is a human imprint causing it. It is very likely that the environments of the extremes being caused because of climate change on the wet side and the dry side, will lead to a backdrop of more fires. The specific attribution on an event basis, I have not seen anything published on that and frankly, it might be a bit careless to do that.

What have you seen in the news coverage of climate and extreme events or climate and wildfires that you think the reporters could have done better?


RICK WEISS: We have a question from Katarina Zimmer. She is a science reporter based in Germany. It is a good general question that I would encourage any or all of the three of you to address. It is just asking you, what have you seen in the news coverage of climate and extreme events or climate and wildfires that you think that the reporters could have done better? Maybe any examples of the kinds of coverage that you think were excellent and on the mark? You do not have to name bylines, I guess on these stories, but sort of high points and low points, in terms of the kind of coverage you have seen of this somewhat complicated relationship. Stephanie, do you want to start? Or Marshall, go ahead.


MARSHALL SHEPHERD: I was just going to say the one that still to me that I see quite a bit of is just the cause. What was that event caused by? I think we just have to–I even wrote something in Forbes a couple of years ago, saying we have to get that out of our–we have to just make it go away. Make it go extinct. Was that storm or was that fire or was that flood caused by climate change? I think that is the one big thing that still kind of drives me nutty, when I see that in the literature. I think one of the things that I am encouraged about. I hope our media colleagues will continue to do so–I think with all the negative discourse about climate from the US pulling out of the Paris agreement and others, I think there is more discourse and chatter about climate change now than I have seen in the past five to ten years. There certainly could be a lot more.

I would just suggest that there are opportunities to cover climate–I know there is always a need to have a peg or sort of a news worthiness angle, but I think the tendency for the public to sort of see just the coverage of the big event, creates some kind of a selective bias, perhaps or selection bias for the public. So, if we can get a bit broader coverage. I know several people that I am looking at their names on this list do, do this. If we can get a broader context of climate and how it is affecting people’s kitchen table issues. So, not just that, oh it is hot again or we broke another heat record, but oh, we broke another heat record that has been causing perhaps more intense or frequent drought in the Midwest, you might pay more for your Cheerios or your popcorn this year. So, this sort of linkages back to the sort of kitchen table. I would love to see more of that.


RICK WEISS: Great point. I think on the cause issue, even when these instances come up, where scientists are determining this would not have happened if not for climate change, even then, it does not mean climate change, at least solely caused the event, right? Many things always add up to every event, even if climate change was in a sense, the last straw in some cases.


MARSHALL SHEPHERD: Absolutely, but I think I want to get back to something Stephanie did say that we are not–I do not want the media here to leave this presentation with, oh the scientists did it again. They are waffling. They cannot really say–which is perhaps what maybe being perceived by some. I think there are some very clear things that we can say about attribution, extreme events and climate change. Just be a bit careful about the nuances, the definitions that I think that Tim talked about and other things. I think we, and Stephanie mentioned, we have moved from an era five or ten years ago, to a point now, where we are very comfortable saying some things about extreme events and climate. I just want that message to come out, ring out.


RICK WEISS: Stephanie, you want to make a couple last points here, as the hour comes to a close?

STEPHANIE HERRING: Sure, one I think actually is that despite how rapidly this deal has changed. We as a scientific community have not made it easy for the journalists out there, but with that being said, I think they do a great job. In general, from what I have seen, especially in the past couple of years. I have been particular of some of the coverage for the BAMS Explaining Extreme Events Report.

I think in general, the media is working incredibly hard to get this right and doing a good job of communicating an incredibly complex nuance area of science. So, kudos to you guys. The other component, I think that we could do more to improve is try and get some of the–I see they have moved a little bit from this binary, yes this was an influence or no there was not, into–this is what we actually think the change and risk is going to be and that quantification component. So, I do think it is very important and again, as Marshall said, we have moved away from this question of did climate change influence the event, the yes or no. we are really good at actually saying when yes it did influence it or no it did not.

The real crux for the research community is how much was that influence, what do we expect to see in the future, what is the predictive capability of this? We are moving in that direction, moving very quickly in that direction, and so, it would be exciting to see more of that get communicated in the media.

RICK WEISS: Thank you. Tim, any closing words?


TIMOTHY BROWN: Yeah, I think that was great what Stephanie just said. I suppose just quickly, particularly when we talk about fire is, is to talk about the human role in fire, as well as the natural climate role in fire, to make sure that picture is painted that it is very closely linked and connected, and that humans, that people have a place in also preventing this, mitigating against fire and adapting to these changing fire environments.


RICK WEISS: I think that is a great point to end on, to remember that there are things that people can do to reduce these risks, where they were talking about fire or some of the other impacts of climate change. We should not forget about solutions, even as we talk about being ever better at qualitatively and quantitatively defining what the problems are.

I am sorry we could not get to the rest of the questions that are on the list. I do want to point out to people one last time that again, if you go to look at the fact sheets, two fact sheets that we have got up, one on attribution science for extreme weather events and one on wildfires. The answers to many of the questions I see coming up in the que are there. These are quite synced fact sheets. They are meant for reports, who are not already–I think if you read through those, it will take you five minutes and you will have at your fingertips, some great factoids that you can drop into your stories to have some real solid evidence plugged into your stories on these topics without having to work very hard.

So, I want to, just in closing, thank everybody for participating. Thank our panelists for participating, for all of you reporters for logging in. I encourage you all to follow SciLine on social media @RealSciLine and to track our activities going forward. With that, I will close this media briefing. Thanks all for participating.

Dr. Timothy Brown

Desert Research Institute

Timothy Brown is a Research Professor at the Desert Research Institute in Reno, Nevada. Dr. Brown also is graduate faculty in the University of Nevada, Reno Atmospheric Science Program and current affiliate at the Monash University School of Earth, Atmosphere and Environment, Science Faculty in Clayton, Victoria, Australia.

His primary academic interests include wildland fire-climate-weather connections; the wildfire environment; applications development for wildland fire management planning, decision-making and policy; and the interface between science and decision-making. He is Director of the Western Regional Climate Center and the Program for Climate, Ecosystem and Fire Applications (CEFA) at DRI.

Dr. Stephanie Herring

National Oceanic and Atmospheric Administration's Center for Weather and Climate

Stephanie is a scientist and senior advisor with National Oceanic and Atmospheric Administration’s (NOAA) Center for Weather and Climate in Boulder, Colorado, where she specializes in extreme weather and weather-related events and climate services. She is the lead editor of the annual Bulletin of the American Meteorological Society report, Explaining Extreme Events from a Climate Perspective, which is aimed at understanding the physical drivers behind extremes and how risk exposure to extremes events is changing over time. Before coming to NOAA, she was an American Association for the Advancement of Science and American Chemical Society Congressional Policy Fellow, working for Congressman Edward Markey on the American Clean Energy and Security Act as well as on climate change and public health, energy and environmental issues.

Herring completed postdoctoral research at the National Institutes of Health in the malaria and vector research laboratory. She received her doctorate from Yale University in molecular biophysics and biochemistry and holds a B.A. in biochemistry from Swarthmore College

Dr. Marshall Shepherd

University of Georgia

Marshall is the Georgia Athletic Association Distinguished Professor of Geography and Atmospheric Sciences at the University of Georgia and director of the university’s Atmospheric Sciences Program. A past president of the American Meteorological Society, he has focused his research on hydrometeorological extremes, urban climate, and the intersections of atmospheric sciences with society. He uses remote sensing, weather-climate modeling, and risk-vulnerability approaches to address challenges such as urban flooding, energy-food-water nexus, weather-climate risk, and communication-warnings. A strong proponent and practitioner of science communication and public engagement, he also serves as host of the Weather Channel’s award-winning show and podcast Weather Geeks, is a contributor to Forbes magazine, and co-authored a children’s book on weather and weather instruments.

Marshall earned his B.S., M.S., and Ph.D. in physical meteorology from Florida State University (becoming the first African American to earn a Ph.D. from the Meteorology Department) and served as a research meteorologist at the NASA Goddard Space Center in Greenbelt, Maryland.

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