Arguments
Climate change and wildfires – how do we know if there is a link?
Posted on 16 August 2018 by Guest Author
Kevin Trenberth, Distinguished Senior Scientist, National Center for Atmospheric Research
This article was originally published on The Conversation. Read the original article.
A firefighter runs after trying to save a home in Lakeport, California, suffering its biggest fires ever. AP Photo/Noah Berger Kevin Trenberth, National Center for Atmospheric Research
Once again, the summer of 2018 in the Northern Hemisphere has brought us an epidemic of major wildfires.
These burn forests, houses and other structures, displace thousands of people and animals, and cause major disruptions in people’s lives. The huge burden of simply firefighting has become a year-round task costing billions of dollars, let alone the cost of the destruction. The smoke veil can extend hundreds or even thousands of miles, affecting air quality and visibility. To many people, it has become very clear that human-induced climate change plays a major role by greatly increasing the risk of wildfire.
Yet it seems the role of climate change is seldom mentioned in many or even most news stories about the multitude of fires and heat waves. In part this is because the issue of attribution is not usually clear. The argument is that there have always been wildfires, and how can we attribute any particular wildfire to climate change?
As a climate scientist, I can say this is the wrong framing of the problem. Global warming does not cause wildfires. The proximate cause is often human carelessness (cigarette butts, camp fires not extinguished properly, etc.), or natural, from “dry lightning” whereby a thunderstorm produces lightning but little rain. Rather, global warming exacerbates the conditions and raises the risk of wildfire.
Even so, there is huge complexity and variability from one fire to the next, and hence the attribution can become complex. Instead, the way to think about this is from the standpoint of basic science – in this case, physics.
This year is proving to be another active wildfire season. Climate Central, CC BY-NC
Global warming is happening
To understand the interplay between global warming and wildfires, consider what’s happening to our planet.
The composition of the atmosphere is changing from human activities: There has been over a 40 percent increase in carbon dioxide, mainly from fossil fuel burning since the 1800s, and over half of the increase is since 1985. Other heat-trapping gases (methane, nitrous oxide, etc.) are also increasing in concentration in the atmosphere from human activities. The rates are accelerating, not declining (as hoped for with the Paris agreement).
This leads to an energy imbalance for the planet.
The flows of energy through the climate system are schematically illustrated with numbers on the top-of-atmosphere values and net energy imbalance at the surface. Trenberth et al 2009
Heat-trapping gases in the atmosphere act as a blanket and inhibit the infrared radiation – that is, heat from the Earth – from escaping back into space to offset the continual radiation coming from the sun. As these gases build up, more of this energy, mostly in the form of heat, remains in our atmosphere. The energy raises the temperature of the land, oceans and atmosphere, melts ice, thaws permafrost, and fuels the water cycle through evaporation.
Moreover, we can estimate Earth’s energy imbalance quite well: It amounts to about 1 watt per square meter, or about 500 terawatts globally.
While this factor is small compared with the natural flow of energy through the system, which is 240 watts per square meter, it is large compared with all other direct effects of human activities. For instance, the electrical power generation in the U.S. last year averaged 0.46 terawatts.
The extra heat is always the same sign and it is spread across the globe. Accordingly, where this energy accumulates matters.
Tracking the Earth’s energy imbalance
The heat mostly accumulates ultimately in the ocean – over 90 percent. This added heat means the ocean expands and sea level rises.
Heat also accumulates in melting ice, causing melting Arctic sea ice and glacier losses in Greenland and Antarctica. This adds water to the ocean, and so the sea level rises from this as well, rising at a rate of over 3 milimeters year, or over a foot per century.
Global ocean heat content for the top 2000 meters of the ocean, with uncertainty estimates by the pink region. ScienceAdvances, CC BY-NC
On land, the effects of the energy imbalance are complicated by water. If water is present, the heat mainly goes into evaporation and drying, and that feeds moisture into storms, which produce heavier rain. But the effects do not accumulate provided that it rains on and off.
However, in a dry spell or drought, the heat accumulates. Firstly, it dries things out, and then secondly it raises temperatures. Of course, “it never rains in southern California” according to the 1970s pop song, at least in the summer half year.
So water acts as the air conditioner of the planet. In the absence of water, the excess heat effects accumulate on land both by drying everything out and wilting plants, and by raising temperatures. In turn, this leads to heat waves and increased risk of wildfire. These factors apply in regions in the western U.S. and in regions with Mediterranean climates. Indeed many of the recent wildfires have occurred not only in the West in the United States, but also in Portugal, Spain, Greece, and other parts of the Mediterranean.
A satellite image of the Carr Fire in California. Drought conditions, in addition to a lot of dead trees and vegetation, are contributing to another year of severe wildfires. NASA
The conditions can also develop in other parts of the world when strong high pressure weather domes (anticyclones) stagnate, as can happen in part by chance, or with increased odds in some weather patterns such as those established by either La Niña or El Niño events (in different places). It is expected that these dry spots move around from year to year, but that their abundance increases over time, as is clearly happening.
How big is the energy imbalance effect over land? Well, 1 Watt per square meter over a month, if accumulated, is equivalent to 720 Watts per square meter over one hour. 720 Watts is equivalent to full power in a small microwave oven. One square meter is about 10 square feet. Hence, after one month this is equivalent to: one microwave oven at full power every square foot for six minutes. No wonder things catch on fire!
Attribution science
Coming back to the original question of wildfires and global warming, this explains the argument: there is extra heat available from climate change and the above indicates just how large it is.
In reality there is moisture in the soil, and plants have root systems that tap soil moisture and delay the effects before they begin to wilt, so that it typically takes over two months for the effects to be large enough to fully set the stage for wildfires. On a day to day basis, the effect is small enough to be lost in the normal weather variability. But after a dry spell of over a month, the risk is noticeably higher. And of course the global mean surface temperature is also going up.
“We can’t attribute a single event to climate change” has been a mantra of climate scientists for a long time. It has recently changed, however.
As in the wildfires example, there has been a realization that climate scientists may be able to make useful statements by assuming that the weather events themselves are relatively unaffected by climate change. This is a good assumption.
Also, climate scientists cannot say that extreme events are due to global warming, because that is a poorly posed question. However, we can say it is highly likely that they would not have had such extreme impacts without global warming. Indeed, all weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be.
In particular, by focusing on Earth’s Energy Imbalance, new research is expected to advance the understanding of what is happening, and why, and what it implies for the future.
Informative article. Southern Australia has been experiencing a drought and high temperatures and serious bush fires recently, associated with persistent anticyclonic conditions. This is in the middle of Winter!
Drought conditions in southern Australia and the associated persistent anticyclones has been linked to climate change here.
Whatever is happening we are getting hammered for the second year in a row in western Canada.
The new normal is going to be hugely expensive in terms of fighting fires, loss of property and loss of resouces like the forests themselves that are burning up.
BC Wildfires Map
Thank you for reminding us of that Doug. Man made dorders matter little to physics. With all the noise made about the California fires, we tend to forget the extent of the BC fires. Over 1.2 million hectares burned and 65,000 evacuees in 2017. Current year shaping up to be as bad.
It's sobering, my brother and his family were evacuated from our hometown for almost a month last year and he wasn't sure if there was going to be anything to go back to. He and his wife were the last car out heading north from that city with flames burning on both sides of the road.
He's a 30 year veteran with BC Forest Service and has managed fire crews for years and has seen nothing like what is happening now.
There were multiple fires started near where I live in mid July, hundreds of people a few kilometers to the north were evacuated and many homes burned.
There have been very few smokeless days for a month and last year was the same for most of the summer.
How we are supposed to treat this as normal is completely beyond me.
Doug_C, @4, I might have part of the answer as to why Canada is experiencing more forest fires. Its related to more lightening strikes. Climate change is leading to thunderstorms moving northwards more into regions like Canada due to climate change according to this article.
I was simply curious as to whether climate change would lead to more lightening strikes as a general rule, and I did a google search, and came across that article. However it appears that its not certain that climate change would cause more lightening strikes for the planet as a whole. Some studies say it will and some don't. Here and here.
I think that's only part of the story Nigel. In BC, a major factor is the biotic stressors, many of which have been inked to climate change.
www.mdpi.com/1999-4907/8/8/280/htm
For those reading and writing comments here a question. Do you think people experiencing extreme climate-related events like wildfires, droughts, and floods firsthand increases their acceptance of climate science or hardens them against it? I'm not offering an opinion, just asking.
nigelj @5
That really seems to be the case.
We had a fairly wet spring and early summer with few wildfires, we were well below the average until recently. The weather warmed up in early July and things dried out. Then we had a series of thunder storms come through that ignited a large number of wildfires. Over 400 in one outburst from what I recall.
And now because smoke covers so much of the entire region, after the latest thunder storms it is very hard to detect new fires.
2018 Wildfire season BC
"In fact, lightning has already sparked more than 1,300 wildfires in B.C. this year, which is more than any year since 2009. That number is likely to increase as the extended weather forecast calls for continued hot and dry conditions, with the risk of thunderstorms in some parts of the province."
Evan, I think people directly experiencing extreme weather first hand would mostly increase their acceptance of climate change science, especially warmists and fence sitters. I'm assuming here they are convinced the weather is getting more extreme or have seen data to that effect. Once the threat becomes real and perhaps painful, it clears the mind.
I dont think it would harden anyones attitudes against climate science , unless they are really deep in conspiracy ideation and think its the government altering the weather, in order to bring on one world government . And yes, I have seen comments like this, but it cant be that many people.
Of course even quite dramatic change probably won't increase acceptance among many of the denialists either, because they just rationalise it away with claims that climate changed before, the data is fake, its just weather. My guess is it would change maybe about half their minds at best.
Needs a poll or survey.
Perhaps I should ask the question another way. Polls say that a little over 50% of the people accept that humans contribute to global warming. Yet IMO far fewer than 50% of the general public are modifying their lives to acknowledge the reality of climate change. For people who already acknowledge climate change as real and our contribution as key, do these extreme weather events move them to start taking stronger action?
Evan @10, that is not a rephrasing, it's more a total restructure of the question :) Still, its a good question.
I think personal upfront experience of weather becoming more extreme has to motivate some degree of action. A slap in the face like this normally motivates change, yet I do not see much evidence of "huge change". There are at least three possible explanations:
1) General reluctance to change well established habits (laziness)
2) Climate change is a gradual thing.Frog being slowly boiled alive syndrome.
3) I think this is the critical one. Fossil fuels are still the cheapest easiest fuel source for many people, and low carbon products are not common or attractively priced. Its human nature to buy the cheapest product that meets immediate needs, and somewhat irrational to do otherwise.
I deplore battery chicken farming, but I still buy the damn things. I deplore single use plastic bags, and have managed to stop that but it took me a while to get there. I dont think Im a hugely lazy or irresponsible person. On the plus side I have a small fuel efficient car, but this was a relatively pain free decision to make.
The answer to 3) should be carbon levy and dividend. This puts a price on carbon, and makes petrol unattractive, and low carbon alternatives more price competitive.
The challenge is then how do we get this carbon fee and dividend policy? Not many people are crying out for it, and not many politicians support it, except for in a few places like British Columbia. I think the reason is over the last 40 years tax has been branded as evil, and as theft and as the wrong sort of economic policy. Therefore we have made things difficult for ourselves, and I think its going to be hard work changing this mindset. But I try to remain an optimist on it.
nigelj@11 very well stated. At least, I agree. Whether or not you like Al Gore, the name of his film "An Inconvenient Truth" was brilliant.
I have worked hard to change my life to be consistent with our knowledge of Global Warming and Climate Change, but as you noted, it is really hard to do without. We are currently building a house, because we bought property 20 years ago with a 100-year old knock down house within which we've been living for 20 years. But we knew we could not live in forever because of the condition of the house. So I am very concerned about carbon expenditure to build a new house. We will put in geothermal and solar, and are making the house as small as possible, but still, it will have a carbon footprint. We are planning to plant fruit trees to compensate for the carbon emissions and get some fruit. Is that sufficient compensation for the carbon emissions to build the house?
We sold our truck and bought an electric vehicle, which we drive about 25,000 miles/year, mainly because my wife volunteers at a rollerskating rink. We have no children of our own and she is amazing working with kids. Does working with kids and helping them grow up well justify the carbon expenditure (even EVs have a carbon footprint)? In some sense I open myself up to criticism in a blog like this because I think that one of the main ways I become motivated to change is when people comment on my degree of hypocrisy. i.e., I write about climate change but am I doing my part to justify my admonitions to others?
But I think your comments nigelj are well stated.
Nigel, you don't see evidence of "huge change" because there isn't any. The depth of the denial and the strength of the entrenched interests are a perfect storm. From studying what happened in Europe in the 30s, I hold very little hope that people will wake up to the reality at hand, at least in the US, where they have been drilled ad-nauseam and where the critical thinking ability of the general population has gone down the tubes in the past 30 years. The propaganda means unleashed in the anglo-saxon world on the subject are simply staggering.
This is a crisis that would require response on a global scale, global cooperation and a mobilization of the kind we have only experienced in large scale wars before. That turns out to be something impossible to muster for the current human animal. The emotional make up of the human simply has no provision for something like that. If we were attacked by aliens and could go at it with guns, there would be no problem, but this is different. It requires a truly, and almost exclusively cooperative effort. Worse yet, it requires us to exercise restraint in our pusrsuit of material goals, while the current economy is entirely based on frantic consumption of innumerable things that we don't really need and overconsumption of the ones we do need.
What is hard for me to understand is the rapacity of the hyper rich, who are safe no matter what, but won't give up anything at all for the long term benefit of all. It's pretty obvious that is is even in their interest to do so. Of course most of them can be expected to die within the next 40 years, but still. I believe them, in fact. I believe that they're in a denial so profound as to be absolutely sincere. It is driven by emotion and mostly greed, but sincere nonetheless.
Evan, I wouldn't feel too guilty about your carbon footprint. No progress will be accomplished until coal fired power plants are displaced on a large scale. In fact, getting rid of coal burning completely and increasing transportation fuel efficiency standards for all vehicles (yes, even trucks) may be enough in the medium term to buy us time. The personal footprint argument is one used against honest folks by dishonest people; nobody can have an expectation that you'd have to live totally outside of norms, or expand all of your resources in an individual effort; that is not only unreasonable but stupid.
Evan @12, I think you are on the right path with your house. I design infrastructure. I dont want to be specific becuase I dont think discussion should be about peoples qualifications, however I know enough to comment on housing and you are on the right track. It would be damn near impossible to build a zero carbon home, so growing trees is a nice way of compensating. I dont see what more you could do.
I suggest look into passive solar design, because this minimises heat loss and heat gain. It does require thermal mass, and normally a concrete floor which is carbon intensive, but theres not much that could be done, unless you build a wooden floor overlaid with natural stone, but this is probably unrealistic.
But passive solar design can significantly reduce energy costs and sometimes all it takes is a little more glass facing the right way, some thermal mass in the floor as a heat sink, (this does mean not having carpet) good insulation etc, and so it doesn't have to cost significantly more than a standard home. Of course I sense you have probably thought about all this anyway.
But this all demonstrates a key point. Individuals cannot solve such a problem as carbon content of concrete. We are reliant on industry to reduce the carbon footprint of products, and to provide clean energy, pushed by government policy. Unfortunately theres a whole industry of climate denialism standing in the way of all this as PC points out.
Philippe Chantreau @13, I agree totally. Theres not much I can add, other than two points.
1) Humanity is not programmed to think very long term in terms of problems that affect us well in the future, and future generations. We respond best to relatively short term immediate shocks.
2)I agree government has indeed become very controlled by business lobby groups and the mega rich. I think its happened since the demise of trade unionism, and the rise of market fundamentalism. That's not to say I idolise trade unions, because I dont, but things seem to have swung to some sort of market fundamentalist extreme that has become absurd, but cracks are appearing and plenty of economists are now conceding its not working.
Not all rich people have toxic intent, and many are philanthropists, but all it takes is a few extremist ideologues to exert considerable power in critical areas, like the Koch Brothers. Some families have more wealth than entire countries, and money is power.
America has no limits on election campaign donations and spending, which means corporations and wealthy business lobbies dominate influence, and the public interest groups struggle to compete. Its hard to see how this changes and theres no organised public outcry, just simmering discontent. Problems like this tend to be solved at the 11th hour when it reaches a crisis point.
New Zealand has some campaign spending limits and stronger climate policies than America, but I admit theres a long way for us to go.
Phillipe@13 and nigelj@14 thanks for your encouragement. I will however, keep holding myself to a tightening standard, because we must. Fortunately in Minnesota 25% of our electricity is nuclear and over 20% is renewable, so driving an EV makes a lot of sense. We've communicated to our architect that low-carbon and low-energy impact is important. He seems to understand, and he even just bought an EV himself two weeks ago.
Definitely agree about passive solar design.
It's interesting that what really drove me to buy an EV was when I started writing at SkS about climate change. To me it was simply unacceptable to be writing about the urgent need for change and driving a gas hog. We still have one vehicle that burns gas, but we drive it very little. And our compact tractor burns diesel, but as soon as John Deere comes out with a compact electric tractor we will trade it in. This is one of the big problems is that it takes time to transition, even when one wants to.
By the way, take a look at CarbonCure, which is an initiative to begin decreasing the carbon footprint of concrete.
The other point here is to be an example. Hopefully, and I do me hopefully not certainly, as extreme weather events become more common place and more people are affected, more people will be open to the message of our need to reduce our carbon footprint. We have to set examples as soon as we can and as best as we can.
Evan@10: I personally think there is a big difference between talking the talk (acknowledging the climate change threat and collective responsibility), and talking the talk (making personal lifestyle changes), simply because the former is much easier to do than the latter. I have tried to reduce my carbon footprint by turning the heating right down in winter and compensating by wearing more clothes, using publicv transport where feasible instead of driving, growing my own food, recycling, reducing consumption, and cycling most local journeys and to work (20 mile round trip). The problem is that doing many of these things requires significantly more effort and less comfort, and in the worst case increased risk. I gave up driving back in 2013 and did all journeys by bicycle and/or train. To do this required living a more localised life, it was not feasible to drive 20 miles out and back to a remote area to go on a group walk. I ultimately nearly paid the price with my life whan I was hit by a careless driver and at my worst, was two days from having the life support switched off before I came out of the coma. My experience is the extreme, but even growing your own food, it is much easier to go to a supermarket for your veg than spend many hours of the week toiling away on an allotment, with pests and poor weather periodically threatening to destroy your crop. The second issue is that making those sacrifices entails the tangible drawbacks I mentioned, but any tangible benefits are far from obvious. When I cycle for utility purposes, it makes no difference to the local air pollution or traffic levels, because everyone else is still driving around, the only personal benefit being an increase in fitness and a small monetary saving. Ultimately, to advocate people changing to a lifestyle with a significantly lower carbon footprint, or more sustainable, is equivalent (at least now) to asking them to sacrifice comfort and convenience for no tangible benefit. That is always going to be a hard sell. Things might be different if the whole system was changed to something where sustainability was prioritised instead of money, but we have a long long way to go to even get close to that, and to get there is beyond the power of any one individual, hence many will say the climate change issue is the responsibility of governments and business.
Just spotted an error, I meant to say at the beginning that there is a big difference between talking the talk, and walking the walk.
alea@17 Quite a change of lifestyle. I understand your points and mostly agree. I do not bicycle because of the dangers, yet we made the change to an EV. Not perfect, not enough, but a step.
I can't argue against your points from the perspective of people choosing the easy path. This is human nature. I am changing my lifestyle because I feel it is incumbant on those of us who are leading the efforts to do so.
If people could connect the dots beween their driving and a more difficult life for their children and grand children, I think that would make a big difference in how people responded.
We also don't know what factors will cause a person to change. We may push gently for years and one day a sequence of factors may come together to cause another person to change. We must set the stage with our actions and keep the pressure on, so that when those opportunities for change come, people are somewhat prepared by positive examples of others, such as what you've been doing.
Where I respectfully differ from your view is that I see the individual action as paramount. I'm not calking about the effect of one bicycle on the rode versus thousands of cars in reducing air pollution, I'm talking more about setting the example and letting others know that the status quo is not acceptable. At a rollerskating rink where we work, a school group came in for a session and brought their own food for the kids. It inlucded some stuff they liked and some fruits and vegies a lot of the kids did not like. A lot of perfectly good food ended up in the trash. So I stood outside in the dumpster for about 30 minutes digging through the trash pulling out the good food. To me this is the worst transgression in the developed world: to throw away perfectly good food. So here I am driving a modern EV and digging through a dumpster to pull out good food. My wife started personally recylcing stuff at the rink that was being thrown away, and now others help her with the recycling effort. I think that deep down people have a sense of what is right and wrong, and they need to be pushed in the direction doing the right thing.
So I really don't disagree with your assessment that it is too easy to do the convenient thing, just saying that there is not time to wait for action to come down from on high. We must act individually if we are going to turn this thing around.
I agree those of us talking about the dangers of climate change have to try to lead by example. I have done some things. I own a small home and drive a small petrol car by choice, and I only use it a couple of times a week. Our public transport is very good. I don't fly very much
But I don't want to sound sanctimonious. Some of those decisions were made for several reasons, I can be indecisive, and I buy some utter rubbish at times, and my heaters are also not very efficient, and I never get around to doing anything about it. Etcetera.
However I dont think anyone expects people to cycle or be cold. I loathe being uncomfortable, so its off the agenda.
But here's another thing. We resolved the ozone problem by using new types of refrigerants, and it was virtuaully entirely an industry issue. Nobody expected people to go without fridges, so we have to keep the climate issue in a similar perspective.
Global warming is different. Switching refrigerants is easy compared to burning fossil fuels without producing CO2. CO2 is not a pollutant, it is simply what you get when you burn fossil fuels. There is no easy fix except to not burn fossil fuels.
Having been close witness to the Durango, Colorado area fires, Missionary Ridge 2002, this summer the 416 Fire (witnessed initial fire on both, from a distance that is), also the Burro Fire and the slightly more distant The Plateau and West Guard Fires north of Dolores.
One of the fire obvious observations is that the warmer it gets the greater the afternoon flare up and fire growth. The colder the nights, the slower the next morning's fire's return to actively growing.
The rapid ignitions are again aways related to heat, dryness, wind. Think San Rosa fire, or the 416, where a home owner saw ignition within moments and they had a small fire appliance spraying water within 5-10minutes, but the hot wind and steep slope made this Steam Train (DSNGRR) Boiler klinker started fire different from the dozens of other similiar fire starts in that area (steep uphill pull, pouring on the coals) over the past decade.
Interestingly, three additional smaller fires within sight of our cabin that were contained within a couple days±, all started in the afternoon with cooling temps, and a night for initial ground attack and preparation for the next day's fire fighter assault. (Those guys/gals do do incredibly good work)
Hmmm, how will a warming drying climate impact future wild fires?
This argument is like being caught stealing and responding with the defense, well the president steals all the time.
It's a cheap Republican rhetorical diversion.
How much of a hypocritical energy pig, or saint, you or I am - has absolutely nothing to do with recognizing and accepting the sober facts of manmade global warmer. NOTHING!
I just finished a pretty good (other's judgement) essay that explores this issue a bit more concretely
(@ 22, Santa Rosa, CA)