Psychological research confirms what I have observed anecdotally – that people prefer simple answers to complex ones, and will often settle on a single cause of even complex events. This is why I often jokingly answer questions of, “Is the cause A, B, or C,” with “yes.” That is usually the correct (if unsatisfactory) answer, all of the options are correct to some degree. Assuming there is “one true cause” can also be considered a false choice fallacy, or a false dichotomy.

I most recently did this when asked if the increase in wildfires were are currently experiencing on the West Coast of the US are caused by global warming or bad forest management. The experts agree that both contribute, and a new review of the literature sheds some additional light on this question. The authors reviewed over 100 studies published since 2013. This same group published an earlier review on the causes of the Australian wild fires last year. The conclusion of the new review is that global warming has had an “unequivocal and pervasive” role in increasing the conditions that contribute to wild fires.

As they say, this is not rocket surgery. As the weather gets warmer we are experiencing a greater portion of the year with high temperatures, lower humidity, decreased rain, and increased winds. These are all conditions that contribute to starting and spreading wildfires, making them more likely and more intense when they occur. The result has been the worst fire season on record, with three of the four worst individual fires occurring this year.

Stepping back a bit to the bigger question – is there global warming – this fire season adds to the growing evidence that there clearly is. Average temperatures are increasing with the top 10 warmest years on record all being since 1998, with 2016 being the warmest. It is too early to tell for sure, but 2020 is on track to being one of the warmest years on record as well, and may even break the record as the warmest. Further, global ice is decreasing steadily. Hurricanes are getting stronger. Flooding is increasing. And of course, wild fires are increasing. You could claim that any one of these is a coincidence, or has a separate explanation. But given the totality of evidence, that amounts to little more than special pleading. Climate models predicted all of these things, and they are all happening. Trying to write off each individual item (and others I didn’t mention) may work rhetorically with some, but only when looked at in isolation. The probability that so many events predicted by climate scientists as a result of global warming are actually happening is not some grand coincidence or conspiracy. The Earth is warming.

But as I said, both answers are true; forest management is also playing a role in the increased wild fires. Primarily this is due to the build up of fuel, dead twigs and branches and fallen trees that are combustible. Prior to human intervention, large forests would regularly experience wild fires, which would burn this fuel. Plants adapted to this cycle, with the forest rebounding after burning, and some plants even evolving to depend on occasional fire. Natural forests in this way reach an equilibrium point.

Humans, however, interfere with this natural equilibrium, primarily because we build structures in and near forests, or we log them for lumber. This creates an incentive to prevent forest fires. Certainly it is reasonable to prevent artificial fires started through negligence, like improperly extinguished camp fires. But rapidly putting out wild fires disrupts the natural equilibrium. This allows for fuel to build up on the forest floor, and then when a fire does occur it can be much greater.

So, over the years we have engaged in forest management to restore a new equilibrium, which involves doing prescribed burning – deliberately setting fires during the wet season, and controlling the burn so it does not get out of control. This burns up a lot of the fuel, and keeps it in check. So what’s the problem? There are a few trends contributing poor forest management. One is encroaching civilization, what experts call “wilderness-urban interface”. Building small towns deep in forests makes it more difficult to do prescribed burning, and may make it more difficult to fight fires when they do occur.

But also we need to do a better job at forest management. This is a complex topic, but here are some issues. Making a forest more fire resistant is about more than just removing wood. Logging, in fact, may remove the larger trees that are relatively fire resistant. More precise “thinning” needs to be done, leaving in place wood that is important for the ecosystem while removing what is most likely to catch or spread fire. So part of the solution is to simply do more science-based and effective forest management, but this is often complicated by other interests, such as logging.

But there is another Catch-22 that likely contributed to the recent terrible fire seasons. Doing prescribed burning occurs not during fire season, which is important to help control the burns. So, you can’t do prescribed burning during fire season. But fire season is getting longer and longer with global warming, and the off season is getting shorter and shorter. Some experts argue that there is simply not enough time between fire seasons to do enough prescribed burning. In fact some worry we are getting close to the point that it will always be fire season.

This, of course, is not just a US phenomenon. In 2019 wildfires raged through Australia. Right now Brazil is seeing unprecendented wild fires. This is also not just a forest phenomenon, with some fires starting and spreading through grassland.

So yes, the challenges of forest management, and some policy choices, are responsible for the severity of the wild fires. But that is not the whole story. Global warming is also a significant contributor, and is also making proper forest management more challenging.