How do we know wildfires are made worse by climate change?

A header image of a forest fire

In 2019 Australia was burning. In 2020 Siberia and California were burning. These are only the more recent examples of dramatic extreme wildfire. People are asking if forest fires are linked to climate change.

The experts tell us that yes, the growing extent and increasing severity of wildfires are indeed driven by climate change.

Warmer temperatures mean higher evaporaton rates – things dry out more quickly, just like your laundry. With that comes drier vegetation that is more likely to burn if anything sparks a flame. In many cases flame is sparked accidently by humans but climate change has also tended to increase the kinds of storms that include lightning. So the changing climate has not only added more tinder but also added more spark.

There have always been wildfires and in most places in the world these have been seasonal. Climate change has tended to lengthen fire seasons. In this way even if the probability of a fire on any given day remained unchanged, there are now more days where fire is a possibility. So that ups the chances.

Climate change has also influenced the likelihood of drought. Not only is vegetation getting drier with warmer temperatures but lack of rainfall can double down on that drying.

Many other factors both related and unrelated to climate change also influence fire severity. For example whether a forest has a lot of dead wood can make a difference. Decades of successful fire suppression can lead to a buildup of fuel and that’s certainly not the fault of climate change. But insects such as the Northern Pine Beetle can turn huge swathes of forest into standing deadwood. The proliferation of insects like these certainly has been linked to the warmer winters associated with climate change. The bugs thrive in the summers and don’t die off as much in the winters because the freezes aren’t as cold as they used to be.

It takes a lot of expertise to be able to determine which factors dominate and to what degree the changing climate is playing a role.

People with wildfire expertise come with a range of backgrounds, motivations and experience. Examples include PhD researchers; actuaries calculating insurance risk; and government employees trying to manage publicly owned forests, or allocating firefighting services. This diversity of expertise will mean that there is a range of opinion on how climate change relates to the frequency and severity of wildfire.

But the best of experts know that the truth lies in facts not opinion. Because it is not simple to tell what all the facts are, or which facts outweigh others, experts seek consensus. They explore which points they collectively agree on when it comes to climate change’s influence on forest fires.

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On the facts of climate change there is one preeminent forum where experts establish consensus. It’s called the Intergovernmental Panel on Climate change, also known as the IPCC. The process they use to achieve consensus is extraordinary and the results achieved irrefutable. The IPCC has been refining and expanding its consensus for more than 30 years.

Founded in 1988, the IPCC’s very first report in 1990 found that that “losses from wildfire will be increasingly extensive.”

More recently the IPCC’s 2019 report Climate Change and Land confirmed that statistics on forest fires show that fire seasons are getting longer and forest fires are becoming bigger and are burning more land.

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Not only does the IPCC find that this is a consequence of the greenhouse gases which we humans have added to the atmosphere, but their reports remind us that the burning of all those trees adds even more greenhouse gas. The carbon dioxide from burning only increases the effects of climate change which intensified the fires in the first place.

To come to its consensus the IPCC relies on volunteers drawn from among the world’s existing experts. They gather and review all that is known about climate change. This includes causes and effects. It includes ways to manage climate change and manage the problems climate change causes, including wildfires. The IPCC assess and summarize what all that accumulated knowledge means. This is done by drawing on studies published in the peer reviewed scientific literature and by calling on other world experts to contribute other information that might have been missed. For any given IPCC report hundreds of experts are involved, over the history of the IPCC many thousands.

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Once the volunteer IPCC authors have worked out what they think it all means and written down their findings, they then invite world experts to comment on the draft report. For a big report like the 2014 Fifth Assessment Report – which examined topics far beyond wildfire – this generated more than 140,000 reviewer comments. All these comments have to be taken into account in writing the final report. As if that wasn’t enough, the IPCC then gathers world experts in plenary meetings where they hammer out line-by-line and word-by-word their agreed-on text. And it isn’t just the scientific experts involved either. Official observers from industry and environmental groups play a role. Government representatives from the 195 member nations of the IPCC participate throughout, culminating in accepting the report as representing the world consensus. So an IPCC report is not only a consensus among the world’s scientists but also an official consensus among the world’s governments.*

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The book Because IPCC is a short, 33 illustrated pages. It’s upbeat, entertaining story explains the history and science of the IPCC. The scene is 100 years in the future when the world has “solved” climate change and people are looking back, inspired by the dedication, rigor and achievements of the scientists of today.

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* 195 member nations of the IPCC is two countries more than the 193 members of the United Nations – so virtually every nation in the world is represented.