A forest fire is likely to rage almost everywhere

Humans have raised CO2 levels in the atmosphere to 50% above what they were before the industrial revolution. As a result, the world has already warmed by 1.1°C over the past century and reports indicate that it could reach 2.7°C of warming by the end of this century.

Episodes of severe drought, heat and low humidity become more extreme as the climate warms. As climate change makes hot, dry conditions – often called “fire weather” – more common and more severe, vegetation dries out and landscapes become more flammable, increasing the risk of dangerous wildfires. Scientists can measure changes in fire weather (temperature, humidity, precipitation, and wind) to assess the danger level of a wildfire.

In a new global analysis, we found that in many parts of the world, the rate at which fire-prone weather conditions are increasing is accelerating faster than climate models predicted. We used weather observations and climate models to assess historical and future trends in fire weather to discover how conditions are changing in specific countries and regions. We also analyzed data from other recent studies to assess the likelihood that future changes in fire weather will lead to more wildfires, based on the relationships between fire and climate, human land use and changes in plant growth. We have found that the length of the fire weather season (when most fires tend to occur) has already lengthened considerably in many regions since the 1980s. On average, this season has lengthened by 27 % globally, but increases have been particularly pronounced in the Amazon, Mediterranean, and forests of western North America.

The number of days with extreme fire-related weather – when temperatures are particularly high, recent rainfall and humidity are particularly low, and winds are capable of fanning a fire – has become 54% more common globally . For this reason, larger and more severe fires that are difficult to contain are now more likely than they were in the past. This is one of the reasons why some of the recent fires in the western United States or Australia have been so widespread and so devastating. More extreme fires burn more vegetation, taking a heavy toll on ecosystems and emitting more CO2 into the atmosphere. We also predicted that the influence of climate change on fire weather will intensify in the future, with each additional degree of global warming dramatically increasing the risk of wildfires by preparing the landscape to burn. If global temperatures reach more than 2°C above the pre-industrial average, fire weather patterns will be virtually unrecognizable compared to those in recent history for most parts of the world.

Human actions strongly affect the chances of hazardous weather conditions causing a wildfire, either pushing or pulling against the effects of climate change. Human-caused fires are particularly relevant outside the vast forests of northern Eurasia and North America, where there are few dense population centers and many fires are ignited by lightning. Closer to towns and settlements, sparks from faulty power lines or agricultural machinery, arson or the use of fire to burn agricultural or forestry residues, for example, increase the risk of forest fires. But people have also inadvertently made large conflagrations less likely by making it harder for wildfires to spread through naturally fire-prone landscapes. This includes, for example, the conversion of forests to agricultural land or the destruction of highly flammable grassy vegetation in savannahs in Africa, Brazil and northern Australia.

The common approach to fighting fires in naturally fire-prone landscapes—applied in many parts of the United States, Australia, and Mediterranean Europe—may suppress fires for a while, but these forests eventually accumulating excessive plant fuel, which contributed to more severe wildfires. , especially in times of drought. Although the weather conditions conducive to wildfires are on an upward trajectory in almost all regions of the world, human actions continue to mitigate or supplant the climatic influence in many regions. This may sound encouraging, but the effectiveness of human efforts to mitigate the role of climate change decreases with each additional decimal of a degree of warming.

It is difficult to predict how climate change and human activity will affect future wildfire risk around the world, but one aspect is very clear. Slowing and reversing the buildup of CO2 and other greenhouse gases in the Earth’s atmosphere will slow the acceleration of wildfire risk. Not keeping global warming below 2°C, the minimum goal of the Paris Agreement, has a dangerous price: unprecedented wildfire risks on the world stage. What we do next matters.

((Written by Stefan H Doerr, Swansea University; Cristina Santín, John Abatzoglou, University of California; Matthew William Jones, University of East Anglia and Pep Canadell, CSIRO; The Conversation)