What are the links between climate change and bushfires? – explainer

Extract from The Guardian

Bushfires

Temperature, fuel load, dryness, wind speed and humidity all affect fire risk and are compounded by global heating

Mon 11 Nov 2019 10.32 AEDT Last modified on Mon 11 Nov 2019 13.24 AEDT

A firefighter works to contain a bushfire near Taree, New South Wales, on Sunday. Scientists agree there is a link between climate change and wildfires. Warmer weather increases the number of days each year on which there is high or extreme bushfire risk. Photograph: Darren Pateman/EPA

The link between rising greenhouse gas emissions and increased bushfire risk is complex but, according to major science agencies, clear. Climate change does not create bushfires but it can and does make them worse. A number of factors contribute to bushfire risk, including temperature, fuel load, dryness, wind speed and humidity.

What is the evidence on rising temperatures?

The Bureau of Meteorology and the CSIRO say Australia has warmed by 1C since 1910 and temperatures will increase in the future. The Intergovernmental Panel on Climate Change says it is extremely likely increased atmospheric concentrations of greenhouse gases since the mid-20th century is the main reason it is getting hotter. The Bushfire and Natural Hazards research centre says the variability of normal events sits on top of that. Warmer weather increases the number of days each year on which there is high or extreme bushfire risk.

What other effects do carbon emissions have?

Dry fuel load – the amount of forest and scrub available to burn – has been linked to rising emissions. Under the right conditions, carbon dioxide acts as a kind of fertiliser that increases plant growth.

So is climate change making everything dryer?

Dryness is more complicated. Complex computer models have not found a consistent climate change signal linked to rising CO2 in the decline in rain that has produced the current eastern Australian drought. But higher temperatures accelerate evaporation. They also extend the growing season for vegetation in many regions, leading to greater transpiration (the process by which water is drawn from the soil and evaporated from plant leaves and flowers). The result is that soils, vegetation and the air may be drier than they would have been with the same amount of rainfall in the past.

What do weather patterns show?

The year coming into the 2019-20 summer has been unusually warm and dry for large parts of Australia. Above-average temperatures now occur most years and 2019 had the fifth-driest start to the year on record, and the driest since 1970. Australia recorded its hottest month in January 2019, its third-hottest July and its hottest October day in some areas, among other temperature records.