Media release
From: Summary for journalists written by Pep Canadell from CSIROGlobal/Australia Highlights
- Globally, the length of the annual fire weather season (number of days per year) has increased by 14 days per year (27%) during 1979-2019 on average and the frequency of days with extreme fire weather has increased by 10 days per year (54%) during 1979-2019 on average globally.
- Fire weather has risen significantly in most world regions since the 1980s. Increases have been particularly pronounced in western North America, Amazonia and the Mediterranean. Fire weather has already emerged beyond its natural variability in the Mediterranean and Amazonia due to historical warming.
- For the whole of Australia, the length of fire weather season has increased from 100 days four decades ago to 130 days in 2019. Days of extreme fire weather has increased by 56% during the same period. All statistically significant trends.
- Days with fire weather in Australia’s southeast forest region has also been increasing, and in fact faster than models predict (see figure; red observed, blue modelled). We found a significant increasing in number of days with fire weather of +48 (that is, additional 24 days year-1) and non-significant (because inherent high year to year variability) increases in extreme fire weather of +52%; (11 days year-1) during 1979-2019.
- Despite the predicted increases, a clear (statistically significant) signature of human climate change on the increase days of fire weather does not emerge from the high background variability until past mid-century. This is due to the inherent high climate variability of the region and therefore highly variable fire weather conditions year-to-year driven by large climate phenomena (eg, El Nino Southern Oscillation, Southern Annular Mode and Indian Ocean Dipole).
- These fire weather trends have already translated into increasing burned area in Australia. A separate continental analysis (published in November 2021) using three burned area datasets had detected a statistically significant linear increase in annual burned area of forests in Australia over the past three decades, and an exponential growth in forest burned area during the cool seasons of autumn and winter (a time in the past when relative few wildfires occurred) (https://www.nature.com/articles/s41467-021-27225-4). This is burned area and therefore real fire activity and impacts, not just fire weather as with the above statistics.
- The global analysis confirms that several of the major wildfires experienced across many regions of the world in recent years, including the Australian bushfires of 2019/2020, have occurred amidst fire weather conditions that were considerably more likely due to climate change.
- At 2°C this will also be the case in the boreal forests of Siberia, Canada and Alaska and the temperate forests of the western US. At 3°C, virtually all world regions will experience unprecedented fire weather.
- Globally, the area burned by fires has decreased by around one-quarter – or 1.1 million km2 – during 2001-2019. Much of the decrease – 590,000 km2 – has been in African savannahs, where 60-70% of the area burned by fire occurs annually. Local/regional human impacts have reduced the area burned by fire in tropical savannahs, in combination with lower grassland productivity during (increasingly drier) wet seasons.
- Large increases in burned area have been observed elsewhere, and especially in temperate and boreal forests. For example, the area burned by fire has increased by 21,400 km2 (93%) in east Siberian forests and by 3,400 km2 (54%) in the forests of western North America (Pacific Canada and US combined). See separate analysis for Australia in link provided above.