BLACK CARBON: Climate Impact of Bushfire in Australia
Porter, Stephen D.
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Fire is a ubiquitous feature of the Australian landscape – characteristics of natural flora suggest that fire has been commonplace since well before the arrival of man some 40,000 years ago. Emissions from bushfire at a continental scale, specifically those of Black Carbon, are not well known and are not included in carbon accounting protocols as they arise from natural, rather than anthropogenic, sources. Impact of climate change on bushfire emissions trajectories, and the feedback potential those same emissions have upon climate, are also not fully understood. This research aimed to at least partially address these gaps in current knowledge through a bottom-up, continental-scale analysis of bushfire in Australia, from April 2000 to May 2013, and then projected that activity onto possible futures for the year 2050. Monthly bushfire burn areas from the MODIS Burned Area Product were aggregated into calendar years and the resultant GHG and Black Carbon emissions fractions converted to CO2 equivalent values for comparison to national accounts and global estimates. With considerable annual and monthly variability in fire activity, identified as primarily correlated to precipitation in the wet season, a mean annual area of almost 6% of Australia is burnt each year. On average, sufficient annual CO2 equivalent emissions of Black Carbon (303 Mt CO2e) and methane (61 Mt CO2e) were calculated that, taken together, nearly doubled Australia’s officially reported accounts for 2010 (434 Mt CO2e). Scenario analysis via the OzClim tool generated nine distinct mean annual precipitation patterns for Australia in the year 2050. These scenarios were converted into unique, countrywide estimates of biomass densities, and the emissions analysis was rerun for each. By holding the historically observed bushfire activity constant, it was observed that average annual emissions in 2050 ranged from 20% less than the 13-year historical mean to 3% greater. The analysis also showed that vegetation patterns in the various scenarios for 2050 could greatly differ from the current distribution, with losses of 9-75% of the area that supports the highest biomass densities. Biome shifts in the Australian landscape are thus a very real possibility. Australia has set itself some challenging reductions targets to achieve by 2020 – equivalent 18% below 2000 levels. A history of ever-rising emissions, and inconsistency and uncertainty surrounding national climate change policy suggest it will be difficult to achieve success. Finally, even should Australia meet their own targets, unless other key emitters do likewise, the trajectory of bushfire emissions in Australia look set to continue, and possibly rise, as global climate change further impacts the continent Down Under.