Historical and future anthropogenic warming effects on droughts, fires and fire emissions of CO2 and PM2.5 in equatorial Asia when 2015-like El Ninõ events occur

Abstract

In 2015, El Nino contributed to severe droughts in equatorial Asia (EA). The severe droughts enhanced fire activity in the dry season (June.November), leading to massive fire emissions of CO2 and aerosols. Based on large event attribution ensembles of the MIROC5 atmospheric global climate model, we suggest that historical anthropogenic warming increased the chances of meteorological droughts exceeding the 2015 observations in the EA area.We also investigate changes in drought in future climate simulations, in which prescribed sea surface temperature data have the same spatial patterns as the 2015 El Nino with long-term warming trends. Large probability increases of stronger droughts than the 2015 event are projected when events like the 2015 El Nino occur in the 1.5 and 2.0 °C warmed climate ensembles according to the Paris Agreement goals. Further drying is projected in the 3.0 °C ensemble according to the current mitigation policies of nations. We use observation-based empirical functions to estimate burned area, fire CO2 emissions and fine (<2.5 μm) particulate matter (PM2.5) emissions from these simulations of precipitation. There are no significant increases in the chances of burned area and CO2 and PM2.5 emissions exceeding the 2015 observations due to past anthropogenic climate change. In contrast, even if the 1.5 and 2.0 °C goals are achieved, there are significant increases in the burned area and CO2 and PM2.5 emissions. If global warming reaches 3.0 °C, as is expected from the current mitigation policies of nations, the chances of burned areas and CO2 and PM2.5 emissions exceeding the 2015 observed values become approximately 100 %, at least in the single model ensembles. We also compare changes in fire CO2 emissions due to climate change and the land-use CO2 emission scenarios of five shared socioeconomic pathways, where the effects of climate change on fire are not considered. There are two main implications. First, in a national policy context, future EA climate policy will need to consider these climate change effects regarding both mitigation and adaptation aspects. Second is the consideration of fire increases changing global CO2 emissions and mitigation strategies, which suggests that future climate change mitigation studies should consider these factors.