Each year landscape fires across the globe emit black and organic carbon smoke particles that can last in the atmosphere for days to weeks. We characterized the climate response to these aerosols using an Earth system model. We used remote sensing observations of aerosol optical depth (AOD) and simulations from the Community Atmosphere Model, version 5 (CAM5) to optimize satellite-derived smoke emissions for high biomass burning regions. Subsequent global simulations using the adjusted fire emissions produced AODs that were in closer agreement with surface and space-based measurements. We then used CAM5, which included radiative aerosol effects, to evaluate the climate response to the fire-aerosol forcing. We conducted two 52 yr simulations, one with four sets of monthly cycling 1997–2009 fire emissions and one without. Fire emissions increased global mean annual AOD by 10% (+0.02) and decreased net all-sky surface radiation by 1% (1.3 W m⁻²). Elevated AODs reduced global surface temperatures by 0.13 ± 0.01 °C. Though global precipitation declined only slightly, patterns of precipitation changed, with large reductions near the Equator offset by smaller increases north and south of the intertropical convergence zone (ITCZ). A combination of increased tropospheric heating and reduced surface temperatures increased equatorial subsidence and weakened the Hadley circulation. As a consequence, precipitation decreased over tropical forests in South America, Africa and equatorial Asia. These results are consistent with the observed correlation between global temperatures and the strength of the Hadley circulation and studies linking tropospheric heating from black carbon aerosols with tropical expansion

During the dry season, anthropogenic fires in tropical forests and peatlands of equatorial Asia produce regionally expansive smoke clouds that have important effects on atmospheric radiation and air quality. Here we estimated the height of smoke on Borneo and Sumatra and characterized its sensitivity to El Niño and regional drought. We used Multiangle Imaging Spectroradiometer (MISR) satellite data and the MISR Interactive Explorer (MINX) software to estimate the heights of 317 smoke plumes on Borneo and 139 plumes on Sumatra during 2001–2009. In addition, we estimated the altitudes of larger smoke regions (smoke clouds) over Borneo using data from MISR and Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) products. Most smoke plumes on Borneo (83%) were observed during El Niño years. Annually averaged plume heights on Borneo were significantly higher during El Niño events. Mean MISR‐derived plume heights were 709 ± 14 m on Borneo and 749 ± 24 m on Sumatra during 2001–2009, with 96% of all plumes confined to within 500 m of the atmospheric boundary layer. Smoke clouds on Borneo were observed at altitudes between 1000 and 2000 m as measured by both MISR and CALIPSO. The difference in height between individual plumes and longer‐lived regional smoke clouds may be related to deeper planetary boundary layers and higher‐intensity fires later in the afternoon or other atmospheric mixing processes that occur on synoptic time scales. Our measurements and analyses suggested that direct injection of smoke into the free troposphere within fire plumes was not an important mechanism for vertical mixing of aerosols in equatorial Asia.

We present an analysis of over 23,000 globally distributed wildfire smoke plume injection heights derived from Multi-angle Imaging SpectroRadiometer (MISR) space-based, multi-angle stereo imaging. Both pixel-weighted and aerosol optical depth (AOD)-weighted results are given, stratified by region, biome, and month or season. This offers an observational resource for assessing first-principle plume-rise modelling, and can provide some constraints on smoke dispersion modelling for climate and air quality applications. The main limitation is that the satellite is in a sun-synchronous orbit, crossing the equator at about 10:30 a.m. local time on the day side. Overall, plumes occur preferentially during the northern mid-latitude burning season, and the vast majority inject smoke near-surface. However, the heavily forested regions of North and South America, and Africa produce the most frequent elevated plumes and the highest AOD values; some smoke is injected to altitudes well above 2 km in nearly all regions and biomes. Planetary boundary layer (PBL) versus free troposphere injection is a critical factor affecting smoke dispersion and environmental impact, and is affected by both the smoke injection height and the PBL height; an example assessment is made here, but constraining the PBL height for this application warrants further work.