Biomass burning can affect climate via the emission of aerosols and their subsequent impact on radiation, cloud microphysics, and surface and atmospheric albedo. Biomass burning emissions (BBEs) over the boreal region have strongly increased during the last decade and are expected to continue increasing as the climate warms. Climate models simulate aerosol processes, yet historical and future Coupled Model Intercomparison Project (CMIP) simulations have no active fire component, and BBEs are prescribed as external forcings. Here, we show that CMIP6 used future boreal BBEs scenarios with unrealistic near-zero trends that have a large impact on climate trends. By running sensitivity experiments with ramped up boreal emissions based on observed trends, we find that increasing boreal BBEs reduces global warming by 12% and Arctic warming by 38%, reducing the loss of sea ice. Tropical precipitation shifts southward as a result of the hemispheric difference in boreal aerosol forcing and subsequent temperature response. These changes stem from the impact of aerosols on clouds, increasing cloud droplet number concentration, cloud optical depth, and low cloud cover, ultimately reducing surface shortwave flux over northern latitudes. Our results highlight the importance of realistic boreal BBEs in climate model simulations and the need for improved understanding of boreal emission trends and aerosol–climate interactions.

中文翻译：

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北方火灾的增加减少了未来的全球变暖和海冰损失

生物质燃烧可以通过气溶胶的排放及其对辐射、云微物理以及地表和大气反照率的后续影响来影响气候。在过去十年中，北方地区的生物质燃烧排放 （BBE） 大幅增加，预计随着气候变暖，排放量将继续增加。气候模型模拟气溶胶过程，但历史和未来的耦合模型比较计划 （CMIP） 模拟没有活跃的火灾成分，BBE 被规定为外部强迫。在这里，我们表明 CMIP6 使用了未来的北方 BBE 情景，这些情景具有不切实际的接近零的趋势，对气候趋势有很大影响。通过根据观察到的趋势对增加的北方排放进行敏感性实验，我们发现增加北方 BBE 可将全球变暖降低 12%，将北极变暖降低 38%，从而减少海冰的损失。热带降水向南移动是由于北方气溶胶强迫和随后的温度响应的半球差异。这些变化源于气溶胶对云的影响，增加了云滴数量浓度、云光学深度和低云覆盖，最终减少了北纬地区的表面短波通量。我们的结果强调了现实北方 BBE 在气候模型模拟中的重要性，以及提高对北方排放趋势和气溶胶-气候相互作用的理解的必要性。