What is the impact of increasing boreal forest fires on Arctic climate and sea ice?

北方森林火灾的增加对北极气候和海冰有何影响？

• 批准号: 2337045
• 负责人: Edward Blanchard-Wrigglesworth
• 金额: $ 34.33万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2024
• 资助国家: 美国
• 起止时间: 2024-04-01 至 2027-03-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2337045&HistoricalAwards=false
• 关键词: What; impact; increasing; boreal; forest

Boreal forests cover large areas of northern Asia and North America, mainly over Siberia, Canada, and Alaska. In recent years, these forests have been affected by an increase in fires, caused in part by warmer summers and less snow in the spring. These fires emit large amounts of smoke which can be blown by winds northward to the Arctic. Once this smoke gets to the Arctic, it can both cool the climate by reflecting sunlight, but also warm it (if the smoke is nearer the surface, or if the small smoke particles reach the ice and snow on the surface, as they can darken it and absorb more sunlight). As we expect temperatures to continue to warm everywhere on the planet, it is likely that large boreal fires will continue and even become more common. We plan to study the impact that the smoke may have on Arctic climate and sea ice using climate models. In the past, these climate models have not taken into consideration an increase in these boreal fires, and our work will help us determine if this is an important process to get right for understanding future changes in Arctic climate and sea ice. As we prepare for the next generation of climate models that help inform the United Nations’ panel on climate change, our results will also help highlight the importance boreal forest fires may have for climate change in the Arctic.Biomass burning from boreal forest fires can impact Arctic climate and sea ice via the atmospheric transport of aerosols, particularly black carbon, from source regions into the Arctic. While in the atmosphere, aerosols can have either a positive (warming) or negative (cooling) radiative forcing, depending on their elevation. Black carbon can also be deposited onto the sea ice or snow at the surface, where it has a positive radiative forcing because it darkens it and absorbs more sunlight. While fully coupled climate models simulate these processes, the amount of biomass burning is prescribed as a set forcing. In the most recent set of climate model runs that help inform the United Nations’ panel on climate change, simulations from 2015 to 2100 used fixed projections of boreal biomass burning emissions that did not anticipate an increase in forest fires. However, in the real world we have observed a dramatic increase in boreal biomass burning over the last 10 years, in part due to warmer summers and reduced spring snow cover (which itself is driven by warmer springs), and the emissions of black carbon are already more than double what the climate models used over 2015-2100. We plan to study the impact that an increase in boreal biomass burning has on Arctic climate and sea ice by running climate model simulations that prescribe an increase in aerosol emissions based on the recent observed growth in these fires. We also plan to study the impact that wind patterns have on the transport of smoke from boreal forest fires, as it is known that certain weather patterns can promote the likelihood of forest fires. This coupled interaction between weather and fires is currently missing in climate models, and our work will help us determine how important winds, in addition to the amount, severity and seasonality of fires are in determining how much black carbon is transported into the Arctic. Our results will serve to inform stakeholders of the importance of boreal forests for Arctic climate in the coming decades. As the community prepares for the next round of climate model simulations, our results will help inform the modeling community on the importance of both increasing boreal forest fires and the interaction of fires and winds on Arctic climate and sea ice.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

北方森林覆盖了亚洲北部和北美的大片地区，主要在西伯利亚、加拿大和阿拉斯加。近年来，这些森林受到火灾增加的影响，部分原因是夏季温暖和春季降雪减少。这些火灾释放出大量的烟雾，这些烟雾可以被风吹向北方的北极。一旦这种烟雾到达北极，它既可以通过反射阳光来冷却气候，也可以使气候变暖（如果烟雾靠近地表，或者如果小烟雾颗粒到达地表的冰雪，因为它们可以使其变暗并吸收更多的阳光）。由于我们预计地球上的气温将继续变暖，北方地区的大火很可能会继续下去，甚至变得更加普遍。我们计划利用气候模型研究烟雾对北极气候和海冰的影响。在过去，这些气候模型没有考虑到这些北方火灾的增加，我们的工作将帮助我们确定这是否是一个重要的过程，以正确理解北极气候和海冰的未来变化。在我们为下一代气候模型做准备的同时，我们的结果也将有助于强调北方森林火灾对北极气候变化的重要性。下一代气候模型将为联合国气候变化专门委员会提供信息。北方森林火灾燃烧的生物质可以通过气溶胶（特别是黑碳）从源区进入北极的大气运输影响北极气候和海冰。而在大气中，气溶胶可以产生正（变暖）或负（变冷）的辐射强迫，这取决于它们的高度。黑碳也可以沉积在海面的海冰或雪上，在那里它具有正的辐射强迫，因为它使其变暗并吸收更多的阳光。虽然完全耦合的气候模式模拟这些过程，但生物质燃烧的量被规定为一组强迫。在联合国气候变化专门委员会最新的一套气候模型运行中，2015年至2100年的模拟使用了北方生物质燃烧排放的固定预测，没有预测森林火灾的增加。然而，在现实世界中，我们观察到在过去10年里，北方生物质燃烧急剧增加，部分原因是夏季变暖和春季积雪减少（这本身是由春季变暖驱动的），黑碳排放量已经是2015-2100年气候模型使用的两倍多。我们计划研究北方生物质燃烧的增加对北极气候和海冰的影响，通过运行气候模型模拟，根据最近观察到的这些火灾的增长，预测气溶胶排放的增加。我们还计划研究风模式对北方森林火灾产生的烟雾运输的影响，因为众所周知，某些天气模式会增加森林火灾的可能性。天气和火灾之间的这种耦合相互作用目前在气候模型中是缺失的，我们的工作将帮助我们确定，除了火灾的数量、严重程度和季节性外，风在决定有多少黑碳被输送到北极方面有多重要。我们的研究结果将有助于向利益攸关方通报未来几十年北方森林对北极气候的重要性。随着社区为下一轮气候模型模拟做准备，我们的结果将有助于告知建模社区，北方森林火灾的增加以及火灾和风对北极气候和海冰的相互作用的重要性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。