Impact of the biosphere on atmospheric aerosol and climate

理解气候变化是当今科学面临的最重要的挑战之一。大气颗粒(气溶胶)对地球有重要的降温影响，部分抵消了工业时期温室气体变暖的影响。对这种气溶胶冷却进行量化是对气候变化做出更准确预测的关键一步。在评估人为(人造)颗粒物排放的气候影响方面已经做出了相当大的努力。这项建议侧重于天然生物气溶胶，但对其研究要少得多，对此也知之甚少。然而，我们需要了解自然情况，才能充分了解人类正在如何改变大气和气候。植被向大气中排放有机物种(众所周知的森林松树气味的原因)，在那里它们可以反应形成颗粒。植物还会直接释放出花粉和真菌孢子等颗粒。观测表明，这些自然的生物气溶胶排放可以控制大部分大气中的总颗粒物负荷。这些颗粒通过反射阳光和使云层更厚、更具反射性来冷却气候。我们还知道，雨滴在这些微小的生物颗粒上形成，因此它们可以在控制全球降雨模式方面发挥作用。尽管有如此明显的重要性，但目前的气候模型对生物颗粒源的代表性非常有限，因此它们对调节气候的重要性并不为人所知。随着气候变化，生态系统将做出反应：光合作用等植物活动被改变，植被分布发生变化。这些变化改变了生物来源的气溶胶排放，改变了大气中颗粒物的数量，从而影响了气溶胶的冷却。这样的气候反馈可能会抑制或放大人为的全球变暖。也就是说，随着世界变暖，来自森林的颗粒物排放可能会增加，有助于冷却气候。通过这种方式，森林可以充当全球的“空调”。但我们不知道这种影响有多重要，因为这些相互作用还没有被气候模型所处理。热带森林砍伐正在迅速改变土地覆盖，但对气候的影响并不为人所知，因为气候模型没有处理植被和气候之间所有必要的相互作用。有意改变土地使用以减缓气候变化也是有兴趣的。例如，植树造林将二氧化碳吸收到植被中，并可用作碳汇，以抵消化石燃料使用造成的温室气体排放。但这种土地利用变化对气候的影响鲜为人知。最近的研究表明，高纬度地区(例如欧洲)的植树造林实际上可能会使气候变暖，因为黑暗的森林植被比白雪覆盖的农田吸收更多的阳光。但这些之前的研究忽略了森林中的颗粒物排放及其对气候的影响。我自己的研究表明，这些来自森林的颗粒物导致了一种重要的降温，这可能在土地利用变化的净气候影响中发挥重要作用。在这个联谊会中，我将大大提高我们对生物圈中的自然粒子的理解。我将首次在气候模型中包括对植被颗粒排放的全面处理。我将回答陆地生物圈排放如何调节全球气溶胶和气候的根本问题。最后，通过对不同生态系统-气候相互作用的综合评估，我将提高我们对土地利用变化如何改变气候的理解。

Understanding climate change is one of the most important challenges facing science today. Atmospheric particles (aerosols) have an important cooling impact on the Earth, partly counteracting greenhouse gas warming over the industrial period. Quantifying this aerosol cooling is a critical step to making more accurate predictions of climate change. Considerable effort has been put into assessing the climate impact of anthropogenic (man-made) particle emissions. This proposal focuses on natural biogenic aerosol, which has been much less studied and is poorly understood. However, we need to understand the natural situation before we can fully understand how mankind is changing the atmosphere and the climate. Vegetation emits organic species to the atmosphere (the cause of the well known forest pine smell) where they can react to form particles. Vegetation also directly emits particles such as pollen and fungal spores. Observations have shown that these natural biogenic aerosol emissions can dominate the total particle load in much of the atmosphere. The particles cool the climate by reflecting sunlight and by making clouds thicker and more reflective. We also know that rain droplets form on these tiny biological particles and so they can play a role in controlling worldwide rainfall patterns. Despite such obvious importance, current climate models have a very limited representation of biological particle sources and so their importance for regulating climate is not well known. As the climate changes ecosystems will respond: plant activity such as photosynthesis is modified and vegetation distributions are changed. These changes modify biogenic aerosol emissions changing the amount of particles in the atmosphere with consequent impacts on aerosol cooling. Such climate feedbacks may dampen or amplify anthropogenic global warming. That is, as the world warms particle emissions from the forests may increase helping to cool the climate. In this way forests may act as a global 'air conditioner'. But we don't know how important this effect is because these interactions have not yet been treated by climate models. Tropical deforestation is rapidly changing land-cover but the impacts on climate are not well known because climate models do not treat all the necessary interactions between vegetation and climate. There is also interest in intentionally modifying land-use to mitigate climate change. For example, afforestation absorbs carbon dioxide into vegetation and could be used as a carbon-sink to offset greenhouse gas emissions from fossil fuel use. But the impact to climate of such changes to land-use is poorly known. Recent studies suggest that afforestation at high-latitudes (for example, in Europe) may actually warm the climate because dark forest vegetation absorbs more sunlight than snow-covered farmland. But these previous studies ignored particle emissions from the forest and their impact on climate. My own research has shown that these forest-derived particles result in an important cooling that can play a significant role in the net climate impact of land-use change. In this fellowship I will substantially improve our understanding of natural particles from the biosphere. I will include a comprehensive treatment of vegetation particle emissions in climate models for the first time. I will answer the fundamental question of how terrestrial biosphere emissions regulate global aerosol and climate. Finally, through an integrated assessment of different ecosystem-climate interactions I will improve our understanding of how changes to land-use alter climate.