Impact of the biosphere on atmospheric aerosol and climate

了解气候变化是当今科学面临的最重要挑战之一。大气颗粒（气溶胶）对地球具有重要的冷却影响，部分抵消了工业时期的温室气体变暖。量化这种气溶胶冷却是更准确地预测气候变化的关键一步。人们投入了大量精力来评估人为（人造）颗粒排放对气候的影响。该提案重点关注天然生物气溶胶，对此的研究较少且了解甚少。然而，我们需要先了解自然情况，然后才能充分了解人类如何改变大气和气候。植被将有机物质排放到大气中（众所周知的森林松树气味的原因），它们可以在大气中发生反应形成颗粒。植被还直接排放花粉和真菌孢子等颗粒。观察表明，这些自然生物气溶胶排放可以主导大部分大气中的总颗粒负荷。这些颗粒通过反射阳光并使云层变得更厚、更具反射性来冷却气候。我们还知道，雨滴是在这些微小的生物颗粒上形成的，因此它们可以在控制全球降雨模式方面发挥作用。尽管重要性如此明显，但当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尚不清楚。随着气候变化，生态系统将做出反应：光合作用等植物活动发生改变，植被分布也发生变化。这些变化改变了生物气溶胶的排放，改变了大气中颗粒的数量，从而影响了气溶胶的冷却。这种气候反馈可能会抑制或加剧人为的全球变暖。也就是说，随着世界变暖，森林排放的颗粒物可能会增加，从而有助于冷却气候。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，因为气候模型尚未处理这些相互作用。热带森林砍伐正在迅速改变土地覆盖，但其对气候的影响尚不清楚，因为气候模型没有考虑植被与气候之间所有必要的相互作用。人们也有兴趣有意改变土地利用以减缓气候变化。例如，植树造林将二氧化碳吸收到植被中，可以用作碳汇，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却鲜为人知。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，因为深色森林植被比冰雪覆盖的农田吸收更多的阳光。但之前的这些研究忽略了森林的颗粒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会导致重要的降温，在土地利用变化对气候的净影响中发挥重要作用。在这次研究金中，我将大大提高我们对生物圈天然颗粒的理解。我将首次在气候模型中纳入植被颗粒排放的综合处理。我将回答陆地生物圈排放如何调节全球气溶胶和气候的基本问题。最后，通过对不同生态系统与气候相互作用的综合评估，我将增进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.