"Since anthropogenic CO2 is the most important long-lived greenhouse gas causing climate change, improved understanding on how it cycles between the active land, ocean, and atmospheric reservoirs is a main concern for humanity. During the past decade, annual fossil fuel CO2 emissions have sharply increased at a rate of 3%/yr, almost doubling the rate of the prior three decades. To a big surprise, the corresponding increases in atmospheric carbon dioxide concentrations were relatively modest during this time frame. This coincidence has led to the hypothesis that the sharp rise in fossil fuel emissions and increase in sink strength especially since early 2000 may be a result of carbon sink processes that are controlled by the increasing emissions themselves, namely increased nitrogen deposition and a larger fraction of diffuse versus direct solar radiation from increased sulfate aerosol emissions.The objective of the proposed work is to estimate changes in global terrestrial carbon uptake over the last decades and attribute their cause(s) through a combination of observation-based and modelling approaches. We will investigate three main hypotheses in regards to increased terrestrial carbon uptake during recent decades, including (i) a progressive relaxation of climatic constraints on plant productivity including warming in northern temperate, boreal and tundra ecosystems and increases in rainfall rates over tropical savannas, (ii) increases in the fraction of diffuse/direct radiation associated predominantly with East Asian sulfate aerosol emissions that spurred plant photosynthetic rates, and (iii) increases in nitrogen deposition from East Asian fossil fuel burning that increased carbon plant uptake.This research is designed to improve our knowledge about carbon cycle feedbacks under climate change, a first-order uncertainty in climate models, leading to more credible projections of future climate."