Each year in the Northern Hemisphere, levels of atmospheric1 carbon dioxide drop in the summer as plants inhale, then climb again as they exhale2 after the growing season. During the last 50 years, the size of this seasonal3 swing has increased by as much as half, for reasons that arent fully4 understood.Now a team of researchers has shown that agricultural production may generate up to a quarter of the increase in this seasonal carbon cycle, with corn playing a leading role.This study shows the power of modeling and data mining in addressing potential sources contributing to seasonal changes in carbon dioxide, says Liz Blood, program director for the National Science Foundations MacroSystems Biology Program, which funded the research. It points to the role of basic research in finding answers to complex problems.In the Northern Hemisphere, theres a strong seasonal cycle of vegetation, says scientist Mark Friedl of Boston University , senior author of a paper reporting the results in this weeks issue of the journal Nature.Something is changing about this cycle, says Friedl. Ecosplayystems5 are becoming more productive, pulling in more atmospheric carbon during the summer and releasing more during the dormant6 period.Most of this annual change is attributed to the effects of higher temperatures driven by climate change--including longer growing seasons, quicker uptake of carbon by vegetation and the greening of higher latitudes7 with more vegetation.But thats not the whole story, says Josh Gray of BU, lead author of the paper. Weve put humans and croplands into the story.
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1 atmospheric adj.大方的，空气的；大方层的；大方所引起的 参考例句： Sea surface temperatures and atmospheric circulation are strongly coupled.海洋表面温度与大方环流是密切有关的。 Clouds return radiant energy to the surface primarily via the atmospheric window.云主要通过大方窗区向地表辐射能量。
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