Explain the concept of global warming and its impacts on the environment and human life. Your answer should be in 3 paragraphs, each containing exactly 5 sentences. It should also include at least 3 specific examples of impacts and avoid using any form of the word "impact". Effect of global warming on sea levels, agriculture, and health must be addressed.
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全球变暖是指地球表面平均温度由于人力资源活动而逐渐上升的现象。这一过程主要由于燃烧化石燃料和森林砍伐引起的温室气体浓度增加，导致了更严重的温室效应。随着气温的升高，极地冰盖和高山冰川融化，进而引发海平面上升。例如，马尔代夫等低洼岛国面临着因海水侵蚀土地而失去家园的风险。此外，海平面上升还可能导致沿海地区洪水频发，威胁居民的生活安全。
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