Based on ten system categories, including marine, coastal, inland water, forest, dryland, island, mountain, polar, cultivated and urban, changes in the world's ecosystems during the second half of the twentieth century were assessed in the report of MA's condition and trends working group. It indicated that the world's ecosystemschanged more rapidly in the second half of the twentieth century than at any time in recorded human history, and virtually all of Earth's ecosystems have now been significantly transformed through human history. The main results are as follows: ① the most significant change in the world's ecosystems has been the transformation of approximately one quarter of Earth's terrestrial surface to cultivated systems, and more land was converted to cropland in the 30 years after 1950 than in the 150 years between 1700 and 1850； ② wetlands, including rivers, lakes, and salt and saltwater marshes, where water abstraction, habitat loss and fragmentation, and pollution by nutrients, sediments, salts, and toxins have significantly impaired ecosystem function and biodiversity in most major drainage basins; ③ in the arid parts of the world,a large, growingand poor population often coincides with water scarcity, cultivation on marginal lands, overgrazing, and overharvesting of trees; ④ particular coastal systems, notably coral reefs, estuaries, mangroves, and urbanized coasts, where habitat loss and fragmentation, overharvesting, pollution, and climate change are the key issues; ⑤ tropical forests, where unsustainable harvesting and clearing for agriculture threatens biodiversity and the global climate.