What is the main idea of the news item?

The report, titled Scientific Assessment of the Effects of Global Change on the United States, concludes that a warming of the earth will have a far-reaching impact on the United States. Not only will winters become milder and summers hotter, climate change will affect rainfall, water supply, hurricane activity, sea levels, agricultural production, energy production, biological diversity, and human health.
    It paints a worrisome picture of more heat waves and wildfires, increased water shortages in regions that depend on mountain snowmelt, greater coastal flooding and erosion, more-intense storms and hurricanes, the disruption and dislocation of ecosystems, and increased risk of crop failures. It also predicts geographic shifts in human settlements, higher heat-related human mortality, and increased risk for some diseases.
    The report notes that climate change is a complicated phenomenon, but concludes that there is "a strong human influence on climate." In particular, human activities that generate carbon dioxide, a so-called "greenhouse gas" is seen as a main culprit.
    The report does not make any specific policy recommendations for combating climate change, but would seem to suggest that reducing the emission of greenhouse gasses would be beneficial. Even so, the report states that some climate change in the future is inevitable regardless of any steps taken, because a certain amount of warming will occur due to greenhouse gas emissions that have already occurred.