The Fourth National Climate Assessment prepared by the U.S. Global Change Research Program in 2018 clearly establishes the nature of the global warming problem:
The impacts of climate change are already being felt in communities across the country. More frequent and intense extreme weather and climate-related events, as well as changes in average climate conditions, are expected to continue to damage infrastructure, ecosystems, and social systems that provide essential benefits to communities. Future climate change is expected to further disrupt many areas of life, exacerbating existing challenges to prosperity posed by aging and deteriorating infrastructure, stressed ecosystems, and economic inequality. Impacts within and across regions will not be distributed equally. People who are already vulnerable, including lower-income and other marginalized communities, have lower capacity to prepare for and cope with extreme weather and climate-related events and are expected to experience greater impacts. Prioritizing adaptation actions for the most vulnerable populations would contribute to a more equitable future within and across communities. Global action to significantly cut greenhouse gas emissions can substantially reduce climate-related risks and increase opportunities for these populations in the longer term.
Global warming is already impacting human health and safety, the economy, and ecosystems. As greenhouse gas (GHG) emissions continue to accumulate in the atmosphere, global warming impacts will increase in severity. The global challenge is twofold: reduce the human-caused emissions of heat-trapping gases and respond to the negative climate impacts already being felt and the likelihood that they will worsen in the future.