A newly-released report on climate change warns that without dramatic reductions in greenhouse gas emissions, temperatures may rise nearly 10 degrees, and seas may rise up to eight feet by the end of this century.
The figures were made public on Friday with the release of the Fourth National Climate Assessment, a congressionally mandated document issued every four years.
The report is based off the latest climate research from some of the nation's top scientists.
Globally, the report says, temperatures have risen an average of 1.8 degrees Fahrenheit (2 degrees Celsius) over the past 115 years.
That makes this period the warmest in the history of modern civilization, it continues.
Researchers say it is "extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of this observed warming since the mid-20th century."
The report says there is no convincing alternative explanation.
That warming has also contributed to an average sea level rise of 7 to 8 inches since 1900. Three inches of that rise has happened since 1993, according to the report.
By the end of the century the report warns that sea levels may rise as much as eight feet. At the very least a rise of 1 to 4 feet is expected by 2100, with a several inch rise in the next 15 years alone.
The report also says that without significant reductions in greenhouse gas emissions global temperatures may rise as much as 9 degrees Fahrenheit (5 degrees Celsius) this century.
With a major reduction in emissions the warming may be limited to a 3.6 degree Fahrenheit increase (2 degrees Celsius), it adds.
An international agreement reached in Paris in 2015 strives to keep global warming capped at 2 degrees Celsius.
President Donald Trump has since said the United States will withdraw from that agreement.
As of this year, the concentration of carbon dioxide in the atmosphere has exceeded 400 parts per million. The report says that is the highest level seen in some 3 million years, a time when sea levels were significantly higher than today and when the world was much warmer.
The report adds that many impacts of climate change are already being felt in the United States. Heavy rain events are increasing in intensity and frequency, heat waves are becoming more common, and prolonged cold stretches are becoming less common.