A draft of a sweeping report from U.S. government researchers has underscored what is already widely accepted among climate scientists: human activities are the main drivers of climate change.

The draft report, named Volume II of the National Climate Assessment, has been in the works for years, and includes research from at least 13 federal agencies.

The final version is slated for publication in December 2018.

The draft concludes that it is "extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century."

It cites recent record-breaking weather extremes, melting arctic ice and three of the warmest years ever recorded. Its conclusions rely on a large body of peer-reviewed research.

Researchers also outlined several predictions from a previous report in 2014 that have now come true, including increased coastal flooding, warming oceans disrupting fisheries, receding permafrost and a long list of damaging effects on agriculture.

The report also estimates the cost of extreme climate events at $1.1 trillion since 1980.

Meanwhile on Wednesday Kathleen Hartnett White, President Trump's top candidate for the White House Council on Environmental Quality, told her Senate confirmation hearing that she had "many questions that remain unanswered by current climate policy."

She called the extent of the link between human activity and climate change "very uncertain."

Environmental Protection Agency head Scott Pruitt earlier this year made similar comments in an interview with CNBC's Joe Kernen, saying that he "would not agree that [carbon dioxide] is a primary contributor to the global warming that we see."

Hartnett White's comments come as Syria pledges to join the Paris climate agreement, leaving the US isolated and off the list of 100 countries invited to the climate summit in Paris this December.

President Trump announced in June that the US would withdraw from the Paris accord, saying the agreement would cost the U.S. 6.5 million jobs and favors countries like China and India.

Read More:

• What the Climate Report Says About the Impact of Global Warming (New York Times)
• Massive Government Report Says Climate Is Warming And Humans Are The Cause (NPR)
• Read the Full Climate Science Special Report (New York Times)
• Trump's Top Environmental Pick Says She Has ‘Many Questions' About Climate Change (Washington Post)
• Paris Climate Accord: Syria To Sign Up, Isolating US (BBC)