The Earth is the hottest it has been in at least four centuries and perhaps in thousands of years, according to a new report released in U.S.

The report also claimed that human activities are responsible for it.

The National Academy of Sciences, US, reaching the conclusion in a broad review of scientific work requested by Congress, reported Wednesday that the "recent warmth is unprecedented for at least the last 400 years and potentially the last several millennia."

Scientists widely believe that emissions of carbon dioxide from power plants and cars that get trapped in the atmosphere are helping drive global warming. 

Noteare responsible for：对...负责unprecedented：空前的
millennia：millennium的复数，millennium一千年emission：（光、热等的散发）
carbon dioxide：二氧化碳