Any remaining doubt about the changing nature of the Earth's climate might be dispelled by numbers. If not actual temperatures, how about signatures?
More than 11,000 scientists put their names on a recent publication warning of a climate emergency, one the signatories say requires immediate attention.
William Moomaw, Professor Emeritus at Tufts University, is one of the creators of the work.
He visits with details of the project and the reaction to it.