The question is a potential deal-killer: If nations ever agree to slash greenhouse gas emissions, how will the world know if they live up to their pledges?
The answer is in space, experts say -- both outer space and cyberspace.
NASA, the wonder agency of the 1960s, and Google, the go-to company of the early 21st Century, are trying to give the world the ability to monitor both the carbon dioxide pollution and the levels of forest destruction that contribute to global warming.
"Just having the thing flying around there imaging would just about make everybody act differently," said professor Steve Pacala, director of the Princeton Environmental Institute. "The idea that you could pull a fast one would be different."
Google, meanwhile, has rolled out a new program call Earth Engine which essentially is a massive storehouse for satellite and other data that forest countries will be able to access for free by the time of the next U.N. climate conference in Mexico next year.