Last year, when G8 leaders agreed a “vision” of halving world greenhouse gases by 2050 at a summit in Tokyo, Japan, German Chancellor Angela Merkel looked around the table and wondered aloud if any of them would still be around to ensure the plan worked — or held to account if it didn’t.

“Probably only Dmitry”, one of the leaders said, referring to Russian President Dmitry Medvedev, according to a G8 source. At the time, Medvedev was 42 and will be 84 in 2050.

At this year’s G8 summit, the discussion came up again when the leaders agreed other distant targets, including an 80 percent reduction in emissions by developed nations by 2050. (Critics said they should have focused more on 2020 goals that are most relevant to a new U.N. climate treaty due in December.)

“We probably have a second person — Barack will still be here,” one of the leaders said of U.S. President Barack Obama, who is now 47 and took over from former President George W. Bush in January.

But then Italian Prime Minister Silvio Berlusconi, the oldest of the leaders at 72, piped up: