Global warming in the past half-century is “unequivocal”, according to the U.N. Climate Panel. Chances that human activities, led by burning fossil fuels, are the main cause of climate change are more than 90 percent, it says…so would you bet $10,000 that it will be warmer in 10 years’ time? 

It sounds like an easy way to make money — assuming the world’s top climate scientists are right and that changes in the sun’s output or other natural factors are not the main drivers. Most decades since 1950 have been warmer than the previous one, and the decade to 2007 was the warmest since records began in the 1850s, according to the U.N.’s World Meteorological Organization.

But before you get out your money, read the fine print of the deal you are offered. 

Several bets have been made about whether the world will be warmer — two Russian sceptics bet $10,000 that the planet will cool, against a British expert who expects a warming. They will decide according to whether global surface temperatures recorded by a U.S. climate centre between 1998 and 2003 are higher or lower than temperatures they will record between 2012 and 2017.

One U.S. scientist willing to bet that temperatures will not rise has been trying in vain to persuade former U.S. Vice President, Nobel Peace Prize winner and climate campaigner Al Gore to bet $10,000 against him. Scott Armstrong, an expert in forecasting methods at the University of Pennsylvania,  first offered the wager last year and says he has given Gore until March 26 to change his mind.

 ”Mr. Gore claims that the temperature will rise rapidly over the near future. If he believes that, it should be an easy bet for him to make,” Armstrong wrote in an e-mail.

The U.N. Climate Panel, which shared the 2007 Nobel Peace Prize with Gore, says temperatures rose by 0.7 Celsius (1.3 Fahrenheit) in the 20th century and gave a best estimate that temperatures will rise by between 1.8 and 4.0 Celsius in the 21st.

But Armstrong says the Climate Panel’s forecasting methods are wrong.

Armstrong’s terms are more complex than the Russians’ bet — he says he is trying to expose the flaws in climate models and that his assumption that temperatures will be unchanged will be more accurate. He wants to pick just 10 measuring stations around the globe — too much of a pinpointing for most climate models which operate on grids 50 km by 50 km at the smallest.

And he might win even if temperatures rise — he would bet every year that temperatures in each year remaining of the decade would be the same as those in the year just ended. (…so if 2009 was exceptionally warm, he would also predict the same for 2010, 2011 etc.)

Solutions such as comparing the global average temperatures for 2008-17, compiled from all measuring stations around the globe used by the World Meteorological Organization, with temperatures for 1998-2007, would give a broader readout the climate.

There would still be unpredictable risks — a big volcanic eruption, for instance, might spew dust into the atmosphere that can dim sunlight and mean a cooling even if the U.N. Climate Panel is right.

So what’s a fair way to organise a bet? On which side would you put your money?