re: small-money bets that denialists can still get in on
You can have a very simple measure of whether you having global warming or global cooling. When total mass of glaciers reduce you have global warming. When total mass of glaciers increase you have global cooling.
One way to measure the melting or the accumulation of glaciers is to measure global sea level. Since the end of last Ice Age over 10,000 year ago, sea level have been rising. In this time the sea level has risen 100 meters. And as far as know, sea levels continue to rise and will probably continue to rise for next 100 year or more.