The dominant line of defense among people trying to avoid action to stop global warming is to acknowledge "some" global warming exists, but then claim it's part of natural warming cycles that have happened off and on since the end of the Northern Hemisphere's "Little Ice Age" in 1850.
So let's look at those cycles. I see the following periods from this temperature record:
years 1855 to 1909: little change
1910 to 1945: warming trend
1946 to 1978: cooler compared to the end of the prior warming period
1979 to present: warming
So the last warming period lasted 35 years, and we are currently 26 years into the current one. Natural warming proponents have got nine more years before we should start seeing cooling, based on the only argument they've made. I'm ignoring the fact that their argument is garbage and has no science to back it up, but am looking at the shred of evidence they try and twist in their direction.
For me it all comes down to betting, and it shouldn't be too hard to design a bet that would be attractive to people who truly believed in natural global warming. Here's one: temperatures in 20 years will be warmer than the average temperature of the next 10 years, and I'll give 2:1 odds in their favor (consistent with the odds I'm willing to give for a 10-year bet). According to the graph I linked to above, if I were making this offer 26 years after the start of the previous warming cycle in 1910, I would lose. And if they want to come up with a different bet that is consistent with their theory, I'm open to it.
The "natural warmers" might argue that this warming cycle could last longer than the 1910-1945 cycle. I suppose that's possible, but the only evidence they rely upon suggests they're more likely to win than lose, and then on top of that, I'm giving them 2:1 odds. So if they really believe what they're saying, they need to back it up.
key: global warming, bet