Clifford Asness and Aaron Brown — non-experimental data guys (like me) — point out that the data on global warming doesn’t show what people say it does.
Their position is much the same as mine. I’m not a climate scientist. But I work with non-experimental data all the time … and it’s been readily apparent since the late 1980’s that the global climate data does not support the idea that global warming is a big deal.
I think they’re more than even-handed:
… The real but rather small trend doesn’t prove that global warming is a minor issue, far from it. We’re just saying the graph taken on its own is actually pretty reassuring …
Instead, they point out that global warming alarmists aren’t using the actual data much at all:
Those predicting that we face a big problem much sooner aren’t arguing this from these data, instead they have to be arguing that historical warming trends will change drastically in the near future…
Then they make a very cool and very reasonable argument: if you’ve seen some symptom occur, and you think the cause is because some other variable changing … that’s fair enough … but you can’t use that same symptom to them argue that the changing variable is getting worse faster. You simply don’t know, and shouldn’t assume either, that the change you’ve seen wasn’t sufficient to produce the symptom.
So things like ice melt must be evidence of the warming that has occurred, i.e. the rather modest warming we and others graph, not evidence for or against a model forecasting the future. It is certainly not new evidence independent of the 0.67° Celsius per century warming trend, but rather the same evidence repeated. Other consequences of warming, like ice melt, can be reported as confirmation of warming, perhaps to convince those who doubt the direct temperature data, but not as evidence that the problem is bigger than the amount of warming we’ve seen.
That’s actually something every parent understands. If you suspect your kid is sick, and you take their temperature, this confirms your diagnosis … but it doesn’t make sense to then argue that this means the fever will get worse.
What is our conclusion from all of this? If you believe in a significant probability of catastrophic global warming in the next 50 years, you cannot base this belief on the last 135 years of global mean temperature data …
The evidence just isn’t there for that conclusion. And yet this is precisely the conclusion being foisted on the public. Instead:
You can believe the models if you like, or you can look at the data and assume the most likely future is an extrapolation of the past. What you cannot do is both.
And in the end, the position of alarmists is even more tenuous:
How much we should worry about future warming, and the answer may indeed be a lot, is entirely about how much one believes in the models’ forecasts that the future will look very different from the data.
That’s a tall order folks, but not uncommon. It’s akin to what sports’ fans hope when all the data points to their team being the weaker one, and yet they hope against hope that they are David setting out against Goliath.
BTW: Asness and Brown use the sort of deterministic trend regressions common in casual analysis of global temperatures to make their point that this isn’t a very serious issue. They do not discuss at all that this method is biased towards finding global warming is a problem in the first place.
Download a copy of Asness and Brown’s It’s Not the Heat, It’s the Tepidity here.