14th October 2018, quoting Senator Marco Rubio and White House economic advisor Larry Kudlow, the Washington Post reported they each claimed that the recent UN report was an `overestimate`:

“I think they overestimate,” Kudlow said of the U.N. report, which found that policy changes must proceed at an unprecedented pace in the next 12 years to stop temperatures from rising more than 1.5 degrees Celsius (2.7 degrees Fahrenheit) above Earth’s preindustrial temperature. “I’m not denying any climate-change issues,” Kudlow said on ABC’s “This Week.” “I’m just saying, do we know precisely . . . things like how much of it is manmade, how much of it is solar, how much of it is oceanic, how much of it is rain forest and other issues?”

And:

Rubio (R-Fla.), speaking on CNN about the effects of Hurricane Michael, said that sea levels and ocean temperatures have risen in a “measurable” way and that humans have played some role. But he questioned how big that role is. “I think many scientists would debate the percentage of what is attributable to man versus normal fluctuations,” Rubio said on “State of the Union.”

Well, actually, it is, surely with some uncertainty, but the contribution of human emissions and activity is three times that of the nearest competitor. Moreover, in the case of volcanic activity, solar irradiance, and ENSO, their forcings are not consistent, the volcanic one being intermittent, and solar being cyclical. Moreover, volcanic forcings overwhelmingly cool Earth, not heat it, and the ENSO can do the same. As is the case for most environmental problems, these kinds of considerations demand assessments be quantitative not merely qualitative or ascribing accuracy of a number to the supposed reputation of the person or group stating it.

Here are the comparisons from Judith Lean and David Rind in 2008 (“How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006”, Geophysical Research Letters, 35, L18701, doi:10.1029/2008GL034864):

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That is, in fact, the go-to source used by, for instance NASA in its site concerning the matter (Riebeek and Simmon, 2010). The NASA page also describes methods used, and provides explanation.

Even at the most extreme positive forcings, human activity is about 1.8 times the combined effects, but that can only happen when solar and ENSO forcings align, which is uncommon. That margin is well beyond measurement uncertainty.

So, sure, these numbers are not known perfectly. But economic and governing policies are seldom based upon perfect or even complete information. This science is far more complete in knowledge than most. And these bounds on uncertainty ought to be more than enough for people to set policy.

And, frankly, the arguments from Rubio and Kudlow are sick examples of the rhetorical fallacies known as Argumentum ad Ignorantiam (Argument from Ignorance) and the Continuum Fallacy (Line Drawing, Bald Man Fallacy).

It is at least disingenuous for Rubio and Kudlow to make these claims. And, given their backgrounds and training, it is more likely to be simply untruthful.

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As a statistician there is another aspect to these opinions which is being wholly neglected. Generally speaking, in order to make a rational decision about anything quantitative and complicated, the losses on either side of the question need to be considered. Indeed, the recent Nobel laureate in Economics, William Nordhaus, won his Nobel for precisely working to identify these costs and losses.

Given that specific, large losses are being realized, losses which are unprecedented in United States (and world!) history, even controlling for additional development, it is open-minded and fair for a Rubio or a Kudlow to consider that their assessments of the benefits of inaction might be incorrect. And, what this means is, that arguments and methods and processes which led to the recent UN report are demonstrating predictive strength, including attribution of cause.

A quick review of history shows Rubio and Kudlow are typical members of a pack of voices who, until recently, denied anything unusual was happening at all.