The key misconception is that all of the warming since the Industrial Revolution — 0.9 degrees Celsius — is a result of human activity.

Hardly. Since the beginning of reliable global temperature records in the late 19th century, there have been two periods of significant warming that are statistically indistinguishable in magnitude. The first period ran from 1910 through about 1945, with a temperature increase of around 0.5 degrees Celsius. There could only be minimal human influence on this period, simply because humans had not emitted very much carbon dioxide.

After a slight cooling, the second one began sometime around 1976 and ended with the big 1998 El Nino. This period was likely in part due to a greenhouse effect.

The reason this period was affected by greenhouse warming is because the lower stratosphere cooled at the same time, which is a prediction of greenhouse theory. If, as some people maintain, “it’s all the sun,” then the whole atmosphere would warm.

Interestingly, when the lower atmospheric warming paused after 1998, the stratosphere also stopped cooling. What’s happening now is quite unclear as surface temperatures are constantly being readjusted.

So, after allowing for a small bit of other influence on the second warming, we’re left with the notion that the maximum warming caused by humans is somewhere between 0.4 and 0.5 degrees Celsius — half of the total since the Industrial Revolution.

This has huge implications. If, as the Paris Agreement erroneously assumes, all of the warming of 0.9 degrees is a result of human activity, there is no way that the aspirational goal of 1.5 degrees can ever be met. Thanks to the huge thermal inertia of the ocean, current models show there’s between 0.4 degrees and 0.6 degrees of warming on the way, even if emissions were capped at 2000 levels.

That’s a total of 1.5 degrees already guaranteed. Meeting the 2 degrees objective allows only an additional half of a degree in wiggle room. The Paris Agreement only mitigates about 0.2 degrees of warming. Again, believing in those models, that would be an additional warming of over 2 degrees Celsius this century.

So according to the United Nation’s own climate models, it is scientifically impossible. President Trump, that’s grounds enough to withdraw.

On top of that, the models that form the basis of the Paris Agreement are predicting way too much warming in the lower atmosphere, and erroneously predicting a dramatic warming of the upper atmosphere over the tropics. Most precipitation on earth is a result of the temperature difference between the lower layers and what’s aloft.

Get that wrong, which the climate models do systematically, and the models are of very little utility.

There are other, more reality‐​based approaches to estimating future warming, and these point to a 21st century increase of closer to 1.4 degrees Celsius. Adding that to the maximum human contribution to‐​date of 0.5 degrees yields 1.9 degrees, meeting the Paris objective without the Paris Agreement.

President Trump, that’s also grounds enough to withdraw.