So, have you accepted my point about the Precautionary Principle?
tl;dr — even the most optimistic appraisals of proposed policy measures delay global warming by less than 4 years at the end of the century. Why should we spend anything to delay something by approximately one presidential term?
Bjorn’s appraisal is anything but optimistic.
The methodology he used to reach his conclusion wasn’t laid out in the video, but what caught my attention was that the shape of the line showing the projected effect on global temperatures is quite obviously wrong, because the graph shows only a temporary effect on emissions lasting only the 14-year duration of the Paris agreement.

Now, I haven’t paid much attention to Paris so I don’t know if there’s any preferred approach to emissions reductions — carbon taxes, investing in clean energy, reforestation, etc.— but all of these schemes will cause long-term effects, not just effects lasting 14 years. For instance if it is used to finance a solar or nuclear plant rather than a coal plant, that effect directly lasts several decades, but also permanently lowers the cost to build such plants (e.g. Swanson’s law). If it helps buy electric cars rather than ICE cars, the effect of that lasts more than just the lifetime of the car, it also helps the electric car maker build out its production capacity, leading to more cars built and sold, with effects likely lasting to the end of the century.
Also, the supposed “optimism” in the video is actually pessimism, because it assumes the costs are uncorrelated with the benefits. That is, it implies the Paris targets will not be met, but the obvious corollary is that failure to honor the Paris agreement implies less money is spent; in fact spending less would be the main motive to renege. Of course he doesn’t mention that.
Then the video gets even more misleading by claiming that
- It continues costing 1–2 trillion globally after 14 years even though the temperature graph showed no further reductions after 14 years!
- We’d have to keep spending 1–2 trillion right up until the end of the century. In fact, spending can stop when warming stops or emissions approach zero.
He also didn’t define the word “cost”. A carbon tax of, say, 1.5% of GDP, can be viewed as a “cost” but actually just moves money from one place to another, without consuming resources. Carbon taxes are just an application of free-market principles to deal with a negative externality.
I note that his past works on climate change have been criticized by scientists, and PragerU is not a university, but was specifically created to share conservative messages that could be labeled “University”; I saw it used before by the anti-science group “Friends of Science”.
Finally, you should be aware that other conservatives including libertarians support carbon taxes, and disagree about the merits of dealing with AGW.
They literally insist that there have been no natural changes from 1951–2010, to within 0.1C. That’s some pretty strong denial of secular trends in natural variability
Natural changes have two parts, forcings and internal variability. Internal variability asymptotically has little or no trend, since it is merely the result of weather shifting energy around. To get long-term warming from internal variability, there would have to be cooling of the subsurface ocean, or at least albedo changes that should be measurable and not attributable to a known forcing. Major ocean processes like ENSO are monitored, so yes, they can plausibly limit the trend to 0.1°C. Why do you disagree?
Meanwhile, given the Milankovitch cycle, decreasing solar output, and volcanoes, it makes sense there would be more cooling than warming in terms of natural forcings.
Of the first four charts, only one has even the slightest indication of error bars.
The first seven figures all have error bars, error envelopes or confidence levels, although the very first plot admittedly has few error bars. The text also contains so many confidence intervals and probabilities that it can start to get distracting.
> The IPCC doesn’t predict the economy 100 years from now.
Then how do you know your efforts will only cost 0–2 percent of GDP?
That’s like saying “how do you know your bank account will only give 0–2 percent interest in 100 years”; I don’t need to predict the economy to know that. Besides, I wasn’t making a prediction about the future, I was saying what it would cost if done now.
No such thing as natural climate change
No one is saying that. All IPCC is saying is that the sum of natural forcings and internal variability is close to zero in the 1950–2010 period.
Judith Curry talks in depth about this:
Curry is making a straw-man argument about ‘bootstrapped plausibility’, since there is a lot of evidence she hasn’t mentioned, much of which I’ve referenced in my “megaresponse”. It is all the evidence together that leads to the conclusions of climatology, not a simple chain of circular reasoning like what she has described.
Mainstream scientists such as James Hansen et al said explicitly back in 1990 that
“the observed global temperature trend of the past century does not provide a very stringent empirical limit on climate sensitivity [to CO2]” — The Ice Core Record (1990)
And consider this quote from this Global Multiproxy Database:
The test multiplicity problem (aka the ‘multiple comparisons problem’ or ‘look-elsewhere effect’) is the propensity for false positives to arise when multiple hypothesis tests are conducted simultaneously; in this case, testing the null hypothesis at 1,000 grid points with a 5% level would be expected to yield fifty spurious ‘discoveries’ even in the absence of any link to temperature. Our analysis controls for both effects (see ‘Relationship to temperature’).
Indeed, the difficulty in avoiding ‘circular reasoning’ may be a big part of the reason that the IPCC has not been able to officially narrow down the CO2 sensitivity range from 1.5°C to 4.5°C (but note that, as the IPCC is consensus-based, individual scientists do tend to believe in a narrower range than this, typically 2.5–3.5.)
So climate scientists are fully aware of the issue, and while the overall effects of CO2 and aerosols are not known precisely, they are still bounded, not just by 20th century data and model simulations but also by paleoclimatological data and who-knows-what-else, and those bounds in turn place bounds on natural internal variability.
So Judith Curry’s assumption is wrong that mainstream scientists haven’t already analyzed this problem to death. She just won’t see that because she prefers to discuss everything with her audience of free-market conservatives instead of other climate scientists.
(And why the constant nitpicking? For instance she nitpicks IPCC’s statement that “Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.” when that statement is pretty much just a quotable version of the conclusion represented more precisely in Figure SPM.3. And since solar irradiance was down from 1950–2010, I don’t even know why she brings up that topic.)
