Crisis Looms in Alarmist Climate Science

Climate science is dominated by alarmists addicted to the idea that increasing carbon dioxide (CO2) will cause dangerous global warming. How much warming is thus the central scientific question—a question with significant implications for public policy responses.

This question has been surprisingly difficult to answer, despite 40 years of research, costing tens of billions of dollars. Now the issue is exploding because two different answers are emerging, one harmlessly low and the other dangerously high. This divergence is a crisis for the alarmist community. How they handle it remains to be seen.

What follows is a slightly technical explanation of the situation.

What is Equilibrium Climate Sensitivity?

The issue centers on a benchmark estimate of the impact of increasing CO2 on global temperature. This is called the “equilibrium climate sensitivity” or ECS. The basic question is, what will the global average temperature be when the CO2 level is double the supposedly original level of 280 parts per million (ppm) in the atmosphere? In other words, what will the average temperature be when we hit 560 ppm?

Since it may take the climate system some time to adjust to this new high level, the question is what the temperature will be when the system equilibrates to this doubling, which may be some time after we hit 560. Also, this is about sensitivity, so ECS is not the new high temperature. It is the number of degrees Celsius (℃) higher than the original temperature that this new high temperature will be.

So if the new high temperature is, say, 2.2℃ higher, then ECS = 2.2℃.

Technically ECS is often an abstraction, something unique to climate models, but modelers and climate alarmists have argued successfully ECS should be taken as an important estimate of real ECS. In the models, ECS is often estimated by simply doubling the CO2 instantaneously, whereas in reality this takes centuries.

Equilibrium Climate Sensitivity Range Widens

All this said, the emerging crisis becomes clear.

For many decades the accepted model estimates of ECS have ranged between 1.5℃ and 4.5℃. Different models give different values, however the acceptable range has not changed. That the range is so big has been a policy problem. Warming as little as 1.5℃ might be harmless, while 4.5℃ might be dangerous. And the ECS range has been stubbornly persistent, refusing to narrow to a specific value over the course of more than three decades of study, despite billions of dollars being spent in an attempt to produce a more precise ECS estimate.

Now, suddenly, there is a huge new problem. ECS has exploded! The problem is not that ECS is higher, or lower — the problem is, it is both! Two new lines of research have diverged sharply on the estimated value of ECS.

Observation Versus Model Sensitivity

The first line of research takes a new approach called observational ECS. The idea is that since the CO2 level is almost half way to doubling we should be able to derive ECS empirically from the observed relationship between CO2 increase and temperature increase.

There have been a number of observational studies and many are finding ECS values well below 1.5℃, which are harmless indeed. Values of 1.2℃ and 1.3℃ are common.

At the same time there has been a new wave of modeling studies producing ECS values well above 4.5℃, which could be truly dangerous. Here values of 5.2℃ and 5.3℃ are to be found.

The modeling community is divided concerning whether or not it should accept these new hot model numbers. After all, the new significantly higher ECS projections imply the modeling done over the last forty years or so has been wrong, including a lot of the recent modeling which produces ECS results within the old range.

The upshot of all this is that the science of ECS is in a shambles. Given that ECS addresses the core science of climate alarmism, this is truly a crisis. Has the modeling been wrong for 40 years? Is it wrong now? What about observation, which is supposed to rule in science? The scientific method says observation trumps theoretical modeling.

Sensitivity Affects Desirable Policy Responses

This is also a policy crisis.

If we have no idea how sensitive the climate system will be to increasing CO2 levels then we have no basis for making climate change policy. If the observation values are right then there simply is no climate emergency.

How will this huge new uncertainty play out? Fortunately we will get at least a glimpse fairly soon. The latest U.N. Intergovernmental Panel on Climate Change (IPCC) assessment report (AR6) is presently under review and should be out in the next year or so. This report is supposed to review the state of climate change science, albeit from an alarmist point of view.

How the IPCC handles the exploding ECS range will be interesting to see. They may choose to ignore it because it has to hurt alarmism. They may simply drop mention of the ECS altogether, it now being very inconvenient. Such a glaring omission will be easy to call out.

Or they may only acknowledge the hot higher values, which favor alarmism. Here the IPCC would risk making modeling look stupid (which it is). Plus this omission of critical observational evidence will also be easy to call out.

With the ECS range exploding the IPCC is caught between a hot rock and a cold hard place. So is alarmism. Stay tuned.