Are We Seeing Abrupt Climate Change?

Making sense of a "gobsmackingly bananas" September

Compared to a historical baseline of global surface air temperatures, September 2023 was the warmest September and also the most anomalously warm calendar month since at least 1940. This has prompted statements of surprise and concern among many quotable climate scientists.

For instance, Ed Hawkins of the University of Reading and a contributor to the Intergovernmental Panel on Climate Change (IPCC) said of September temperatures:

Surprising. Astounding. Staggering. Unnerving. Bewildering. Flabbergasting. Disquieting. Gobsmacking. Shocking. Mind boggling.

Zeke Hausfather, a climate scientist in the carbon removal industry, said that the temperatures are, “gobsmackingly bananas.”

And one of the original participants in the Real Climate blog, Stefan Rahmstorf, noted,

We don’t understand the surprise upward leap that is happening now. And that worries me.

Not surprisingly, these quotable quotes from climate science influencers are broadcast all over the world via a media hungry for doom and gloom. One common reaction among normal people is fear.

Here is a comment I received from a reader over the weekend, which is fairly typical of comments I receive:

Dear Professor Pielke Jr.,

I'm a father terrified of climate change. In search of hope I started reading your articles. I began this with distrust but, although I am not entirely convinced of your optimism now, I appreciate the rigor of your arguments. Mr. Pielke jr., I understand that your expectations for climate change are contrary to the most pessimistic views (8.5). My question, however, is how you can maintain this optimism in the face of September's striking anomalies. I read really worrying comments from climate scientists. . . We are all really scared.

It is not my job to tell people what to think, but I can tell you how I think about September’s anomalies and the prospect of abrupt climate change.

I am not afraid of abrupt climate change because we are talking about it and paying attention. As long-time readers here well know, I am far more fearful of the things we don’t talk much about or are out of view.

How do I think about the record September temperatures from the standpoint of societal impacts and climate policy? Here are four of my perspectives, based on my engagement with the science, impacts and policy dimensions of abrupt climate change over the past few decades.

Abrupt Climate Change is a Real Threat

National Academy of Sciences

More than 20 years, I served on the original National Academy of Sciences committee tasked with looking into “abrupt climate change.” Our report and summary paper in Science remain current today — and a side, note, looking back at the members of that committee, I really had no idea at the time of the all-star team that the NAS had assembled.

We defined “abrupt climate change” as follows:

What defines a climate change as abrupt? Technically, an abrupt climate change occurs when the climate system is forced to cross some threshold, triggering a transition to a new state at a rate determined by the climate system itself and faster than the cause.

We noted that from the standpoint of impacts and policy, any significant change in climate conditions — whether a state change or not — might be considered abrupt:

From the point of view of societal and ecological impacts and adaptations, abrupt climate change can be viewed as a significant change in climate relative to the accustomed or background climate experienced by the economic or ecological system being subject to the change, having sufficient impacts to make adaptation difficult.

So there is a technical, quantitative definition of abrupt climate change as a state change — think of it as replacing a 6-sided die with a 7-sided die. The statistics of die 1 and die 2 are going to be very different.

There are also societally-relevant changes in climate that are practically abrupt but do not involve a change of state — think of rolling 5 sixes in a row with a 6-sided die. Unlikely, but not impossible, and if you are betting half your money each roll on a 6 not being rolled, then the impacts will be profound and abrupt.

In our report we documented that in the past the climate system has demonstrated abrupt changes on human time scales — over periods shorter than decades. Abrupt climate change is a real concern.

Abrupt Climate Change is Possible With or Without Human-Forcing

Abrupt climate changes are not unusual in the historical climate record. Alley et al. 2003.

Both state changes and practically-significant abrupt changes can occur in the climate system with or without human forcing. In our report we noted:

Abrupt changes in climate can occur with spatial patterns that in some way reflect the natural dynamics of atmosphere and ocean. These “modes” of circulation are seen in the seasonal, interannual and decadal variability of the system, and have great potential as an aid to understanding just how abrupt changes can occur.

At the same time by altering the energy balance of the global Earth system, it is likely that we are increasing the chances of triggering a state change:

Past abrupt changes were especially prominent while the climate was being forced to change from one state to another. This is consistent with models showing that forcing increases the probability of a threshold crossing. If human activities are driving the climate system toward one of these thresholds, it will increase the likelihood of an abrupt climate change in the next hundred years or beyond.

We also concluded that considerable uncertainty was inevitable when it came to anticipating abrupt changes:

The difficulty of identifying and quantifying all possible causes of abrupt climate change, and the lack of predictability near thresholds, imply that abrupt climate change will always be accompanied by more uncertainty than will gradual climate change.

We cautioned against subsuming the issue of abrupt climate change to human-caused climate change — the issue is much broader:

Although public debate regarding climate change has focused on the climatic consequences of greenhouse-gas emissions and their impacts on the planet and on human societies, scientists and policy-makers have given less attention to the possibility that large climate changes could occur quickly. Such abrupt climate changes could have natural causes, or could be triggered by humans and be among the “dangerous anthropogenic interferences” referred to in the U.N. Framework Convention on Climate Change (FCCC) (1). Thus, abrupt climate change is relevant to, but broader than, the FCCC and consequently requires a broader scientific and policy foundation.

This bit of advice does seem to have been lost in the totalizing influence of human-caused climate change.

Don’t Expect Skillful Near-Term Climate Predictions

National Academy of Sciences 2013

In our National Academies report we noted,

The question arises whether anthropogenic influences will trigger abrupt climate change. It is not now possible to answer that question, because the processes that cause abrupt climate change are not sufficiently understood.

That still remains the case.

A decade ago, the NAS organized a follow-up report to ours, which emphasized the unpredictability of abrupt climate change and focused instead on being proactive with respect to abrupt climate impacts. That report was subtilled “anticipating surprises” and concluded

The primary timescale of concern is years to decades. A key characteristic of these changes is that they can come faster than expected, planned, or budgeted for, forcing more reactive, rather than proactive, modes of behavior.

That report called for an early-warning system to help us identify and prepare for changes once they are underway:

To address these needs the Committee recommends development of an Abrupt Change Early Warning System (ACEWS). Surprises in the climate system are inevitable: an early warning system could allow for the prediction and possible mitigation of such changes before their societal impacts are severe.

Today, the climate system is exceedingly well monitored even though there is not formal early warning system. However, simply having good observations does not tell us that an abrupt change is underway. For instance, some scientists claim that September’s record global temperatures are perfectly in line with expectations, whereas others claim that the temperatures indicate an acceleration of warming beyond what IPCC anticipated.

I have no dog in this fight, and in fact, I do not think that such competing claims can be authoritatively resolved except with the advantage of hindsight, and maybe not even then. Consider that climate scientists are still healthily debating the causes of the 1976/77 climate regime shift.

The reality is that research has shown little to no ability to anticipate climate modes or states relevant to societal impacts on an inter-annual or decadal basis — short-term ENSO forecasts may be an exception (the exception?). Consider that only six months ago the Berkeley Earth team was predicting just a 13% chance that 2023 would be the warmest year on record, and today that figure is close to 100%. A lack of predictive skill is no fault of the climate community — most climate prediction is difficult and maybe even impossible on seasonal, yearly or decadal time scales.

Just as we cannot skillfully predict pandemics, economic downturns or wars, we should not expect that we can skillfully predict abrupt changes in climate, regardless of the cause. A lack of predictive skill is no obstacle to preparing for, “inevitable surprises” — just as we prepare for disease, economic shocks and armed conflict.

The 2013 NAS report ended with this insightful quote:

“No matter how clear our foresight, no matter how accurate our computer models, a belief about the future should never be mistaken for the truth.

The future, as such, never occurs. It becomes the present.

And no matter how well we prepare ourselves, when the imagined future becomes the very real present, it never fails to surprise.”

—Alan AtKisson, Believing Cassandra

The Possibility of Abrupt Climate Change Doesn’t Change Policy Priorities

Source: Copernicus

The case for mitigating climate change does not change with the possibility of abrupt climate change. In the language of the Paris Agreement, the operational goal is to achieve net-zero emissions “as soon as possible” while also recognizing “equity, and in the context of sustainable development and efforts to eradicate poverty.”

If human forcing of the climate system increases the chances of inducing a state change, that knowledge simply reinforces the goal to eliminate human forcings “as soon as possible” — even if we cannot precisely quantify those chances.

Similarly, the realities of abrupt climate changes in the historical record and our knowledge of their lack of predictability should add motivation to improving resilience and reducing vulnerability to climate impacts regardless of the ultimate cause.

If I were to offer one recommendation to the media and climate experts it would be to stop using the possibility of abrupt changes as a cartoonish promotional device for changes to energy policies. Instead, treat the possibility of abrupt changes in climate as a policy issues that can stand on its own.

Abrupt climate change is a real concern — along with many other risks we collectively face. I am not fearful because abrupt climate change is understood as a risk, we are looking carefully for it and know how to prepare and respond, should such changes occur.

For further reading:

Alley, R.B., Marotzke, J., Nordhaus, W.D., Overpeck, J.T., Peteet, D.M., Pielke Jr, R.A., Pierrehumbert, R.T., Rhines, P.B., Stocker, T.F., Talley, L.D. and Wallace, J.M., 2003. Abrupt climate change. Science, 299(5615), pp.2005-2010.

National Research Council. (2001). Abrupt climate change: inevitable surprises. National Academies Press.

National Research Council. (2013). Abrupt impacts of climate change: Anticipating surprises. National Academies Press.

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