‘Climate Drama’ is About to Get Real
Source Article: Myhre, G., Hodnebrog, Ø., Loeb, N., & Forster, P. M. (2025). Observed trend in Earth energy imbalance may provide a constraint for low climate sensitivity models. Science, 388(6752), 1210–1213. https://doi.org/10.1126/science.adt0647
Featured Image Caption: rising concentrations of greenhouse gases are turning our planet warmer. But in setting our emission budgets, we might have been too indulgent, underestimating how sensitive Earth would be. (Industrial Morning by Vasily Iakovlev is licensed under CC BY 4.0, via Wikimedia Commons)
If you have never heard of climate sensitivity, no worries. Until a few months ago, I knew next to nothing about it. But as I began digging into research papers and books, I quickly realized that this particular subject had been a staple of scientific debate for several years already and still numbers among the most contentious topics you could ever bring up at a climatologists’ hangout.
I had to know more.
While sifting through the literature on the matter, I came across a recently published article in Science. The study focused on climate models and showed that those assuming low sensitivity consistently missed observational benchmarks established by two decades of satellite data. It grabbed my attention.
It’s never good news when our understanding of phenomena falls short of reality, especially when our planet’s climate is concerned, and, whenever that happens, follow-up questions in my mind are: what does the mismatch exactly mean and how bad can it turn out to be?
So, I set out to unpack the paper and see where its conclusions led.
On Sensitivity and Dangerous Optimism
First and foremost, what scientists refer to as climate sensitivity – or, rather, equilibrium climate sensitivity (ECS) – is the mean increase in global surface temperature when atmospheric amounts of CO2 double compared to pre-industrial levels. The lower the ECS, the less Earth heats up due to rising concentrations of carbon dioxide.
It is a handy metric to evaluate our current position concerning global warming and where we might be headed, but assessing our planet’s sensitivity is not straightforward. That is because climate perturbations, like greenhouse gas emissions, require millennia before the whole system re-settles into a steady state (an equilibrium), and so we can’t rely on direct observations to retrieve an ECS value. We need simulations.
And what do they say?
The latest endeavors, shared in the last IPCC report, determined that climate sensitivity falls in the 2 K to 5 K range, and, since the temperature increase trend has been modest so far, it is most likely closer to the lower end of the estimates. Great, there is still time to cut down on CO2 and barely make it before Earth turns into a scorching wasteland. Right?
The problem is that these results can be a sensible indication, at best. Simulations run on a variety of assumptions and represent only the fraction of reality we can appreciate, definitely not the whole picture. And yet, there are ways to anchor these findings to observations which could, at least, boost the confidence that we are on the right track.
That is where our article chimes in. Worryingly so.
Earth’s Vulnerability Exposed
A team of scientists from the Center for International Climate Research, in Norway, NASA, and the University of Leeds, in the UK, took satellite measurements performed over our planet between 2001 and 2023 and stacked them against the same-period results from acclaimed climate models.
In conducting a comparison between the two data sets, the paper’s analysis focused on a physical quantity, known as Earth Energy Imbalance (EEI), defined as the difference between radiation entering and leaving our planet. Specifically, researchers were interested in evaluating how much the EEI would change in response to rising amounts of greenhouse gases, with an increased imbalance denoting an Earth less capable of releasing energy.
To achieve this objective, the team computed an average of the shift per decade, both on observational and model-produced data, and split the outgoing radiation value into its two primary contributions: shortwave (SW), typically associated with sunlight reflected to space, and longwave (LW), due to infrared thermal emission.
This way, satellite and model outputs could be easily represented as points on a plot, with coordinates corresponding to the SW and LW components of our planet’s behavioral change. On top of that, the study obtained estimates of the ECS for each of the models involved and then color-coded the resulting values into the same graph.
What researchers discovered is a meaningful physical relation between climate sensitivity, practically unfeasible to assess, and the shortwave-longwave strength shift, a relatively accessible piece of information. But what does this correlation tell us?
It looks as though models with low ECS tend to exhibit weaker SW-LW strength changes, whereas the opposite happens when high ECS models are considered.
Though these conclusions alone might not be cause for too much stir, the plot also features a peculiar point amongst all others, representing the article’s satellite data. Perched up where shortwave-longwave strength shifts hit substantial values, the observational benchmark, according to the relation that was found and even considering significant uncertainty, seems to better align with high climate sensitivity scenarios.
This troublesome result was also confirmed by other investigation avenues that were explored throughout the paper, clearly attesting to its reliability and decisively challenging the reassuring projections mentioned above.
Time for a Makeover
So, we have gone over what was meant by “mismatch” between theoretical and empirical data on climate sensitivity: through a correlation with an actually measurable quantity, the average SW-LW changes to outgoing radiation, a team of scientists drew up a comparison and were able to infer that predictions on ECS might very well be too optimistic.
But what about the second question – is it bad? Well, imagine we fix a carbon budget. We spend it all and then some more. Suddenly, we realize that the expected temperature increase caused by our emissions is higher than we had anticipated. Too much. And even if we instantly cut carbon release, the amounts already present in the atmosphere would still push Earth over acceptable thresholds. It’s not bad.
It is a terrifying prospect that might require a whole paradigm shift in the strategies we develop and apply to curb climate change. Would we be ready or even have any time to adapt, if it turned out to be true?
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