The Super Greenhouse Effect and Winds as Global Temperature Controllers

A useful perspective to understand the role of natural ecosystems in climate regulation

It says something about our species that, once humans could grow more food than each person needed, they began supporting individuals whose role was not to hunt or harvest, but to ask questions and do science. Apparently, this activity was perceived by (some part of) the society as useful. In the case of fundamental science, the value, in addition to sharing the pure intellectual joy of discovery (and the ability to experience and share this joy must be genetically encoded in Homo sapiens), lies in offering new perspectives on how the world functions. Before any problem can be solved, it must be properly framed. It does matter whether we see the Earth as flat or spherical, which is the kind of foundational perspective that basic science provides.

Likewise, in inhabiting a living planet, it matters whether we correctly understand the role of life in shaping the conditions that support our existence. Today I will discuss some rarely mentioned aspects of the notion of climate stability, which is important in this context. It is a scheduled post; I will be offline till the end of September.

The Super Greenhouse Effect

Our planet absorbs shortwave radiation from the Sun and emits longwave radiation back to space. To visualize this: The incoming shortwave photons are, on average, about 20 times more energetic than the outgoing longwave ones—a ratio stemming from the temperature difference between the Sun (around 6,000 K) and Earth (about 300 K). In a steady state, where incoming and outgoing energy balances, this means each absorbed solar photon effectively "decays" into roughly 20 thermal photons that Earth radiates away. This is what supports life.

The Earth's atmosphere is largely transparent to incoming shortwave solar radiation, allowing it to reach the surface. However, it absorbs much of the outgoing longwave thermal radiation and re-emits part of it back toward the surface. As a result, the longwave radiation escaping to space, which balances the absorbed solar radiation, is considerably smaller than that emitted by the planetary surface. The stronger the greenhouse effect, the smaller this escaping fraction becomes.

We can quantify the greenhouse effect by this ratio, let it be k, of the longwave radiation escaping to space to the longwave radiation emitted by the surface. (For our current climate, k = 0.6.) Climate stability will depend on how the greenhouse effect responds to changes in the planet’s temperature.

What we also need to remember is that the planet's surface emits more radiation as it warms and less as it cools. This acts as a key stabilizer: in the absence of a greenhouse effect, if the planet warms temporarily—for instance, due to heightened solar activity—it will emit more radiation until the outgoing flux balances the increased incoming solar radiation. The temperature then stabilizes at a new equilibrium.

Now let us imagine that as the planet’s surface warms, the atmosphere becomes even more opaque to longwave radiation—so much so that the outgoing radiation at the top of the atmosphere decreases even as surface radiation increases. This phenomenon is known as the Super Greenhouse Effect. It represents a potential source of climate instability.

To clarify once again: the “usual” greenhouse effect refers to the fact that outgoing radiation to space is lower than the radiation emitted by the planet’s surface. As the surface temperature and radiation increase, the ratio between outgoing and surface radiation may increase (though unlikely), remain constant, or decrease. In a special case of this ratio decreasing even more rapidly than surface radiation increases, the outgoing radiation will decline as the surface warms. In this case, we are dealing with a Super Greenhouse Effect.

Getting rid of heat

The graph below shows the ratio of surface radiation to outgoing radiation, i.e., 1/k, under cloudless and cloudy conditions. It reveals a sharp increase in this ratio at higher temperatures. This occurs because outgoing radiation diminishes rapidly, preventing the atmosphere from efficiently releasing its heat.

Fig. 9a from Stephens and Greenwald (1991) shows the ratio of surface radiation to outgoing radiation (i.e., 1/k) as a function of surface temperature. According to the Stefan-Boltzmann law, surface radiation increases proportionally to the fourth power of temperature. The spike at higher temperatures is caused by the decline in outgoing radiation. A similar but smaller decline was found under clear-sky conditions by Raval and Ramanathan (1989).

The following images illustrate the geography of the super greenhouse effect in a model experiment, which started from conditions similar to those in 1860 and, with a 1% per year increase in CO₂, quadrupled CO₂ concentrations by about 1999.

Fig. 1 from Stephens et al. 2016

The top-left panel shows that the planetary surface has warmed everywhere, resulting in a ubiquitous increase in surface radiation. However, outgoing radiation has declined over much of the tropical ocean, particularly in the Northern Hemisphere. This is depicted in the top-right panel for cloudy conditions and the bottom-left panel for cloudless conditions.

If a surface heats up but cannot radiate the excess heat away, it will continue warming. If this process affects the entire planet, it could rapidly lead to conditions incompatible with photosynthesis and modern life. The only way to avert such a runaway scenario is to export the excess heat from regions experiencing the super greenhouse effect and radiate it to space elsewhere.

This heat export occurs via atmospheric circulation, highlighting the critical role of winds.

Winds as Temperature Controllers: What Do We Know?

From the figures above, we can see that, at least according to models, the regions in the tropics that do not experience the super greenhouse effect are land areas. Efficient atmospheric transport of excess heat from ocean to land could help avert runaway conditions.

In particular, the atmospheric transport of moisture from the Atlantic Ocean to the Amazon rainforest can mitigate super greenhouse conditions over the ocean. This highlights the potential importance of the biotic pump circulation for tropical and global climate.

Given the importance of atmospheric circulation, understanding its quantitative parameters is paramount for comprehending climate change. While the most obvious characteristic is the near-surface wind speed that we all experience, another crucial parameter is the rate at which the kinetic energy of winds is generated to sustain circulation against frictional losses.

Although everyone knows that typical wind speeds are a few meters per second, few could specify the rate of kinetic energy generation in Earth's atmosphere. Yet, this is a vital parameter. Without continuous regeneration of kinetic energy by air pressure gradients (which drive air from high to low pressure), the atmosphere would quickly come to a standstill, rendering heat export from local hotspots impossible.

How well do we know this rate? According to a recent textbook (Bohren and Albrecht, 2023, 2nd edition of Atmospheric Thermodynamics), not very well. Speaking of the global atmospheric heat engine, they note:

In the atmosphere the global kinetic energy dissipation rate, which balances the generation rate, is about 2–5 W m⁻².

Is this good precision? Not really. For example, in a modeling study of Marvel et al. 2013 aimed at estimating how much additional wind power could be retrieved from the atmosphere, it was found that approximately doubling atmospheric power resulted in 11 K of global cooling! The Hadley cell extended to the poles, suppressing rainfall and cloud formation at higher latitudes.

This does not mean there is a (linear) relationship between planetary temperature and the power of atmospheric circulation, but it illustrates that air circulation has an enormous impact on the planet's climate. Remaining uncertain about its key quantitative characteristics is unhelpful.

Here, we point out that condensation-induced atmospheric dynamics (the physical mechanism behind the biotic pump) makes it possible to theoretically estimate the rate of kinetic energy generation from the known rate of precipitation (because biotic pump winds are driven by condensation-induced pressure gradients). That is to say, we take observed precipitation, multiply it by the theoretically derived potential energy release from 1 mol of condensed water vapor, and obtain a prediction for global atmospheric power.

We can then compare this prediction with observed atmospheric power, calculated from independently measured wind speeds and pressure gradients.

When this global comparison was made, the mismatch between theory and observation was about 30%, which is a remarkable result, especially in the absence of any competing theories for global atmospheric power. Thanks to this and other successful theoretical predictions, our work could not be easily dismissed early on, despite numerous attempts. Instead, it was recognized as offering a fundamentally new perspective on atmospheric dynamics.

A successful theory links independently observed variables. Condensation-induced dynamics does exactly that—for precipitation, wind speeds, and pressure gradients. This does not rule out differential heating as a driver of winds. But, as Hertz noted in his unpublished lecture on atmospheric dynamics,

If the atmosphere were dry, the temperature differences existing in it would by themselves give rise merely to movements of minor significance.

How close are we to a runaway greenhouse?

In fact, we may be closer than we'd like, or at least not safely far away. Modern climate models are calibrated using data from the present-day climate, which is relatively stable and clearly not experiencing a runaway greenhouse (otherwise, we wouldn’t be writing or reading this).

These same models are applied to reconstruct much warmer past climates, known as "hothouses." Some of these ancient climates are also described as "equable," meaning they had a very small temperature difference between the equator and the poles. This implies an efficient meridional heat transport.

However, models have difficulty reproducing these conditions. In particular, they often fail to match the known combination of very high temperatures and more moderately elevated CO₂ concentrations. Some models, in the process of trying to replicate these past states, display runaway behavior.

The graphs below show how different models attempt to recreate the hothouse conditions of the early Eocene.

Fig. 1a,b from Zhu et al. (2024).
Panel (a) shows how different climate models (listed below the figure) try to match the global mean surface temperature (GMST) and CO₂ levels (relative to preindustrial) during the early Eocene “equable” hothouse, shown as the large gray boxes. Model CESM1 gets into the core of the box but starts to run away at higher CO₂. CESM2 runs away even earlier, at lower CO₂ levels.
Panel (b) shows the meridional sea surface temperature difference (ΔSSTₘ), which some proxies suggest was very small in the Eocene.
Together, these panels show that none of the models both match the Eocene temperature and ΔSSTₘ and avoid runaway warming.

Scientists dismiss runaway climate behavior in models as physically implausible, arguing first that there is no geological evidence for a runaway greenhouse in Earth’s recent history, and second, that some models do not show such behavior. But these are weak arguments. Just because something hasn’t happened before does not mean it cannot happen.

Moreover, if we accept the climate community’s own approach to estimating probabilities, such as in Palmer (2025), where the likelihood of more than 4 K of warming from CO₂ doubling is calculated simply as the proportion of IPCC models that predict it, then the fact that two out of three CESM models (CESM1, CESM2, CESM3) exhibit runaway behavior is hardly reassuring.

Some might argue these runaway scenarios only appear at extremely high CO₂ levels, but perhaps that is simply because no one has funded the development of models that would run away at lower, more realistic concentrations.

How confident can we be about what is not possible if the modeling community gravitates toward similar assumptions and scenarios instead of welcoming and investigating discrepancies to better define the boundaries of possibility? How can we be sure all the right questions have been asked?

What makes our current situation fundamentally different from past high CO₂ climates is that no species back then had declared war on the biosphere. Today, we are systematically exterminating life wherever we can, while pretending scientifically and politically that this has no impact on climate. And then we are surprised when our models fail to predict warming anomalies or disruptions to the water cycle.

Let us hope the runaway has not started yet and let us act fast to protect the biosphere. Stop destroying it. Give it room to breathe. We may be surprised at how quickly the environment can begin to recover.

Simplified takeaways

• When it gets hot and humid enough, the atmosphere can stop releasing extra heat into space. This is called the super greenhouse effect.

• If this happens across the planet, it could lead to a runaway greenhouse effect—a rapid warming that might continue until much of the ocean evaporates. Something like this may have happened on Venus.

• Some modern climate models show this runaway behavior, which means it could also be possible on Earth.

• To prevent this, heat must be moved away from hot, humid regions and released into space somewhere else. This job is done by winds.

• Moving atmospheric water from oceans to tropical forests can be especially important for keeping the climate stable.

• To study this, we need to understand how winds are powered. Condensation-induced atmospheric dynamics behind the biotic pump helps explain this process.

• When we destroy natural ecosystems, we weaken the climate’s ability to stay stable.