ʹڲƱ
Sunset above the clouds. Sunset above the clouds.

The climate wild cards still missing from our models

Play icon

An ice corridor in a glacier. Photo: Sergey Torbik, Pexels.

Elva Darnell
Elva Darnell,

Climate models have been remarkably effective at projecting global warming trends, but they still fail to fully capture some crucial processes that could dramatically accelerate climate change, according to experts at ʹڲƱ.

Most climate change models look similar, with temperatures slowly rising year by year. But history shows Earth’s climate doesn’t always follow a linear path – it lurches and jumps, says Professor Katrin Meissner, Director of the ʹڲƱ Climate Change Research Centre.

Prof. Meissner studies abrupt climate shifts and the thresholds and feedback loops that drive them. While today’s climate models have proven remarkably accurate, she warns they overlook key processes that could lead to more rapid, unpredictable warming in the future.

The challenge of improving climate models is immense. But Prof. Meissner says the science already gives us a strong mandate for action.

How climate models work

Climate models use equations based on physical laws to simulate future warming. These models incorporate forcings – elements that drive climate, such as greenhouse gases and solar radiation.

Since their inception in the 1970s, climate models have grown more complex. Early models included representations of the atmosphere, oceans, land surfaces, and sea ice. Over time, scientists have added aerosols, the carbon cycle, vegetation, atmospheric chemistry, and land ice.

“Our current models do a good job of simulating today’s climate and have been fairly accurate predicting recent decades of warming, but they struggle as temperatures get higher,” Prof. Meissner says.

“This is because many complex processes, which interact, are not fully represented in existing models.”

One key constraint is computational power. Climate models divide the Earth into 3D grid boxes across space and time.

Horizontal resolution and time steps are closely linked in atmospheric models. Since elements like wind can't 'skip' over grid boxes, smaller grid sizes require correspondingly smaller time steps to maintain accuracy and stability.

Doubling the resolution of models increases the number of grid boxes at least eightfold, and time steps twofold, requiring roughly 16 times more computing power.

Clouds, carbon, and chaos

Clouds present a major modelling challenge, says ʹڲƱ Professor Steven Sherwood, whose work has focused on their impact.

Clouds can both cool and warm the planet, depending on their type, altitude, and location. But the turbulent processes that drive their formation are still not fully understood or modelled, making them a major source of uncertainty.

Recent research indicates that Earth is absorbing significantly more heat than climate models have predicted, with changes in cloud cover identified as a possible contributing factor, says Prof. Sherwood.

Media enquiries

For enquiries about this story or interview requests please contact Elva Darnell

ձ:+61 431 601 216
Email: e.darnell@unsw.edu.au
Katrin Meissner
Steven Sherwood
Featured experts
Katrin Meissner, Steven Sherwood,
The sun sets above the clouds. Photo: Aleksejs Bergmanis, Pexels

Prof. Meissner’s research into ancient climates, where CO₂ levels rival or exceed today’s, also points to clouds as a major wildcard.

“Paleoclimate data shows warming near the poles far beyond what current models predict,” she says. “One explanation involves high-altitude clouds that most models don't simulate well due to upper-atmosphere limitations.”

In high-resolution tests, Prof. Meissner and Prof. Sherwood and their teams simulated such clouds under high CO₂ conditions.

“We found that these clouds not only formed but could contribute up to 7°C of additional warming at high latitudes – a staggering increase,” Prof. Meissner says.

Other atmospheric factors add further complexity. Air pollutants behave differently depending on whether they reflect sunlight or absorb heat, but their interactions with surrounding elements can also change their climate effects.

The (IPCC) is developing improved methods to help countries better track and report short-lived climate pollutants, to help refine future climate projections.
Brolgas wading. Photo: Adobe Stock

Complexity in the carbon cycle

Vegetation, soils, and microbes also interact in intricate ways and influence the amount of carbon stored on land. Likewise, life in the oceans, the chemistry of seawater, and ocean circulation influence the amount of carbon stored in oceans. Yet, says Prof. Meissner, models still treat these processes too simplistically to capture the full interaction with the climate, particularly the carbon cycle in oceans.

“The ocean holds 60 times more carbon than the atmosphere, and small shifts in ocean circulation or biological activity can reshape the carbon sink, with consequences for atmospheric CO₂.

“Unfortunately, our ocean biogeochemistry process understanding and models are still in their infancy and quite crude.”

Ice sheet dynamics are another relative weak spot. Processes such as the flow of ocean water beneath ice shelves, leading to melting and potential collapse, are too complex to simulate accurately in global models.

Tipping points and cascading risks

Tipping points  — critical thresholds where the climate system shifts suddenly and irreversibly — add further complexity to climate predictions.

History shows that the Earth’s climate has shifted abruptly before. In the Palaeocene-Eocene Thermal Maximum (PETM) around 56 million years ago, global temperatures rose by 5 to 8°C over a few thousand years, leading to mass extinctions in the deep ocean.

Carbon emissions during this period were estimated between 2,000 and 10,000 billion tonnes, but the annual release rate was likely below 1.1 billion tonnes, about one-tenth of today’s human-driven emissions.

“Comparing today’s climate change to events like the PETM puts our actions into perspective.

If such dramatic shifts unfolded under much slower carbon release, what might we expect today, when the brakes are off?", says Prof. Meissner.
If such dramatic shifts unfolded under much slower carbon release, what might we expect today, when the brakes are off?
Prof. Katrin Meissner
ʹڲƱ Climate Change Research Centre Director

Prof. Meissner says the events of the past show tipping points aren’t just theoretical risks, and that risk increases with global warming.

"Tipping points aren’t just about rising temperatures, but involve feedback loops and nonlinear reactions," she says.

“Current models rarely include these feedbacks because simulating them requires intensive computation and, occasionally, a deeper level of understanding of highly dynamic systems than our science currently allows.

“Tipping points can trigger others in a domino effect known as a tipping cascade. For instance, ice loss in West Antarctica or Greenland will lead to changes in and warming at high latitudes, which in turn could activate other tipping points, such as the thawing of permafrost or the degradation of boreal forests.

“So, crossing one tipping point can trigger more tipping points, and, at this point, we don’t know what the consequences will be. It is also possible that we don’t even know all the tipping points that exist in the climate system.

“Incorporating a better representation of clouds, feedbacks, and tipping cascades into our models is one of the biggest scientific hurdles we face,” she says. “It won’t be solved quickly, but we already know enough to act decisively.”

Related stories