The Earth Holds More Heat Than Climate Models Predict, and That’s Troubling

[Un article de The Conversation écrit par Steven Sherwood – Professor of Atmospheric Sciences, Climate Change Research Centre, UNSW Sydney – ; Benoit Meyssignac – Associate Research Scientist in Climate Science, Université de Toulouse – & Thorsten Mauritsen – Professor of Climate Science, Stockholm University]

But another approach can give us a very clear idea of what is happening: it is a question of following the amount of heat which enters the earth's atmosphere and the amount of heat that comes out. This amounts to drawing up the energy budget of the Earth, and it is now unbalanced.

Our recent study has shown that this imbalance has more than doubled in the past twenty years. Other researchers have come to the same conclusions. This imbalance is much more important today than what the climatic models estimated.

In the mid -2000s, the energy imbalance was approximately 0.6 watts per square meter (W/M²) on average. In recent years, the average has been closer to 1.3 W/M². This means that the speed at which energy accumulates on the surface of the planet has doubled.

These results suggest that climate change may well accelerate in the years to come. Worse, this disturbing imbalance appears even as uncertainty concerning the US funding for climate study threatens our ability to follow heat flows.

Balance of what enters and what comes out

The energy budget of the land works a bit like a bank account, where energy serves as money, and can enter and go out. By reducing expenses, money is accumulated on the account. Life on earth depends on the balance between heat from the sun and the one that comes out towards space. This balance is changing on one side.

Solar energy strikes the earth and warms it. The greenhouse gases that trap heat in the atmosphere retain part of this energy. But the combustion of coal, oil and gas has added more than two billions (two thousand billion) tonnes of CO₂ and other greenhouse gases in the atmosphere. These gases imprison more and more heat, preventing him from escaping.

Part of this additional heat warms the earth or melts the banquards, glaciers and glacial tablecloths. But this represents only a tiny part of the energy that the earth receives: 90 % of this heat is absorbed by the oceans because of their enormous calorific capacity.

The earth naturally loses heat in several ways. One of them is to think about the incoming heat on the clouds, snow and ice and send it back to space. Our planet also loses part of its energy in the form of infrared radiation which is also emitted to space.

From the start of human civilization until just a century ago, the average temperature on the surface was around 14 ° C. The energy imbalance that accumulates has now increased the average temperatures from 1.3 to 1.5 ° C.

Measure the energy balance from space and on earth

Scientists follow the energy balance in two ways. First of all, we can directly measure the heat from the sun and returning to space, using radiometers, on -board instruments on surveillance satellites. This data set and its predecessors have existed since the late 1980s.

Then we can accurately follow the accumulation of heat in the oceans and the atmosphere by performing temperature statements. Thousands of robotic floats have monitored temperatures in the world's oceans since the 1990s.

The two methods show that the energy imbalance has increased quickly. This doubling was a shock, because the most elaborate climatic models we use did not provide such a significant and fast change. In general, they provide less than half of the change that we actually observe.

Why this quick change?

We do not yet fully explain this situation. But new research suggests that an important factor is to be found in the clouds.

The clouds generally have a cooling effect. But the area covered by the very reflective white clouds has decreased, while the area covered by scattered and less reflective clouds increased.

We don't know exactly why the clouds change. A possible explanation could be the consequences of the fruitful efforts deployed to reduce the sulfur content of the fuels used for maritime transport since 2020, because the combustion of dirty fuel could have had a clarification effect of the clouds. However, the acceleration of the imbalance of the terrestrial energy budget began before this evolution.

Natural fluctuations in the climate system, such as the ten -year Pacific oscillation, could also play a role. Finally, and it is the most worrying, the change in the nature of the clouds could be part of a trend caused by global warming itself: it would be a positive feedback, which amplifies warming.

Is global warming more intense than expected?

These results suggest that extremely high temperatures in recent years are not isolated cases, but that they could reflect a strengthening of warming over the next decade, or even for even longer. This means that there will be more risks that climatic events are more intense, whether waves of scorching heat, droughts or extreme rain, or more intense and more durable marine heat waves.

This imbalance could have more serious long -term consequences. New research shows that the only climatic models that approach a simulation that reflects real measures are those whose “climate sensitivity” is higher. These models provide for greater warming beyond the next decades, in scenarios where emissions are not quickly reduced. However, we do not yet know if other factors come into play. It is still too early to say that we are on a high sensitivity trajectory.

Keep monitoring

We have known the solution for a long time: stop the combustion of fossil fuels and gradually suppress human activities that cause emissions, such as deforestation.

Keeping precise data over long periods is essential if we want to detect unexpected changes.

Satellites, in particular, constitute our early alert system, because they inform us of changes in heat storage processes about a decade before other methods.

But budget cuts and radical changes in priority in the United States could threaten the essential surveillance of the satellite climate.