Will changes in clouds exacerbate global warming? Today, let's sit together and watch the clouds rise.

When we bask in the sunshine under a clear sky, we may not realize that the clouds above our heads are quietly affecting the temperature of the earth.

Clouds play a complex and critical role in regulating the Earth's climate. Scientists have been studying the cloud radiation feedback mechanism. In December 2024, a study published in Science pointed out that the total amount of low-level clouds on Earth has dropped sharply, and the ability to reflect sunlight has gradually weakened, which in turn has exacerbated global warming . In January 2025, a study published in Nature pointed out that changes in clouds have led to a weakening of long-wave radiation directed to the ground, which can alleviate the trend of global warming to a certain extent.

Image source: Science

So how do clouds regulate the Earth's climate? Today is World Meteorological Day, so let's unveil the mystery of clouds.

01 The climate effect of clouds: both a "sunshade" and a "thermal blanket"

Clouds are the most sophisticated climate regulation system, affecting the Earth's energy balance through two diametrically opposed mechanisms.

(1) Cooling effect

Cloud cover has a significant impact on temperature, one of the important effects of which is the cooling effect. For example, low-level clouds (such as stratocumulus and cumulonimbus clouds) composed of tiny and dense water droplets can reflect 30%-60% of the sun's shortwave radiation, like a " sunshade " for the earth. The albedo of cumulonimbus clouds (note: the ability of the earth to reflect solar radiation back into space) is as high as about 0.9, which means that most (90%) of the solar radiation that hits cumulonimbus clouds will be reflected back into space. This "sunshade effect" can effectively reduce the earth's energy absorption and lower the surface temperature.

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(2) Greenhouse effect

High-level clouds (such as cirrus clouds) are composed of ice crystals. Affected by the optical properties of ice crystals and the vertical structure of the atmosphere, they reflect and absorb less short-wave radiation from the sun, but their long-wave radiation absorption capacity is more than three times that of liquid clouds. They absorb a large amount of long-wave radiation emitted by the surface and re-radiate heat to the ground. This greenhouse effect is particularly significant at night, including low-level clouds, which also emit long-wave radiation to the ground at night, like covering the earth with a " thermal blanket ". This can be clearly felt in cloudy and cloudless mornings in winter. When the night is starry and cloudless, the morning is generally unusually cold, and when the night is covered with stratus clouds, the temperature in the morning is milder. This is a manifestation of the greenhouse effect of clouds.

Overall, this dual radiation property makes clouds a "dynamic regulator" of the Earth's energy balance.

02 Since clouds can reduce the amount of heat received by the ground, why might they actually exacerbate global warming?

Research shows that the Earth's cloud coverage is decreasing at a rate of about 1.5% per decade. This seemingly small change triggers a chain reaction. Generally speaking, the overall cooling effect of clouds is greater than the greenhouse effect , but climate change and human activities are quietly affecting the formation and dissipation of clouds, and further affecting the regulation of clouds on the climate through the cloud radiation feedback mechanism.

Studies have shown that the sharp reduction in low-level ocean clouds has reduced the Earth's albedo, thereby exacerbating global warming. Further exploration of the reasons for the reduction, on the one hand, the continued melting of snow and sea ice has changed the water vapor and cooling conditions required for the formation of low-altitude clouds; on the other hand, the optimization of air quality has reduced cloud condensation nuclei. In addition, changes in atmospheric circulation and ocean current patterns caused by natural climate change have also interfered with the formation and distribution of low-altitude clouds.

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In general, the dynamic changes of clouds are affected by both natural and human factors, and their formation and dissipation mechanisms are complex and interrelated .

Since the Industrial Revolution, greenhouse gas emissions have increased, and studies have shown that the increase in carbon dioxide and methane concentrations have an impact on the formation of stratocumulus and cirrus clouds, respectively. Anthropogenic aerosol emissions will affect cloud amount and cloud life; land use changes caused by urbanization will reduce surface albedo and evapotranspiration, inhibiting cloud formation.

03 Why are clouds considered one of the most uncertain factors in climate prediction?

The composition of clouds and the physical processes in clouds are complex, and the observation of cloud changes has always been a great challenge, all of which have led to difficulties in the study of cloud feedback mechanisms. Although modern climate models can accurately simulate typhoon paths, the global climate models currently used to predict climate change in the next few decades are mainly based on atmospheric dynamics equations, which make it difficult to accurately simulate the precise changes in clouds, making the prediction of the impact of clouds on climate warming full of uncertainty . Global warming causes changes in clouds, which will further affect the climate through cloud radiation feedback mechanisms. However, the extent to which these feedbacks will affect climate warming varies greatly from model to model.

After years of hard work, scientists have made considerable progress in improving the accuracy of cloud radiation simulation. Some scientists are also seeking breakthroughs from the perspective of observational data, no longer relying on complex measurements of cloud physical properties, but instead using electromagnetic wavelength data that can reflect clouds and long-wave radiation to analyze physical processes.

However, there is still a long way to go to fully answer the question of "the combined effect of cloud changes on climate", and scientists are working together to tackle this problem from different angles. For example, cloud microphysics research is carried out through cloud chamber equipment, and high-resolution climate models are developed to simulate atmospheric conditions to improve prediction accuracy. Machine learning algorithms can also play an auxiliary role based on cloud analysis models. In addition, the development of a modern integrated meteorological observation system will also provide more accurate cloud data, providing strong support for the study of the Earth's radiation balance.

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04 Conclusion

The story of clouds tells us that the climate system is far more sophisticated and fragile than we thought. We need to work together to protect this blue dome - because every cloud carries the breath of the earth's future.

The public can use clean energy to reduce the burning of fossil fuels, choose low-carbon travel methods, reduce carbon emissions, and reduce greenhouse gas concentrations to slow down the dissipation of clouds, especially low clouds; support environmental protection policies, promote aerosol emission control, and balance cloud microphysical processes; enhance climate awareness and conscious action, and promote systematic climate governance.

Author: Cui Guohui, reporter of China Meteorological Administration Meteorological Publicity and Science Center (China Meteorological News Agency)

Reviewer: Wei Ke, Researcher at the Institute of Atmospheric Physics, Chinese Academy of Sciences, Deputy Director of the Monsoon System Research Center

Produced by: Science Popularization China

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