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The fact that planet Earth is getting warmer is not news. However, the alarming rate at which it warmed over the course of 2023 took even the most expert of climate scientists by surprise. In an effort to understand what could be responsible, climatologists turned their sights to a previously understudied potential factor in climate change: low-level cloud cover.
Curious? Check out this gallery to find out more.
In 2023, there was a dramatic rise in the temperature of the Earth. Global temperatures went up by 0.2°C (0.36°F), which was much more than climate models had predicted.
Of course, global warming can to a large extent be explained by greenhouse gas emissions, which serve to trap heat in the atmosphere.
However, even taking this into account, the 2023 increase was far too dramatic for climate scientists to ignore or explain away with harmful gases.
In a bid to explain the worrying surge, climatologists looked at factors such as the loss of polar ice and the decrease in fine particles (aerosols) in the atmosphere.
It was not until the end of 2024, however, that scientists in Germany claimed to have discovered the most important culprit: a decrease in low-level clouds.
When it comes to keeping the planet cool, low-level clouds play an important role: they reflect roughly 50% of the sunlight that reaches them, thereby cooling the Earth's surface.
According to experts, a decrease in low-level cloud cover is a cause for concern, particularly since the trend may be the result of global warming itself.
It is helpful, in the first instance, to understand a little bit about how clouds help regulate the temperature of the planet.
Unfortunately, the theory is little complex, because clouds actually warm the planet up at the same time as they cool it down.
On the one hand, clouds can block light and heat from the sun, which helps keep the Earth cool. This is the effect that you notice on a cloudy day.
On the other hand, clouds also serve to trap any heat from the sun that does make it down to Earth. This effect carries on through the night, even when there is no sunlight.
Clouds within a mile or so of the Earth's surface tend to have a cooling effect, while clouds higher up in the atmosphere tend to have more of a warming effect.
Scientists at the Alfred Wegener Institute in Bremerhaven, Germany, first started to consider clouds as a climate change factor when temperatures rose unexpectedly quickly in 2023.
They started to look at NASA satellite imagery, as well as weather records compiled by the European Center for Medium-range Weather Forecasts (ECMWF).
Their investigations revealed a deficit of lower-level clouds, while upper-level clouds, on the other hand, appeared to be holding steady.
In terms of what is causing the deficit of low-level clouds, scientists are concerned that it may be a consequence of global warming itself.
According to Helge Goessling, climate physicist at the Alfred Wegener Institute, there are many climate models that suggest greenhouse gas-induced warming has an impact on clouds, particularly at a low level.
Confusingly, the decrease in low-level cloud cover could also be the result of reduced fumes from burning coal and stricter controls on marine shipping exhaust.
This is because, in an unfortunate twist of fate, the fine particles found in polluted air can actually act as seeds for forming clouds.
The irony is, therefore, that by cleaning up the air, we may actually trigger more climate change.
According to Goessling's colleague, Thomas Rackow, ocean currents may also have a role to play in diminishing low-level cloud cover.
As the upper layers of the ocean become shallower, as they do periodically, they also start to warm more easily. Studies have shown that this may reduce low-level cloud.
It is worth bearing in mind that oceanic cycles tend to be long term. Indeed, they are known to vary over the course of decades.
While a particular oceanic circulation may reduce low-level cloud cover and contribute to global warming at one time, it may have the opposite effect at another time.
This means that it can be very difficult to work out the extent to which these oceanic ups and downs are confounding current trends.
There are still plenty of unknowns when it comes to the relationship between climate change and low-level cloud cover.
It seems likely, however, that variations in the amount of low-level cloud are more important than people had previously imagined.
Sources: (Astronomy Magazine) (American Association for the Advancement of Science)
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LIFESTYLE Climate change
The fact that planet Earth is getting warmer is not news. However, the alarming rate at which it warmed over the course of 2023 took even the most expert of climate scientists by surprise. In an effort to understand what could be responsible, climatologists turned their sights to a previously understudied potential factor in climate change: low-level cloud cover.
Curious? Check out this gallery to find out more.