The world's shrinking cloud cover is driving record temperatures, new research finds
The world's cloud cover has been shrinking significantly and may help explain the extraordinary heat of the last two years, new research led by NASA found.
The research, published this month, analysed satellite observations during the past 24 years.
It found areas over the ocean where storm clouds often form have dwindled by between 1.5 and 3 per cent per decade.
It may not sound like much, but Monash University professor Christian Jakob, who leads the ARC's 21st Century Weather Centre of Excellence, said that loss has amounted to a significant portion of sunlight being absorbed by the Earth instead of being reflected out to space.
"So that increase is what's providing extra warming to the climate in addition to the greenhouse effect, that's also increasing," Professor Jakob, who was a contributing author to the study, said.
He said the new finding could even help explain one of the big climate mysteries of the past couple of years.
The years 2023 and 2024 saw global average temperature reach record highs — each becoming the hottest year on record, and by a long way.
While most of the extraordinary heat could be explained by greenhouse gas emissions and the presence of the El Niño climate driver, there was still a margin at the top that puzzled climate scientists.
Scientists were looking into several possible explanations, including changes to shipping regulations and the underwater volcano Hunga Tonga-Hunga Ha'apai eruption in January 2022.
However, Professor Jakob said the change in clouds amounted to a significantly larger difference.
"What we found is the effect of clouds, and the shrinking of highly reflective clouds, is much, much larger," he said.
"I would say it's at least three or four times the influence of the other effects that have been put forward.
"So, while we can't say with certainty that it's the reason 2024 was so warm, it's fair to assume it contributed to the extraordinary warmth over the last few years."
The loss of clouds has to do with the changes in wind patterns, as a response to climate change, according to Professor Jakob.
This has led to a growth of the subtropical regions — where cloud is generally more sparse and patchy — while stormy regions have retracted toward the North and South poles.
These stormy regions, to the north and south, contain extensive cloud cover, which is highly reflective, sending sunlight back into space.
"The patchy clouds … these are the clouds that we are getting more of, while these intense grey skies, where more or less the entire sky is covered, are reducing," he said.
"And so, therefore, the area of the clouds that are very good at reflecting sunlight is getting smaller. And the area of the clouds that are not so good at reflecting sunlight is getting bigger."
Professor Jakob said this change was particularly evident at the boundary of these climate zones, including to the south of Australia.
"The most affected regions are actually over the oceans," he said.
"The ocean is an extremely good storer of energy, and it warms in the process of storing that energy.
"So, as the clouds no longer reflect the sunlight, it now reaches the ocean surface.
"The ocean takes up that energy that comes from the sun, and the sea surface temperatures go up, and that has major implications for how weather systems behave, but also major implications for the general warming of the planet."
Clouds are a really important part of the Earth's climate system, yet they remain one of the most challenging features in our climate models.
Professor Jakob said one of the keys to understanding them better was to understand changes to our weather.
"The clouds don't just magically change; they change because climate change changes how weather systems behave," he said.
"In this case, where they (the weather systems producing high cloud cover) occur is pushed further towards the poles."
Investigating changes in our weather and climate systems is the main aim of ARC Centre of Excellence for 21st Century Weather.
He said that for communities to be better prepared for a future climate, a shift in thinking from climate change to weather change needed to take place.
"The poster child numbers we use to describe climate change are things like global mean temperature. Global mean temperature is really a very nice and very clear indicator that the climate system is affected by humans," he said.
"However, when's the last time you've planned a barbecue on a forecast of global mean temperature?
"What are we actually interested in in terms of the impacts that change in global mean temperature will have on us? And that's of course the weather."
He said we had a good knowledge about how climate change was currently affecting temperatures on the ground and several types of extreme weather, but there was still a lot to learn.
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