For the past two decades, low-level cloud cover has been declining, increasing the amount of sunlight absorbed by Earth and amplifying global warming.
As global temperatures have reached record highs in recent years, there has been concern that the decline in cloudiness may be enhancing warming more than previously expected.
In a new study, published in Atmospheric Chemistry and Physics Letters, we investigate how the decline in global cloudiness affects the Earth’s “energy imbalance” – the difference between absorbed solar energy and heat radiated into space that results in global warming.
This imbalance has more than doubled over the past 20 years, as greenhouse gases have trapped more heat in the atmosphere.
We find that, since 2003, the decrease of cloudiness has been responsible for half of the increase of Earth’s energy imbalance.
Analysing the drivers of global changes to cloud cover, we find that the decrease in cloudiness over the past two decades has been primarily driven by humans, rather than being caused by natural variations in Earth’s climate.
Taken together, our findings mean that scientists can even more confidently attribute recent warming to human activities.
Low-level clouds and warming
Low-level clouds are those that have a base below 6,500 feet (2,000 metres) above Earth and include stratus, stratocumulus and cumulus. They are typically found over large areas of the global ocean, where there is a large moisture supply from evaporation.
These clouds have a powerful impact on the Earth’s climate because they reflect a substantial fraction of incoming sunlight back into space.
By acting as the Earth’s “sunscreen”, they keep the climate cooler than it would otherwise be.
Satellite observations reveal a global decline in these low-level clouds since the turn of the millennium. This is shown in the chart below, where the black line represents the average percentage of the Earth covered by low-level clouds and the dashed line the downward trend.
Our research shows that the decline in cloudiness over the past 20 years has played a major role in increasing the Earth’s energy imbalance and, therefore, warming.
The Earth’s energy imbalance is the difference between the amount of energy arriving at the Earth from the sun and what is reflected and radiated back to space.
Rising greenhouse gas emissions from human activity are upsetting this balance by trapping more energy in the atmosphere, leading to warming.
A less cloudy atmosphere also helps supercharge the energy imbalance, because it means more sunlight reaches the Earth.
In our research, we use a simple model to assess how changes in low-level clouds between July 2003 and June 2024 contributed to the Earth’s energy imbalance.
We find that, averaged globally, changes in low-level cloudiness caused an extra 0.22 watts per metre squared (W/m2) per decade of absorbed sunlight. This amounts to exactly half of the concurrent increase in Earth’s energy imbalance over the same time period.
This is shown in the chart below, where the green line represents the increase in the Earth’s energy imbalance over 2003-24 and the black line shows the contribution of low-level clouds to that trend.
Why is cloudiness changing?
Scientists have attributed declining cloud cover in the 21st century to three main causes.
The first is a decrease in human-caused aerosol emissions over recent decades. Aerosols – tiny, light‑scattering particles produced mainly by burning fossil fuels – influence the formation of clouds, by acting as “seeds” for cloud droplets to form.
In recent years, aerosol emissions have been reduced due to efforts to clean up air pollution, such as cleaner shipping fuel regulations. Cleaner air has resulted in a decline in cloudiness.
Second, increasing concentration of greenhouse gases in the atmosphere has led to a warmer and drier atmosphere, which also helps to dissipate clouds.
Although a warmer atmosphere generally holds more water vapour in absolute terms, what matters for clouds is the “relative humidity” of the air, which has been declining in many places. This is a measure of how “saturated” the air is, or how much water vapour the air contains compared to the maximum it could hold.
Finally, cloud cover decreases have also been linked to ocean surface warming, which affects atmospheric humidity and, thus, cloudiness. Reduced cloudiness leads to more sunlight being absorbed at the ocean surface – and more warming. This amplifying loop is known as a “cloud feedback”.
However, the exact strength of these three effects on cloud cover is still unclear.
In fact, cloud feedbacks are among the main uncertainties in climate model projections of global warming.
Attributing low-cloud cover changes
In the next step of our study, we explore how the three human-caused factors mentioned above – aerosols, greenhouse gases and cloud feedback – contributed to recent low-level cloud changes.
We also look at the extent to which cloud changes could be explained by natural climate variability, which causes substantial year-to-year fluctuations in cloudiness and energy imbalance.
To do this, we use a statistical technique known as “cloud-controlling factor analysis”.
This analysis involves calculating the sensitivity of clouds to their “controlling factors”, including meteorological variables, such as temperature, humidity and winds, as well as aerosol concentrations.
To calculate how each factor contributed to the bigger picture of declining cloud cover, we combine sensitivity calculations with observed trends in meteorology and aerosol emissions.
This analysis allows us to attribute trends in cloud cover to known physical drivers: either natural climate variability, or human activities linked to aerosols, greenhouse gases and cloud feedback.
Our research finds that about 40% of the low-level cloud decrease since 2003 was driven by warming of the ocean surface – in other words, the cloud feedback process. This is followed by the effects of greenhouse gases (21%) and aerosols (14%).
Natural climate variability accounts for just 3% of the low-level cloud trend.
(The remaining 23% of the trend cannot be explained by our statistical method. This could be due to the limitations of cloud, temperature, humidity and aerosol concentration observations.)
The chart below shows how human-driven factors – the sum of aerosol effects (red), greenhouse gas emissions (pink) and cloud feedback (burgundy) – were responsible for almost three quarters of the decrease in low-level cloudiness over 2003-24. Natural climate variability (blue), on the other hand, played a minor role.
Thus, our analysis indicates that, at global scales, the observed cloud decrease is primarily driven by humans, rather than being caused by natural variations in Earth’s climate.
And, since low-level clouds contribute to half of the energy imbalance increase over the same period, it follows that a significant part of recent rises in energy imbalance can also be attributed to humans.
Clouds in climate models
So, should we be concerned that this cloudiness decrease means the Earth could see more warming than already anticipated?
To answer this, we looked at whether the climate models used by scientists to project future global warming accurately simulate recent declines in low-cloud cover.
While the models produce a wide range of outcomes, we found that, on average, the simulated changes in low-level cloudiness changes are in close agreement with real-world trends.
This is reassuring, as it means the effects of low-cloud cover are already accounted for in existing warming projections.
However, questions still remain around what is driving recent increases to the Earth’s energy imbalance, which have outpaced projections made by climate models.
Our findings rule out declines in low-level clouds as the reason that climate models have been underestimating the Earth’s energy imbalance, and, as a result, warming. But it is still possible that models are underrepresenting future global warming to some extent.
Low-level clouds are just one of several drivers of changes in energy imbalance. Future work will therefore need to assess other observed and simulated drivers of energy imbalance changes: for example, the impact of upper-level clouds, or changes in water vapour or sea ice.
Finally, it is important to stress that, while our findings are reassuring, they should certainly not make us complacent about the current global warming trend. The impacts of climate change are serious enough as they are – even if there is no evidence of a missing amplifying feedback in our projections.
The post Guest post: How declining cloudiness is accelerating global warming appeared first on Carbon Brief.
Guest post: How declining cloudiness is accelerating global warming
Climate Change
Large flotilla brings Pacific voices and message to leaders at Pre-COP meeting: Keep 1.5C Alive
NADI, FIJI Wednesday 7 October 2026 — Around 80 people including Pacific and Torres Strait community members, Elders and youth activists travelled as part of a colourful flotilla past the Pre-COP venues with a message for leaders: ‘Keep 1.5°C Alive’.
High res footage and images available here
The large flotilla included traditional Fijian voyaging vessel the Uto Ni Yalo, six 6-person outrigger canoes, and Greenpeace campaigning vessel the Oceania which sailed from Sydney to the Pre-COP in Nadi. On board were Elders, climate-vulnerable communities members from across the Pacific and Torres Strait, youth activists and poets, and campaigners and climate experts from across the region.
Messaging on canoes and banners said ‘Hold the Line at 1.5°C’ and ‘Keep 1.5°C Alive’ — a reminder to leaders that the climate limit established under the Paris Agreement is a non-negotiable survival line.
Shiva Gounden, Head of Pacific at Greenpeace Australia Pacific, said: “People from across the Pacific and Australia have come together today to make sure the voices of our communities are heard by leaders meeting here in Nadi for the Pre-COP climate talks. The Taku Pakasoa Declaration adopted here at Pre-COP means ‘Strength in Unity’, and that’s how we’re coming together today.
“Our message is clear: Hold the Line on 1.5°C and centre those most impacted by the climate crisis in your decision-making. Our children’s futures must not be stolen away so that polluting nations can continue down the fossil-fuel path.
“Limiting global heating to 1.5°C is a non-negotiable survival line for Pacific communities and for humanity. Every cyclone, every storm now blows with the deadly force of accumulated emissions and gives a warning of what is to come as we face a dangerous summer of climate-fuelled extreme weather. Do not ignore our voices.”
On board, Aigagalefili Fepulea’i-Tapua’i, Pacific youth climate advocate and poet from Aotearoa Climate Action Network, said: “To hold the line on 1.5C for our Pacific family, New Zealand, as the only country where the connection between environmental protection and indigenous rights is legally validated by our constitutional document, must protect the rights of Māori.”
ENDS
Media contact: Kate O’Callaghan in Nadi on +61 406 231 892 (Whatsapp/Signal)
Large flotilla brings Pacific voices and message to leaders at Pre-COP meeting: Keep 1.5C Alive
Climate Change
A ‘victory’ for communities as High Court rules climate impacts from coal and gas must be considered even where fossil fuels are exported
SYDNEY, Wednesday 7 October 2026 — In response to the landmark High Court ruling that climate impacts of fossil fuel projects must be considered by NSW planning authorities, the following lines can be attributed to Joe Rafalowicz, Head of Climate and Energy at Greenpeace Australia Pacific
“The High Court decision today is a victory for communities that bear the brunt of the storms, bushfires and extreme weather fuelled by Australian fossil fuel corporations.
“Coal and gas companies have claimed they are not responsible for their pollution because it happens overseas, but today Australia’s highest court sided with common sense and scientific evidence to find that every new coal and gas approval in this country could put us at risk, no matter where it is sold or burnt.
“As leaders meet at the Pre-COP talks in Fiji this week, Pacific communities are reaffirming the importance of the 1.5C temperature limit as a survival line for humanity, and is a scientific, moral and legal obligation as affirmed by the landmark Pacific-led ICJ Advisory Opinion. The highest court in the world, and now in Australia, have been clear: it is legally imperative that all of the pollution from fossil fuel projects be considered before approving a new project.
“Now is the moment for the Australian Government, as COP31 President of Negotiations, to find the courage, leadership and grit our country is known for to chart a new course away from fossil fuels. This begins with showing leadership at home by ending new coal and gas approvals.”
-ENDS-
After witnessing the effects of sea-level rise in the low-lying island nation of Tuvalu, Pacific leaders on Tuesday used the pre-COP31 summit in Fiji to voice their frustration at the difficulties they have experienced in tapping the global climate finance system.
A small group of government leaders, climate negotiators and heads of development banks and climate funds took a trip to Tuvalu’s Funafuti atoll on Tuesday morning, travelling by road over land just 10-20 metres wide to visit a project that is building barriers to keep the sea from the land.
They then flew to Fiji for the pre-COP summit, where several Pacific leaders said they had been let down by the insufficient quantity, bad terms and slow speed of international finance to help them adapt to a warming climate that is bringing higher oceans, drought and more powerful storms to their shores.
“Right now, our islands are like a canoe that has been rammed by a massive foreign ship. Our canoe is taking on water, we are sinking, and what is the world’s response?” asked Palau’s President Surangel Whipps Jr.
“They hand us a tiny patch to cover a gaping hole,” he continued, “but the bureaucratic process just to receive that patch is so slow that the water fills the hole while we wait. Then to rebuild the vessel so that we can survive the next storm, we are offered loans, debt that adds weight to a sinking boat packaged in red tape so thick we can barely access it. And while we wait, the water continues to fill.”
Pacific leaders and Australia called again on governments to invest in the new Pacific Resilience Facility (PRF), which has been designed by the Pacific Islands Forum and is seeking $500 million in investments by COP31 in November.
It has around $180 million so far, but did not receive additional pledges during the UN General Assembly in New York. The PRF aims to invest to generate annual returns which it can give to projects like water tanks for drought-hit communities.
Witnessing sea level rise
The annual pre-COP gathering is usually a low-profile technical meeting of climate negotiators. But this year, Australia – which is the president of negotiations at COP31 – partnered with the Pacific to introduce a “leaders segment” in an attempt to shine a spotlight on climate issues affecting the region.
Fourteen government leaders – from Australia, Timor-Leste, Mauritius and the Pacific – made the trip. They were joined by the European Union’s climate commissioner Wopke Hoekstra, the heads of the Green Climate Fund and the Asian Development Bank and former Australian prime minister Julia Gillard.
On their return to Fiji, Solomon Islands Prime Minister Matthew Wale told the pre-COP leaders roundtable that the sea level rise they had witnessed was personal for him.
“Tuvalu was not just a site visit for me. I saw the story of my own saltwater people,” he said, adding that he, his daughter and his grandfather had lost their houses to sea level rise and that three-quarters of his electorate live on land that will be underwater in the next 30 years.
From the other side of the world, Antigua and Barbuda’s environment minister Michael Joseph said Tuvalu’s problems felt similar to those of his own Caribbean islands. “I saw vulnerable communities… just metres from the sea and people determined to remain on their land, preserve their culture and way of life,” he said.
A group of Fijian schoolchildren told the leaders it was not just sea level rise the Pacific struggles with but also heatwaves, droughts and storms, which worry their families and prevent them from learning.
Climate finance red-tape
Several Pacific leaders criticised the world’s leaders for not doing enough to combat climate change. Cook Islands Prime Minister Mark Brown expressed disappointment that only two non-Pacific leaders had come to the pre-COP, a fact Australian media widely picked up on to label the event a flop and question its A$20 million (US$14m) price tag.
“We’ve heard a lot of numbers these last two days,” Brown said. “Let me share one of my own. More than 50 invitations extended to world leaders… to see for themselves what high emissions are doing to our nations and our ocean – an ocean that covers nearly one-third of the Earth’s surface.”
-
Pacific islands seek backing for new regional fund ahead of COP31
Pacific leaders will appeal for pledges to a new regional fund designed to swiftly channel climate finance to local communities -
The Pacific made history in the courts – now we must do it in the negotiations
Legal clarity alone will not lead to reduced emissions, more finance or stronger national climate plans – political will is key to meeting states’ obligations -
Civil servants warn fossil fuel exploration could harm New Zealand’s climate reputation
Advice to politicians says revoking a ban on oil and gas drilling could damage relations with Pacific neighbours and risk lawsuits
He called for more climate finance for the Pacific, asking “if the world is prepared to assess our suitability for climate finance, why is it not equally prepared to scrutinise whether those responsible for delivering it are meeting their obligations?”
Like Palau’s president Whipps, Naoero’s President David Adeang criticised the red tape that is hindering access to climate finance as well as a lack of money, complaining especially about “complicated procedures, heavy reporting, delays in approval and disbursement”.
Adeang added that “the way we assess vulnerability matters”, adding that it should be measured by more than income. Naoero, for example, is classified by the World Bank as high-income, restricting which climate finance it is eligible for.
Action plan to improve access
On Thursday, the Australian government will present a statement and action plan on improving access to climate finance for small island developing states and least developed countries, which it is asking other countries and organisations to endorse.
The statement addresses some of these Pacific complaints as well as acknowledging that progress has already been made on simplifying access by multilateral development banks and climate funds.
In Fiji, Asian Development Bank head Masato Kanda said his institution is “tailoring our finance and operations to island realities” because “your children and their children should be able to grow old in the countries their ancestors have called home for millennia”.
The executive director of the Green Climate Fund (GCF), Mafalda Duarte, said that the GCF-backed coastal adaptation project leaders visited in Tuvalu shows that “climate finance works” although – as the project took eight years to implement – “it takes time, and therefore we have no time to waste”.
Australia calls for optimism
While Pacific leaders expressed concern that the world is set to blast past its agreed 1.5C warming limit, endangering their nations, Australia’s Prime Minister Anthony Albanese called for “optimism”. “If people think there is no hope, then they will not strive to get the change that we need,” he said.
He said that when he attended his first COP in 2005, Australia’s renewable energy target was 2%. Its target is now 82% renewable electricity by 2030.
While Albanese promoted Australia’s success at electrifying homes and businesses and rolling out renewables, he has been criticised by climate campaigners for extending the production of fossil fuels, including coal – largely for export.
France’s Minister for Ecological Transition Monique Barbut defended the European Union’s climate action at the pre-COP meeting. She said the continent was heating up and reducing emissions faster and providing more climate finance than anywhere else in the world.
“It is time for all major emitters to step up and do their fair share” on climate finance, she said. Most developing countries with large emissions have fiercely resisted joining the club of climate finance donors, arguing they have played a disproportionately small historic role in causing climate change.
Barbut, as well as Palau’s president Whipps, called for the next flagship scientific assessment report of the Intergovernmental Panel on Climate Change (IPCC) to be finished by COP33 in 2028, in time to inform the next global stocktake of national climate action.
This timeline has been opposed by countries like India, Saudi Arabia and China, who argue it would put an unfair burden on developing countries. Barbut said countries should “support the work of the IPCC rather