Disappearing clouds are contributing to faster global warming and tumbling temperature records.
Scientists have seen a decline of somewhere between 1.5 per cent and three per cent in the world's storm cloud zones each decade over the past 24 years.
The shrinking coverage, observed by a National Aeronautics and Space Administration-led team, results in less sunlight reflected back into space, allowing more in to boost global warming.
Overall clearer skies, a trend driven by evolving wind patterns, the expanding tropics and other shifts linked to climate change, is now thought to be the largest contributor to the planet's higher absorption of solar radiation.
Christian Jakob, a co-author of the study and director at the Monash-led Australian Research Council Centre of Excellence for 21st Century Weather, said the major heating consequences of shrinking cloud cover was now evident.
"It's an important piece in the puzzle of understanding the extraordinary recent warming we observed, and a wake-up call for urgent climate action," Professor Jakob said.
Last year was the hottest on record, the United Nation's World Meteorological Organization (WMO) said, clocking in at about 1.55 degrees above the pre-industrial era average.
A single year above 1.5C is not enough to breach the Paris Agreement, however, as the global pact's goals are based on long-term averages measured over decades.
The UN weather agency expects temperatures to keep rising, with a 70 per cent chance the 2025-2029 five-year mean will exceed 1.5C.
Unprecedented ocean heating has been felt particularly acutely in the waters surrounding Australia, leading to coral bleaching, fish kills and algal blooms.
The elevated rate of warming is due to global greenhouse gas emissions holding at all-time highs, largely due to burning fossil fuels and deforestation, according to the latest Indicators of Global Climate Change study released on Thursday.
If current emissions trends continue, the report prepared by dozens of scientists from around the world says there will be just over three years left in the carbon budget to achieve 1.5C of heating.
Policymakers and experts have gathered in Germany for a mid-year convention ahead of the main UN Climate Change Conference in Brazil scheduled for November.
