A novel investigation has indicated that the Earth’s cloud cover is potentially exacerbating the intensity of global heating worldwide.
The study, conducted by scientists at Imperial College London and the University of East Anglia, utilised satellite data to identify that global heating is likely being enhanced by the Earth’s cloud cover, providing the most definitive evidence yet that global heating will increase over the long term, intensifying climate change.
the climate is not likely to warm below 2°C, with a global heating average increase of 3°C being more likely.
The study is published in Proceedings of the National Academy of Sciences.
Forecasting climate sensitivity
Pre-industrial CO2 levels were around 280 ppm (parts per million); however, levels today are closing in on 420 ppm and could rise as high as double the pre-industrial amount by the mid-century unless there are substantial decreases in emissions. The quantity of global heating estimated from doubling the pre-industrial levels of CO2 is known as the ‘climate sensitivity’, which is a measure of how powerfully the Earth’s climate will respond to such a change.
The most considerable ambiguity in predicting climate sensitivity is the influence of clouds and how they may change in the future due to their unpredictable properties, such as their height in the atmosphere and density, either increasing or decreasing global heating.
Dr Paulo Ceppi, the co-author of the study from the Grantham Institute – Climate Change and the Environment at Imperial, said: “The value of the climate sensitivity is highly uncertain, and this translates into uncertainty in future global warming projections and in the remaining ‘carbon budget’ – how much we can emit before we reach common targets of 1.5°C or 2°C of global heating.
“There is, therefore, a critical need to more accurately quantify how clouds will affect future global warming. Our results will mean we are more confident in climate projections, and we can get a clearer picture of the severity of future climate change. This should help us know our limits – and take action to stay within them.”
Cloudy with a chance of global heating
Characteristically, low clouds provide a cooling effect due to them obstructing the Sun from reaching the ground, whereas high clouds allow solar energy to reach the ground, which in turn causes a warming effect. The energy emitted back from Earth is different in this scenario, as this energy can be trapped by the clouds, which heightens the greenhouse effect, demonstrating how varying types and frequencies of clouds can significantly impact global heating.
To analyse the influence of clouds, the team developed an innovative method to measure the relationships between global satellite observations of clouds and the associated temperature, winds conditions, and humidity, which gave them a more comprehensive forecast of how clouds will change as the Earth warms.
The scientists observed a more than 97.5% probability that clouds will enhance global heating, doing this by both reflecting less solar radiation and increasing the greenhouse effect, inferring that a doubling of CO2 concentrations will result in nearly 3.2°C of warming.
Dr Peer Nowack, the co-author of the research from the School of Environmental Sciences and Climatic Research Unit at the University of East Anglia and Imperial’s Grantham Institute and Data Science Institute, said: “Over the last few years, there’s been a growing amount of evidence that clouds probably have an amplifying effect on global warming. However, our new approach allowed us for the first time to derive a global value for this feedback effect using only the highest quality satellite data as our preferred line of evidence.
“Our paper makes a major step towards narrowing the most important uncertainty factor in climate sensitivity projections. As such, our work also highlights a new pathway in which machine learning methods can help us constrain the key remaining uncertainty factors in climate science.”