According to a new technique of analyzing satellite data of Earth's cloud cover, clouds are highly likely to exacerbate global warming.
Scientists from Imperial College London and the University of East Anglia conducted the study, which provides the best evidence that clouds would increase global warming over time, aggravating climate change.
The findings published today in the Proceedings of the National Academy of Sciences also show that at twice atmospheric CO2 concentrations over pre-industrial levels, the climate is unlikely to warm below 2°C, and is more likely to rise more than 3°C on average.
CO2 levels were approximately 280 ppm (parts per million) before the industrial revolution, but they are now reaching 420 ppm and may quadruple by mid-century if significant emissions reductions are not achieved. The 'climate sensitivity' - a measure of how strongly our climate will respond to such a shift - is the amount of global warming anticipated from a doubling of pre-industrial CO2 levels.
How Clouds can Affect the Climate
The effect of clouds and how they may change in the future is the biggest source of uncertainty in climate sensitivity forecasts. This is because clouds may either accelerate or decrease warming depending on density and altitude in the atmosphere.
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"The value of the climate sensitivity is highly uncertain, and this translates into uncertainty in future global warming projections and the remaining 'carbon budget' - how much we can emit before we reach common targets of 1.5°C or 2°C of global warming," said co-author Dr. Paulo Ceppi of Imperial College's Grantham Institute - Climate Change and the Environment.
"As a result, it's important to better understand how clouds will impact future global warming. Our findings will increase our confidence in climate forecasts and better understand the severity of future climate change. This should assist us in recognizing our boundaries and taking steps to stay inside them."
Low clouds have a cooling effect by blocking the sun's rays from reaching the Earth. On the other hand, high clouds cause warmth because, although allowing solar energy to reach the ground, the energy radiated back by the Earth is different. The clouds can trap this energy, amplifying the greenhouse effect. As a result, the kind and amount of cloud produced by a warming globe influence future warming potential.
Developing a New Technique
The researchers devised a new technique to quantify connections between state-of-the-art global satellite measurements of clouds and the related temperature, humidity, and wind conditions, inspired by concepts from the artificial intelligence field. They were then able to further limit how clouds would evolve as the Earth warms based on these observed correlations.
Accelerating Global Warmings
They discovered that clouds will accelerate global warming by reflecting less solar energy and boosting the greenhouse effect, with a 97.5 percent likelihood. These findings also imply that doubling CO2 emissions will result in a 3.2°C increase in global warming. This study has the highest level of confidence of any study to date, and it is based on data from worldwide observations rather than data from specific locations or cloud kinds.
Stepping Up Climate Research
"Over the last few years, there's been a growing amount of evidence that clouds probably have an amplifying effect on global warming," said co-author Dr. Peer Nowack of the University of East Anglia's School of Environmental Sciences and Climatic Research Unit and Imperial College's Grantham Institute and Data Science Institute. However, utilizing just the highest quality satellite data as our preferred line of evidence, we estimated a worldwide number for this feedback effect for the first time.
"Our study takes a significant step toward reducing the most significant source of uncertainty in climate sensitivity estimates. As a result, our research points to a new direction in which machine learning approaches might aid in constraining the significant remaining uncertainties in climate science," the team claimed.
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