Image Credit: Jag_cz/Shutterstock.com
Clouds play a critical role in our climate; they influence heat circulation whilst also reflecting sunlight to keep the planet cool. However, current climate models do not accurately account for their contribution to global warming.
Recent climate models predict a doubling of atmospheric carbon dioxide above pre-industrial levels, which could cause global temperatures to soar. Researchers say this will cause a loss of clouds, allowing more solar energy to hit the planet; it has been described as the most concerning development in the science of climate change for a long time.
The models challenge a long settled-upon conclusion about how sensitive the climate is to greenhouse gas exposure.
Up in the Clouds
Scientists currently use models with theoretical representations of clouds to understand their role in the climate system and to predict how rising temperatures may affect cloud production and function.
A new study being conducted by over 40 different institutions aims to measure the interactions between cloud, convection, atmospheric circulation, and the climate in the hope that the findings can change the way cloud processes are represented in climate models.
The argument about the role of clouds in climate change is part of a wider concern about feedback in a warming world. The greenhouse effect of a doubling of carbon dioxide in the atmosphere will directly raise global temperatures by 1 °C, but it is more complex than this because of the amplifying responses of natural systems to the initial warming.
For example, ice and snow cover large parts of the planet, but as it melts, light-reflecting surfaces are replaced with darker ones that absorb solar radiation. As a result, there will be additional water vapor in the air, which itself acts as a greenhouse gas. Models suggest this extra vapor could double the direct greenhouse effect.
Clouds have always been the greatest uncertainty in climate calculations; their dynamics are complicated and occur on a small scale, making them difficult to include in climate models. Not only can they shade the Earth, they also trap heat. The effect of heat depends on how reflective the clouds are, their height, and whether it is day or night.
It has been assumed that the warming and cooling effects of clouds cancel each other out and would continue to do so as the world warms, but new models suggest this might not be the case.
The ability of clouds to keep the planet cool would be drastically reduced as the world warms, pushing global heating into overdrive. As the atmosphere becomes warmer, clouds at lower levels will thin out and contain less water, or burn off altogether, leaving clear skies. This thinning means less of the sun’s energy will be reflected back into space, causing a warming of the Earth’s surface.
One study focused on the blankets of low clouds over the ocean and how accurately models handle these. Marine status and stratocumulus cool the Earth, providing shade for around a fifth of the ocean and reflecting 30%–60% of solar radiation back into space. This is believed to cut the amount of energy reaching the Earth by 4 to 7%.
If global warming leads to fewer and thinner clouds, this could cause additional warming above that resulting from greenhouse gases, magnifying the effects of global warming. The amplifying effect is stronger in the latest simulations and could add another degree or more to global warming.
Rather than trying to simulate a plausible increase in greenhouse gases, other research has analyzed how much the climate warmed in response to an abrupt increase in carbon dioxide. The study was designed to easily diagnose climate sensitivity, which is the amount of global warming that occurs as a result of a doubling of carbon dioxide. The measure is used to determine how far we should go to combat global warming.
Global Warming Effect Underestimated
Additional studies have suggested that the global warming effect has been underestimated; the most up-to-date computer simulations suggest greenhouse gases emitted by human activity will leave the planet hotter than previously thought.
New computer models simulating the Earth’s climate suggest that if the concentration of carbon dioxide doubles then the average global temperature might increase by 3.9 °C. This is 0.6 °C more than previously estimatedby the IPCC (Intergovernmental Panel on Climate Change).
All its previous assessments agreed a doubling of carbon dioxide from pre-industrial levels will warm the Earthby around 3 °C, but this could rise to 5.6 °C based on a projected doubling of carbon dioxide levels according to most leading climate models. It’s likely the findings of recent research will feature highly in the 2021 IPCC assessment of the physical science of climate change.
Real-world data suggests researchers’ predictions may be coming true. A sharp rise in global average temperatures since 2013 coincided with a decrease in cloud cover over the oceans, and fewer low-level clouds over the tropics in warmer years.
Scientists predict global cloud cover may have a tipping point, past which clouds would become unstable and break-up, causing warming to head into an upward spiral. It is predicted that this point will not be reached until levels are at 1200 ppm – four times pre-industrial levels and three times current levels. Once passed, temperatures could soar by 8 °C as a result of lost clouds.
Whether the results of the latest simulations are more plausible than previous ones is the pressing question. The results are potentially concerning, but it is too early to say that climate sensitivity is higher than previously thought. What is required is further testing of the models against observations, and to understand the physics of the amplifying effects of clouds.
Scientists will continue to compare the results of computer simulations with records of changing global temperatures to determine where they are working and where improvement is needed, then it might be possible to confirm if there is greater warming to come.
References and Further Reading
Levey, S. (2020) Thanks to clouds, new climate simulations predict more warming than predecessors. [Online] Imperial College London. Available at: https://www.imperial.ac.uk/news/194738/thanks-clouds-climate-simulations-predict-more/ (Accessed on 6 March 2020).
Neill, P. (2020) Scientists will look at the clouds to predict climate change. [Online] Environment Journal. Available at: https://environmentjournal.online/articles/scientists-will-look-at-the-clouds-to-predict-climate-change/ (Accessed on 6 March 2020).
Pearce, F. (2020) Why Clouds Are the Key to New Troubling Projections on Warming. [Online] Yale Environment E360. Available at: https://e360.yale.edu/about#about-e360 (Accessed on 6 March 2020).