Do Clouds Cloud Our Vision of Climate Change?

A few weeks ago I answered a question posed in Quora about clouds and how they are factored into climatology models. I stated that “Clouds are the least understood when looking at climate models. It remains a variable that is difficult to quantify. Most climate models make generalized assumptions about cloud impacts as a result.” A comment came back stating clouds had been “thoroughly investigated and the effects are well known.” In response to this comment, I had to investigate further.

NASA, a number of years ago, set up a project to study cloud climatology which today is archived on the International Satellite Cloud Climatology website. It describes clouds as complicating climate feedbacks. Why? Because:

• Clouds cool the Earth’s surface when they reflect incoming sunlight.
• Clouds warm the Earth’s surface when they absorb heat from the surface and re-radiate it downward.
• Clouds warm or cool the Earth’s atmosphere by absorbing heat from the surface and radiating it into space.
• Clouds warm and dry the Earth’s atmosphere and through condensation of the water vapour contained within them, produce different types of precipitation based on the ambient temperature of the air.
• Clouds are created by atmospheric motion caused by warming, cooling, solar radiation, and precipitation.

So are clouds influencers of climate change, or are they, in presentation, an end product of atmospheric warming?

Ever since I was a very young boy I took an avid interest in meteorology. I don’t know if it was because my father knew a meteorologist who was on CBC television during the news telling us the weather to come, or because I was just a nerdy kid. But I had a field guide to clouds, and a barometer, and could predict daily the coming weather by identifying what was in the skies above our home each day and checking changing air pressures.

Clouds have always been a sign of the weather to come. Fluffy cumulus clouds were fair-weather friends. Cirrus clouds with wispy mares’ tails meant the weather was going to change in 24 hours. Stratus clouds usually meant rain showers. And cumulonimbus on the horizon forecasted thunder, lightning and heavy rain on the way. These changes we observe in clouds have a modifying effect on the radiative energy balance and water exchange within the atmosphere that determines the weather.

The NASA study notes that “clouds respond to changes in the climate are so complex that it is hard to determine their net effect on the energy and water balances and to determine how much climate might change.” 

Clouds are part of the water cycle. The vast majority of water found on our planet is contained in the global ocean and in the crust. If averaged out that water would convert to a 2.5-kilometre (1.5-mile) deep body of water covering the entire planet. The remaining water is found in freshwater lakes and rivers, and in glaciers and ice sheets found in Antarctica, Greenland, and Canada’s northern islands.

So how much water is in the atmosphere at any one time? It amounts to about 2.5 centimetres (a little over an inch). And clouds constitute about 0.05 millimetres (about 0.002 inches) of that total. Water that evaporates from the surface requires energy to produce a phase change turning the liquid into a gas (water vapour is a gas). That energy cools the atmosphere. The cooling causes atmospheric circulation pushing the water vapour upward which then produces a second phase change causing the gas to revert back to a liquid and releasing the energy originally needed for the first phase change. The NASA study states, “The average evaporation and precipitation rates mean that all the water in the atmosphere is exchanged about once every 10 days.” 

All of these atmospheric changes caused by the water cycle we have described above creates uncertainty for climate modellers studying global warming and the added issues of increases in greenhouse gases. One thing these climate modellers have noted is that global warming is changing clouds but whether that’s making the atmosphere hotter or cooler remains contentious.

The latest study published on July 27, 2021, in the Proceedings of the National Academy of Sciences, entitled, “Observational evidence that cloud feedback amplifies global warming,” based on two decades of data collection, concludes that increased atmospheric carbon dioxide (CO2) as it interacts with clouds will cause warming and decrease cloud reflectivity which would normally cause cooling. This research refutes a 2018 study done by the University of Reading which concluded clouds caused overall planetary cooling. The new study sees increases in energy in the atmosphere from added CO2 causing clouds to rise higher which in turn is amplifying the warming effect. This study states its conclusion with 97.5% certainty: Changes to clouds because of increased greenhouse gases are adding to the warming of the planet.

But no cloud modelling study is a complex as the atmosphere itself. Look up into the sky and you often see more than one type of cloud and multiple layers of them. So figuring out the reflective and non-reflective characteristics of each cloud type at any given moment and its warming or cooling effect is a level of complexity with which climate modellers continue to struggle.