Global warming: Why clouds may be less helpful than models forecast

The ability of clouds to reflect ever greater quantities of solar radiation as global temperatures rise, helping to dampen the effects of global warming, may be less pronounced than scientists thought, according to new research.

|
Robert F. Bukaty/AP
Storm clouds build prior to the arrival of a thunderstorm in Poland, Maine, in March.

As global surface temperatures continue to rise as a result of human industrial activity, climate models may be overestimating the ability of clouds to curb climate change, new research has found.

The study, published Friday in the journal Science, used newly available satellite technology to analyze clouds and determine the proportion of ice versus liquid water.

This ratio has important implications for climate modeling, as it impacts the amount of solar radiation being thrown back into space.

"The broader implication of this work is that for the same amount of carbon dioxide in the atmosphere, we'll see greater global warming than currently predicted," explains the study's lead researcher, Trude Storelvmo, a Yale assistant professor of geology and geophysics, in a telephone interview with The Christian Science Monitor, "so for global policy it means more fossil fuels need to stay in the ground."

Clouds sit on a spectrum, in terms of their water composition, with the coldest being full of ice and the warmest full of water; this study focused on clouds that lie somewhere between the two extremes, known as mixed-phase clouds.

The more liquid water a cloud contains, the better it is at reflecting solar radiation back into space, helping to keep the Earth cool by preventing the sun's rays from ever hitting the surface. So, as our atmospheric temperatures rise, and the ice in mixed-phase clouds melts, those clouds become more reflective, in what represents a negative feedback loop for global temperature.

In other words, the more ice the clouds have in them, the stronger the buffer they are against global warming. What this study found was that climate models have overestimated the amount of ice in our clouds, meaning there is less available to melt and offset temperature rises.

"It’s really in the last couple of years that this problem has been identified in the models," says Dr. Storelvmo, "and it's because of the new instruments available on CALIPSO."

CALIPSO is a NASA satellite, launched in 2006, that carries out climate observations. It uses lidar to fire a laser toward Earth and, based on the back-scattering of light, it can determine the proportion of liquid water and ice in the cloud cover.

While Storelvmo acknowledges that this hardware has been orbiting our planet for a decade, she explains that it takes time to see the patterns emerge and then to determine the studies to be undertaken, on top of the time and computer power it takes to carry out the research.

The actual numbers are up for debate, but there does seem to be fairly broad acceptance in the scientific community as to the fundamentals of the work’s conclusions, as Michael Mann, distinguished professor of atmospheric science at Pennsylvania State University, explains to the Monitor.

"I find the paper reasonably compelling that shortcomings in how certain key cloud processes are treated could well be leading to an overestimation of the ability of cloud feedbacks to ameliorate global warming," says Dr. Mann in an e-mail interview. "There is indeed other recent work that makes a similar case."

But he describes the study as more of a " 'proof-of-concept' than a precise estimate of the impact of the effects studied," pointing out that the authors themselves are hesitant to commit to any definite figures in relation to temperature rises.

Yet the study does give a range.

The Intergovernmental Panel on Climate Change (IPCC) in 2013 estimated climate sensitivity – the increase in global temperature as a result of a doubling in atmospheric carbon dioxide – to be within a range of 2 to 4.7 degrees Celsius.

Storelvmo and her colleagues push that upper bound to as high as 5.3 degrees Celsius, based on their new findings.

There is, however, more work to be done: Storelvmo wants to broaden the impact of the research by using it to consider a wider range of climate models, as well as digging into the reasons underlying the flaws it has exposed.

As Mann of Penn State explains, these findings present "an even greater challenge for efforts to reduce carbon emissions fast enough to avoid breaching the dangerous 2 degree C (3.5 F) warming limit," a temperature rise that has become widely accepted as the barrier the planet must not breach.

You've read  of  free articles. Subscribe to continue.
Real news can be honest, hopeful, credible, constructive.
What is the Monitor difference? Tackling the tough headlines – with humanity. Listening to sources – with respect. Seeing the story that others are missing by reporting what so often gets overlooked: the values that connect us. That’s Monitor reporting – news that changes how you see the world.

Dear Reader,

About a year ago, I happened upon this statement about the Monitor in the Harvard Business Review – under the charming heading of “do things that don’t interest you”:

“Many things that end up” being meaningful, writes social scientist Joseph Grenny, “have come from conference workshops, articles, or online videos that began as a chore and ended with an insight. My work in Kenya, for example, was heavily influenced by a Christian Science Monitor article I had forced myself to read 10 years earlier. Sometimes, we call things ‘boring’ simply because they lie outside the box we are currently in.”

If you were to come up with a punchline to a joke about the Monitor, that would probably be it. We’re seen as being global, fair, insightful, and perhaps a bit too earnest. We’re the bran muffin of journalism.

But you know what? We change lives. And I’m going to argue that we change lives precisely because we force open that too-small box that most human beings think they live in.

The Monitor is a peculiar little publication that’s hard for the world to figure out. We’re run by a church, but we’re not only for church members and we’re not about converting people. We’re known as being fair even as the world becomes as polarized as at any time since the newspaper’s founding in 1908.

We have a mission beyond circulation, we want to bridge divides. We’re about kicking down the door of thought everywhere and saying, “You are bigger and more capable than you realize. And we can prove it.”

If you’re looking for bran muffin journalism, you can subscribe to the Monitor for $15. You’ll get the Monitor Weekly magazine, the Monitor Daily email, and unlimited access to CSMonitor.com.

QR Code to Global warming: Why clouds may be less helpful than models forecast
Read this article in
https://www.csmonitor.com/Science/2016/0408/Global-warming-Why-clouds-may-be-less-helpful-than-models-forecast
QR Code to Subscription page
Start your subscription today
https://www.csmonitor.com/subscribe