Despite the fact that clouds cover two-thirds of the planet at any given time, transport water on the wind and shield the Earth from the sun, surprisingly little is known about how climate change affects them. For example, atmospheric scientists are not yet sure whether rising temperatures will lead to more or fewer clouds, or make them better or worse at reflecting the sun’s heat.
To help unravel those mysteries and others, the European Space Agency and the Japanese Aerospace Exploration Agency flew a satellite into orbit aboard a SpaceX rocket last week. The Earth Cloud Aerosol and Radiation Explorerknown as EarthCARE, will uncover the inner workings of clouds, as well as how they, and tiny airborne particles called aerosols, shape – and are shaped by – climate change.
“Clouds are the number one cooling blanket we have on the planet,” said Pavlos Kollias, an atmospheric scientist from Stony Brook University who has supported the EarthCARE mission since 2008.
A cloud’s effect on temperature depends largely on the height at which it happens to float. Low-level formations, such as the blanket-like stratocumulus, do a particularly good job of keeping the planet cool by reflecting most of the sunlight that hits them. Since they fly so close to the ground, their ambient temperatures are similar to those of the landscape below, and they carry most of the Earth’s heat into space rather than keeping it in the atmosphere.
The cooling effect it provides is so pronounced, Kollias said, that without it the planet would be 15 degrees Celsius warmer — or nearly 30 degrees Fahrenheit. It’s the difference between a mild spring and a blistering summer.
Although the impact of clouds on the planet is well known today, scientists are unsure about how it might evolve as temperatures rise. “If you perturb the system by adding temperature,” Kollias said, “we don’t know how the clouds will respond.” They can become more common and denser, thus mitigating climate change in a minor way, or they can become less common and less dense, accelerating climate change.
Clouds at high altitude, such as thick cirrus, are typically made of small ice crystals and often captures the earth’s heat more effectively than they block the sun’s light, which seems to make both more sensitive to warming. Aerosols, small particles such as sulfates and sea salts, introducing further complications by influencing the climate directly, by reflecting sunlight, and indirectly by acting as the nuclei around which clouds condense. Efforts to clean up industrial emissions reduce airborne aerosols, with pronounced effects on climate.
All this makes cloud dynamics one of the biggest sources of uncertainty in climate models, something that EarthCARE aims to help solve.
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Kollias is eager to work with the data that will begin beaming from the new satellite later this year. The mission carries an instrument never before used in space: a cloud profiling radar. The device will emit successive bursts of radio waves and measure the signal reflected by the vapor below. This information will help researchers better understand the size and circulation of the countless droplets that make up a cloud. EarthCARE will also map the surface profile of clouds and aerosols using a method known as lidar that reflects a low-power laser from these atmospheric formations. Those measurements along with images captured by the spacecraft will provide a three-dimensional view of the ubiquitous pillows and blankets of condensation floating through the air.
The European Space Agency named EarthCARE its sixth Earth Explorer mission back in 2001. Although delays plague seemingly every satellite, EarthCARE faced significant and protracted setbacks due to the complexity and sophistication of the radar and lidar systems. It reached a point where, Kollias said, some outside the mission began to doubt whether the nearly $900 million satellite would ever reach the launch pad. Still, “no one gave up,” Kollias said. “Everyone kept working.”
All of which made last week’s successful launch a particularly emotional affair.
“Personally, I was very nervous at the moment,” Kollias said of the launch. But he added that the drawn-out process inadvertently gave the scientific community more time to prepare to work with EarthCARE’s data. Numerical models have improved dramatically in the 23 years between selection and launch, researchers have more computing power at their disposal than ever before, and machine learning now allows big data to be digested with comparative ease.
The intervening years have also given the world a foretaste of the climate disasters yet to come. As a result, an added urgency drives the desire to resolve the uncertainties that clouds introduce into climate models, so that scientists can look out with keener eyes to tell us what the decades ahead hold.
