To understand why the climate is changing, scientists say they need to understand the role of aerosols, such as desert dust, in precipitation and cloud formation.
By all estimates, the Aerosol-Cloud-Ecosystems (ACE) mission is probably the most expensive of the 15 NASA satellite systems recommended by the National Academy of Sciences in its first-ever decadal survey of next-generation, Earth-observing spacecraft. But to some Earth scientists, the data that ACE could gather is the linchpin to understanding what is actually causing climate change.
Among those are Goddard scientist Mark Schoeberl, who led a team funded by the Center’s Internal Research and Development program to outline a possible mission, and Bob Connerton, chief engineer for Goddard’s Earth Science Division. In October, Schoeberl released his mission recommendations in a white paper requested by NASA Headquarters, which also requested mission concepts for the other Academy-recommended missions.
Because of Schoeberl’s work, “we now have a good idea of what ACE will really cost and that it’s the right science,” Connerton says. “It attacks the driving causes of climate change. It goes to the question of why.”
The proposed mission Schoeberl and his team conceived features six passive and active sensors either flying on the same platform or in close formation in a 650-km orbit, chosen because it provides 2-day global coverage. Included are an advanced multi-beam lidar, a dual-frequency radar, an advanced multi-band spectroradiometer, and an imaging polarimeter. Schoeberl’s team also concluded that ACE should include both high- and low-frequency submillimeter radiometers.
Answering the Aerosol Question
These instruments, he says, will help answer the consuming question of why the climate is changing. “For climate forcing, we need to understand the role of aerosols in precipitation and cloud formation. The biggest uncertainty in climate change has to do with aerosols,” Schoeberl says. “In short, aerosols are a huge lever and we don’t have any idea of their impact on the Earth system.”
For example, aerosols — minute particles that are suspended in the atmosphere — can both reflect and absorb solar radiation, either warming or cooling the planet. They interact with clouds, possibly altering precipitation patterns that contribute to floods and drought. They also affect ocean ecosystems. Desert dust provides iron, a key nutrient for phytoplankton, the base of the ocean food chain. Another related question involves the role of the oceans as a sink for carbon dioxide, a major greenhouse gas. The question that ACE could answer is whether changes in the ocean ecosystem are altering its ability to absorb carbon dioxide.
“Current satellite missions are adding to our knowledge,” Schoeberl says. “But even the Terra and A-Train sensors don’t make the measurements that will allow us to fully answer many fundamental questions.”
Reinvigorating Earth-Observing Assets
While Schoeberl and Connerton believe that ACE gets to the heart of today’s climate change debate, the mission currently is not ranked in the first group of the Academy’s recommended investigations. The Academy suggested that NASA first begin planning ICESat-II (Ice, Cloud, and land Elevation Satellite), CLARREO (Climate Absolute Radiance and Refractivity Observatory), SMAP (Soil Moisture Active Passive), and DESDynI (Deformation, Ecosystem Structure and Dynamics of Ice). “Many were already on the books. Even with the Academy’s proposed budget for Earth science, we can’t do everything at once,” Connerton says. ACE and four others would follow in the 2013-2016 timeframe, and an additional six would come online between 2016-2020.
The important thing now, Schoeberl says, is reinvigorating NASA’s Earth-observing assets. “At the very least, we need to continue viewing Earth’s important systems well into the next decade with the capabilities that we have now to identify climatically significant trends and other changes.”
Goddard technologists win new work, secure follow-on funding to mature new technologies, formulate concepts, and validate new instrument concepts in flight demonstrations — successes that benefit Goddard and the scientific community as a whole.