University of Wollongong (UOW) statistician Distinguished Professor Noel Cressie is a member of the science team behind NASA’s satellite mission devoted to measuring carbon dioxide, a critical component of Earth’s carbon cycle and the leading greenhouse gas driving changes in Earth’s climate.

NASA’s Orbiting Carbon Observatory-2 (OCO-2) satellite based at the Jet Propulsion Laboratory (JPL), launched July 2 from Vandenberg Air Force Base, California, United States.

When fossil fuels are burned, carbon dioxide is emitted, or exhaled, into the atmosphere. Natural sources such as fires add to the amount of carbon dioxide emitted. Earth absorbs, or inhales, carbon dioxide through vegetation growth and uptake by the oceans that form carbon sinks.

Currently, only about half the total carbon dioxide emitted per year is absorbed by the carbon sinks.

The United Launch Alliance Delta II rocket lifts off through the fog at Space Launch Complex 2 on Vandenberg Air Force Base in California, engines blazing, carrying NASA’s Orbiting Carbon Observatory-2, or OCO-2, to orbit. PHOTO CREDIT: NASA or National Aeronautics and Space Administration

While scientists understand and can measure carbon dioxide emissions from burning fossil fuels, a less-understood problem that the OCO-2 mission will address is the extent and location of the sources and sinks. This knowledge is crucial to understanding the carbon cycle and its effect on climate change.

Professor Cressie is Director of the Centre for Environmental Informatics in the National Institute for Applied Statistics Research Australia (NIASRA) at UOW as well as serving a two-year appointment as a JPL Distinguished Visiting Scientist and he is a member of the OCO-2 mission’s science team.

Professor Cressie said data collected by the observatory would help scientists reduce uncertainties in how much carbon dioxide is in the atmosphere and how much the sinks absorb. Since carbon dioxide is a leading greenhouse gas, this will improve the accuracy of climate-change projections.

“The observatory will be in a polar orbit at an altitude of 705 kilometres (km), circling the planet every 98 minutes,” Professor Cressie said. “It will collect up to 24 measurements a second from a band of Earth’s surface as it orbits, and global coverage will be obtained after the observatory completes 233 orbits every 16 days.”

In conjunction with NASA’s Earth Science Technology Office, Professor Cressie and JPL statistician, Dr Amy Braverman, are correlating data of this type with those from other satellites to build a more precise picture of the abundance of atmospheric carbon dioxide.

Carbon dioxide in the atmosphere is measured in parts per million (ppm), the number of molecules of carbon dioxide in every million molecules of air. The Mauna Loa observatory currently records that number at around 400 ppm, the highest in recorded history.

The data produced by OCO-2 will be an average of the number of carbon dioxide molecules per million molecules of dry air in an atmospheric column from the satellite to Earth’s surface. The mission is designed to achieve unprecedented precision of 1.2 ppm on geographic scales of 100 km over land and 1000 km over ocean.

“These massive datasets require sophisticated modelling and carefully derived measures of uncertainty to enable us to ultimately obtain accurate and precise estimates of carbon dioxide sources and sinks,” Professor Cressie said.

Learn more about the Orbiting Carbon Observatory-2