Carbon is a building block of life on our planet. It is stored in reservoirs on Earth – in rocks, plants and soil – in the oceans, and in the atmosphere. And it cycles constantly between these reservoirs.
Understanding the carbon cycle is crucially important for many reasons. It provides us with energy, stored as fossil fuel. Carbon gases in the atmosphere help regulate Earth’s temperature and are essential to the growth of plants. Carbon passing from the atmosphere to the ocean supports photosynthesis of marine phytoplankton and the development of reefs. These processes and myriad others are all interwoven with Earth’s climate, but the manner in which the processes respond to variability and change in climate is not well-quantified.
Our research group at the University of Oklahoma is leading NASA’s latest Earth Venture Mission, the Geostationary Carbon Observatory, or GeoCarb. This mission will place an advanced payload on a satellite to study the Earth from more than 22,000 miles above the Earth’s equator. Observing changes in concentrations of three key carbon gases – carbon dioxide (CO2), methane (CH4) and carbon monoxide (CO) – from day to day and year to year will help us to make a major leap forward in understanding natural and human changes in the carbon cycle.
GeoCarb is also an innovative collaboration between NASA, a public university, a commercial technology development firm (Lockheed Martin Advanced Technology Center) and a commercial communications launch and hosting firm (SES). Our “hosted payload” approach will place a scientific observatory on a commercial communications satellite, paving the way for future low-cost, commercially enabled Earth observations.
Observing the carbon cycle
The famous “Keeling curve,” which tracks CO2 concentrations in Earth’s atmosphere, is based on daily measurements at Mauna Loa Observatory on Hawaii. It shows that global CO2 levels are rising over time, but also change seasonally due to biological processes. CO2 decreases during the Northern Hemisphere’s spring and summer months, as plants grow and take CO2 out of the air. It rises again in fall and winter when plants go relatively dormant and ecosystems “exhale” CO2.
A closer look shows that every year’s cycle is slightly different. In some years the biosphere takes more CO2 out of the atmosphere; in others it releases more to the atmosphere. We want to know more about what causes the year-to-year differences because that contains clues on how the carbon cycle works.
For example, during the El Niño of 1997-1998, a sharp rise in CO2 was largely driven by fires in Indonesia. The most recent El Niño in 2015-2016 also led to a rise in CO2, but the cause was probably a complex mixture of effects across the tropics – including reduced photosynthesis in Amazonia, temperature-driven soil release of CO2 in Africa and fires in tropical Asia.
These two examples of year-to-year variability in the carbon cycle, both globally and regionally, reflect what we now believe – namely, that variability is largely driven by terrestrial ecosystems. The ability to probe the climate-carbon interaction will require a much more quantitative understanding of the causes of this variability at the process level of various ecosystems.