Carbon Detectives
NOAA Scientists Track CO₂ Increase

Katy Human
NOAA Office of Oceanic and Atmospheric Research

February 2, 2009 — Wanted: The notorious greenhouse gas carbon dioxide and a detailed investigation into its activities.

Description: Invisible.

NOAA scientists are using a variety of tools to track and visualize CO₂ gas as it swirls around the globe. They have placed instruments on tall towers, used air flask analysis, and depend greatly on a data assimilation system called CarbonTracker.  

Wouter Peters, from the Earth System Research Laboratory’s Carbon Cycle Greenhouse Gases group, developed the initial version of CarbonTracker for release in 2007. This system allows us to follow better the origins and destinations of atmospheric CO₂. The gas has been increasing steadily since the Industrial Revolution due to fossil fuel burning and other human activities.

“CarbonTracker is a new way to model the sources and sinks of CO₂ in a way that maintains consistency with observations of CO₂ in the atmosphere,” said Pieter Tans, CCGG leader. “CO₂ is the main human-controlled driver of climate change, and it is going to be even more important in the future,” Tans said. Eventually, carbon regulations may require governments or industries to account for greenhouse gas emissions — some municipalities are already trying to do so.

Last fall, ESRL scientists, in collaboration with many others, updated CarbonTracker with quality controlled CO₂ data gathered from more sites around the world, and with improved models. CarbonTracker data are available free online in several formats, but among the most popular are short movies that animate the invisible gas. In the Northern Hemisphere’s summer, purples and blues, indicating lowered CO₂, swirl across North America, as growing forests and other ecosystems pull CO₂out of the atmosphere and into plant tissue. In spring, fall, and winter, reds and yellows highlight CO₂ emissions from cars, cities, power plants, and natural cycles.

“Because it is invisible and non-toxic, CO₂ is just not very real to many people. That may contribute to skepticism,” Tans said. “So there is value in simply visualizing these swirls.”

Eventually, the ESRL team and colleagues hope to make the system precise enough to inventory CO₂ sources and sinks by sector and by region, accounting for power plants, cars, growing forests, regional drought, and more.

“For that, we really need much higher resolution observations and higher resolution transport models,” Tans said.

NOAA’s relatively sparse network of observations picked up a clear atmospheric signature of the 2002 drought, which affected the entire North American continent, but the network could not catch last summer’s drought in the U.S. Southeast.

Every month, more than 200 users download some kind of data from the CarbonTracker Web site, said ESRL’s Ken Masarie, and at least 10 researchers per month are downloading the actual CarbonTracker source code.

“They’re using CarbonTracker results to compare with other reanalysis products and with detailed, regional measurements, and to provide initial conditions for their high-resolution, regional scale models,” Masarie said.

Scott Denning, a Colorado State University atmospheric scientist, said he has used CarbonTracker in his own work, and is grateful that ESRL has made the source code for the system free and easy to access.

“As scientists, we get credit with our community by publishing results, and so normally, when people do analysis like this, they might publish a few plots and several pages of information,” Denning said. “This is amazing in that this is completely open. You can actually re-create the whole thing.”

Denning said he has shown CarbonTracker movies to students, and also to his 73-year-old mother. “My mom is never going to read the Journal of Geophysical Research or learn about inverse modeling, but she can watch the movie and say, ‘Wow! So why is it green over there?’

Denning said CarbonTracker is being used by a growing community of scientists around the world who are trying to piece together the planet’s precise carbon budget. A new NASA satellite, scheduled for launch next year, will help clarify carbon sources and sinks. Sinks are critical, Denning said. “Half the world’s fossil fuel emissions are being vacuumed up by poorly understood processes. We need programs like CarbonTracker to help us understand how it works so we’ll be able to predict how it might change in the future.”