Ralph Keeling, the director of an acclaimed Scripps program that keeps track of the amounts of carbon dioxide and oxygen in the atmosphere, has renewed his plea for public support of the research, which has suffered from flagging federal grants.

"The Scripps CO 2 and O 2 measurements now face severe funding challenges," Keeling wrote in a letter posted on Dec. 24. "The situation is most urgent for the O 2 measurements. These measurements have been supported for decades through proposals submitted every few years to the federal agencies. The value of these measurements is not questioned, but federal funding for these programs has never been so tenuous."

The famous Keeling Curve sampling program at the Mauna Loa volcano in Hawaii was set up by his father, Dave Keeling, in the late 1950s and has tracked atmospheric concentrations of carbon dioxide ever since. But the part of the work that is less familiar to many—and that is in more dire economic straits—is the tracking of oxygen concentrations.

When it comes to understanding the carbon cycle and climate change, oxygen is carbon dioxide's benign sibling.

Just as burning fossil fuels adds carbon dioxide to the atmosphere, that same combustion subtracts oxygen molecules from the air we breathe. Of course, oxygen is so abundant there's no danger that we'll run out of it, Keeling was quick to note in an interview with InsideClimate News. He said he and other researchers have been painstakingly tracking oxygen's presence for another reason: They need the data to fully understand the carbon cycle that is at the heart of global warming.

When plants grow, they absorb carbon dioxide from the atmosphere, storing the carbon and giving off the oxygen. That's why forests are called carbon "sinks." But how the planet locks up that carbon, and just how much is absorbed by growing plants, is relatively hard to measure. A much easier way to get at that information is to measure the plants' resulting emissions of oxygen by sampling the air. That's what the Scripps oxygen program does.

Oxygen measurements show that "the land really is hanging in there as a sink for carbon," Keeling said in an interview. "There is more biomass on earth now than there was a generation ago."

It's important for scientists and policymakers concerned about global warming to fully understand the future of the planet's carbon balance.

The work at Scripps has led to many findings beyond just showing how much carbon dioxide and oxygen are in the air at any given moment, although that measurement has generated the most headlines—such as when carbon dioxide levels surpassed 400 parts per million, more than at any time in human history.

A recent paper co-authored by Keeling in Science, for example, described striking seasonal variations in high-latitude atmospheric concentrations of CO 2 , the main greenhouse gas. In other words, the atmospheric sampling showed that boreal forests are breathing more deeply.

The problem, Keeling said, is that his kind of research has to continue for decades, and federal science grants are usually geared toward shorter-term results—the more so when budgets are tight. Longevity can be the death of a research project, it seems.

Keeling said the oxygen research costs about a half million dollars a year, and the carbon dioxide measurements another few hundred thousand dollars.

A November piece in Nature noted that his initial appeal last July garnered only modest contributions.

While Keeling looks for longer-term support, he said, "I need to be able to make it through the next year. I don't think crowdsourcing long-term observations will do, not indefinitely."

In his latest appeal for (tax-deductible) donations, Keeling wrote:

"The need to continue these measurements has not diminished. The planet is undergoing dramatic changes, unprecedented for millions of years. This past year, our group reported that CO 2 topped 400 parts per million at Mauna Loa for the first time. We also reported a shockingly large and unexpected increase in the seasonal swings in CO 2 between summer and winter at high latitudes in the Northern Hemisphere. The boreal forests are evidently behaving very differently than 50 years ago. Meanwhile, the oceans are acidifying, ice is melting, sea level is rising, the frequency of extreme storms seems to be increasing. Scientists from around the world are scrambling to figure out what is going on and what the future holds, as CO 2 continues to rise."

He says he has not pressed federal agencies too hard to renew his grants, as he recognizes that there are many equally valid competing research projects.

"We are all kind of in it together," he said. "I am just the bleeding edge of the problem."

University of California at San Diego, home of the Scripps program, is accepting donations here.