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Want to learn about greenhouse gas research at the Institute of Arctic and Alpine Research (INSTAAR) in person? Join us for “Greenhouse Gases Up Close” on Thursday, October 15th.��.

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With each passing year, Earth’s atmosphere takes on higher and higher concentrations of greenhouse gases like carbon dioxide and methane. Yet, these changes are invisible to us. We can’t directly see, taste, smell, or feel them in the air.

Instead, we rely on precise measurements made by scientists day after day, year after year.��

Above: Pieter Tans stands for an interview in the Carbon-14 lab in 2026. Below: Scott Lehman holds up graphite extracted from an atmospheric air sample while he meets with CU �Ǹ�Թ� Chancellor Justin Schwartz in 2025. (Gabe Allen)

INSTAAR Fellows Emeriti Pieter Tans and Scott Lehman are two scientists who have contributed immensely to this record. From 1985 to 2019, Tans led the effort to maintain and refine a global record of atmospheric greenhouse gas concentrations at the National Oceanic and Atmospheric Administration (NOAA). In the early 2000s, Tans recruited Lehman to develop a method for recording radiocarbon concentrations — an isotopic tracer of the sources of greenhouse gases in the atmosphere.

Both of these efforts continue to this day — at NOAA’s�� and INSTAAR’s��Laboratory for AMS Radiocarbon Preparation and Research, respectively. INSTAAR sat down with Tans and Lehman to discuss the history and future of atmospheric monitoring, as well as its role in international environmental policy.

How does the Carbon-14 Lab contribute to global atmospheric monitoring of greenhouse gases?

Scott: We've known for quite some time that carbon-14, also known as radiocarbon, is a theoretically ideal tracer for anthropogenic emissions of carbon dioxide derived from combustion of fossil fuels and cement production. In around 2003, Pieter came to me asking whether we would consider developing ultra-precise measurement capabilities for samples coming from the global atmospheric sampling network that Pieter had helped to develop through NOAA’s Global Monitoring Laboratory.��

We very quickly obtained measurement precisions that were scientifically meaningful. And so, for the first time, we had a tracer in the atmosphere that we could track back sources on the ground in order to estimate the timing and intensity of anthropogenic emissions. We can aggregate these values to come up with emissions estimates for specific regions, nations, or for the whole world.��

Pieter: This really is an important capability for society. When governments decide to decrease emissions, you need to have an objective and transparent way to measure the outcome.��

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A heat map of the ratio of Carbon-14 found in atmospheric carbon dioxide around the world. Low Carbon-14 ratios occur in areas above or downwind of major fossil fuel emissions — seen in warm colors here. (Courtesy Scott Lehman)

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This operation has been ongoing for more than two decades now. Give us a brief overview of how it got started and how it works today.

Scott: So Pieter came to us in 2003, and we started a pilot program making measurements on flasks of air gathered from�� right here in our backyard. That location gives us a pretty good baseline for the composition of well-mixed air over the North American continent, so that's where we chose to get started. It also happens to be the site of NOAA’s first-ever atmospheric CO2 measurement, which they sampled back in 1967, using INSTAAR’s Mountain Research Station.

The program grew substantially, through a series of grants that Pieter, our NOAA colleague John Miller, and I wrote over the next few years. This enabled us to extend the measurements into a number of different sites within the NOAA network that Pieter had helped to establish earlier.��

Today, we measure roughly 50 sites around the world, mostly in North America — our initial focus was on independently determining US emissions. Basically, flasks come in and out of the central operational hub at the NOAA building here in �Ǹ�Թ�, where they measure a whole suite of greenhouse gases. Then we work with the air that's left over. Three times a week, flasks are brought to INSTAAR and returned from INSTAAR to NOAA. We have to turn those flasks around quickly so that they can get back into circulation within the global network.

From very early on, we streamlined a system where the Global Monitoring Lab and INSTAAR’s Carbon-14 Lab can basically function as one lab. Our databases are linked and we provide information back and forth in a secure way.

The "T-Van" air sampling site sits at more than 11,000 feet above sea level high in the Indian Peaks to the West of �Ǹ�Թ�. The site's high elevation allows researchers to gather baseline values for continental atmospheric gases. It is home to the second-longest continuous record of atmospheric carbon dioxide in the world, which INSTAAR has maintained since the 1960s. (Gabe Allen)

Field Technician Austin Willbern climbs into the "T-Van" air sampling cabin at Niwot Ridge high in the mountains south of Nederland, CO. The first sample Lehman's team ever analyzed for carbon-14 was gathered at this site in 2003. The Carbon-14 lab has continued to analyze air samples from the site ever since, creating a 23-year record. (Gabe Allen)

Pieter, you have played an outsized role in developing the field of greenhouse gas measurement and monitoring. What motivated you?

Pieter: When I was a student in physics, I wanted to do something where I could do real science, find the truth, and at the same time, do something of value to society. In 1972, I came across this book called “Study of Man's Impact on Climate.” It was an important early scientific assessment of potential climate changes caused by CO2 emissions. So I thought, ‘that’s what I’m going to do.’ I picked climate change.

Scott: Pieter has had a foot in isotopic measurement for a very long time, and the algorithms that we use to understand our measurements are, to this day, based on his early work. When this whole thing got started, Pieter had the vision to know that isotopic measurements weren’t feasible at NOAA, but he could get them through collaboration with INSTAAR.��

Why is this work important?

Scott: You cannot manage what you cannot see. So whether it's looking at the changing atmospheric concentrations of the gases themselves, or looking at the isotopes, which tell us about sources and sinks of those gases, it’s essential that we be able to see what's going on. The decision about what to do about it is not ours to make — though we might have our opinions.��

Importantly, at any given moment, spatial�� gradients of CO2 over large land areas are dominated by exchange with the biosphere, and local concentrations rise and fall throughout the day and the year due to natural processes. Carbon-14 allows us to look past those variations and track contributions solely from fossil fuel use. This tells us on a region-by-region or nation-by-nation basis whether emissions are rising or falling, which is information you can't get from measuring CO2 alone.

Can you expand on that? What potential do these measurements have for measuring emissions on a national or international scale?

Scott: UN member nations are required to report their emissions using a set of mostly economic statistics. You have receipts for fossil fuel use, and you base the calculations off that. The problem is that this method requires almost perfect a priori knowledge of every emissions process and its intensity everywhere. You're more likely to undercount than overcount in a system like that.��

Our methodology is top-down, because you're actually looking at the result of our emissions — the full impact of human activities. We can sense virtually all the emissions out there. And we tend to find that our estimates are larger than the so-called bottom-up or inventory-based estimates.��

For instance, China is now the largest emitter of fossil fuel-derived CO2, but their methods of accounting have been changing over time in ways that sometimes seem favorable to them in terms of meeting emissions reduction targets. Our method theoretically allows a third party to look over their shoulder and say, ‘okay, this is what's really happening,’ based on the truth teller here, which is the atmosphere, which integrates all emissions at all temporal and spatial scales.��

This work has to be international. It’s essential that we share our methods and data across international borders and encourage scientists in other countries to replicate this effort. We are currently working on a proposal to train other scientists around the world how to detect CO2 emitted by fossil fuel combustion using our methods. This would include a key collaboration with Chinese investigators so they can do their own top-down observations.

And, our work here in the US has recently taken on added importance. The US stopped reporting emissions data to the UN and the international community last year, so now records like ours are all we have.

Chad Wolak presses a graphite sample in the Carbon-14 lab. In order to measure the precise ratio of carbon isotopes in an air sample, technicians must first extract carbon atoms from each sample using a process called "graphitization." (Ethan Welty)

Graphite samples await analysis on a mass spectrometer in the Carbon-14 Lab. Each of these tiny pieces of graphite is made entirely of carbon atoms stripped from the carbon dioxide in a sample of air from Earth's atmosphere. (Ethan Welty)

This work has made it into a wide array of governmental and intergovernmental reports over the years. What makes it pertinent from a policymaking perspective?

Scott: Just about every scientific and policy exercise aimed at trying to understand changes in atmospheric composition and climate makes use of the NOAA Global Monitoring Laboratory data, which greatly expanded under Pieter’s leadership. It’s a fundamental aspect of every�� (IPCC) report. It was there in the very first IPCC report, which former INSTAAR Director Mark Meier also contributed important work to.��

More recently in 2025, the National Academy of Sciences, Engineering and Medicine did a�� — the 2009 EPA determination that greenhouse gases threaten public health and welfare. Again, NOAA's data features very prominently in that Academy-level effort to defend the finding. The report upheld and even expanded on the science underlying the original finding, but ultimately it was ignored — the finding was rescinded by the EPA earlier this year.

Pieter: We don't advise on policy, but we also don’t omit or hold back information. That is our duty as scientists.

Scott: The records produced by the Global Monitoring Laboratory and INSTAAR are essentially unassailable. We do ongoing quality control, and if we find a measurement bias in the data we go back and correct it throughout our records.��

Who has access to the information gathered by the Carbon-14 Lab? Is it accessible to the public?

Scott: One important thing for people to know is that all of the data we create is freely available to the public. Anybody else anywhere in the world can access the data, do their own analysis, and see what they think. That level of transparency is extremely important to the enterprise because it's fundamentally apolitical.

Pieter: Here’s a nice example of why transparency is important. In the mid-90s we had a lot of people questioning our data. I got an e-mail from somebody in Belgium who demanded to see the raw data from the Mauna Loa Baseline Observatory in Hawaii. I said, well the raw data is all voltages, but I can get you those — it's a long file. The voltages give you concentrations based on the voltages of standards with known concentrations. I said ‘pick a year, and then I'll send you everything you need.’ Then I gave him our conversion algorithm, and told him that he could make his own algorithm too if he liked. He came back a couple weeks later and said, ‘yeah, I get the same result as you guys do.’��

Now, a few years later, there was some discussion in Europe between prominent climate skeptics and this guy actually defended us. Despite his general skepticism, he had faith in our data because he had seen the backend.

What is the current state of funding for the Carbon-14 Lab?

Scott: Our lab and the Stable Isotope Lab have relied on funding from NOAA to perform measurements for the Global Monitoring Laboratory for the past two plus decades. The contracts run for five years, and don't obligate NOAA to spend a dime. Instead, they set a cap for NOAA to spend on our services. Recently, we recompeted and were awarded a follow-up contract, but we received only about a third of the money we expected for this fiscal year.

It's not yet clear whether we might get a top-up next year to help offset this year’s reduction. The latest budget proposal from the federal Office of Management and Budget once again proposed a large cut to NOAA. This could be an existential threat to our operation long-term, unless Congress again steps in to preserve the organization’s research functions. This reality, along with recent federal rule changes, means there is a lot of uncertainty moving forward.

I think on that basis, we need to be on the lookout for private sector and foundation support. Maintaining the continuity and integrity of these long-term records is really important, and right now we need all the help we can get. That’s true no matter how our federal funding ends up. The best case scenario for us is flat funding, which equates to a funding cut if you factor in inflation.

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