Zeroing in on the carbon cycle

Fortunat Joos is an expert in the physics of the carbon cycle – the constant flow of carbon dioxide and other gases from the planet’s land and oceans to the atmosphere and back again. He’s also the conference chair of an event next week in Interlaken, Switzerland, called the 10th International Carbon Dioxide Conference. This conference will bring together scientists from across the globe to discuss the latest research on those fluxes, and how humans have thrown a wrench into the carbon cycle.  

Joos, a professor of physics at the University of Bern in Switzerland, sat down with Future Earth to talk about the upcoming event. He also discussed what scientists have learned about the carbon cycle since the inaugural International Carbon Dioxide Conference was held in 1981. At that time, he says, researchers depended on relatively simple calculations, called box models, to investigate the ins and outs of carbon dioxide in the atmosphere. Today, they use complex simulations, called Earth System Models, to more accurately study how carbon flows between various parts of the planet – research that has shown the magnitude by which humans are now shifting the climate.

Several of Future Earth’s Global Research Projects are supporting the 10th International Carbon Dioxide Conference. They include the Global Carbon Project, Global Land Programme, Integrated Marine Biosphere Research (IMBeR), Past Global Changes (PAGES) and the Surface Ocean-Lower Atmosphere Study (SOLAS).

Daniel Strain: What can participants in this year’s International Carbon Dioxide Conference expect?

Fortunat Joos: The conference will provide a synthesis of our current understanding of the carbon cycle relying on measurements from the atmosphere, ocean and land and from satellite data, as well as from numerical models. Most of the talks will be given as plenary presentations. The goal will be to bring together scientists from different disciplines working on the carbon cycle – basic Earth system scientists, human dimensions researchers, people doing measurements, researchers who develop models.

We will also offer a stimulating set of excursions with the opportunity to view the glaciers of Switzerland – an opportunity that will be lost over the coming decades as glaciers melt and shrink dramatically with ongoing human caused global warming.

DS: It’s been almost 40 years since the first International Carbon Dioxide Conference was held. How has this area of research changed over that time?

FJ: Fossil-fuel CO₂ emissions have almost doubled in the less than 40 years since 1981 when the first conference was held in Bern. At the same time, research activity has increased, which is reflected by the number of participants. At the first conference, there were 40 scientists who attended. Now, we are looking forward to welcome 500 participants coming to Interlaken.

In terms of science, back then people relied on box models to do projections, drawing from an understanding of carbonate chemistry that had been basic knowledge since the 19th Century. Today, we’re running fully-coupled Earth System Models that link to things like ecosystems or nutrient cycling.

Also in terms of measurements, there has been huge progress. Back then, there were a few atmospheric stations like the iconic ones at Mauna Loa and at the South Pole started by David Keeling. Now, ice core data show that the current rise in atmospheric CO₂ is exceptional for at least the last million years. Today, we also use a comprehensive network of measurement stations, in addition to satellite data, to map out CO₂.

DS: Have scientists also shifted to focus more on how the world can reduce carbon emissions?

FJ: There were papers published in 1970s that called for the mitigation of CO₂ emissions to avoid dangerous climate interference. So already in the 70s and 80s, scientists were aware that our combustion of fossil fuels had serious implications. They formulated it carefully, saying it “may” cause problems because it wasn’t clear from their measurements. In comparison, the Fifth Assessment Report of the IPCC [Intergovernmental Panel on Climate Change] now reports, based on more science, that the human influence on climate is clear and that emissions of CO₂ and other greenhouse gases cause global warming. The visionary picture of our pioneers has survived.

DS: Even with that research, there’s still a lot that we don’t know. What are some of the biggest gaps in our understanding of the carbon cycle?

FJ: There are still improvements needed in what is known about extreme events, in terms of how multiple stressors affect the marine and terrestrial carbon cycle. I’m thinking of marine and atmospheric heatwaves, droughts on land, ocean acidification and deoxygenation of the ocean, and how these extreme events will affect ecosystems and human systems – food production, for example.

Also, we are still struggling to quantitatively explain the evolution of the carbon cycle over past abrupt events. We know from paleodata that the climate has shifted over years and decades, as well as on glacial-interglacial time scales. This has implications for our understanding of the evolution of peat and permafrost carbon.

Another area where more research is needed is the link between human activities and the carbon cycle. That includes the consequences of land management and the use of resources.

DS: It seems like people are one of the biggest sources of uncertainty.

FJ: Which brings me to another area of research: how to transform social systems to be compatible with the goals of the Paris Agreement. And, perhaps, scientists also need to highlight how society can benefit from switching away from fossil fuel-based technologies, for example, by reducing air pollution.

Despite all these research needs, we have quite a few decades of firm knowledge that for every 100 billion tonnes of carbon that we emit – the amount emitted during the last decade – a significant fraction will stay airborne over centuries, up to one hundred thousand years. It will have an irreversible impact on atmospheric CO₂ concentrations, ocean acidification, sea level, warming and climate.

DS: The conference places a large emphasis of understanding the carbon cycle in Earth’s past, or on “paleoclimate” data. Why is this important to those who care about modern changes to the climate?

FJ: We are entering a climate space that is unprecedented in human history, and even more so in our relatively short instrumental records that go back a few decades for many observations, or a few centuries for selected variables. Paleo archives give us information over the last 1000 years, over glacial cycles and even over millions of years. They allow us to put the current ongoing climate perturbation due to human activities in the context of the planet’s past variation in climate and to demonstrate how extreme the current perturbation is. Paleo data also provides us with an opportunity to improve our understanding of the climate by analysing a broad range of different climate states and evolutions and by looking at period of abrupt climate changes in the past.

DS: Another big focus is on how carbon cycle research can support international efforts to slow climate change, such as the Paris Agreement. How can your work contribute to that effort, which seeks to limit the rise in global temperatures to at least 2 degrees Celsius?

FJ: The first contribution comes from gathering and synthesising research that provides the scientific basis that has led to the Paris Agreement, and maybe to the strengthening of the Paris Agreement. A key fact is that the use of oil, coal, and gas for heating, cooling, car driving, transportation and industrial production is the dominant contributor to global warming. It’s clear that without reducing emissions from fossil fuels, mitigation in other areas like cutting non-CO₂ greenhouse gases will be inefficient in terms of reducing radiative forcing. That’s because CO₂ stays for such a long time in the atmosphere.

The second contribution is a solid understanding of how much emissions can be released and have the world still achieve the Paris goal of 2 degrees or even 1.5 degrees of global warming. Current research suggests that we have consumed at least 60% or more of allowable emissions if we want meet the 1.5 degree target with a reasonable chance.

DS: You mentioned that a goal of this conference is to bring together scientists who study the carbon cycle from different angles. Why is that important?

FJ: It’s important to get an overall view so that we can get out of the box each individual research is in and to see what other people do. Sometimes important questions are at the interface. Ocean data, for example, can help us to understand atmospheric changes and vice-versa. Bringing together information from different compartments adds an additional consistency check, where our understanding of the carbon cycle does not only depend on the measurements from one particular area. It shows us that what terrestrial scientists suggest is compatible with the observations that atmospheric scientists collect, and more.