The fate of carbon emissions from fossil fuel burning and deforestation determines the rate of increase of atmospheric CO₂ increase, and in turn, climate change. The physics-based models used for future climate projections predict a weakening of both land and ocean sinks (e.g. absorption)  in response to a warming climate, resulting in a steeper rise in atmospheric CO₂. The magnitude of this amplifying carbon-climate feedback differs by a factor of five among current models, which significantly hinders future climate projections, especially for high warming projections if carbon emissions are not cut rapidly towards zero.

Many known terrestrial and marine ecosystem processes that could reinforce or weaken this feedback are missing or poorly represented in current models. Thus, the key research question being addressed by the CALIPSO researchers focuses on the extent to which the natural carbon cycle may be destabilized by climate change.

“Biological carbon loss and mortality processes are major gaps in our current knowledge of the carbon cycle, which have been ignored or oversimplified in current models, failing to reproduce the observed complexity of living systems” explains Philippe Ciais, senior researcher at Laboratoire des Sciences du Climat and coordinator of the CALIPSO project.

To better understand how increasingly frequent extreme events may trigger a destabilization of biological carbon reservoirs, an international team of leading scientists across six countries will work together in the CALIPSO project to develop biologically accurate representation of how climate change will impact the mortality and resilience of trees following drought and fire, the efficiency of diverse soil microbial communities that decompose organic matter, and the recycling and deep export of ocean carbon resulting from activities of viruses and diverse zooplankton communities.

“Recent theoretical and empirical breakthroughs make it possible to change the paradigm from a ‘physically mediated’ to a ‘biologically mediated’ representation of the carbon cycle in climate models. New empirical datasets will be analyzed in the project to reduce uncertainty on critical processes which could previously only be observed at a handful of locations: satellite constellations delivering daily spectral images of the whole Earth at meter resolution; compilations of thousands of measurements of functional traits for plants, soil microbes and ocean organisms; and millions of images from automated under-water cameras to map ocean particles and organisms. With new machine learning methods, these high- dimensionality observations will guide the development of a new generation of carbon cycle models” explains Pr. Pierre Friedlingstein at University of Exeter, one of the prime investigators of CALIPSO.

Finally, “Theory has now progressed to extend the model representations of plant mortality, and organic matter decay and recycling processes in soils and in the ocean by microbial communities, including nutrient limitations and acclimation of ecosystems. This means models will be much more realistic and potentially sensitive to changes in the environment” adds Pr. Corinne Le Quéré at University of East Anglia (UEA), who leads the ocean research work in CALIPSO.

We expect that CALIPSO will make a giant leap in the representation of carbon loss processes in climate models and fill in critical knowledge gaps in the global carbon cycle. All the model codes and data collected in the project will be publicly available, to benefit the research community and help develop a new generation of models that will accurately predict the fate of future CO₂ and climate change and the risks to our planet.

Visit the CALIPSO website here