Acceptance Speech – Rome, 18.11.2021 (Video + Text)

Germany/USA

Susan Trumbore

2020 Balzan Prize for Earth System Dynamics

For her outstanding contributions to the study of the carbon cycle and its effects on climate, and for pioneering the use of radiocarbon measurements in Earth system research.

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Mr. President,
Members of the Balzan Foundation,
Ladies and Gentlemen,

It is with deep gratitude to the Balzan Foundation and the Balzan General Prize Committee that I accept this generous award. Thank you not only for this great honor, but also for highlighting the importance of the changing earth system with the 2020 Prizes.

During my lifetime, the concentration of CO2 in the atmosphere has risen by 30%. As a result, global temperatures have risen by 1 degree Celsius over 60 years. In central Germany, we experience this as earlier springs, milder winters, and more really hot summer days. The planet’s ecosystems are responding to these changes that are occurring faster than any previously known climate change.

I study the dynamics of the Earth’s carbon cycle, the collective set of pro- cesses that transfer carbon between atmosphere, land and ocean, and regulate its transformation between inorganic forms like carbon dioxide and organic molecules found in all living organisms. This carbon cycle is especially important as the ocean and land together absorb half of the carbon dioxide we emit by burning forests and fossil fuels – protecting us from even greater climate change.

Specifically, I study the timescales associated with transformations and exchanges of carbon between land vegetation, soils and the atmosphere. Imagine the possible fates of a carbon atom in CO2 fixed by a tree leaf. during photosynthesis. It can be respired within a few days to fuel the trees’ metabolic needs. Alternatively, it can be used to build leaves that survive for a year, or wood that lasts for centuries. Dead leaves and wood fall to the forest floor and take time to decompose, releasing carbon that was fixed to the atmosphere years to centuries earlier back. A fraction of this carbon can be recycled or stabilized in soils and stored for millennia.

To trace these pathways and their timescales, I use radiocarbon (14C) produced by atmospheric weapons testing. Basically, documented changes in the 14C content of atmospheric CO2 over the past 60 years provide a ‘time stamp’ that allows us to determine how many years have passed since carbon in and respired from ecosystems was fixed. Quantifying the elapsed time lets us answer fundamental questions about how trees function and what processes stabilize carbon in soil. By studying plants and soils in different climates, we can better predict how global warming is altering carbon storage on land. This is vital, as we need to know whether we can count on land to keep storing a quarter to a third of the carbon humans add to the atmosphere every year. It also provides knowledge needed to assess the capacity of ecosystems to store carbon over the next critical decades, when we need not only to slow emissions but also to remove CO2 from the atmosphere to minimize climate risks.

I am fundamentally a person who measures isotopes, and not an expert in ecosystem ecology. Any success I’ve had is directly traceable to the generous. colleagues who have shared their knowledge, laboratory methods and field sites in the best tradition of open, discipline-crossing science. These people have also enriched my life with friendship and shared adventure. I was also lucky to be born at a time and in a place where being female did not prevent me from dreaming of or achieving a career in science. In particular, I thank my parents and mentors who fostered my confidence and encouraged me to seize opportunities.

Thank you once again for this tremendous honor. I am using my Balzan Prize to support several junior scientists to use radiocarbon together with other methods to enable research in carbon cycling in the Brazilian Amazon.