Interview - The greening of the earth is approaching its limit


    Vegetation has a key role in mitigating climate change because it reduces the excess CO2 that we humans emit into the atmosphere. Just as when sportsmen and women are doped with oxygen, plants also benefit from the large amounts of CO2 that accumulate in the atmosphere. If more CO2 is available, they photosynthesize and grow more, which is called the fertilizing effect of CO2. When plants absorb this gas to grow, they remove it from the atmosphere and it is sequestered in their branches, trunk or roots.

    An article published in Science shows that this fertilizing effect of CO2 is decreasing worldwide, according to the text co-directed by Professor Josep Peñuelas of the CSIC at CREAF and Professor Yongguan Zhang of the University of Nanjin, with the participation of CREAF researchers Jordi Sardans and Marcos Fernández. The study, carried out by an international team, concludes that the reduction has reached 50% progressively since 1982 due basically to two key factors: the availability of water and nutrients.

    [Read more: The greening of the earth is approaching its limit ]

     

    We interviewed Prof. Josep Peñuelas of the CSIC at CREAF; PhD student Songhan Wang (first author of the article) and Professor Yongguang Zhang both of the University of Nanjin.

    Prof. Josep PenuelasPicture - Prof. Josep Peñuelas - Credits: By Rcasber - Own work, CC BY-SA 3.0, from Wikipedia

     

    #1. What are the discoveries that have lead up to your current work?

    R.: Based on multi sources of long-term satellite data, ground observations and model outputs, we found that the positive effects of increasing CO2 on vegetation (the CO2 fertilization effect) has declined during 1982-2015.

     

    #2. What question or challenge were you setting out to address when you started this work?

    R.: Our manuscript deals with one of the largest sources of uncertainty in climate science, namely the future behavior of terrestrial vegetation under a CO2 enriched atmosphere. 

    The vegetation photosynthesis and carbon uptake have been enhanced by the increasing atmospheric CO2 concentration, which is called the CO2 fertilization effect (CFE). 

    Although the CFE plays an important role in mitigating global warming, whether this crucial feedback in the climate systems will persist for the future decades remains unclear. 

    Therefore, this work aims to investigate the temporal variations of CFE during the recent decades.

     

    #3. What do you want to achieve with your research?

    R.: Our work aims to investigate the temporal dynamics of CFE during the near four decades, and try to answer the possible mechanisms accounting for these changes. 

     

    #4.Why is your research important? What are the possible real world applications?

    R.: In the past several decades, the airborne fraction of anthropogenic CO2 (the fraction that remained in the atmosphere) stayed almost constant, mostly because the vegetation photosynthesis and carbon uptake have been enhanced by the increasing atmospheric CO2 concentration, which is called the CO2 fertilization effect (CFE). Our analyses suggest that the positive CFE on  vegetation photosynthesis has declined in recent decades, which may point to the emerging saturation of the vegetation carbon uptake, with important implications on the potentials of land-based mitigation strategies and policies.

     

    [Read more: The greening of the earth is approaching its limit ]

    #5.What happens next in the process of discovery?

     

    R: We will continue with further works related to this topic based on multi-sources datasets, namely satellite datasets, long-term ground observations, control experiments etc. And we may also assimilate the satellite data into ecosystem models to better simulate the global carbon fluxes and stocks.



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