K. Keller

Harvard University Press

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Fortunat Joos

Oeschger Centre for Climate Change Research

K. J. Davis

Pennsylvania State University

Christoph C. Raible

Oeschger Centre for Climate Change Research

Flavio Lehner

Cornell University

Thomas Lauvaux

Université de Reims Champagne-Ardenne

C. A. Williams

Clark University

Sha Feng

Pennsylvania State University

A. E. Schuh

Colorado State University

Emmanuel Mignot

Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques

A. R. Jacobson

Joint Base San Antonio

Cooperative Institutions

Pennsylvania State University

University of Bern

Oeschger Centre for Climate Change Research

Langley Research Center

Cooperative Institute for Research in Environmental Sciences

University of Colorado Boulder

Swiss Federal Institute for Forest, Snow and Landscape Research

University of Arizona

National Oceanic and Atmospheric Administration

Laboratoire des Sciences du Climat et de l'Environnement

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A source-oriented evaluation of CO2 inverse flux estimates in North America using ACT-America

AGU Fall Meeting Abstracts (2020)

Y. Cui A. R. Jacobson Sha Feng Daniel Wesloh Tobias Gerken

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Time of Emergence of trends in ocean biogeochemistry

K. Keller Fortunat Joos Christoph C. Raible

Abstract. For the detection of climate change, not only the magnitude of a trend signal is of significance. An essential issue is the time period required by the trend to be detectable in the first place. An illustrative measure for this is Time of Emergence (ToE), i.e., the point in time when a signal finally emerges from the background noise of natural variability. We investigate the ToE of trend signals in different biogeochemical and physical surface variables utilizing a multi-model ensemble comprising simulations of 17 ESMs. We find that signals in ocean biogeochemical variables emerge on much shorter timescales than the physical variable sea surface temperature (SST). The ToE patterns of pCO2 and pH are spatially very similar to DIC, yet the trends emerge much faster – after roughly 12 yr for the majority of the global ocean area, compared to between 10–30 yr for DIC and 45–90 yr for SST. In general, the background noise is of higher importance in determining ToE than the strength of the trend signal. In areas with high natural variability, even strong trends both in the physical climate and carbon cycle system are masked by variability over decadal timescales. In contrast to the trend, natural variability is affected by the seasonal cycle. This has important implications for observations, since it implies that intra-annual variability could question the representativeness of irregularly seasonal sampled measurements for the entire year and, thus, the interpretation of observed trends.

Predictability

Biogeochemical Cycle

Biogeochemistry

10.5194/bgd-10-18065-2013

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Quantification of modeled atmospheric CO 2 uncertainty from various sources using ACT-America aircraft data

AGU Fall Meeting Abstracts (2018)

Sha Feng Thomas Lauvaux K. Keller K. J. Davis P. J. Rayner

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Late Holocene Changes to the South Florida Mangrove Coastline and Projections for the 22 nd Century: Interaction of Climate, Sea Level, and Local Factors

AGU Fall Meeting Abstracts (2018)

G. Lynn Wingard M. Jones Sarah E. Bergstresser Bethany L. Stackhouse K. Keller

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K. Keller

10.5194/bg-2016-515-ac1

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ACT-America: Gridded Ensembles of Surface Biogenic Carbon Fluxes, 2003-2019

ORNL DAAC (2020)

Yu Zhou C. A. Williams Thomas Lauvaux Sha Feng I. Baker

Carbon flux

10.3334/ornldaac/1675

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Can we improve top-down GHG inverse methods through informed prior and better representations of atmospheric transport? Insights from the Atmospheric Carbon and Transport (ACT) - America Aircraft Mission

AGU Fall Meeting Abstracts (2016)

Shuzhuang Feng Thomas Lauvaux K. Keller K. J. Davis

Passenger transport

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Land surface model parameterization strategies and North American regional CO2 flux interannual variability examined with a simple land surface model

AGU Fall Meeting Abstracts (2010)

T. W. Hilton K. J. Davis K. Keller

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Variability of dissolved oxygen over the last millennium and the 21st century in CESM

EGU General Assembly Conference Abstracts (2017)

Angélique Hameau Fortunat Joos Emmanuel Mignot K. Keller

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20th century changes in carbon isotopes and water-use efficiency: tree-ring-based evaluation of the CLM4.5 and LPX-Bern models

Biogeosciences (2017)

K. Keller Sebastian Lienert Anil Bozbiyik Thomas F. Stocker Olga V. Churakova

Abstract. Measurements of the stable carbon isotope ratio (δ13C) on annual tree rings offer new opportunities to evaluate mechanisms of variations in photosynthesis and stomatal conductance under changing CO2 and climate conditions, especially in conjunction with process-based biogeochemical model simulations. The isotopic discrimination is indicative of the ratio between the CO2 partial pressure in the intercellular cavities and the atmosphere (ci∕ca) and of the ratio of assimilation to stomatal conductance, termed intrinsic water-use efficiency (iWUE). We performed isotope-enabled simulations over the industrial period with the land biosphere module (CLM4.5) of the Community Earth System Model and the Land Surface Processes and Exchanges (LPX-Bern) dynamic global vegetation model. Results for C3 tree species show good agreement with a global compilation of δ13C measurements on leaves, though modeled 13C discrimination by C3 trees is smaller in arid regions than measured. A compilation of 76 tree-ring records, mainly from Europe, boreal Asia, and western North America, suggests on average small 20th century changes in isotopic discrimination and in ci∕ca and an increase in iWUE of about 27 % since 1900. LPX-Bern results match these century-scale reconstructions, supporting the idea that the physiology of stomata has evolved to optimize trade-offs between carbon gain by assimilation and water loss by transpiration. In contrast, CLM4.5 simulates an increase in discrimination and in turn a change in iWUE that is almost twice as large as that revealed by the tree-ring data. Factorial simulations show that these changes are mainly in response to rising atmospheric CO2. The results suggest that the downregulation of ci∕ca and of photosynthesis by nitrogen limitation is possibly too strong in the standard setup of CLM4.5 or that there may be problems associated with the implementation of conductance, assimilation, and related adjustment processes on long-term environmental changes.

Stomatal Conductance

Water Use Efficiency

Global Change

10.5194/bg-14-2641-2017

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Citations (99)