Luke Gregor

Last Name

Gregor

First Name

Luke

ORCID

0000-0001-6071-1857

Organisational unit

02286 - Swiss Data Science Center (SDSC) / Swiss Data Science Center (SDSC)

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Publications 1 - 10 of 30

High-resolution satellite predictions of air-sea CO2 flux capture short-lived, high-intensity events
Gregor, Luke; Gruber, Nicolas; Shutler, Jamie (2024)
Ocean Sciences Meeting 2024 Online Program
Ocean Biogeochemical Extremes and compound events
Gruber, Nicolas; Boyd, Philip W.; Desmet, Flora; et al. (2021)
Compounding Ocean Acidification Extremes and Marine Heatwaves from Satellite
Gregor, Luke; Gruber, Nicolas (2022)
Global Carbon Budget 2023
Friedlingstein, Pierre; O'Sullivan, Michael; Jones, Matthew W.; et al. (2023)
Earth System Science Data
Accurate assessment of anthropogenic carbon dioxide (CO₂) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesize data sets and methodology to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO₂ emissions (EFOS) are based on energy statistics and cement production data, while emissions from land-use change (ELUC), mainly deforestation, are based on land-use and land-use change data and bookkeeping models. Atmospheric CO₂ concentration is measured directly, and its growth rate (GATM) is computed from the annual changes in concentration. The ocean CO₂ sink (SOCEAN) is estimated with global ocean biogeochemistry models and observation-based fCO₂ products. The terrestrial CO₂ sink (SLAND) is estimated with dynamic global vegetation models. Additional lines of evidence on land and ocean sinks are provided by atmospheric inversions, atmospheric oxygen measurements, and Earth system models. The resulting carbon budget imbalance (BIM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and incomplete understanding of the contemporary carbon cycle. All uncertainties are reported as ±1σ. For the year 2022, EFOS increased by 0.9 % relative to 2021, with fossil emissions at 9.9±0.5 Gt C yr⁻¹ (10.2±0.5 Gt C yr⁻¹ when the cement carbonation sink is not included), and ELUC was 1.2±0.7 Gt C yr⁻¹, for a total anthropogenic CO2 emission (including the cement carbonation sink) of 11.1±0.8 Gt C yr⁻¹ (40.7±3.2 Gt CO2 yr−1). Also, for 2022, GATM was 4.6±0.2 Gt C yr⁻¹ (2.18±0.1 ppm yr⁻¹; ppm denotes parts per million), SOCEAN was 2.8±0.4 Gt C yr⁻¹, and SLAND was 3.8±0.8 Gt C yr⁻¹, with a BIM of −0.1 Gt C yr⁻¹ (i.e. total estimated sources marginally too low or sinks marginally too high). The global atmospheric CO₂ concentration averaged over 2022 reached 417.1±0.1 ppm. Preliminary data for 2023 suggest an increase in EFOS relative to 2022 of +1.1 % (0.0 % to 2.1 %) globally and atmospheric CO₂ concentration reaching 419.3 ppm, 51 % above the pre-industrial level (around 278 ppm in 1750). Overall, the mean of and trend in the components of the global carbon budget are consistently estimated over the period 1959–2022, with a near-zero overall budget imbalance, although discrepancies of up to around 1 Gt C yr⁻¹ persist for the representation of annual to semi-decadal variability in CO₂ fluxes. Comparison of estimates from multiple approaches and observations shows the following: (1) a persistent large uncertainty in the estimate of land-use changes emissions, (2) a low agreement between the different methods on the magnitude of the land CO₂ flux in the northern extra-tropics, and (3) a discrepancy between the different methods on the strength of the ocean sink over the last decade. This living-data update documents changes in methods and data sets applied to this most recent global carbon budget as well as evolving community understanding of the global carbon cycle. The data presented in this work are available at https://doi.org/10.18160/GCP-2023 (Friedlingstein et al., 2023).
Enhance seasonal amplitude of atmospheric CO2 by the changing Southern Ocean carbon sink
Jeongmin, Yun; Sujong, Jeong; Gruber, Nicolas; et al. (2022)
Science Advances
The enhanced seasonal amplitude of atmospheric CO2 has been viewed so far primarily as a Northern Hemisphere phenomenon. Yet, analyses of atmospheric CO2 records from 49 stations between 1980 and 2018 reveal substantial trends and variations in this amplitude globally. While no significant trends can be discerned before 2000 in most places, strong positive trends emerge after 2000 in the southern high latitudes. Using factorial simulations with an atmospheric transport model and analyses of surface ocean Pco2 observations, we show that the increase is best explained by the onset of increasing seasonality of air-sea CO2 exchange over the Southern Ocean around 2000. Underlying these changes is the long-term ocean acidification trend that tends to enhance the seasonality of the air-sea fluxes, but this trend is modified by the decadal variability of the Southern Ocean carbon sink. The seasonal variations of atmospheric CO2 thus emerge as a sensitive recorder of the variations of the Southern Ocean carbon sink.
Integrated Ocean Carbon Research: A Summary of Ocean Carbon Research, and Vision of Coordinated Ocean Carbon Research and Observations for the Next Decade
IOC Working Group on Integrated Ocean Carbon Research (IOC-R); Aricò, Salvatore; Arrieta, Jesús M.; et al. (2021)
IOC Technical Series
Four Decades of Trends and Drivers of Global Surface Ocean Acidification
Ma, Danling; Gregor, Luke; Gruber, Nicolas (2023)
Global Biogeochemical Cycles
The oceans are acidifying in response to the oceanic uptake of anthropogenic carbon dioxide (CO2) from the atmosphere, yet the global-scale progression of this acidification has been poorly documented so far by observations. Here, we fill this gap and use an updated version of the in situ and satellite observation-based product OceanSODA-ETHZ to determine the trends and drivers of the surface ocean aragonite saturation state (Ωar) and pH = –log([H+]) (total scale) over the last four decades (1982–2021). In the global mean, Ωar and pH declined at rates of −0.071 ± 0.006 decade−1 and −0.0166 ± 0.0010 decade−1, respectively, with the errors of the trends largely reflecting the uncertainties in the reconstructed pH and Ωar fields. These global mean trends are driven primarily by the increase in surface ocean concentration of dissolved inorganic carbon (DIC) in response to the uptake of anthropogenic CO2, but moderated by changes in natural DIC. Surface warming enhances the decrease in pH, accounting for ∼15% of the global trend. The long-term trends vary substantially across regions and also differ distinctly between pH and Ωar. The highest trends in pH are found in the high latitudes, while Ωar decreases the fastest in the low latitudes. These regional differences are primarily a consequence of regional differences in the ability of the surface ocean to take up and buffer the anthropogenic CO2. Substantial El Niño-driven interannual variability is superimposed on these trends, with Ωar showing greater variability than pH, resulting in substantially longer time of emergence for Ωar.
CO 2 uptake in the Pacific from 1985 to 2018: a comparative assessment of observation-and model-based estimates
Ishii, Masao; Carter, Brendan R.; Toyama, Katsuya; et al. (2024)
ESS Open Archive
As a contribution to the second REgional Carbon Cycle Assessment and Processes effort, we compare net and anthropogenic sea-to-air CO2 fluxes, CO2 accumulation rates in the ocean interior and their trends in the Pacific Ocean by analyzing results from state-of-the-art observation-based estimates and global ocean biogeochemistry models (GOBMs) over the period 1985 – 2018. The ensemble-mean net CO2 fluxes integrated over the Pacific (44ºS – 62ºN) are -0.41 ±0.12 PgC yr-1 from pCO2 products and -0.51 ±0.16 PgC yr-1 from GOBMs. The anthropogenic CO2 flux from GOBMs (-0.71 ±0.10 PgC yr-1) is 1.4 times as large as the net CO2 flux, with particularly large uptake in the equatorial region (-0.34 ±0.03 PgC yr-1) largely offsetting the large natural CO2 outgassing there (+0.72 ±0.06 PgC yr-1). The basin-wide net CO2 uptake has increased at similar mean rates of -0.088 ±0.062 and -0.079 ±0.016 PgC yr-1 decade-1 in pCO2 products and GOBMs, respectively, comparable with the rate of increase in anthropogenic CO2 uptake at -0.102 ±0.013 PgC yr-1 decade-1 in GOBMs. However, a notable mismatch in the trend of the net CO2 flux change that exists between pCO2 products (+0.001 ±0.020 PgC yr-1 decade-1) and GOBMs (-0.040 ±0.013 PgC yr-1 decade-1) in the equatorial region is yet to be resolved. The rate of anthropogenic CO2 accumulation from GOBMs is +0.76 ±0.17 PgC yr-1. This is nearly balanced with the anthropogenic CO2 flux and is also encompassed by the previous observation-based estimates. But a better consistency is still required in the South Pacific
The growing exposure of Pacific coral reefs to compound extremes caused by marine heatwaves coalescing with low saturation state extremes
Gregor, Luke; Gruber, Nicolas (2021)
EGUsphere
The ocean has played a key role in mitigating the impact of climate change by taking up excess anthropogenic heat and CO2 leading to warming and increased ocean acidity, which goes in hand with a reduction of the saturation state of seawater with regard to the mineral carbonate aragonite, i.e., ΩAR. While the threats posed by these long-term changes to marine organisms and ecosystems are well recognized, only more recently has the community realized that these threats might be much more imminent owing to extreme events. This is the result of these extremes exposing vulnerable ecosystems already today to conditions that lie in the far future when considering only the changes in the mean conditions. Of particular concern are so-called compound events, i.e., conditions when both temperatures are extremely hot and the saturation states extremely low, as this compounding might be particularly threatening for marine ecosystems, especially for warm water coral reefs. Here we use satellite records of sea surface temperature (SST) and satellite ΩAR to map globally the occurrence of marine heat waves (MHW) and low saturation state extreme events and their compounding for the period 1985 and 2018. We use SSTs from the OSTIA product, while we take ΩAR from the newly developed OceanSODA-ETHZ (monthly 1°x1°) observation-based product that extrapolates ship observations with satellite data. Our study focuses on the Pacific Ocean between 25°S and 25°N, a region with more than 1000 identified coral reefs. We define extremes using the approach of Hobday et al. (2018) with a fixed baseline determined from the entire record (1985-2018) and where extremes are below/above the 10th/90th percentiles for Ω/SST respectively. The majority of the compound extreme events (too hot and too low saturation state) occur in the western tropical Pacific, with 757 of the 1206 reefs in the Pacific experiencing at least three months of compound extreme events over the entire period. The average duration of these compound extremes was 3.6 months, and the average area was 247 600 km2 (roughly the size of the United Kingdom). The compound events had an average intensity of –0.13 for ΩAR and 0.71°C, where the intensity is the anomaly from the climatology. The largest and longest lasting extreme event started in 2016 and lasted nearly three years, coinciding with the El Niño event over the same period, covering an area equivalent to Australia. These findings suggest that more than 60% of coral reefs in the Pacific Ocean are located in regions where heating events may have been compounded by decreased potential for calcification. Given the continuing increase in atmospheric CO2, the severity of this type of compound events is bound to increase in the future.
The Southern Ocean Carbon Cycle 1985–2018: Mean, Seasonal Cycle, Trends, and Storage
Hauck, Judith; Gregor, Luke; Nissen, Cara; et al. (2023)
Global Biogeochemical Cycles
We assess the Southern Ocean CO₂ uptake (1985–2018) using data sets gathered in the REgional Carbon Cycle Assessment and Processes Project Phase 2. The Southern Ocean acted as a sink for CO₂ with close agreement between simulation results from global ocean biogeochemistry models (GOBMs, 0.75 ± 0.28 PgC yr⁻¹) and pCO₂-observation-based products (0.73 ± 0.07 PgC yr⁻¹). This sink is only half that reported by RECCAP1 for the same region and timeframe. The present-day net uptake is to first order a response to rising atmospheric CO₂, driving large amounts of anthropogenic CO₂ (Cant) into the ocean, thereby overcompensating the loss of natural CO2 to the atmosphere. An apparent knowledge gap is the increase of the sink since 2000, with pCO₂-products suggesting a growth that is more than twice as strong and uncertain as that of GOBMs (0.26 ± 0.06 and 0.11 ± 0.03 Pg C yr⁻¹ decade⁻¹, respectively). This is despite nearly identical pCO₂ trends in GOBMs and pCO2-products when both products are compared only at the locations where pCO₂ was measured. Seasonal analyses revealed agreement in driving processes in winter with uncertainty in the magnitude of outgassing, whereas discrepancies are more fundamental in summer, when GOBMs exhibit difficulties in simulating the effects of the non-thermal processes of biology and mixing/circulation. Ocean interior accumulation of Cant points to an underestimate of Cant uptake and storage in GOBMs. Future work needs to link surface fluxes and interior ocean transport, build long overdue systematic observation networks and push toward better process understanding of drivers of the carbon cycle.

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