Ralph F. Keeling's research while affiliated with University of California, San Diego and other places
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Publications (212)
Tropospheric helium variations are tightly linked to CO2 due to the co-emission of He and CO2 from natural-gas burning. Recently, Birner et al. (2022a) showed that the global consumption of natural gas has measurably increased the He content of the atmosphere. Like CO2, He is also predicted to exhibit complex spatial and temporal variability on sho...
![A record of historical carbon emissions [1] (yellow) and the range of...](publication/369235459/figure/fig1/AS:11431281126875601@1678853393667/A-record-of-historical-carbon-emissions-1-yellow-and-the-range-of-future-CO2_Q320.jpg)
A central challenge for sustaining international cooperation to cut global greenhouse gas emissions is confidence that national policy efforts are leading to a meaningful impact on the climate. Here, we apply a detection protocol to determine when the measurable signal of atmospheric CO2 can be distinguished from the noise of the carbon cycle and u...
Understanding terrestrial ecosystems and their response to anthropogenic climate change requires quantification of land‐atmosphere carbon exchange. However, top‐down and bottom‐up estimates of large‐scale land‐atmosphere fluxes, including the northern extratropical growing season net flux (GSNF), show significant discrepancies. We developed a data‐...
We explore the ability of the atmospheric CO2 record since 1900 to constrain the source of CO2 from land use and land cover change (hereafter "land use"), taking account of uncertainties in other terms in the global carbon budget. We find that the atmospheric constraint favors land use CO2 flux estimates with lower decadal variability and can ident...
Tropospheric helium variations are tightly linked to CO2 due to the co-emission of He and CO2 from natural gas burning. Recently Birner et al. (2022) showed that the global consumption of natural gas has measurably increased the He content of the atmosphere. Like CO2, He is also predicted to exhibit complex spatial and temporal variability on short...
Long‐term measurements at the Mauna Loa Observatory (MLO) show that the CO2 seasonal cycle amplitude (SCA) increased from 1959 to 2019 at an overall rate of 0.22 ± $\pm $ 0.034 ppm decade⁻¹ while also varying on interannual to decadal time scales. These SCA changes are a signature of changes in land ecological CO2 fluxes as well as shifting winds....
Urban regions emit a large fraction of anthropogenic emissions of greenhouse gases (GHG) such as carbon dioxide (CO2) and methane (CH4) that contribute to modern-day climate change. As such, a growing number of urban policymakers and stakeholders are adopting emission reduction targets and implementing policies to reach those targets. Over the past...
This study considers year-to-year and decadal variations in as well as secular trends of the sea–air CO2 flux over the 1957–2020 period, as constrained by the pCO2 measurements from the SOCATv2021 database. In a first step, we relate interannual anomalies in ocean-internal carbon sources and sinks to local interannual anomalies in sea surface tempe...
Fossil fuels contain small amounts of helium, which are co-released into the atmosphere together with carbon dioxide. However, a clear build-up of helium in the atmosphere has not previously been detected. Using a high-precision mass spectrometry technique to determine the atmospheric ratio of helium-4 to nitrogen, we show that helium-4 concentrati...
This article provides an overview of the NASA Atmospheric Tomography (ATom) mission and a summary of selected scientific findings to date. ATom was an airborne measurements and modeling campaign aimed at characterizing the composition and chemistry of the troposphere over the most remote regions of the Pacific, Southern, Atlantic, and Arctic Oceans...
Up in the air
Understanding ocean-atmospheric carbon dioxide (CO 2 ) fluxes in the Southern Ocean is necessary for quantifying the global CO 2 budget, but measurements in the harsh conditions there make collecting good data difficult, so a quantitative picture still is out of reach. Long et al . present measurements of atmospheric CO 2 concentratio...
We assess the detectability of COVID-like emissions reductions in global atmospheric CO₂ concentrations using a suite of large ensembles conducted with an Earth system model. We find a unique fingerprint of COVID in the simulated growth rate of CO₂ sampled at the locations of surface measurement sites. Negative anomalies in growth rates persist fro...
We assess the detectability of COVID‐like emissions reductions in global atmospheric CO2 concentrations using a suite of large ensembles conducted with an Earth system model. We find a unique fingerprint of COVID in the simulated growth rate of CO2 sampled at the locations of surface measurement sites. Negative anomalies in growth rates persist fro...
The past century has been a time of unparalleled changes in global climate and global biogeochemistry. At the forefront of the study of these changes are regular time-series observations at remote stations of atmospheric CO 2 , isotopes of CO 2 , and related species, such as O 2 and carbonyl sulfide (COS). These records now span many decades and co...
A study was conducted to compare the δ(O2/N2)
scales used by four laboratories engaged in atmospheric δ(O2/N2) measurements. These laboratories are the Research
Institute for Environmental Management Technology, Advanced Industrial
Science and Technology (EMRI/AIST); the National Institute for Environmental
Studies (NIES); Tohoku University (TU); a...
The air‐sea exchange of oxygen (O2) is driven by changes in solubility, biological activity, and circulation. The total air‐sea exchange of O2 has been shown to be closely related to the air‐sea exchange of heat on seasonal timescales, with the ratio of the seasonal flux of O2 to heat varying with latitude, being higher in the extratropics and lowe...
Responses to COVID-19 have resulted in unintended reductions of city-scale carbon dioxide (CO2) emissions. Here, we detect and estimate decreases in CO2 emissions in Los Angeles and Washington DC/Baltimore during March and April 2020. We present three lines of evidence using methods that have increasing model dependency, including an inverse model...
The 2015−2016 El Niño was one of the strongest on record, but its influence on the carbon balance is less clear. Using Northern Hemisphere atmospheric CO2 observations, we found both detrended atmospheric CO2 growth rate (CGR) and CO2 seasonal‐cycle amplitude (SCA) of 2015−2016 were much higher than that of other El Niño events. The simultaneous hi...
We have developed in situ and flask sampling systems for airborne measurements of variations in the O2/N2 ratio at the part per million level.
We have deployed these instruments on a series of aircraft campaigns to measure the distribution of atmospheric O2 from 0–14 km and 87∘ N to 86∘ S throughout the seasonal cycle.
The National Center for Atmos...
The atmospheric He/N2 ratio is expected to increase due to the emission of He associated with fossil fuels and is
expected to also vary in both space and time due to gravitational separation
in the stratosphere. These signals may be useful indicators of fossil fuel
exploitation and variability in stratospheric circulation, but direct
measurements o...
Concern is often voiced over the ongoing loss of atmospheric O2. This loss, which is caused by fossil-fuel burning but also influenced by other processes, is likely to continue at least for the next few centuries. We argue that this loss is quite well understood, and the eventual decrease is bounded by the fossil-fuel resource base. Because the atm...
Fossil fuels contain small amounts of helium which are incidentally co-released to the atmosphere together with CO 2 . However, a clear buildup of He in the atmosphere has not previously been detected. Using results from our novel mass spectrometry technique that constrains relative changes in the atmospheric helium-to-nitrogen ratio ( ⁴ He/N 2 ) a...
We introduce a transformed isentropic coordinate Mθe, defined as the dry air mass under a given equivalent potential temperature surface (θe) within a hemisphere. Like θe, the coordinate Mθe follows the synoptic distortions of the atmosphere but, unlike θe, has a nearly fixed relationship with latitude and altitude over the seasonal cycle. Calculat...
A study was conducted to compare the δ(O2/N2) scales used by four laboratories engaged in atmospheric δ(O2/N2) measurements. These laboratories are the Research Institute for Environmental Management Technology, Advanced Industrial Science and Technology (EMRI/AIST), the National Institute for Environmental Studies (NIES), Tohoku University (TU), a...
In this "Grand Challenges" paper, we review how the carbon isotopic composition of atmospheric CO2 has changed since the Industrial Revolution due to human activities and their influence on the natural carbon cycle, and we provide new estimates of possible future changes for a range of scenarios. Emissions of CO2 from fossil fuel combustion and lan...
Accurate simulation of atmospheric circulation,
particularly in the lower stratosphere, is challenging due to unresolved
wave–mean flow interactions and limited high-resolution observations for validation. Gravity-induced pressure gradients lead to a small but
measurable separation of heavy and light gases by molecular diffusion in the
stratosphere...
The atmospheric He/N2 ratio is expected to be increasing due to the emission of He associated with fossil fuels and is expected to also vary in both space and time due to gravitational separation in the stratosphere. These signals may be useful indicators of fossil-fuel exploitation and variability in stratospheric circulation, but direct measureme...
We have developed in situ and flask sampling systems for airborne measurements of variations in the O2/N2 ratio at the part per million level. We have deployed these instruments on a series of aircraft campaigns to measure the distribution of atmospheric O2 from 0–14 km and 87° N to 85° S throughout the seasonal cycle. The NCAR airborne oxygen inst...
We introduce a transformed isentropic coordinate Mθe, defined as the dry air mass under a given equivalent potential temperature surface (θe) within a hemisphere. Like θe, the coordinate Mθe follows the synoptic distortions of the atmosphere, but unlike θe, has a nearly fixed relationship with latitude and altitude over the seasonal cycle. Calculat...
Atmospheric carbon dioxide concentration ([CO2]) is increasing, which increases leaf‐scale photosynthesis and intrinsic water‐use efficiency. These direct responses have the potential to increase plant growth, vegetation biomass, and soil organic matter; transferring carbon from the atmosphere into terrestrial ecosystems (a carbon sink). A substant...
Changing amplitude of the seasonal cycle of atmospheric CO2 (SCA) in the northern hemisphere is an emerging carbon cycle property. Mauna Loa (MLO) station (20oN, 156oW), which has the longest continuous northern hemisphere CO2 record, shows an increasing SCA before the 1980s (P < 0.01), followed by no significant change thereafter. We analyzed the...
Plain Language Summary
The Southern Annular Mode (SAM) is characterized by variability in the strength of the westerly winds that encircle Antarctica. A more positive SAM index is associated with stronger westerly winds over the ocean at about 60°S latitude. Previous studies based mostly on model simulations have suggested that a positive SAM index...
Abstract. Accurate simulation of atmospheric circulation, particularly in the lower stratosphere, is challenging due to unresolved wave-mean flow interactions and limited high-resolution observations for validation. Gravity-induced pressure gradients lead to a small but measurable separation of heavy and light gases by molecular diffusion in the st...
The ocean is the main source of thermal inertia in the climate system. Ocean heat uptake during recent decades has been quantified using ocean temperature measurements. However, these estimates all use the same imperfect ocean dataset and share additional uncertainty due to sparse coverage, especially before 2007. Here, we provide an independent es...
We present airborne observations of the vertical gradient of atmospheric oxygen (δ(O2/N2)) and carbon dioxide (CO2) through the atmospheric boundary layer (BL) over the Drake Passage region of the Southern Ocean, during the O2/N2 Ratio and CO2 Airborne Southern Ocean Study, from 15 January to 29 February 2016. Gradients were predominately anticorre...
Fluxes of halogenated volatile organic compounds (VOCs) over the Southern
Ocean remain poorly understood, and few atmospheric measurements exist to
constrain modeled emissions of these compounds. We present observations of
CHBr3, CH2Br2, CH3I, CHClBr2, CHBrCl2, and
CH3Br during the O2∕N2 Ratio and CO2 Airborne Southern
Ocean (ORCAS) study and the s...
This Article has been retracted; see accompanying Retraction Note.
A multitude of disturbance agents, such as wildfires, land use, and climate‐driven expansion of woody shrubs, are transforming the distribution of plant functional types across Arctic‐Boreal ecosystems, which has significant implications for interactions and feedbacks between terrestrial ecosystems and climate in the northern high‐latitudes. Howeve...
We present observations of CHBr3, CH2Br2, CH3I, CHClBr2, and CHBrCl2 from the Trace Gas Organic Analyzer (TOGA) during the O2/N2 Ratio and CO2 Airborne Southern Ocean (ORCAS) study and the 2nd Atmospheric Tomography mission (ATom-2), in January and February of 2016 and 2017. We also use CH3Br from the University of Miami Advanced Whole Air Sampler...
The oceanic response to recent tropical eruptions is examined in Large Ensemble (LE) experiments from two fully coupled global climate models, the Community Earth System Model (CESM) and the Geophysical Fluid Dynamics Laboratory Earth System Model (ESM2M), each forced by a distinct volcanic forcing dataset. Following the simulated eruptions of Agun...
Accurate assessment of anthropogenic carbon dioxide
(CO2) emissions and their redistribution among the atmosphere,
ocean, and terrestrial biosphere – the “global carbon budget” – is
important to better understand the global carbon cycle, support the
development of climate policies, and project future climate change. Here we
describe data sets and m...
In early 2016, we predicted that the annual rise in carbon dioxide concentration at Mauna Loa would be the largest on record. Our forecast used a statistical relationship between observed and forecast sea surface temperatures in the Niño 3.4 region and the annual CO2 rise. Here, we provide a formal verification of that forecast. The observed rise o...
The ocean is the main source of thermal inertia in the climate system¹. During recent decades, ocean heat uptake has been quantified by using hydrographic temperature measurements and data from the Argo float program, which expanded its coverage after 20072,3. However, these estimates all use the same imperfect ocean dataset and share additional un...
Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere – the ‘global carbon budget’ – is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and m...
Measurements of atmospheric CO2 concentration provide a tight constraint on the sum of the land and ocean sinks. This constraint has been combined with estimates of ocean carbon flux and riverine transport of carbon from land to oceans to isolate the land sink. Uncertainties in the ocean and river fluxes therefore translate into uncertainties in th...
Analysis systems incorporating atmospheric observations could provide a powerful tool for validating fossil fuel CO2 (ffCO2) emissions reported for individual regions, provided that fossil fuel sources can be separated from other CO2 sources or sinks and atmospheric transport can be accurately accounted for. We quantified ffCO2 by measuring radioca...
Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution
among the atmosphere, ocean, and terrestrial biosphere – the “global carbon budget” – is important to better understand
the global carbon cycle, support the development of climate policies, and project future climate change.
Here we describe data sets and m...
Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere - the "global carbon budget" - is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and m...
Significance
Climate change and rising CO 2 are altering the behavior of land plants in ways that influence how much biomass they produce relative to how much water they need for growth. This study shows that it is possible to detect changes occurring in plants using long-term measurements of the isotopic composition of atmospheric CO 2 . These mea...
The Southern Ocean plays a critical role in the global climate system by mediating atmosphere–ocean partitioning of heat and carbon dioxide. However, Earth system models are demonstrably deficient in the Southern Ocean, leading to large uncertainties in future air–sea CO2 flux projections under climate warming and incomplete interpretations of natu...
The isotopic composition of carbon (Δ14C and δ13C) in
atmospheric CO2 and in oceanic and terrestrial carbon reservoirs is
influenced by anthropogenic emissions and by natural carbon exchanges, which
can respond to and drive changes in climate. Simulations of 14C and
13C in the ocean and terrestrial components of Earth system models
(ESMs) present o...
We report continuous surface observations of carbon dioxide (CO2) and methane (CH4) from the Los Angeles (LA) Megacity Carbon Project during 2015. We devised a calibration strategy, methods for selection of background air masses, calculation of urban enhancements, and a detailed algorithm for estimating uncertainties in urban-scale CO2 and CH4 meas...
Models and observations of Atmospheric Potential Oxygen (APO ≃ O2 + 1.1*CO2) are used to investigate the influence of El Niño Southern Oscillation (ENSO) on air-sea O2 exchange. An atmospheric transport inversion of APO data from the Scripps flask network shows significant interannual variability in tropical APO fluxes that is positively correlated...