Search for: All records

The interannual to decadal variability in natural carbon sinks limits the explanation of recent changes in atmospheric CO₂concentration. Here we account for interannual and decadal variability using a simple quasi-mechanistic model of the net land carbon exchange with terms scaling with atmospheric CO₂and a weighted spatial average of temperature anomalies. This approach reduces the unexplained residual in Earth’s carbon cycle budget from ±0.76 GtC per year obtained using process models to ±0.50 GtC per year, with the largest improvements on decadal timescales despite assuming constant dynamics. Our findings reveal remarkable stability of the carbon cycle and allow verification of reported global emissions to within 4.4% (95% confidence level) over the five-year stocktake cycle of the Paris Agreement—half the uncertainty reported previously.

 

Abstract. Tropospheric helium variations are tightly linked to CO2 due to the co-emission of He and CO2 from natural-gasburning. Recently, Birner et al. (2022a) showed that the global consumption of natural gas has measurably increased the He content of theatmosphere. Like CO2, He is also predicted to exhibit complex spatial and temporal variability on shorter timescales, butmeasurements of these short-term variations are lacking. Here, we present the development of an improved gas delivery and purification system for thesemi-continuous mass spectrometric measurement of the atmospheric He-to-nitrogen ratio (He/N2). The method replaces the chemicalgetter used previously by Birner et al. (2021, 2022a) to preconcentrate He in an air stream with a cryogenic trap which can be more simplyregenerated by heating and which improves the precision of the measurement to 22 per meg (i.e., 0.022 ‰) in10 min (1σ). Using this “cryo-enrichment” method, we measured the He/N2 ratios in ambient air at La Jolla (California,USA) over 5 weeks in 2022. During this period, He/N2 was strongly correlated with atmospheric CO2 concentrations, as expectedfrom anthropogenic emissions, with a diurnal cycle of 450–500 per meg (max–min) caused by the sea–land breeze pattern of local winds,which modulates the influence of local pollution sources.

 

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 CO₂can be distinguished from the noise of the carbon cycle and uncertainties in emission trends. We test that protocol with a database of 226 emission mitigation scenarios—the universe of scenarios vetted by the Intergovernmental Panel on Climate Change. These scenarios are descriptive of ‘baseline’ trajectories of emissions trends in the absence of new policies along with trajectories that reflect substantial policy efforts to stop warming at 1.5 °C–2 °C above pre-industrial levels, as embodied in the Paris Agreement. The most aggressive mitigation scenarios (i.e. 1.5 °C) require 11–16 years to detect a signal of demonstrable progress from the noise; 2 °C scenarios lengthen detection by at least a decade. As more climate policy analysts face the reality that goals of 1.5 °C–2 °C seem infeasible, they have developed ‘overshoot’ scenarios with emissions that rise above the agreed goal and then, later on, fall aggressively to achieve it. These pathways come at the political cost of a 1–2 decade delay in detection, even for the 1.5 °C scenarios. The Paris Agreement requires a global ‘stocktake’ that interrogates national mitigation efforts; our results suggest that this effort must grapple with the question of when the world can gain confidence that the diplomacy on climate is demonstrably making an impact.

 

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 contain a wide spectrum of signals, from seasonal cycles to long-term trends. These signals are variously related to carbon sources and sinks, rates of photosynthesis and respiration of both land and oceanic ecosystems, and rates of air-sea exchange, providing unique insights into natural biogeochemical cycles and their ongoing changes. This review provides a broad overview of these records, focusing on what they have taught us about large-scale global biogeochemical change. 

Abstract. This study considersyear-to-year and decadal variations in as well as secular trendsof 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 sinksto local interannual anomalies insea surface temperature (SST), the temporal changes in SST (dSST/dt),and squared wind speed (u2),employing a multi-linear regression.In the tropical Pacific, we find interannual variability to be dominated by dSST/dt,as arising from variations in the upwelling of colder and more carbon-rich waters into the mixed layer.In the eastern upwelling zones as well as in circumpolar bands in the high latitudes of both hemispheres,we find sensitivity to wind speed,compatible with the entrainment of carbon-rich water during wind-driven deepening of the mixed layerand wind-driven upwelling.In the Southern Ocean,the secular increase in wind speed leads to a secular increase in the carbon source into the mixed layer,with an estimated reduction in the sink trend in the range of 17 % to 42 %.In a second step,we combined the result of the multi-linear regression andan explicitly interannual pCO2-based additive correctioninto a “hybrid” estimate of the sea–air CO2 flux over the period 1957–2020.As a pCO2 mapping method,it combines (a) the ability of a regression to bridge data gaps and extrapolate intothe early decades almost void of pCO2 databased on process-related observablesand (b) the ability of an auto-regressive interpolation to follow signalseven if not represented in the chosen set of explanatory variables.The “hybrid” estimate can be applied as an ocean flux prior foratmospheric CO2 inversions covering the whole period of atmospheric CO2 data since 1957. 

Abstract. The atmospheric He/N2 ratio is expected to increase due to the emission of He associated with fossil fuels and isexpected to also vary in both space and time due to gravitational separationin the stratosphere. These signals may be useful indicators of fossil fuelexploitation and variability in stratospheric circulation, but directmeasurements of He/N2 ratio are lacking on all timescales. Here wepresent a high-precision custom inlet system for mass spectrometers thatcontinuously stabilizes the flow of gas during sample–standard comparisonand removes all non-noble gases from the gas stream. This enablesunprecedented accuracy in measurement of relative changes in the helium molefraction, which can be directly related to the 4He/N2 ratio usingsupplementary measurements of O2/N2, Ar/N2 and CO2.Repeat measurements of the same combination of high-pressure tanks using ourinlet system achieves a He/N2 reproducibility of∼ 10 per meg (i.e., 0.001 %) in 6–8 h analyses. This compares to interannual changesof gravitational enrichment at ∼ 35 km in the midlatitudestratosphere of order 300–400 per meg and an annual tropospheric increasefrom human fossil fuel activity of less than ∼ 30 per meg yr−1 (bounded by previous work on helium isotopes). The gettering andflow-stabilizing inlet may also be used for the analysis of other noble-gasisotopes and could resolve previously unobserved seasonal cycles inKr/N2 and Xe/N2. 

Concern is often voiced over the ongoing loss of atmospheric O 2 . 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 atmospheric O 2 reservoir is so large, the predicted relative drop in O 2 is very small even for extreme scenarios of future fossil-fuel usage which produce increases in atmospheric CO 2 sufficient to cause catastrophic climate changes. At sea level, the ultimate drop in oxygen partial pressure will be less than 2.5 mm Hg out of a baseline of 159 mmHg. The drop by year 2300 is likely to be between 0.5 and 1.3 mmHg. The implications for normal human health is negligible because respiratory O 2 consumption in healthy individuals is only weakly dependent on ambient partial pressure, especially at sea level. The impacts on top athlete performance, on disease, on reproduction, and on cognition, will also be very small. For people living at higher elevations, the implications of this loss will be even smaller, because of a counteracting increase in barometric pressure at higher elevations due to global warming. 

Abstract. We introduce a transformed isentropic coordinate Mθe,defined as the dry air mass under a given equivalent potential temperaturesurface (θe) within a hemisphere. Like θe, thecoordinate Mθe follows the synoptic distortions of theatmosphere but, unlike θe, has a nearly fixedrelationship with latitude and altitude over the seasonal cycle. Calculationof Mθe is straightforward from meteorological fields. Usingobservations from the recent HIAPER Pole-to-Pole Observations (HIPPO) and Atmospheric Tomography Mission (ATom) airborne campaigns, we map theCO2 seasonal cycle as a function of pressure and Mθe, whereMθe is thereby effectively used as an alternative tolatitude. We show that the CO2 seasonal cycles are more constantas a function of pressure using Mθe as the horizontal coordinatecompared to latitude. Furthermore, short-term variability inCO2 relative to the mean seasonal cycle is also smaller when the dataare organized by Mθe and pressure than when organized by latitudeand pressure. We also present a method using Mθe to computemass-weighted averages of CO2 on a hemispheric scale. Using this methodwith the same airborne data and applying corrections for limited coverage,we resolve the average CO2 seasonal cycle in the Northern Hemisphere(mass-weighted tropospheric climatological average for 2009–2018), yieldingan amplitude of 7.8 ± 0.14 ppm and a downward zero-crossing on Julianday 173 ± 6.1 (i.e., late June). Mθe may be similarlyuseful for mapping the distribution and computing inventories of anylong-lived chemical tracer.