The Montreal Protocol was designed to protect the stratospheric ozone layer by enabling reductions in the abundance of ozone-depleting substances such as chlorofluorocarbons (CFCs) in the atmosphere
.... The reduction in the atmospheric concentration of trichlorofluoromethane (CFC-11) has made the second-largest contribution to the decline in the total atmospheric concentration of ozone-depleting chlorine since the 1990s
. However, CFC-11 still contributes one-quarter of all chlorine reaching the stratosphere, and a timely recovery of the stratospheric ozone layer depends on a sustained decline in CFC-11 concentrations
. Here we show that the rate of decline of atmospheric CFC-11 concentrations observed at remote measurement sites was constant from 2002 to 2012, and then slowed by about 50 per cent after 2012. The observed slowdown in the decline of CFC-11 concentration was concurrent with a 50 per cent increase in the mean concentration difference observed between the Northern and Southern Hemispheres, and also with the emergence of strong correlations at the Mauna Loa Observatory between concentrations of CFC-11 and other chemicals associated with anthropogenic emissions. A simple model analysis of our findings suggests an increase in CFC-11 emissions of 13 ± 5 gigagrams per year (25 ± 13 per cent) since 2012, despite reported production being close to zero
since 2006. Our three-dimensional model simulations confirm the increase in CFC-11 emissions, but indicate that this increase may have been as much as 50 per cent smaller as a result of changes in stratospheric processes or dynamics. The increase in emission of CFC-11 appears unrelated to past production; this suggests unreported new production, which is inconsistent with the Montreal Protocol agreement to phase out global CFC production by 2010.
It is well established that anthropogenic chlorine-containing chemicals contribute to ozone layer depletion. The successful implementation of the Montreal Protocol has led to reductions in the ...atmospheric concentration of many ozone-depleting gases, such as chlorofluorocarbons. As a consequence, stratospheric chlorine levels are declining and ozone is projected to return to levels observed pre-1980 later this century. However, recent observations show the atmospheric concentration of dichloromethane-an ozone-depleting gas not controlled by the Montreal Protocol-is increasing rapidly. Using atmospheric model simulations, we show that although currently modest, the impact of dichloromethane on ozone has increased markedly in recent years and if these increases continue into the future, the return of Antarctic ozone to pre-1980 levels could be substantially delayed. Sustained growth in dichloromethane would therefore offset some of the gains achieved by the Montreal Protocol, further delaying recovery of Earth's ozone layer.
Methane (CH4) emissions from natural gas production are not well quantified and have the potential to offset the climate benefits of natural gas over other fossil fuels. We use atmospheric ...measurements in a mass balance approach to estimate CH4 emissions of 55 ± 15 × 103 kg h−1 from a natural gas and oil production field in Uintah County, Utah, on 1 day: 3 February 2012. This emission rate corresponds to 6.2%–11.7% (1σ) of average hourly natural gas production in Uintah County in the month of February. This study demonstrates the mass balance technique as a valuable tool for estimating emissions from oil and gas production regions and illustrates the need for further atmospheric measurements to determine the representativeness of our single‐day estimate and to better assess inventories of CH4 emissions.
Key Points
A mass balance is used to estimate a methane leak rate from a natural gas field.
Single day methane emissions are excessive relative to average production.
This study quantitatively estimates the spatial distribution of anthropogenic methane sources in the United States by combining comprehensive atmospheric methane observations, extensive spatial ...datasets, and a high-resolution atmospheric transport model. Results show that current inventories from the US Environmental Protection Agency (EPA) and the Emissions Database for Global Atmospheric Research underestimate methane emissions nationally by a factor of ∼1.5 and ∼1.7, respectively. Our study indicates that emissions due to ruminants and manure are up to twice the magnitude of existing inventories. In addition, the discrepancy in methane source estimates is particularly pronounced in the south-central United States, where we find total emissions are ∼2.7 times greater than in most inventories and account for 24 ± 3% of national emissions. The spatial patterns of our emission fluxes and observed methane–propane correlations indicate that fossil fuel extraction and refining are major contributors (45 ± 13%) in the south-central United States. This result suggests that regional methane emissions due to fossil fuel extraction and processing could be 4.9 ± 2.6 times larger than in EDGAR, the most comprehensive global methane inventory. These results cast doubt on the US EPA’s recent decision to downscale its estimate of national natural gas emissions by 25–30%. Overall, we conclude that methane emissions associated with both the animal husbandry and fossil fuel industries have larger greenhouse gas impacts than indicated by existing inventories.
Role of atmospheric oxidation in recent methane growth Rigby, Matthew; Montzka, Stephen A.; Prinn, Ronald G. ...
Proceedings of the National Academy of Sciences - PNAS,
05/2017, Letnik:
114, Številka:
21
Journal Article
Recenzirano
Odprti dostop
The growth in global methane (CH₄) concentration, which had been ongoing since the industrial revolution, stalled around the year 2000 before resuming globally in 2007. We evaluate the role of the ...hydroxyl radical (OH), the major CH₄ sink, in the recent CH₄ growth. We also examine the influence of systematic uncertainties in OH concentrations on CH₄ emissions inferred from atmospheric observations. We use observations of 1,1,1-trichloroethane (CH₃CCl₃), which is lost primarily through reaction with OH, to estimate OH levels as well as CH₃CCl₃ emissions, which have uncertainty that previously limited the accuracy of OH estimates. We find a 64–70% probability that a decline in OH has contributed to the post-2007 methane rise. Our median solution suggests that CH₄ emissions increased relatively steadily during the late 1990s and early 2000s, after which growth was more modest. This solution obviates the need for a sudden statistically significant change in total CH₄ emissions around the year 2007 to explain the atmospheric observations and can explain some of the decline in the atmospheric 13CH₄/12CH₄ ratio and the recent growth in C₂H₆. Our approach indicates that significant OH-related uncertainties in the CH₄ budget remain, and we find that it is not possible to implicate, with a high degree of confidence, rapid global CH₄ emissions changes as the primary driver of recent trends when our inferred OH trends and these uncertainties are considered.
The hydroxyl radical (OH) is the main atmospheric oxidant and the primary sink of
the greenhouse gas CH4. In an attempt to constrain atmospheric levels
of OH, two recent studies combined a ...tropospheric two-box model with
hemispheric-mean observations of methyl chloroform (MCF) and CH4.
These studies reached different conclusions concerning the most likely
explanation of the renewed CH4 growth rate, which reflects the
uncertain and underdetermined nature of the problem. Here, we investigated
how the use of a tropospheric two-box model can affect the derived
constraints on OH due to simplifying assumptions inherent to a two-box
model. To this end, we derived species- and time-dependent quantities from a
full 3-D transport model to drive two-box model simulations. Furthermore, we
quantified differences between the 3-D simulated tropospheric burden and the
burden seen by the surface measurement network of the National Oceanic and
Atmospheric Administration (NOAA). Compared to commonly used parameters in
two-box models, we found significant deviations in the magnitude and
time-dependence of the interhemispheric exchange rate, exposure to OH, and
stratospheric loss rate. For MCF these deviations can be large due to changes
in the balance of its sources and sinks over time. We also found that changes
in the yearly averaged tropospheric burden of CH4 and MCF can be
obtained within 0.96 ppb yr−1 and
0.14 % yr−1 by the NOAA surface network, but that substantial
systematic biases exist in the interhemispheric mixing ratio gradients that
are input to two-box model inversions. To investigate the impact of the identified biases on constraints on OH, we
accounted for these biases in a two-box model inversion of MCF and
CH4. We found that the sensitivity of interannual OH anomalies
to the biases is modest (1 %–2 %), relative to the uncertainties on
derived OH (3 %–4 %). However, in an inversion where we implemented all
four bias corrections simultaneously, we found a shift to a positive trend in
OH concentrations over the 1994–2015 period, compared to the standard
inversion. Moreover, the absolute magnitude of derived global mean OH,
and by extent, that of global CH4 emissions, was affected much more strongly
by the bias corrections than their anomalies (∼10 %). Through our
analysis, we identified and quantified limitations in the two-box model
approach as well as an opportunity for full 3-D simulations to address these
limitations. However, we also found that this derivation is an extensive and
species-dependent exercise and that the biases were not always entirely
resolvable. In future attempts to improve constraints on the atmospheric
oxidative capacity through the use of simple models, a crucial first step is
to consider and account for biases similar to those we have identified for
the two-box model.
Chlorofluorocarbon (CFC) banks from uses such as air conditioners or foams can be emitted after global production stops. Recent reports of unexpected emissions of CFC-11 raise the need to better ...quantify releases from these banks, and associated impacts on ozone depletion and climate change. Here we develop a Bayesian probabilistic model for CFC-11, 12, and 113 banks and their emissions, incorporating the broadest range of constraints to date. We find that bank sizes of CFC-11 and CFC-12 are larger than recent international scientific assessments suggested, and can account for much of current estimated CFC-11 and 12 emissions (with the exception of increased CFC-11 emissions after 2012). Left unrecovered, these CFC banks could delay Antarctic ozone hole recovery by about six years and contribute 9 billion metric tonnes of equivalent CO
emission. Derived CFC-113 emissions are subject to uncertainty, but are much larger than expected, raising questions about its sources.
The emissions of hydrofluorocarbons (HFCs) have increased significantly in the past 2 decades, primarily as a result of the phaseout of ozone-depleting substances under the Montreal Protocol and the ...use of HFCs as their replacements. In 2015, large increases were projected in HFC use and emissions in this century in the absence of regulations, contributing up to 0.5 ∘C to global surface warming by 2100. In 2019, the Kigali Amendment to the Montreal Protocol came into force with the goal of limiting the use of HFCs globally, and currently, regulations to limit the use of HFCs are in effect in several countries. Here, we analyze trends in HFC emissions inferred from observations of atmospheric abundances and compare them with previous projections. Total CO2 eq. inferred HFC emissions continue to increase through 2019 (to about 0.8 GtCO2eq.yr-1) but are about 20 % lower than previously projected for 2017–2019, mainly because of the lower global emissions
of HFC-143a. This indicates that HFCs are used much less in industrial and commercial refrigeration (ICR) applications than previously projected. This is supported by data reported by the developed countries and the lower reported consumption of HFC-143a in China. Because this time period preceded the beginning of the Kigali provisions, this reduction cannot be linked directly to the provisions of the Kigali Amendment. However, it could indicate that companies transitioned away from the HFC-143a with its high global warming potential (GWP) for ICR applications in anticipation of national or global mandates. There are two new HFC scenarios developed based (1) on current trends in HFC use and Kigali-independent (K-I) control policies currently existing in several countries and (2) current HFC trends and compliance with the Kigali Amendment (KA-2022). These current policies reduce projected emissions in 2050 from the previously calculated 4.0–5.3 GtCO2eq.yr-1 to 1.9–3.6 GtCO2eq.yr-1. The added provisions of the Kigali Amendment are projected to
reduce the emissions further to 0.9–1.0 GtCO2eq.yr-1 in 2050. Without any controls, projections suggest a HFC contribution of
0.28–0.44 ∘C to global surface warming by 2100, compared to a temperature contribution of 0.14–0.31 ∘C that is projected
considering the national K-I policies current in place. Warming from HFCs is additionally limited by the Kigali Amendment controls to a contribution of about 0.04 ∘C by 2100.
Anthropogenic increases in atmospheric greenhouse gas
concentrations are the main driver of current and future climate change. The
integrated assessment community has quantified anthropogenic ...emissions for
the shared socio-economic pathway (SSP) scenarios, each of which represents
a different future socio-economic projection and political environment.
Here, we provide the greenhouse gas concentrations for these SSP scenarios
– using the reduced-complexity climate–carbon-cycle model MAGICC7.0. We
extend historical, observationally based concentration data with SSP
concentration projections from 2015 to 2500 for 43 greenhouse gases with monthly and latitudinal resolution. CO2 concentrations by 2100 range
from 393 to 1135 ppm for the lowest (SSP1-1.9) and highest (SSP5-8.5)
emission scenarios, respectively. We also provide the concentration
extensions beyond 2100 based on assumptions regarding the trajectories of fossil
fuels and land use change emissions, net negative emissions, and the
fraction of non-CO2 emissions. By 2150, CO2 concentrations in the
lowest emission scenario are approximately 350 ppm and approximately plateau
at that level until 2500, whereas the highest fossil-fuel-driven scenario
projects CO2 concentrations of 1737 ppm and reaches concentrations
beyond 2000 ppm by 2250. We estimate that the share of CO2 in the total
radiative forcing contribution of all considered 43 long-lived greenhouse
gases increases from 66 % for the present day to roughly 68 % to 85 % by
the time of maximum forcing in the 21st century. For this estimation,
we updated simple radiative forcing parameterizations that reflect the Oslo
Line-By-Line model results. In comparison to the representative concentration pathways (RCPs), the five main SSPs
(SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5) are more evenly spaced
and extend to lower 2100 radiative forcing and temperatures. Performing two
pairs of six-member historical ensembles with CESM1.2.2, we estimate the
effect on surface air temperatures of applying latitudinally and seasonally
resolved GHG concentrations. We find that the ensemble differences in the
March–April–May (MAM) season provide a regional warming in higher northern
latitudes of up to 0.4 K over the historical period, latitudinally averaged
of about 0.1 K, which we estimate to be comparable to the upper bound
(∼5 % level) of natural variability. In comparison to the
comparatively straight line of the last 2000 years, the greenhouse gas
concentrations since the onset of the industrial period and this studies'
projections over the next 100 to 500 years unequivocally depict a
“hockey-stick” upwards shape. The SSP concentration time series derived in
this study provide a harmonized set of input assumptions for long-term
climate science analysis; they also provide an indication of the wide set of
futures that societal developments and policy implementations can lead to –
ranging from multiple degrees of future warming on the one side to
approximately 1.5 ∘C warming on the other.
The identification and quantification of methane emissions from natural gas production has become increasingly important owing to the increase in the natural gas component of the energy sector. An ...instrumented aircraft platform was used to identify large sources of methane and quantify emission rates in southwestern PA in June 2012. A large regional flux, 2.0–14 g CH ₄ s ⁻¹ km ⁻², was quantified for a ∼2,800-km ² area, which did not differ statistically from a bottom-up inventory, 2.3–4.6 g CH ₄ s ⁻¹ km ⁻². Large emissions averaging 34 g CH ₄/s per well were observed from seven well pads determined to be in the drilling phase, 2 to 3 orders of magnitude greater than US Environmental Protection Agency estimates for this operational phase. The emissions from these well pads, representing ∼1% of the total number of wells, account for 4–30% of the observed regional flux. More work is needed to determine all of the sources of methane emissions from natural gas production, to ascertain why these emissions occur and to evaluate their climate and atmospheric chemistry impacts.
PDF
