Changes in Global Tropospheric OH Expected as a Result of Climate Change Over the Last Several Decades

Nicely, Julie M.; Canty, T. P.; Manyin, Michael; Oman, Luke D.; Salawitch, R. J.; Steenrod, Stephen D.; Strahan, S. E.; Strode, Sarah A.

doi:10.1029/2018jd028388

Cited by 49 publications

(78 citation statements)

References 130 publications

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“…As OH destruction is likely modulated by strong changes in meteorology (C. D. Holmes et al, 2013), such as may have taken place in the past decade in tropical midtropospheric moisture and cloud structure, it is possible that significant interannual variability in OH destruction may indeed occur, though detailed mechanisms capable of driving such large changes in the oxidative capacity of the atmosphere have not been proposed. However, in this context, Nicely et al (2018) and Lelieveld et al (2016) agreed with Montzka et al (2011) in finding that interannual variability of OH has probably been fairly small.…”

Section: Methane Sources and Sinks: The Insight From Carbon Isotopessupporting

confidence: 72%

“…In this context, Thompson et al () found that OH appears not to have contributed significantly to recent methane growth. Further insight into the OH problem came from Nicely et al () who showed that atmospheric OH is probably currently well buffered, with mean anomalies of 1.6%. Although OH would be expected to decrease as methane rises, this effect is countered by the tropical widening as the Hadley cells expand (R. J. Allen et al, ), combined with the influences of changing H 2 O, NO x , and overhead O 3.…”

Section: Testing the Hypotheses That May Explain The Recent Rise In Mmentioning

confidence: 99%

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Very Strong Atmospheric Methane Growth in the 4 Years 2014–2017: Implications for the Paris Agreement

Nisbet

Manning

Dlugokencky

et al. 2019

Global Biogeochemical Cycles

470

447

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Atmospheric methane grew very rapidly in 2014 (12.7 ± 0.5 ppb/year), 2015 (10.1 ± 0.7 ppb/year), 2016 (7.0 ± 0.7 ppb/year), and 2017 (7.7 ± 0.7 ppb/year), at rates not observed since the 1980s. The increase in the methane burden began in 2007, with the mean global mole fraction in remote surface background air rising from about 1,775 ppb in 2006 to 1,850 ppb in 2017. Simultaneously the 13C/12C isotopic ratio (expressed as δ13CCH4) has shifted, now trending negative for more than a decade. The causes of methane's recent mole fraction increase are therefore either a change in the relative proportions (and totals) of emissions from biogenic and thermogenic and pyrogenic sources, especially in the tropics and subtropics, or a decline in the atmospheric sink of methane, or both. Unfortunately, with limited measurement data sets, it is not currently possible to be more definitive. The climate warming impact of the observed methane increase over the past decade, if continued at >5 ppb/year in the coming decades, is sufficient to challenge the Paris Agreement, which requires sharp cuts in the atmospheric methane burden. However, anthropogenic methane emissions are relatively very large and thus offer attractive targets for rapid reduction, which are essential if the Paris Agreement aims are to be attained.

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Section: Methane Sources and Sinks: The Insight From Carbon Isotopessupporting

confidence: 72%

Section: Testing the Hypotheses That May Explain The Recent Rise In Mmentioning

confidence: 99%

Very Strong Atmospheric Methane Growth in the 4 Years 2014–2017: Implications for the Paris Agreement

Nisbet

Manning

Dlugokencky

et al. 2019

Global Biogeochemical Cycles

470

447

View full text Add to dashboard Cite

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“…However, accounting for OH source variability results in methane emissions estimates with similar trend and variability to Rigby et al (2017) and Turner et al (2017), where OH concentrations are fitted directly without interactive chemistry. This is due to compensating OH production accounting for variabilities in (Holmes et al, 2013;Naik et al, 2013;Nicely et al, 2018) are not explicitly represented in our model, so the question "How does OH production and recycling vary over time?" remains and should be a priority research objective.…”

Section: Summary and Recommendationsmentioning

confidence: 99%

Effects of Chemical Feedbacks on Decadal Methane Emissions Estimates

Nguyen

Turner

Yin

et al. 2020

Geophysical Research Letters

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The coupled chemistry of methane, carbon monoxide (CO), and hydroxyl radical (OH) can modulate methane's 9‐year lifetime. This is often ignored in methane flux inversions, and the impacts of neglecting interactive chemistry have not been quantified. Using a coupled‐chemistry box model, we show that neglecting the effect of methane source perturbation on [OH] can lead to a 25% bias in estimating abrupt changes in methane sources after only 10 years. Further, large CO emissions, such as from biomass burning, can increase methane concentrations by extending the methane lifetime through impacts on [OH]. Finally, we quantify the biases of including (or excluding) coupled chemistry in the context of recent methane and CO trends. Decreasing CO concentrations, beginning in the 2000's, have notable impacts on methane flux inversions. Given these nonnegligible errors, decadal methane emissions inversions should incorporate chemical feedbacks for more robust methane trend analyses and source attributions.

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“…In the coming years, estimation of [OH] using MCF will become more uncertain as its atmospheric mole fraction declines (Prinn et al, ). While some recent MCF, budget‐based studies have suggested that [OH] changes could be a major contributor to recent methane growth rate variability, albeit with very large uncertainty (Rigby et al, ; Turner et al, ), atmospheric photochemical models do not tend to find evidence for strong variability in global [OH] (e.g., Figure , Nicely et al, ). However, photochemical models disagree substantially in their predictions of the average global [OH] (Voulgarakis et al, ).…”

Section: Top‐down Source and Sink Estimation At Global And Regional Smentioning

confidence: 99%

“…Anomalies are presented to indicate the magnitude of interannual variability in [OH]. (Source: Julie Nicely, Nicely et al, ).…”

Section: Top‐down Source and Sink Estimation At Global And Regional Smentioning

confidence: 99%

Advancing Scientific Understanding of the Global Methane Budget in Support of the Paris Agreement

Ganesan

Schwietzke²,

Poulter

et al. 2019

Global Biogeochemical Cycles

102

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The 2015 Paris Agreement of the United Nations Framework Convention on Climate Change aims to keep global average temperature increases well below 2 °C of preindustrial levels in the Year 2100. Vital to its success is achieving a decrease in the abundance of atmospheric methane (CH4), the second most important anthropogenic greenhouse gas. If this reduction is to be achieved, individual nations must make and meet reduction goals in their nationally determined contributions, with regular and independently verifiable global stock taking. Targets for the Paris Agreement have been set, and now the capability must follow to determine whether CH4 reductions are actually occurring. At present, however, there are significant limitations in the ability of scientists to quantify CH4 emissions accurately at global and national scales and to diagnose what mechanisms have altered trends in atmospheric mole fractions in the past decades. For example, in 2007, mole fractions suddenly started rising globally after a decade of almost no growth. More than a decade later, scientists are still debating the mechanisms behind this increase. This study reviews the main approaches and limitations in our current capability to diagnose the drivers of changes in atmospheric CH4 and, crucially, proposes ways to improve this capability in the coming decade. Recommendations include the following: (i) improvements to process‐based models of the main sectors of CH4 emissions—proposed developments call for the expansion of tropical wetland flux measurements, bridging remote sensing products for improved measurement of wetland area and dynamics, expanding measurements of fossil fuel emissions at the facility and regional levels, expanding country‐specific data on the composition of waste sent to landfill and the types of wastewater treatment systems implemented, characterizing and representing temporal profiles of crop growing seasons, implementing parameters related to ruminant emissions such as animal feed, and improving the detection of small fires associated with agriculture and deforestation; (ii) improvements to measurements of CH4 mole fraction and its isotopic variations—developments include greater vertical profiling at background sites, expanding networks of dense urban measurements with a greater focus on relatively poor countries, improving the precision of isotopic ratio measurements of 13CH4, CH3D, 14CH4, and clumped isotopes, creating isotopic reference materials for international‐scale development, and expanding spatial and temporal characterization of isotopic source signatures; and (iii) improvements to inverse modeling systems to derive emissions from atmospheric measurements—advances are proposed in the areas of hydroxyl radical quantification, in systematic uncertainty quantification through validation of chemical transport models, in the use of source tracers for estimating sector‐level emissions, and in the development of time and space resolved national inventories. These and other recommendations are proposed for...

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Changes in Global Tropospheric OH Expected as a Result of Climate Change Over the Last Several Decades

Cited by 49 publications

References 130 publications

Very Strong Atmospheric Methane Growth in the 4 Years 2014–2017: Implications for the Paris Agreement

Very Strong Atmospheric Methane Growth in the 4 Years 2014–2017: Implications for the Paris Agreement

Effects of Chemical Feedbacks on Decadal Methane Emissions Estimates

Advancing Scientific Understanding of the Global Methane Budget in Support of the Paris Agreement

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