[RELATED POST ON METHANE]

[LINK TO SOURCE DOCUMENT]

Scientists are baffled by a giant spike in this greenhouse gas (it’s not CO2)
By Leta Dickinson on May 17, 2019

FULL TEXT OF THE SOURCE DOCUMENT

The unexpected culprit that could throw a wrench in the world’s efforts to stop climate change? Runaway methane levels. Researchers monitoring air samples have noticed an alarming observation: Methane levels are on the rise and no one’s quite sure why. NOAA’s Earth System Research Laboratory scientists have been analyzing air samples since 1983. Once a week, metal flasks containing air from around the world at different elevations find their way to the Boulder, Colorado, lab. The scientists look at 55 greenhouse gases, including methane and its more-famous climate villain, CO2. You might know methane as the stuff of cow farts, natural gas, and landfills. It’s also an incredibly potent greenhouse gas, absorbing heat 25 times more effectively than CO2. While the rise of carbon dioxide has been stealing the spotlight as of late, methane levels have also been on the incline. Methane levels, not surprisingly, have been steadily rising since the Industrial Revolution. Things picked up in 1980 and soon after, the NOAA scientists began consistently measuring methane. Levels were high but flattened out by the turn of the millenium. So when levels began to increase at a rapid rate in 2007, and then even faster in 2014, scientists were baffled. No one’s best guesses came close to predicting current methane levels of around 1,867 parts per billion as of 2018. This means studies evaluating the effects of climate change and action plans to address them, like the Paris Climate Agreement, may be based on downplayed climate crisis forecasts.

Methane levels from 1950 to present. 2° Institute

So what’s the big deal? Carbon dioxide emissions are relatively well understood and can be tracked to various human activities like transportation and electricity, which means policies can be enacted to target and lower emissions. Pinning down the source of methane, on the other hand, is a little more complicated. “The really fascinating thing about methane,” Lori Bruhwiler, a NOAA research scientist, told Undark, “is the fact that almost everything we humans do has an effect on the methane budget, from producing food to producing fuel to disposing of waste.” As if things weren’t complicated enough, a study published in AGU100 distinguished microbe-produced methane from fossil fuel methane — historically the more abundant one — and found that “natural” methane had taken the lead. This unexpected result might explain the upticks in methane levels that do not seem correlated with human activity.

Of course, it could also be any number of human-made causes, including warming temperatures freeing up the gas and more frequent floods amplifying the methane output of wetlands. Natural methane or not, this finding doesn’t exonerate anyone. The study’s authors made that clear in their concluding remarks. “If the increased methane burden is driven by increased emissions from natural sources,” they wrote, “and if this is a climate feedback—the warming feeding the warming—then there is urgency to reduce anthropogenic emissions, which we can control.”

Curbing methane could be a powerful tool in our upcoming climate fight. Since the greenhouse gas is relatively short lived, only around 12 years, versus the 20 to 200 years of CO2, and is more effective at trapping heat than carbon dioxide, addressing methane emissions could be effective as a short-term climate remediation tool. The first step? Bringing more attention to methane so we can figure out where it comes from and nip it in the bud.

CRITICAL COMMENTARY

1. That “natural microbe-produced methane” has taken the lead and that “upticks in methane levels are not correlated with human activity” does not imply that “Curbing methane could be a powerful tool in our upcoming climate fight against AGW climate change”. It implies that this is nature at work and not human activity of the industrial economy from which the climate and the planet need to be saved.
2. Related post on “upticks in methane levels are not correlated with human activity” [LINK] . 
3. Related post on NOAA: [LINK] 

METHANE EMISSIONS BIBLIOGRAPHY

1. Saunois, Marielle, et al. “The global methane budget 2000–2012.” Earth System Science Data 8.2 (2016): 697-751.  The global methane (CH4) budget is becoming an increasingly important component for managing realistic pathways to mitigate climate change. This relevance, due to a shorter atmospheric lifetime and a stronger warming potential than carbon dioxide, is challenged by the still unexplained changes of atmospheric CH4 over the past decade. Emissions and concentrations of CH4 are continuing to increase, making CH4 the second most important human-induced greenhouse gas after carbon dioxide. Two major difficulties in reducing uncertainties come from the large variety of diffusive CH4 sources that overlap geographically, and from the destruction of CH4 by the very short-lived hydroxyl radical (OH). To address these difficulties, we have established a consortium of multi-disciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate research on the methane cycle, and producing regular (∼ biennial) updates of the global methane budget. For the 2003–2012 decade, global methane emissions are estimated by top-down inversions at 558 Tg CH4 yr−1 , range 540–568. About 60 % of global emissions are anthropogenic (range 50–65 %). Since 2010, the bottom-up global emission inventories have been closer to methane emissions in the most carbonintensive Representative Concentrations Pathway (RCP8.5) and higher than all other RCP scenarios. Bottom-up approaches suggest larger global emissions (736 Tg CH4 yr−1 , range 596–884) mostly because of larger natural emissions from individual sources such as inland waters, natural wetlands and geological sources. Considering the atmospheric constraints on the top-down budget, it is likely that some of the individual emissions reported by the bottom-up approaches are overestimated, leading to too large global emissions. Latitudinal data from top-down emissions indicate a predominance of tropical emissions (∼ 64 % of the global budget, < 30◦ N) as compared to mid (∼ 32 %, 30–60◦ N) and high northern latitudes (∼ 4 %, 60–90◦ N). Top-down inversions consistently infer lower emissions in China (∼ 58 Tg CH4 yr−1 , range 51–72, −14 %) and higher emissions in Africa (86 Tg CH4 yr−1 , range 73–108, +19 %) than bottom-up values used as prior estimates. Overall, uncertainties for anthropogenic emissions appear smaller than those from natural sources, and the uncertainties on source categories appear larger for top-down inversions than for bottom-up inventories and models. The most important source of uncertainty on the methane budget is attributable to emissions from wetland and other inland waters. We show that the wetland extent could contribute 30–40 % on the estimated range for wetland emissions. [LINK TO DATA]
2. Saunois, Marielle, et al. “The growing role of methane in anthropogenic climate change.” Environ. Res. Lett 11.12 (2016): 12.  Unlike CO2, atmospheric methane concentrations are rising faster than at any time in the past two decades and, since 2014, are now approaching the most greenhouse-gas-intensive scenarios. The reasons for this renewed growth are still unclear, primarily because of uncertainties in the global methane budget. New analysis suggests that the recent rapid rise in global methane concentrations is predominantly biogenic-most likely from agriculture-with smaller contributions from fossil fuel use and possibly wetlands. Additional attention is urgently needed to quantify and reduce methane
   emissions. Methane mitigation offers rapid climate benefits and economic, health and agricultural co-benefits that are highly complementary to CO2 mitigation.
3. Nisbet, E. G., et al. “Rising atmospheric methane: 2007–2014 growth and isotopic shift.” Global Biogeochemical Cycles 30.9 (2016): 1356-1370.  From 2007 to 2013, the globally averaged mole fraction of methane in the atmosphere increased by 5.7 ± 1.2 ppb yr−1. Simultaneously, δ13CCH4 (a measure of the 13C/12C isotope ratio in methane) has shifted to significantly more negative values since 2007. Growth was extreme in 2014, at 12.5 ± 0.4 ppb, with a further shift to more negative values being observed at most latitudes. The isotopic evidence presented here suggests that the methane rise was dominated by significant increases in biogenic methane emissions, particularly in the tropics, for example, from expansion of tropical wetlands in years with strongly positive rainfall anomalies or emissions from increased agricultural sources such as ruminants and rice paddies. Changes in the removal rate of methane by the OH radical have not been seen in other tracers of atmospheric chemistry and do not appear to explain short‐term variations in methane. Fossil fuel emissions may also have grown, but the sustained shift to more 13C‐depleted values and its significant interannual variability, and the tropical and Southern Hemisphere loci of post‐2007 growth, both indicate that fossil fuel emissions have not been the dominant factor driving the increase. A major cause of increased tropical wetland and tropical agricultural methane emissions, the likely major contributors to growth, may be their responses to meteorological change.
4. Schaefer, Hinrich, et al. “A 21st-century shift from fossil-fuel to biogenic methane emissions indicated by 13CH4.” Science 352.6281 (2016): 80-84.  Between 1999 and 2006, a plateau interrupted the otherwise continuous increase of atmospheric methane concentration [CH₄] since preindustrial times. Causes could be sink variability or a temporary reduction in industrial or climate-sensitive sources. We reconstructed the global history of [CH₄] and its stable carbon isotopes from ice cores, archived air, and a global network of monitoring stations. A box-model analysis suggests that diminishing thermogenic emissions, probably from the fossil-fuel industry, and/or variations in the hydroxyl CH₄ sink caused the [CH₄] plateau. Thermogenic emissions did not resume to cause the renewed [CH₄] rise after 2006, which contradicts emission inventories. Post-2006 source increases are predominantly biogenic, outside the Arctic, and arguably more consistent with agriculture than wetlands. If so, mitigating CH₄ emissions must be balanced with the need for food production.
5. Turner, Alex J., et al. “A large increase in US methane emissions over the past decade inferred from satellite data and surface observations.” Geophysical Research Letters 43.5 (2016): 2218-2224.  The global burden of atmospheric methane has been increasing over the past decade, but the causes are not well understood. National inventory estimates from the U.S. Environmental Protection Agency indicate no significant trend in U.S. anthropogenic methane emissions from 2002 to present. Here we use satellite retrievals and surface observations of atmospheric methane to suggest that U.S. methane emissions have increased by more than 30% over the 2002–2014 period. The trend is largest in the central part of the country, but we cannot readily attribute it to any specific source type. This large increase in U.S. methane emissions could account for 30–60% of the global growth of atmospheric methane seen in the past decade.
6. Hausmann, Petra, Ralf Sussmann, and Dan Smale. “Contribution of oil and natural gas production to renewed increase in atmospheric methane (2007–2014): top–down estimate from ethane and methane column observations.” Atmospheric Chemistry and Physics 16.5 (2016): 3227-3244.   Harmonized time series of column-averaged mole fractions of atmospheric methane and ethane over the period 1999–2014 are derived from solar Fourier transform infrared (FTIR) measurements at the Zugspitze summit (47° N, 11° E; 2964 m a.s.l.) and at Lauder (45° S, 170° E; 370 m a.s.l.). Long-term trend analysis reveals a consistent renewed methane increase since 2007 of 6.2 [5.6, 6.9] ppb yr⁻¹ (parts-per-billion per year) at the Zugspitze and 6.0 [5.3, 6.7] ppb yr⁻¹ at Lauder (95 % confidence intervals). Several recent studies provide pieces of evidence that the renewed methane increase is most likely driven by two main factors: (i) increased methane emissions from tropical wetlands, followed by (ii) increased thermogenic methane emissions due to growing oil and natural gas production. Here, we quantify the magnitude of the second class of sources, using long-term measurements of atmospheric ethane as a tracer for thermogenic methane emissions. In 2007, after years of weak decline, the Zugspitze ethane time series shows the sudden onset of a significant positive trend (2.3 [1.8, 2.8]  ×  10⁻² ppb yr⁻¹ for 2007–2014), while a negative trend persists at Lauder after 2007 (−0.4 [−0.6, −0.1]  ×  10⁻² ppb yr⁻¹). Zugspitze methane and ethane time series are significantly correlated for the period 2007–2014 and can be assigned to thermogenic methane emissions with an ethane-to-methane ratio (EMR) of 12–19 %. We present optimized emission scenarios for 2007–2014 derived from an atmospheric two-box model. From our trend observations we infer a total ethane emission increase over the period 2007–2014 from oil and natural gas sources of 1–11 Tg yr⁻¹ along with an overall methane emission increase of 24–45 Tg yr⁻¹. Based on these results, the oil and natural gas emission contribution (C) to the renewed methane increase is deduced using three different emission scenarios with dedicated EMR ranges. Reference scenario 1 assumes an oil and gas emission combination with EMR  =  7.0–16.2 %, which results in a minimum contribution C  >  39 % (given as lower bound of 95 % confidence interval). Beside this most plausible scenario 1, we consider two less realistic limiting cases of pure oil-related emissions (scenario 2 with EMR  =  16.2–31.4 %) and pure natural gas sources (scenario 3 with EMR  =  4.4–7.0  %), which result in C  >  18 % and C  >  73 %, respectively. Our results suggest that long-term observations of column-averaged ethane provide a valuable constraint on the source attribution of methane emission changes and provide basic knowledge for developing effective climate change mitigation strategies.
7. Allen, Grant. “Biogeochemistry: Rebalancing the global methane budget.” Nature 538.7623 (2016): 46.
8. Schwietzke, Stefan, et al. “Upward revision of global fossil fuel methane emissions based on isotope database.” Nature 538.7623 (2016): 88.  Methane has the second-largest global radiative forcing impact of anthropogenic greenhouse gases after carbon dioxide, but our understanding of the global atmospheric methane budget is incomplete. The global fossil fuel industry (production and usage of natural gas, oil and coal) is thought to contribute 15 to 22 per cent of methane emissions^{1,2,3,4,5,6,7,8,9,10} to the total atmospheric methane budget¹¹. However, questions remain regarding methane emission trends as a result of fossil fuel industrial activity and the contribution to total methane emissions of sources from the fossil fuel industry and from natural geological seepage^12,13, which are often co-located. Here we re-evaluate the global methane budget and the contribution of the fossil fuel industry to methane emissions based on long-term global methane and methane carbon isotope records. We compile the largest isotopic methane source signature database so far, including fossil fuel, microbial and biomass-burning methane emission sources. We find that total fossil fuel methane emissions (fossil fuel industry plus natural geological seepage) are not increasing over time, but are 60 to 110 per cent greater than current estimates^{1,2,3,4,5,6,7,8,9,10} owing to large revisions in isotope source signatures. We show that this is consistent with the observed global latitudinal methane gradient. After accounting for natural geological methane seepage^12,13, we find that methane emissions from natural gas, oil and coal production and their usage are 20 to 60 per cent greater than inventories^1,2. Our findings imply a greater potential for the fossil fuel industry to mitigate anthropogenic climate forcing, but we also find that methane emissions from natural gas as a fraction of production have declined from approximately 8 per cent to approximately 2 per cent over the past three decades.
9. Rigby, Matthew, et al. “Role of atmospheric oxidation in recent methane growth.” Proceedings of the National Academy of Sciences 114.21 (2017): 5373-5377.  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 CH₃CC₃ 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.
10. Turner, Alexander J., et al. “Ambiguity in the causes for decadal trends in atmospheric methane and hydroxyl.” Proceedings of the National Academy of Sciences 114.21 (2017): 5367-5372.  Methane is the second strongest anthropogenic greenhouse gas and its atmospheric burden has more than doubled since 1850. Methane concentrations stabilized in the early 2000s and began increasing again in 2007. Neither the stabilization nor the recent growth are well understood, as evidenced by multiple competing hypotheses in recent literature. Here we use a multispecies two-box model inversion to jointly constrain 36 y of methane sources and sinks, using ground-based measurements of methane, methyl chloroform, and the C¹³/C¹² ratio in atmospheric methane (δ¹³CH₄) from 1983 through 2015. We find that the problem, as currently formulated, is underdetermined and solutions obtained in previous work are strongly dependent on prior assumptions. Based on our analysis, the mathematically most likely explanation for the renewed growth in atmospheric methane, counterintuitively, involves a 25-Tg/y decrease in methane emissions from 2003 to 2016 that is offset by a 7% decrease in global mean hydroxyl (OH) concentrations, the primary sink for atmospheric methane, over the same period. However, we are still able to fit the observations if we assume that OH concentrations are time invariant (as much of the previous work has assumed) and we then find solutions that are largely consistent with other proposed hypotheses for the renewed growth of atmospheric methane since 2007. We conclude that the current surface observing system does not allow unambiguous attribution of the decadal trends in methane without robust constraints on OH variability, which currently rely purely on methyl chloroform data and its uncertain emissions estimates.
11. Zhang, Zhen, et al. “Emerging role of wetland methane emissions in driving 21st century climate change.” Proceedings of the National Academy of Sciences 114.36 (2017): 9647-9652.  ABSTRACT: Wetland methane (CH₄) emissions are the largest natural source in the global CH₄ budget, contributing to roughly one third of total natural and anthropogenic emissions. As the second most important anthropogenic greenhouse gas in the atmosphere after CO₂, CH₄ is strongly associated with climate feedbacks. However, due to the paucity of data, wetland CH₄ feedbacks were not fully assessed in the Intergovernmental Panel on Climate Change Fifth Assessment Report. The degree to which future expansion of wetlands and CH₄ emissions will evolve and consequently drive climate feedbacks is thus a question of major concern. Here we present an ensemble estimate of wetland CH₄ emissions driven by 38 general circulation models for the 21st century. We find that climate change-induced increases in boreal wetland extent and temperature-driven increases in tropical CH₄ emissions will dominate anthropogenic CH₄ emissions by 38 to 56% toward the end of the 21st century under the Representative Concentration Pathway (RCP2.6). Depending on scenarios, wetland CH₄ feedbacks translate to an increase in additional global mean radiative forcing of 0.04 W·m⁻² to 0.19 W·m⁻² by the end of the 21st century. Under the “worst-case” RCP8.5 scenario, with no climate mitigation, boreal CH₄ emissions are enhanced by 18.05 Tg to 41.69 Tg, due to thawing of inundated areas during the cold season (December to May) and rising temperature, while tropical CH₄ emissions accelerate with a total increment of 48.36 Tg to 87.37 Tg by 2099. Our results suggest that climate mitigation policies must consider mitigation of wetland CH₄ feedbacks to maintain average global warming below 2 °C.
12. Dyonisius, Michael, et al. “The contribution of geologic emissions, thawing permafrost and methane hydrates to the global methane budget-perspective from ice core records.” AGU Fall Meeting Abstracts. 2018.  Studies of methane (CH₄) mole fraction and isotopes from trapped air in ice cores provide a long-term perspective on the natural CH₄ budget. Among the CH₄ isotopes, ¹⁴CH₄ is unique in providing a definitive top-down constraint on the total fossil CH₄ emissions from old carbon reservoirs (marine hydrates, permafrost, natural geologic seeps). We present new measurements of ¹⁴CH₄ throughout most of the Last Deglaciation (≈15-8ka). Our ¹⁴CH₄ data show that ¹⁴C-depleted CH₄ sources (marine hydrates, geologic seeps and old permafrost) were not significant contributors to the deglacial CH₄ rise. As the relatively large deglacial global warming (≈4^oC, with warming further amplified at high latitudes) did not trigger CH₄ emissions from old carbon reservoirs, such emissions in response to future warming also appear unlikely. Our results also strengthen the suggestion from an earlier study (Petrenko et al. 2017) that natural geologic emissions of CH₄ are much lower (less than 15 Tg CH₄ yr^-1, 95% confidence) than recent bottom-up estimates (54-60 Tg CH₄ yr^-1) (Etiope 2015; Cias et al. 2013) and that, by extension, estimates of present-day total anthropogenic fossil CH₄ emissions are likely too low.
13. Bruhwiler, Lori E., E. J. Dlugokencky, and S. E. Michel. “The Uncertain Global Methane Budget.” AGU Fall Meeting Abstracts. 2018.  Numerous recent studies attempt to explain the observed increase in global atmospheric methane since 2006. Atmospheric methane is so compelling because if natural emissions are increasing, then feedback between CH₄ emissions and climate change becomes possible, with consequences for future climate. On the other hand, if methane is increasing due to fossil fuel production or agriculture, then it is possible that emissions of this powerful greenhouse gas can be mitigated. Also, if the increase in global methane is due to a decrease in the atmospheric sink, then we must ask what processes are changing and what are the implications for atmospheric oxidizing capacity.
    Current ideas about the global methane increase include (1) increased microbial emissions (anthropogenic or natural) (2) increased emissions from fossil fuel production (3) decreased chemical loss due to decreased OH. Hypothesis 1 is mainly based on atmospheric observations of d¹³CH₄, which suggest a trend towards isotopically lighter sources such as wetlands and ruminants. Some studies have suggested that ruminants are likely to have accounted for most of the increase, an idea that seems to be supported by current generation wetland emission models using spaced-based inundation data. Hypotheses 2 and 3 rely either on isotopic observations being a weak constraint, or that decreases in isotopically heavy biomass burning emissions imply increases in fossil fuel emissions.We add a Hypothesis 4: the recent increase is likely to be due to a combination of processes, including a significant contribution from wetlands (in conflict with wetland models). We argue that observed d¹³CH₄is indeed a strong constraint on global CH₄emissions, and that any hypothesis must be consistent with atmospheric d¹³CH₄. We find that ruminants and rice agriculture are unlikely to have grown enough to account for the observed methane increase notwithstanding considerable uncertainty in agricultural statistics. We also show that a downward trend in biomass burning observed from space-based observations is likely to be balanced or exceeded by an increase in small biomass burning events. Using model studies of CH₄and d¹³CH₄, we explore whether wetland models are likely to realistically simulate recent trends in wetland emissions.