Unexpected Surge in Atmospheric Methane

Unexpected Surge in Atmospheric Methane

Summary

A dramatic and surprising surge in atmospheric methane has emerged over the past several years. The size of the surge is significant. If not mitigated, this new trend could, for example, wipe out the gains anticipated from the Paris Climate Agreement.  In response, scientists have begun ringing alarm bells in several high-profile peer-reviewed publications.

It is not entirely clear what factors are driving the surge. However, there is a firm consensus among scientists that the best response is deep and rapid reductions in methane emitted from the production and distribution of natural gas.

Methane pollution from the natural gas sector is responsible for a lion’s share of current anthropogenic emissions. This baseline pollution sustains methane in the atmosphere at a level far above pre-industrial conditions.  This pollution is also the most easily addressed source of methane. The International Energy Agency estimates that the global oil and gas industry can reduce 40-50% of methane emissions at zero net cost. Looking at end uses, clean alternatives to gas-fired power (e.g. utility-scale wind and solar) are now cost-competitive options.

In the United States, the fossil fuel industry is the largest source of methane pollution, and emissions from the oil and gas sector have grown at least 40% over the last decade.

Overview

Unexpected Surge in Atmospheric MethaneMonthly data for atmospheric methane in 2019 indicates that a recent unanticipated surge in atmospheric methane has continued. The average year-over-year increase for each of the months January through November in 2019 is 9.5 ppb.[1] Should the final annual number for 2019 fall close to that number (9.5 ppb), it would stand as the 3rd biggest annual increase in methane over the last 20 years.[2]

The 2019 jump extends an unanticipated multi-year resurgence of atmospheric methane that has set off alarm bells in the science community. Scientists report that the new and unexpected methane increases threaten to virtually wipe out the anticipated gains of the Paris Climate Agreement, an agreement built upon models that assumed a stable level of methane in the atmosphere going forward.[3]

The “why” behind this resurgence is hotly debated and not well understood. That said, most experts in the field suspect that all traditional sources (natural and anthropogenic) are contributing at least in part to the surge, including oil and gas production, and that the biggest contributor might be tropical wetlands responding to climate change (though there are differing views on this point).[4] While the U.S. oil and gas sector is contributing to the surge, there is conflicting evidence about the size of the contribution.[5]

However, the answer to the question about which emissions sources are driving the methane surge is very different from the answer to the question about which emissions source is best targeted in order to address the surge. It is extremely challenging, if not impossible, to control how wetlands respond to climate change.

There is wide agreement among experts that reducing emissions from fossil-fuel production and distribution, primarily through ending leaks and venting, is one of the few options available to control global methane levels, and they agree that this option is the most practical one.[6]  In addition, scientists report that there are narrow opportunities to address agricultural emissions, e.g. changes in the diet of livestock that can reduce the production of methane without affecting production.

Methane pollution from the oil and gas sector is responsible for a lion’s share of current anthropogenic emissions, and this stream of pollution sustains methane in the atmosphere at a level far above pre-industrial conditions. Globally, fossil-fuel methane emissions account for roughly 34% of total anthropogenic emissions which in turn account for as much as 60% of total methane emissions.[7]

The most recent isotope research reports that methane emissions from fossil fuel production  are under-estimated by as much as 40%, while natural geologic sources contribute correspondingly less (relative to the shares reported in the paragraph above). Though disturbing, these findings include a silver lining. They indicate that better management of methane emissions from fossil-fuel production and distribution would have an even greater impact on global methane levels than understood prior.[8]

In the United States, the natural gas and petroleum system is the largest source of methane emissions.[9]  The most recent analysis suggests that U.S. methane emissions from oil and gas activity have increased over the last 10 years at 3.4% per year [10], about 40% over the decade, in line with increased production [11], while livestock emissions have been flat.

Looking forward, an analysis by the Rhodium Group finds that “if the natural gas boom in the US continues, and the Trump administration is successful in walking back Obama-era regulation, the oil and gas sector could see a nearly 30% increase in methane emissions from today’s levels by 2025.”[12]

Detail

Methane is a short-lived but super-potent greenhouse gas and is the second most important contributor to anthropogenic global warming after CO2, accounting for one-quarter of the anthropogenic radiative imbalance (the human forcing of warming) since the pre-industrial era.[13]  Prior to the industrial era global methane levels were low and relatively stable for the last 800,000 years, ranging from 300–800 ppb. With the advent of agriculture and then fossil fuel operations, methane levels skyrocketed to more than 1,800 ppb.[14]

Unexpected Surge in Atmospheric MethaneStarting in the 1990s, the growth in global methane levels began to slow down, and global methane became relatively stable over the period of 2000-2006.  A resurgence of global methane was not anticipated and came as a surprise.[15] Crucially, methane levels were forecast to be stable in the pathway models prepared for the Paris Climate Agreement.[16]

Atmospheric methane resumed rapid growth starting in 2007. Growth accelerated further starting in 2014, extending through 2018.[17] This exceptional growth continued in 2019.[18] The rate of methane increase accelerated beginning in 2014, jumping 50 percent over the growth rate observed 2007-2013.[19] The sustained growth of the last six years was last observed in the 1980s when the Soviet Union’s gas industry was developing very rapidly.[20]

At first the durability of this emerging trend was questioned, and years of rapid growth were seen as anomalies.[21] However, the period of resumed growth in global methane levels now stands at 13 years (2007-2019) compared to the 7-year period of stable methane levels (2000-2006).

In this light, the era of stable global methane levels is increasingly seen as the anomaly, and growth in global methane seen as the resumption of a long-standing trend.[22] This emerging consensus is highlighted in several recent high-profile papers representing the consensus view of a large array of experts in the field.[23]

The threat posed by this resumption in methane growth is significant. A group of 23 scientists reports: “Thus even if anthropogenic CO2 emissions are successfully constrained to a RCP2.6-like pathway, the unexpected and sustained current rise in methane may so greatly overwhelm all progress from the other reduction efforts that the Paris Agreement will fail.”[24]

While the resumption of growth in global methane is now well documented, the drivers are less well understood and hotly debated. Present global environmental monitoring networks only provide sparse information about methane concentrations, making it challenging and complex to distinguish between the myriad individual sources of methane from the fossil fuel industries, and dispersed sources like wetlands and agriculture. Gaps in monitoring also make it impossible to rule out a decrease in the efficacy of natural mechanisms that sweep methane from the atmosphere (aka “sinks”).[25]

Potential drivers in the category of increased emissions include emissions from intensive agricultural practices, emissions from oil and gas operations, seepage from coal mines, and increased emissions from wetlands responding to global warming.[26] [This last potential driver is particularly worrisome as it implies the engagement of a global warming feedback loop.][27]

A number of studies have assigned and evaluated the role of each of these drivers, with different studies assigning greater weight to different drivers; all are generally considered to play at least a minor role.[28]

Chapter 2 of the IPCC Special Report on Lands finds that “Fugitive emissions likely contribute to the renewed growth after 2006” and points to increased fracking in America as a contributor: “the increased production of natural gas in the US from the mid 2000’s is of particular interest because it coincides with renewed atmospheric aCH4 growth” and notes that “The importance of fugitive emissions in the global atmospheric accumulation rate is growing.”

Most recently, separate studies have found conflicting evidence about the role of fracking in North America. One recent isotope analysis indicates that fracking may be a major driver of the recent multi-year surge of global methane above the elevated baseline.[29]  Yet, another recent isotope analysis concludes otherwise.[30]

Ethane and propane emissions are used as proxies for tracking methane emissions from fossil fuel operation, and studies tracking ethane and propane assign a significant role to U.S. fossil production in driving the surge in global methane.[31]

Recent research has also revealed that natural gas pipelines in U.S. metropolitan areas are now leaking significant levels of methane, at twice the rate previously believed.[32]

Recent review papers allow a role for U.S. oil and gas production in the methane surge but tend to discount a primary role, generally pointing instead to emissions from tropical wetlands, though they acknowledge uncertainty on this question.[33]

While the size of the role of fossil-fuel production and distribution in driving the recent surge in global methane is still under investigation, it is already well documented that fossil-fuel production is one of the major drivers in sustaining industrial era methane levels.[34] As a result, reducing fossil-fuel methane emissions would have a significant impact in addressing impact of the methane surge. The lifetime of methane in the atmosphere is relatively short (∼11 years), i.e. it washes out of the atmosphere fairly quickly (unlike CO2). Thus, large anthropogenic emissions are required to simply sustain the elevated global methane levels of the industrial era. A significant reduction in anthropogenic emissions quickly translates into a reduction in atmospheric methane.

Fossil-fuel methane emissions are also the most easily addressed source of emissions. The International Energy Agency estimates industry can reduce its worldwide emissions by 75 percent—and that up to two-thirds of those reductions (40-50% of total emissions) can be realized at zero net cost.[35]

In addition, there are particular opportunities to address emissions from agriculture. Changes in the diet of livestock could reduce the production of methane in dairy cattle without reducing milk production.[36]

In this context the 23 authors of Nisbet et al wrote: “We may not be able to influence the factors driving the new rise in methane, especially if it is a climate change feedback, but by monitoring, quantifying and reducing the very large anthropogenic inputs, especially from the gas, coal and cattle industries, and perhaps by direct removal, we may be able to cut the total methane burden to be compliant with the Paris goals.”[37]


References


[1] Climate Nexus 2020. NOAA/ESRL.
[2] NOAA/ESRL.
[3] Nisbet et al., 2019. Turner, Frankenberg, and Kort, 2019. Ganeson et al. 2019. Fletcher and Schaefer, 2019.
[4] Nisbet et al., 2019. Turner, Frankenberg, and Kort, 2019. Ganeson et al. 2019. Fletcher and Schaefer, 2019. Maasakkers et al., 2019.
[5] See, for example, Howarth, 2019; Milkov, 2020; and Worden, 2017.
[6] Nisbet et al., 2019. Turner, Frankenberg, and Kort, 2019. Schaefer, 2019. Milkov et al 2020.
[7] Dean et al., 2018. Ganeson et al 2019.
[8] Hmiel et al 2020. Dalsøren et al., 2018.  Petrenko et al., 2017.
[9] EPA GHG Emissions Inventory.
[10] Lan et al. 2019.
[11] Lyon and Schwietzke, 2019. Milkov et al 2020.
[12] Pitt et al., 2019.
[13] Ganeson et al 2019. Turner, Frankenberg, and Kort, 2019.
[14] Dean et al., 2018. Ganeson et al 2019.
[15] Nisbet et al., 2019. Turner, Frankenberg, and Kort, 2019. Underwood, 2019.
[16] Nisbet et al., 2019.
[17] Nisbet et al., 2019. Turner, Frankenberg, and Kort, 2019. Underwood, 2019.
[18] NOAA/ESRL: Earth System Research Laboratory Global Monitoring Division.
[19] Nisbet et al., 2019.
[20] Nisbet et al., 2019.
[21] Turner, Frankenberg, and Kort, 2019.
[22] Turner et al., 2019.
[23] Nisbet et al., 2019. Turner, Frankenberg, and Kort, 2019. Fletcher and Schaefer, 2019. Maasakkers et al., 2019. Schaefer, 2019. Milkov et al 2020.
[24] Nisbet et al., 2019.
[25] Ganeson et al 2019. Maasakkers et al., 2019.
[26] Ganeson et al 2019. Maasakkers et al., 2019. Nisbet et al., 2019. Turner, Frankenberg, and Kort, 2019. Fletcher and Schaefer, 2019.
[27] Fletcher and Schaefer, 2019. Schaefer, 2019.
[28] Nisbet et al., 2019. Turner, Frankenberg, and Kort, 2019. Fletcher and Schaefer, 2019. Maasakkers et al., 2019. Schaefer, 2019. Milkov et al 2020.
[29] Howarth, 2019.
[30] Milkov, 2020.
[31] Dalsøren et al., 2018. Hausmann et al 2016. Helmig et al. 2016. Hakola and Hellén, 2016.
[32] Perkins, 2019. He et al. 2019
[33] Schaefer, 2019. Maasakkers et al., 2019. Nisbet et al., 2019.
[34] Dean et al., 2018. Nisbet et al., 2019. Turner, Frankenberg, and Kort, 2019. Hmiel et al. 2020.
[35] International Energy Agency, 2020.
[36] Turner et al. 2019. Shindell, 2017.
[37] Nisbet et al., 2019.

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