Understanding methane

There was a recent Conversation article about methane called Climate explained: methane is short-lived in the atmosphere but leaves long-term damage that caused a bit of a stir on Twitter. One way people assess the significance of different greenhouse gases, is to use what is called the Global Warming Potential (GWP). This is determined by integrating the radiative forcing due to a pulse of a particular greenhouse gas over some time interval and then comparing that to the equivalent calculation for a pulse of CO2 of the same mass.

A greenhouse gas like methane has a lifetime of only about a decade, but the initial radiative impact is so large that even if you calculate the GWP over a period of 100 years, it is still has a much larger GWP than CO2. This calculation is correct, but people then interpret this as suggesting that the climate impact of a pulse of methane after 100 years will be much greater than the impact of a pulse of CO2 of the same mass. This is not correct, because most – if not all – of the pulse of methane will be gone after 100 years.

Credit: Carbon Brief, Michelle Cain

There’s a really nice Carbon Brief article, by Michelle Cain, about a new way to assess the global warming potential of short-lived pollutants. It also includes the figure on the right that illustrates the issue really nicely.

If you consider CO2, then if emissions are increasing, warming accelerates. If emissions are constant, then we continue warming at a constant rate. If emissions are going down, then we continue to warm until emissions get to zero.

Methane, on the other hand behaves quite differently. Methane emissions can increase and we could still end up warming at a constant rate. If methane emissions are constant, then we’d relatively quickly reach a state where methane-driven warming stabilised. If methane emissions start going down, then the impact of methane would actually lead to cooling, and we could eventually reverse all the methane-driven warming. By comparison, the only way to reverse CO2-driven warming is to actively remove CO2 from the atmosphere.

There are, however, some complications. If we’ve had increasing methane emissions for a long time, then this could have led to warming of the deep ocean, which will persist for a long time. If the source of methane is fossil-fuel-related, then when it decays to water and CO2, this will be a new CO2 molecule, which will contribute to long-term warming. However, relative to the long-term impact of direct CO22 emissions, these impacts are probably still quite small.

One reason why I think this is important is highlighted in this Realclimate post by Ray Pierrehumbert. If we think that there is some long-term benefit to rapidly reducing methane emissions and we do so at the expense of reductions in CO2 emissions, then we could end up reducing emissions of a species that will have little long-term impact while failing to reduce the emissions of one the impact of which will persist for generations.

This is not, though, to argue that we shouldn’t be looking at reducing methane emissions. All I’m suggesting is that we should be properly comparing the impact of the different greenhouse gas species when deciding what we should do and should not be basing these decisions on a metric that probably over-esimates the impact of short-lived greenhouse gases, like methane.

There’s also a potential fairness issue. When we expect a CO2-emitting industry to reduce their emissions, we’re effectively asking them to limit how much they contribute to future warming. When we expect a methane-emitting industry to reduce their emissions, we’re effectively asking them to reverse some of their past warming. There may be good reasons for doing this, but I would argue that it’s better to be clear about this than to suggest an equivalence that isn’t actually correct.

Links:
Climate explained: methane is short-lived in the atmosphere but leaves long-term damage – The Conversation article by Zebedee Nicholls and Tim Baxter.
Guest post: A new way to assess ‘global warming potential’ of short-lived pollutants – Carbon Brief article by Michelle Cain.
Losing time, not buying time – Realclimate post by Ray Pierrehumbert.

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38 Responses to Understanding methane

  1. JCH says:

    I don’t see anything in the Cain diagram that indicates methane is 84 times more potent than CO2.

  2. JCH,
    Well, that’s probably because it isn’t.

  3. “By comparison, the only way to reverse CO2-driven warming is to actively remove CO2 from the atmosphere.”

    Not true. We could reduce CO2 emissions to zero, Similar to CH4 but for ~20% fraction that stays around like almost forever,


    Oh and no to thoughts that we can magically remove CH4 and N2O considering that these are essentially coupled to CO2 emissions as byproducts of FF extraction and FF emissions byproducts.

    It will be about as easy to remove CH4 and N2O emissions as it has been easy to remove C02 emissions to date.

    Calculating GWP’s is simply a matter of proper bookkeeping and rather reasonable projections of future GHG emissions/atmospheric concentrations. And to 1st order O(1), GWP100 is just as good as any other method of bookkeeping as the uncertainties overwhelm their differences. It is like arguing over spilt milk.

    Oh and right now those so-called reasonable assumptions have CO2, CH4 and N2O all only going up, So that this …

    … is rather bogus. Old graphs no less with peaks circa 2010-2020, newsflash it is already 2020, negative CH4 emissions ba-ha-ha-ha-ha-ha-ha … RCP 2.6 is an abject joke by humanity for humanity. ;/

    Lessons learned? Make unreasonable assumptions about future GHG emissions = GIGO.

  4. So, how much cooling from anthropogenic aerosols are we currently seeing and how much further cooing is projected under future BAU anthropogenic aerosols emissions (say what, you actually expect a cleaner planet)? If we could remove those aerosols AND remove the so called GWP100 bad bookkeeping, heck lets just remove all other GHG’s from the proverbial equation, would the planet be warmer or cooler for similar CO2 atmospheric concentrations. I’m pretty sure warmer is the correct answer. Humans are good.

  5. EFS,

    Not true. We could reduce CO2 emissions to zero, Similar to CH4 but for ~20% fraction that stays around like almost forever,

    If we reduce CO2 emissions to zero, then warming stabilises. It doesn’t lead to cooling (on relevant timescales).

    Also, currently estimates are that the aerosol cooling is roughly balanced by warming due to short-lived GHGs. If we halted *all* emissions then warming would stabilise (with some initial warming as the aerosols precipitated, and the cooling back down again as the short-lived GHGs decayed).

  6. jacksmith4tx says:

    Maybe we are thinking about this backward? Technology (+human nature) got into this mess but what if we embrace the future by designing it ourselves?
    Don’t laugh, there are some serious people working on this @ https://theterraforming.strelka.com/
    This somewhat long (1h:50m) video covers the scope and multidisciplinary makeup of the project.

  7. ATTP,

    Very recent reference(s) needed if you don’t mind. Instantaneous cessation of anthropogenic CO2 emissions type references. TIA

    You said …
    “By comparison, the only way to reverse CO2-driven warming is to actively remove CO2 from the atmosphere.”

    So stopping CO2 emissions would remove, or lower, the atmospheric CO2 concentration, yes? If not, then please explain how the land/ocean sinks instantaneously lower themselves in keeping with an instantaneous cessation (and 12 years appears to me, at least, to be an instantaneous cessation) of carbon emissions.

    By your own definition, that is one way to remove anthropogenic sourced CO2 from the atmosphere. And just like they do 2X or 4X instantiations CO2 experiments, I am talking about an instantaneous cessation of anthropogenic CO2 emissions. Even without that rather steep point-of-access, I believe that there are CMIP5/6 time series showing a peak temperature this century without negative emissions if the ACO2 drawdown is fast enough (the proverbial 12 years).

    Centennial-to-tricentennial (2300CE as in AR5) is the current time-frame of interest (e. g. one-to-three hundred years), yes?

  8. EFS,
    This was pointed out in the IPCC SR15 report. If we halt all emissions, then the warming commitment is small. There’s an uncertainty, so there could be some warming commitment, or it could even be cooling. It’s essentially because the continued drawdown of CO2 happens to balance the warming to equilibrium. There is a slightly complication, because of the difference land masses in the Northern and Southern hemispheres. We would expect the Northern Hemisphere to cool slightly, while the Southern Oceans continued to take up energy. Hence sea level rise will continue.

    Below is a Figure from the IPCC SR15 report that shows the small warming commitment if we halt *all* emissions (yellow line).

  9. “Below is a Figure from the IPCC SR15 report that shows the small warming commitment if we halt *all* emissions (yellow line).”

    (1) Zero CO2 emissions (or not = 1)
    (2) Constant aerosol forcing (or not = 1)
    (3) Constant non-GHG forcing (or not =1)

    So 0 for (1), (2) and (3), I don’t think I see that combination in that IPCC figure, three binary choices leads to eight possible combinations and I only see four (suggesting only two binary choices) solid lines. Also not sure what constant means (a fixed future time series or an actual constant value for future forcing and why whatever that choice of its actual value).

  10. “Constant non-GHG forcing”

    … should be …

    “Constant non-CO2 forcing”

  11. And if there is a real difference between “emissions” and “forcing” then that is 2^6 = 64 combinations. Even more if each of them have different forcing/emissions pathways (no longer just binary choices).

    Oh and the blue line does not say a thing about aerosol emissions/forcing, the yellow (humanity vanishes) and purple (humanity vanishes except for their cooling air pollution aerosols) show aerosol forcing/emissions (???), I’m assuming aerosols are from air pollution, not cloud forcing(s). both of those two lines show cooling. The legend in that figure is rather confusing.

    I also thought that there were scenarios where we overshoot 2C but get back below 2C before 2100 (perhaps all those are for CCS or negative carbon emissions).

  12. EFS,
    Yellow line – “Zero GHG and aerosol emissions”.

  13. ATTP,

    Sorry for getting into the weeds so to speak. Your larger point, which I think is the major thrust of this post, is well taken, regardless of GWP100 or GWP*.

    It’s the CO2, stupid.
    https://en.wikipedia.org/wiki/It%27s_the_economy,_stupid

  14. Well, I already linked to a so-called GWP* (revised) paper by Cain, et. al. (2019) published in ERL …
    Improved calculation of warming-equivalent emissions for short-lived climate pollutants
    https://www.nature.com/articles/s41612-019-0086-4

    The main weakness of said GWP* is the continued increase of all non-CO2 GHG’s at current linear rates or greater then linear rates (which ARE occurring in the observational datasets) …
    https://www.esrl.noaa.gov/gmd/ccgg/trends/
    Common era for all four (CO2, CH4, N2O and SF6) is 2001-01 thru 2020-05 (sorry about the relatively short time span as it is all that is available, the longer CO2 and CH4, common to the CH4 time span (1983-07 thru 2020-05) show roughly similar linear behaviors) and all four exhibit concave up behaviors (greater then linear, 2001-01 thru 2020-05). Relative to 2020-05 levels the LINEAR (all underestimates of current greater then linear behaviors for their mutual common era, 2001-01 thru 2020-05) increases are: CO2 = 0.5%/yr, CH4 = 0.3%/yr, N2O = 0.3%/yr and SF6 = 3%/yr (rounded to one significant digit).

    So after C19 was published (in ERL), three additional papers were published (in ERL), concerned with the so-called GWP* (revised) metric as applied to Paris15 …
    Unintentional unfairness when applying new greenhouse gas emissions metrics at country level
    https://iopscience.iop.org/article/10.1088/1748-9326/ab4928
    Inconsistencies when applying novel metrics for emissions accounting to the Paris agreement
    https://iopscience.iop.org/article/10.1088/1748-9326/ab56e7
    Guidance on emissions metrics for nationally determined contributions under the Paris Agreement
    https://iopscience.iop.org/article/10.1088/1748-9326/ab4df4

    “In light of such equity-dependent accounting differences, GHG metrics like GWP* should only be used at the global level. A common, transparent and equity-neutral accounting metric is vital for the Paris Agreement’s effectiveness and its environmental integrity.”

    “We show that interpreting the Paris Agreement goals in a metric like GWP* that is significantly different from the standard metric used in the IPCC Fifth Assessment Report can lead to profound inconsistencies in the mitigation architecture of the Agreement.”

    “Options of reducing this ambiguity include using a different emissions metric or adding supplementary information in NDCs about the emissions levels of individual GHGs. We suggest the latter on the grounds of simplicity and because it does not require agreement on the use of a different emissions metric.”

    This was then followed (in the same ERL publication) by …
    Demonstrating GWP*: a means of reporting warming-equivalent emissions that captures the contrasting impacts of short- and long-lived climate pollutants
    https://iopscience.iop.org/article/10.1088/1748-9326/ab6d7e
    John Lynch, Michelle Cain, Raymond Pierrehumbert and Myles Allen (which I will use C20)

    “We demonstrate that GWP* provides a useful indication of warming, while conventional application of GWP100 falls short in many scenarios and particularly when methane emissions are stable or declining,”

    Non-CO2 emissions are not “stable or declining” currently (well maybe they are, but that does not ameliorate rising atmospheric concentrations, it would appear). Non-CO2 atmospheric concentrations are increasing at greater then linear rates (as shown above). Who gives a frack about bottom up emissions accounting that is trumped by top down observations. Bad bookkeeping indeed (greater uncertainty then then their differences, as noted above).

    C20 does not reference the three concerning papers. Never attribute to malice that which is adequately explained by … ignorance …
    https://en.wikipedia.org/wiki/Hanlon%27s_razor

    Bottom line? There appears to be issues with GWP* (revised), something IMHO that will not be settled by, or in, AR6 WG1. 😉

  15. EFS,
    The problem I have with some of the criticism iof GWP* is that it seems to basically be saying “this is what we’ve agreed to do using GWP100. If we switch to GWP*, then it would change what we would need to do”. The problem is, though, that GWP can indeed over-estimate the impact of short-lived GHGs and, hence, misrepresent the relative importance of methane and CO2 emission reductions. In my view, GWP* does a better job of comparing the impact of methane and CO2 emissions, when compared to GWP.

    This doesn’t mean that we should necessarily change what we plan to do with regards to emission reductions, but we should (I think) acknowledge that we may be basing this on a metric that doesn’t do all that good a job of representing the actual impact of these short-lived GHGs.

  16. Two more rather recent papers …
    Stable climate metrics for emissions of short and long-lived species—combining steps and pulses
    https://iopscience.iop.org/article/10.1088/1748-9326/ab6039

    “We show how the GWP* relates to CGWP and CGTP and that it systematically underestimates the temperature effects of SLCFs by up to 20%. These step-pulse metrics are all more appropriate than the conventional GWP for comparing the relative contributions of different species to future temperature targets and for SLCFs they are much less dependent on time horizon than GTP.”

    So, I guess we should call this one GWP** (not revised yet)

    Updated Global Warming Potentials and Radiative Efficiencies of Halocarbons and Other Weak Atmospheric Absorbers
    https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019RG000691

    “There continues to be a vigorous debate about the applicability of different emission metrics (e.g., Myhre et al., 2013); metric choice depends on the particular policy context in which they are applied, and the degree to which continuity of choice is important in that context (e.g., Allen et al., 2018; Cain et al., 2019; Rogelj & Schleussner, 2019). A specific development has been the suggested use of metrics that compare one‐off pulse emissions of long‐lived gases (such as CO2) with step‐changes in emissions of short‐lived species (e.g., gases with lifetimes less than a few decades), on the basis that this leads to a more informed comparison of their ultimate impact on temperature; such approaches can either adopt GWP values, but adapt their usage (Allen et al., 2016) or more directly compute the pulse‐step equivalence (W. J. Collins et al., 2019). In the context of this review, the important point is that all such metrics require the same set of inputs (RE and lifetimes).”

    So, GWP20, GWP50, GWP100, GWP500, GWP*, GWP* (revised), GWP** (not revised yet), … :/

  17. Ruh-roh …

    It appears that some are rather PO’ed …
    Comment on ‘Unintentional unfairness when applying new greenhouse gas emissions metrics at country level.’
    https://eartharxiv.org/r7epb/

    “Abstract

    Here, we provide a comment in response to a recently published paper ‘Unintentional unfairness when applying new greenhouse gas emissions metrics at country level’ by Rogelj and Schleussner (2019). We note a number of errors in their critique of the use of GWP* to relate cumulative and short-lived climate pollutants, argue that their logic is flawed, their ethical considerations are narrow and their conclusions not justified by the results presented.”

    I am sort of expecting a counter comment before publication in ERL (if ERL/IOP even accepts these kind of comments). At that point, it would be one down and two to go (or all 3×2 are handled in one publication). IMHO, proposing GWP* followed by GWP* (revised) in an ~ one year time frame, is/was not helpful at all, in so far as adoption strategies go.

  18. “So after C19 was published (in ERL)”

    … should be …

    “So after C19 was published (in CAS a Nature publication)”

    My bad.

  19. EFS,
    Glancing through some of the papers you’ve highlighted, it looks as though they’re also suggesting alternative metrics that better account for the differences between short-lived and long-lived GHGs. I don’t know if they’re better than GWP*, but I do think that GWP* is better than a naive application of GWP.

  20. ATTP,
    Agreed, but only time will tell. I really do appreciate the post as it forces me to at least try to learn new stuff. Most of the above is just me thinking out loud and posting links for future use (all are now also bookmarked). There are others, three (two in discussion) about recent CH4 atmospheric concentrations including through 2017/18 plus one on CO2-fe …
    https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GB006009
    https://acp.copernicus.org/preprints/acp-2020-649/
    https://acp.copernicus.org/preprints/acp-2020-964/
    https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL076173

  21. Willard says:

    > Most of the above is just me thinking out loud

    “Not true,” “is rather bogus,” and “make unreasonable assumptions about future GHG emissions = GIGO” go beyond that.

  22. So, GWP20, GWP50, GWP100, GWP500, GWP*, GWP* (revised), GWP** (not revised yet), …
    … should be …
    So, GWP20, GWP100, GWP500, CO2-fe, GWP*, GWP* (revised), GWP** (not revised yet), …

  23. Greg Robie says:

    Would not this post be better titled if such included the qualifier (within climate modeling conventions)?

    Climate models are continuing to be challenged to model the polar cryosphere well (understatement?). In August, a paper reanalyzes data to conclude Greenland ice sheet tipped a generation ago. Isn’t it just a matter of time [and a bit more data] before calculations dictate that West Antarctica is tipped? If so, how much motivated reasoning needs to be disengaged from to see what will soon be concluded regarding East Antarctica’s tip?

    The CO2e convention is a reasoned work-around regarding modeling constraints. Doesn’t the widening gap between cryosphere observations and trusted model’s predictions of such, and in the vernacular, say the models suck? Isn’t this post’s assertion based on what sucks? (I note in the comments reference to SR15 and its assertion of no committed warming at zero CO2 emissions that is based on calculations that do not include the cryosphere. *sigh*)

    The Inuit have told academia all it needs to know about its embedded assumptions (if, systemically, there was any interest in/curiosity about them). So far, and as a stand-in for academia, this ATTP space has proven itself insular to such self-examination of assumptions.

    So, attempting – again – to make a missed point in the context of this argument concerning methane, first a review:

    Due to the tilt of the earth’s axis and its rotation as it revolves around its sun, the polar zones experience a seasonal lift in the tropopause.

    The Inuit observations establish that this lift has increased and with three separate observational metrics: a shift in the location of the polar day’s sunset; extended huntable twilight; a shift in polar night navigational stars’ locations. Increased refraction, due to a tropopause lift, explain all three.

    The Industrial Age’s fossil carbon soot, and as a new forcing in the top of the troposphere, and effecting heat gain by conduction, is dismissed as inconsequential, and by conventions that are ensconced in modeling parameters this heat source is dismissed. This ‘invisibility’-by-trusted-convention constitutes an observer bias that, and roughly quantified by me, reveals an omitted forcing that closes the gap between Arctic sea ice loss observations and modeled predictions.

    The impact of this seasonal lift has been studied regarding microwave communication issues in the Arctic at the bottom of the troposphere, and more recently, a study that links high pressure cells over Greenland to increased melt rates confirms a lift in the tropopause’s impact. The SOUSY radar data collected at Svalbard documents the lift (but the data has not been collected long enough to establish (to academic standards) any trend.

    Now some new reasoned conjecture relative to methane being significant in its ten year life time:

    Any seasonal polar lift will, in conjunction with the stratosphere and mesosphere, effect gravitational wave dynamics that currently cannot be quantified nor modeled. The stratosphere exhibits seasonal dynamics that are harmonic-like. Stratospheric dynamics that would coincide with the Inuit observations baseline do not exist. I know zip concerning the mesosphere, but I play music. Gravitational wave harmonics are only silent in a vacuum.

    Now let’s factor in methane in the Arctic. 2009, Bloom et al. published a paper there at the University of Edinburg that crunched satellite data and quantified both the increase and amount of atmospheric methane exiting the Arctic. Increase refraction, increased methane, increased retention of heat gain by conduction; increased ice loss … and there still is an apparent blind faith in models that are programmed to ignore these increases. Is it time for established academic assumptions to get down off their throne?

    =)

    sNAILmALEnotHAIL …but pace’n myself

    https://m.youtube.com/channel/UCeDkezgoyyZAlN7nW1tlfeA

    life is for learning so all my failures must mean that I’m wicked smart

    >

  24. Dave_Geologist says:

    Greg, when scientists can’t represent some aspect of nature in their models, scientists are not putting themselves on a throne. They’re acknowledging their limitations.

    As in this related bad-news-in-the Arctic note: Arctic fires re-emerging.

    Early burning season
    Wildland fire experts generally believe that fires in the extreme early season in the Arctic — before aboveground vegetation tends to be flammable — are caused by holdover or ‘zombie fires’. One of the most fascinating aspects of zombie fires is that they represent a continuation of a previous growing season’s fire rather than a new ignition source, such as lightning or campfires. Zombie fires can smoulder in carbon-rich peat below the surface for months or years, often only detectable through smoke released at the surface, and can even occur through cold winter months despite heavy snowmelt. These types of fires are in general poorly understood, including their impacts on fuels and emissions of greenhouse gases and aerosols to the atmosphere. However, if these fires, their increasing prevalence and large burn areas or deep burning conditions drive substantial emissions, then this would represent a strong feedback in the Arctic fire regime that needs to be considered by Earth-system models or simulations of global biomass burning.

    The challenge of detecting change
    Current modelling tools used to predict biomass burning around the world often cannot be relied upon in the Arctic because of lack of data. The severe 2020 Arctic fires emphasize the urgent need to investigate the role of holdover (zombie) fires versus new ignitions in driving Arctic fires and to efficiently assimilate this information into current global satellite products and emission databases. New tools and approaches are required to quantify the influence of zombie fires on surface burning and their sources — whether they are caused by severe late-summer surface fires in the Arctic, or point sources such as campfires and pile burning.

    A global call to action
    It will be a tremendous collaborative, inclusive and multi-disciplinary effort to tackle the intensifying Arctic fire regime, but it is one of critical importance. We will not understand how the Arctic fire regime is changing without interdisciplinary collaborations between various knowledge holders. Addressing the gaps in our current understanding will require critical input from Indigenous and local communities and collaboration across scientific disciplines. Local communities have the ability to access remote locations and enable invaluable long-term in situ observations, including signs of holdover fires during winter months, guiding coordinated efforts across the full range of fire research, including management, ecology and climate impacts.

  25. Dave_Geologist says:

    And from one of the references, some of those feedbacks: Wildfire as a major driver of recent permafrost thaw in boreal peatlands.

    Effects of wildfire on permafrost peatlands last for 30 years and include a warmer and deeper active layer, and spatial expansion of continuously thawed soil layers (taliks). These impacts on the soil thermal regime are associated with a tripled rate of thermokarst bog expansion along permafrost edges. Our results suggest that wildfire is directly responsible for 2200 ± 1500 km2 (95% CI) of thermokarst bog development in the study region over the last 30 years, representing ~25% of all thermokarst bog expansion during this period. With increasing fire frequency under a warming climate, this study emphasizes the need to consider wildfires when projecting future circumpolar permafrost thaw.

    Deeper active layers and warmer soils on peat plateaus for decades following wildfire may increase the soil carbon dioxide respiration rate, given the predominately aerobic soil environment. Conversely, increased methane emissions are caused by the land subsidence and anaerobic conditions that are associated with thermokarst bog expansion. However, thermokarst bogs may have a long term cooling effect on the climate if the resulting anaerobic soil conditions along with Sphagnum moss productivity favor increased carbon accumulation. Given the widespread occurrence of wildfire in the study region, projections of the future carbon balance of the study region will need to consider the effects of wildfire described in this study.

  26. Dave_Geologist says:

    As with other things that have positive and negative feedback, like clouds, the impact depends on whether positive outweighs negative or vice versa, and whether that flips, perhaps more than once, in future decades.

    It’s a lot harder than feedbacks where we can say “positive, more warming, we just can’t be sure quite how much”.

  27. Dave_Geologist says:

    Although it’s drifting off the methane topic, this illustrates some of the complexity: Increasing wildfires threaten historic carbon sink of boreal forest soils

    We found no evidence for the combustion of legacy carbon in forests that were older than the historic fire-return interval of northwestern boreal forests. In forests that were in dry landscapes and less than 60 years old at the time of the fire, legacy carbon that had escaped burning in the previous fire cycle was combusted. We estimate that 0.34 million hectares of young forests (<60 years) that burned in the 2014 fires could have experienced legacy carbon combustion. This implies a shift to a domain of carbon cycling in which these forests become a net source—instead of a sink—of carbon to the atmosphere over consecutive fires. As boreal wildfires continue to increase in size, frequency and intensity, the area of young forests that experience legacy carbon combustion will probably increase and have a key role in shifting the boreal carbon balance.

    IOW as fires become more frequent, places that had been net carbon sink despite periodic burning will turn into net carbon sources.

  28. Ben McMillan says:

    I think Pierrehumbert’s point that the amount of methane emitted now makes essentially no difference to meeting the 2C target is the killer argument.

    Only if you think you will get to net-zero in the next 15 years does it matter much (compared to what GWP100 suggests, let alone GWP20)

  29. Greg Robie says:

    @Dave_G: Thx for the interaction. I stopped checking for such shortly before you took the time to do so. I’m back today to get the link to my comment for an email and now see your thoughts.

    I feel we are on quite different pages. It’s the assumptions that have long been integral to climate models that I feel merit revisiting. Also, concerning climate system complexity, my thinking is based on the assumption that we are two generations of Moore’s Law and computational power increases (not to mention the data we don’t yet have for more detailed and regional modeling) removed from doing much better than what is being done right now. That there are are various forcings in the Arctic … and the increased refraction and fossil carbon soot as a ‘new’ forcing within the Arctic troposphere is NOT among them, should, if motivated reasoning was not in play, be a cause to pause.

    Can you, with your industry-based experience and thinking, explain away the Inuit observations commensurate with how the trusted modeling do so?

    Do you agree that the SR15 assertion regarding no committed warming explicitly leaves out the cryosphere?

    Do you acknowledge that the latent heat of ice is a massive reserve of stored cold which, when it is gone, renders assumptions regarding climate models ‘a bit’ in need of revisiting/dethroning?

    =)

  30. Greg Robie says:

    … and I should have said: as the stored cold of the latent heat of ice continues to go away…”. I struggle with my iteration of motivated reasoning that our cultural hopium induces; that linguistic conventions reinforce.

    Greenland tipped a generation ago. Mid-August, this research is published. When might such either be disproved or incorporated into modeling assumptions?

    8)

  31. Dave_Geologist says:

    It’s a long time since the Inuit observation discussion Greg, so I can’t remember the details but I remember not being convinced at the time. My industry experience doesn’t help as the closest I got was Anchorage and I stayed in town.

    I don’t think raw compute power helps if the problem is we don’t understand the physics well enough to know how the balance between high cloud and low cloud will evolve decades hence. For the competing feedbacks I mentioned above I suspect lack of data is the problem. These are not experiments that are easily carried out in controlled trials, and even then each location is different so it’s hard to extrapolate.

    A agree that climate models “miss things out” which are too hard or uncalibrated. I said as much. My point is that the reason we know those things are missing is because scientists are explicit about what is in and not in their models. They don’t pretend everything is in. That doesn’t mean they’re useless. George Box’s maxim applies.

    I’d be astonished if the (negative) latent heat of the cryosphere is not included in even the simplest one-box models. That’s the easy part. The hard part is the kinetics of how the energy in the ocean and atmosphere contacts that ice and how quickly heat is transferred to melt it. Thermodynamics s always much easier than kinetics.

  32. Chubbs says:

    Global methane for June just came in at 1872.2 ppb vs 1858.8 last June. Rate of increase spiking a bit despite the pandemic. We are far from having methane under control.

  33. Greg Robie says:

    Here is another view of methane, and by latitude. I watched this a lot in the late ‘00s when trying to wrap my head around how it dances around the planet.

    The visualization I linked it to is also pretty cool. Thinking in global averages is pretty much unmitigated motivated reasoning.

  34. Willard says:

    > Thinking in global averages is pretty much unmitigated motivated reasoning.

    Not sure what you mean, Greg, but I’m quite sure you can’t really afford to expand on that line of thinking.

  35. Greg Robie says:

    Please clarify what “afford” means in this context. Thx. =)

  36. Willard says:

    It means that all you got is mind probing, Greg, and mind probing will get moderated.

    Venting is fine. Jabbing is fine too. Constant jabbing is not.

    If you have more questions, feel free to ask them on Twitter, not here.

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