‘Net zero’

There’s been some recent debate about the term ‘net-zero’. Just to give some basic background, given that the zero emission commitment is close to zero (i.e., when we get anthropogenic emissions to zero, global surface temperatures should soon stabilise) means we can define a carbon budget. This tells us how much more we can emit if we want some chance of staying below some temperature target. It also tells us that our emissions must go to zero. The complication is that this could occur through emissions actually going to zero, or through some kind of negative emission technology offseting some continued human-caused emissions (this could include some active land management).

What some are concerned about is the possibility that some future negative emission technology could allow some to make ‘net zero’ promises that they may not be able to keep, or never actually intended to keep. In other words, they will claim that they’re aiming to get to a stage where they are offsetting all of their emissions despite it not yet being known if such technologies can actually operate at a suitable scale. Essentially, this becomes a form of greenwashing.

Another problem, though, is that some are interpreting ‘net zero’ in ways that aren’t consistent with what is intended. Mark Carney, for example, claimed that a company for which he is vice-Chair was ‘net zero’ because their enormous renewables business had avoided emissions that were comparable to their actual emissions. However, this isn’t ‘net zero’, it just means that they’ve ended up emitting about half of what they might have emitted.

‘Net zero’ requires actively sequestering an amount comparable to the amount actually emitted, not avoiding emitting an amount comparable to how much was actually emitted. I managed to come up with a reasonably popular tweet that illustrated the problem with Mark Carney’s suggestion.

I also came across another complication today, where someone interpreted ‘net zero’ as being the point when actual emissions are offset by negative emission technologies and by natural sinks. If this means that there is no net emission of any kind (anthropogenic, or natural), then it would imply constant concentrations. However, the reason that the zero emission commitment is probably small is because the natural sinks continue to take up some of our emissions after our emissions have gone to zero so that atmospheric CO2 concentrations actually decrease.

If we get to a stage where atmospheric concentrations stabilise, then we would actually continue to warm (this is the constant concentration commitment, which is different to the zero emission commitment). Hence, ‘net zero’ in this context means ‘net zero’ anthropogenic, not ‘net zero’ anthropogenic and natural. I should make clear that the above interpretation was, I think, more some confusion about ‘net zero’ than any attempt to define it in some convenient way, but it does illustrate how this can be a tricky concept.

So, I can see why some are concerned about the term ‘net zero’ and, as Simon Lewis points out, we can’t solve climate change using accounting tricks. However, I do think that the term ‘net zero’ is fine and that we should be careful of changing terminology just because some aren’t using it appropriately. However, it is important to stress that ‘net zero’ means ‘net zero’ anthropogenic emissions and that in the absence of negative emission technologies ‘net zero’ is the same as real zero. In other words, if negative emission technologies are unlikely to operate effectively at scale, then ‘net zero’ requires simply getting anthropogenic emissions to zero.


Warming commitments – post of mine about warming commitments with a number of useful links at the end.
Mark Carney Walks Back Brookfield Net-Zero Claim After Criticism – article describing Mark Carney’s misinterpretation of ‘net zero’.
The climate crisis can’t be solved by carbon accounting tricks – Guardian article by Simon Lewis.

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23 Responses to ‘Net zero’

  1. Good post. I think there is almost no chance that entities will engage in mixing the various ideas you describe as they talk about net zero. I actually think things are more complicated because I think the warming that we have accumulated and will continue to produce are likely to force changes in the natural global carbon cycle with some features taking up less carbon, some more carbon with the warming and the same thing with natural carbon cycle sources that emit carbon. I expect the science to advance and describe the anthro warming impact on the natural global carbon cycle as we see the warming arrive and discover the extent to which assumptions and projections about the natural global carbon cycle turn out to be accurate or how much we may have missed the mark with assumptions and projections about the natural global carbon cycle on a warmed planet.

    That said, I expect that changes we might see in the natural global carbon cycle will not produce ups or downs on the scale of the up carbon bump that humans have produced or the down carbon cut that we need to produce to get to a spot where atmospheric CO2e levels stabilize.

    In that case, the discussion of potential changes in the natural global carbon cycle is similar to the discussion that happened with stock versus flow emissions/pollutants or with the discussion about whether to focus on CO2 or CH4 or N2O. And in a similar sense we might focus on the “near term” version of net zero where we see atmospheric CO2e stabilize/stop rising, then we can and should see how bad things have become and whether temps actually stop rising in close link to the stabilization of CO2e as most think will happen. The real world status of our climate will help us decide how much and how fast we need to take the steps to allow atmospheric CO2e levels to fall by way of the natural carbon cycle or to force atmospheric CO2e levels to fall through investment and deployment of technology that might cause the atmospheric CO2e numbers to start dropping.

    In this instance, the differences between the “net zero” definitions you discuss exist on the same pathway, so we don’t have to consider whether to focus on one or the other as we might when we are discussing flow versus stock pollutants, or CO2 or CH4 or N2O.

    I don’t know if I have been clear or not with these points.



  2. should have read “almost no chance that entities will fail to engage in mixing” the net zero definitions

  3. I wonder whether temperatures will start falling as soon as anthropogenic green-house gas emissions stop. The natural rate of removal of green-house gases (today) is very small. So what you would have reached is a quasi-stable mix in the atmosphere. Simple static homogeneous earth and atmosphere absorption-emission models seem to indicate that the temperature will rise until an uncomfortably high temperature is reached. Perhaps there are major effects that these models miss?

  4. I.J.,
    I’m not quite sure what you’re suggesting, but the natural uptake is likely to continue taking up some of our emissions when we get our emissions to zero. Consequently, when we get emissions to zero, global surface temperatures should soon stop rising. We could still have reached uncomfortable high temperatures, but this would be because we’d emitted enough to do so, not because warming continued once we stopped emitting.

  5. angech says:

    127 countries have now stated that by mid-century their overall emissions of carbon dioxide will be zero. That includes the EU, US, and UK by 2050 – and China by 2060.

    I feel so much better now.
    Only 40 years to wait for net zero.

    Or as a previous commentator wrote.
    “I wonder whether temperatures will start falling as soon as anthropogenic green-house gas emissions stop”

  6. “I wonder whether temperatures will start falling as soon as anthropogenic green-house gas emissions stop”

    No, they probably won’t.

  7. David B Benson says:

    Those pledges are just for direct production of carbon dioxide. The sources of methane and N2O remain “unpledged”.

  8. izen says:

    In reading the Oil and Gas energy industry forecasts I see little acknowledgement of zero emissions. There seems to be a consensus agreement that demand will increase until 2035 at least, with a slow fall thereafter.

    While most of the offshore-oil-producing regions will be under pressure in an accelerated energy-transition scenario, the sector will still require new production of nearly 23 MMb/d to meet demand after 2030.

    Peak Oil is forcast for around 2050 with a slow decline in the second half of the century.

    Click to access DNV-GL_Energy-Transistion-Outlook-2017_oil-gas_lowres-single_3108_3.pdf

    Oil and gas will play a very important role in the
    energy mix throughout our forecasting period.
    Although we expect renewable energy sources to
    take an increasing share of this mix, we forecast oil
    and gas to account for 44% of the world’s primary
    energy supply in 2050, down from 53% today.

    The main concern of the Oil and Gas industry seems to be whether the price will rise enough to allow offshore and the US Permian basin sources to compete with Middle East and Russian supplies. If OPEC continues to restrict supply and prices exceed $60/b then sources other than the Middle East can compete, but if Iran and Iraq come back online in any significant amount then the Oil/Gas will come from them.
    There is no great insight into all these sources being stranded assets, or a zero emissions scenario by 2060. On the contrary they seem to envision a future where Oil and Gas reduce to a little less than half the world source of energy for the rest of the century.

  9. Chubbs says:

    Building on Izen’s point. Future forecasts for oil and gas generally change slowly with time, i.e. alternatives are slow to displace oil and gas. Why is that? Oil and gas must maintain some economic advantage into the far future in these projections. That can only be possible by assuming: 1) The alternatives that are already displacing oil and gas don’t improve much more; and. 2) Future carbon damage from burning oil and gas is minor or ignored. Both assumptions are questionable and only one needs to be wrong for oil and gas to be abandoned more rapidly than projected. Of course that is not the sort of thing CEO’s like to present to shareholders.

  10. izen says:

    “Future forecasts for oil and gas generally change slowly with time, i.e. alternatives are slow to displace oil and gas. Why is that? ”

    The predictions tend to be self-fulfilling, not least because of the economic and political interests behind them.
    There is also the fact of the long life of vehicles, ships, and aircraft. Even if electric or hydrogen versions are available shortly, does anyone think that the present fleets of ships, planes and automobiles are going tro be abandoned is anything less than 20 years ?

    While the industry sees little chance of expansion in transport, it does foresee a continued need for fossil fuels in plastics, fertilizer, and concrete/steel manufacture. While alternatives may become available, does anyone see these taking over until all the current and new plant being built is completely worn out ?

  11. izen says:

    If we take a conservative estimate of 30Gt of CO2 per year for the next 20 years that’s an additional 600Gt of CO2 or about another 40ppm CO2 in the atmosphere.
    How does this impact global temperatures ?

  12. Could use the TCRE, which is something like 1.8C per 1000 GtC, or per 3670 GtCO2. So, another 600 GtCO2 would be about 0.3C. The range, though, for the TCRE is something like 1C – 2.5C per 1000 GtC.

  13. Ben McMillan says:

    Well, the official SSPs also see oil/gas not peaking for ~20 years for RCP2.6 (peaking a bit above 2C), which is giving the oil/gas industry cover (coal drops faster).

    Oil is expensive outside transport (and plastics), so being supplanted. A lot of shipping is transporting fossil fuels. About 50% of oil use is ground transport… cars last ~20 years but do most of their miles in the first 5, so I’m a bit more optimistic that oil use in land transport might change pretty fast if EV sales are dominant in 2030. Air travel probably increases though.

    I could believe oil use flat/increasing up to 2030, but beyond that it looks downhill. Gas is a slightly different story.

  14. Chubbs says:

    Izen, yes it takes time to turn over the fleet of fossil fuel equipment and some sectors will be more resistant to change. On the flip-side however, the energy modelers are assuming there is limited pull for the non-fossil technologies. If EVs become more attractive than gasoline cars, who is going to want to buy a gasoline car? and which governments are going to facilitate gasoline use? The transition could occur surprisingly quickly.

  15. angech says:

    If EVs become more attractive than gasoline cars, who is going to want to buy a gasoline car?

    Diversity can be good.
    Say there is a power outage and you cannot charge the EV a gasoline back up might be attractive.
    The second point that comes to mind is the distance that needs to be traveled.
    Around town, 20 to 150 Km a day is fine but a 3 hour trip?
    The economies of battery weight and type to distance capable of being covered is still heavily tilted towards gasoline at the moment.
    Obviously if cheap reliable attractive alternatives become available they would be taken up.

    Just bought some battery tools, hedger and whipper snipper, very impressed.

  16. Ben McMillan says:

    At least in Europe, people are banning dirtier cars from city centers and look to be gearing up to ban ICE cars from cities entirely. The cost to other people, in health terms, of operating a ICE car in London is pretty close to the total personal cost of ownership. Once there is a plausible alternative to ICEs for personal+business purposes it is pretty hard to argue they should be allowed in these cities at all.

    I think that means that non-EVs will become increasingly inconvenient. At some point you can’t drive them in cities, and new infrastructure like e.g. indoor parking and tunnels won’t be designed for combustion vehicles. Fuel stations mostly closing down might be only a minor annoyance by comparison.

    It will be interesting to see what the interaction between EVs and the grid end up being: the total battery capacity of EVs is considerably bigger than the estimated requirement for grid-linked battery storage.

  17. Exactly right, Ben. In a safe and sane world we would build infrastructure where a person could park their car on the street or in their garage or in a parking lot and the car could be easily plugged in to the grid to recharge (if needed) and to simultaneously serve as the grid storage that will be needed for a net zero emission system.

    If we wanted to move ahead along that path we would need to decide if a green net zero emission grid is a public service like the fire department and roads and bridges or whether this is something that should be left to the private sector so the market can do its magic! I watched the market magic in Texas recently and it reinforced my appreciation for the idea of a publicly owned power grid.



  18. mrkenfabian says:

    Ben said – “It will be interesting to see what the interaction between EVs and the grid end up being”

    I’m thinking like Mike, that grid operators will be pleased to have lots of EV’s plugged in whilst not being driven, especially under arrangements that allow them to vary charge timing and rates in line with grid demand/supply fluctuations.

    And there could indeed be agreed arrangements to allow the grid to draw on that stored power, with user discretion, ie if you need full charge ASAP you can choose that but if not you can allow some portion of battery capacity (above a user designated retained minimum) and get payments and or discounts; schemes are being trialled for aggregating home batteries along similar lines.

    The parking meter of the future will probably be everywhere and feature a car charging option. I would like to think it can be done without physical plugs and cables… induction built into the pavement? Investing in the infrastructure for that could be an alternative to new gas plants or grid batteries.

    I rather like the idea that an EV parked and plugged in at a workplace carpark can be charged by home PV, via a single electricity account that includes EV charging wherever it is, an account where household PV contributions to the grid count towards charging. More use of daytime excess solar that way than using overnight “off peak” from coal or gas.

    Freight transport may need other solutions, being in more constant use; I’d been thinking battery swap systems, but fast charging capability is improving faster than I expected.

  19. David B Benson says:

    mrkenfabien — Truck drivers have mandatory rest stops. These are long enough to recharge batteries.

  20. Ben McMillan says:

    There are already some schemes for vehicle to grid (mostly Nissan Leaf/NV200):

    And virtual power plants using Tesla Powerwalls:

    I think using cars as a virtual power plant is still at the research stage, but at the simplest level, even controlled charging is very helpful. Smart chargers with variable tariffs already exist…

    Particularly in places where people don’t bury electricity distribution cables and electricity infrastructure is unreliable, being able to run your house islanded from the grid using mostly your car battery is also going to be attractive.

    Also, I agree with DBB: upcoming electric trucks look well suited to freight operations. Low speed limits for heavy vehicles in most places and mandatory stops makes it not too hard to design a competitive electric truck. This is just going to be cheaper, which is all that matters.

    The replacement can faster than you might think based on average vehicle lifespan. Once it is obvious to everyone that, e.g. ICEs are doomed: people just start holding off on buying a new vehicle.

  21. David,
    But it also points out that

    A second takeaway is that methane may be 21 times worse than carbon dioxide over 100 years, but after 100 years it is basically gone and has no effects besides its byproducts (carbon dioxide and water).

    Which I don’t think is quite right (since if methane concentrations have been elevated for long enough, then there will be some deep ocean that will persist) but it does illustrate that the GWP values are averages over some period, rather than the impact after that period.

  22. I think I have normally heard that methane emissions are something like 27 times as harmful as CO2, so the 164 number was kind of disturbing at first glance. It’s reassuring to note that the methane emissions don’t matter very much in the long run. After 100 years, our methane emissions mean almost nothing. That’s the blink of an eye in geologic time.

    Humans tend to focus on short time frames. Maybe we do that because of our tiny geologic time average lifespan? So many human considerations and discussions on emissions don’t even stretch to 100 years, most discussion is about the 80 year consequences or even shorter time frames. It’s good to have balance in the discussion and understanding that methane emissions mean almost nothing if we simply stretch the time frames a bit.

    I guess maybe the takeaway is that we should relax on methane and focus on the CO2 net zero target. We should achieve that CO2 net zero soon as we reasonably to play it safe. Once we hit that happy target, it should be a simple matter to apply the net zero technology and knowledge we have gained to reduce the methane emissions if we think that’s really necessary. Maybe increasing worries with alarming methane numbers is not very helpful, right?



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