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How much CO2 your country can still emit, in three simple steps

Filed under: — stefan @ 6 August 2019

Everyone is talking about emissions budgets – what are they and what do they mean for your country?

Our CO2 emissions are causing global heating. If we want to stop global warming at a given temperature level, we can emit only a limited amount of CO2. That’s our emissions budget. I explained it here at RealClimate a couple of years ago:

First of all – what the heck is an “emissions budget” for CO2? Behind this concept is the fact that the amount of global warming that is reached before temperatures stabilise depends (to good approximation) on the cumulative emissions of CO2, i.e. the grand total that humanity has emitted. That is because any additional amount of CO2 in the atmosphere will remain there for a very long time (to the extent that our emissions this century will like prevent the next Ice Age due to begin 50 000 years from now). That is quite different from many atmospheric pollutants that we are used to, for example smog. When you put filters on dirty power stations, the smog will disappear. When you do this ten years later, you just have to stand the smog for a further ten years before it goes away. Not so with CO2 and global warming. If you keep emitting CO2 for another ten years, CO2 levels in the atmosphere will increase further for another ten years, and then stay higher for centuries to come. Limiting global warming to a given level (like 1.5 °C) will require more and more rapid (and thus costly) emissions reductions with every year of delay, and simply become unattainable at some point.

In her recent speech at the French National Assembly, Greta Thunberg rightly made the emissions budget her central issue.

So let’s look at how the emissions budget concept can be used to guide policy on future emissions trajectories for countries.

Step 1: The temperature goal

First we need to determine at what level we want to stop global warming. That’s quite simple because it has already been agreed in 2015 by all nations in the Paris Agreement. That has taken decades of discussion and negotiations, ever since nations agreed in 1992 at the Rio Earth Summit to stabilize greenhouse gas concentrations “at a level that would prevent dangerous anthropogenic (human induced) interference with the climate system.” In Paris a consensus was finally reached on “limiting global temperature increase to well below 2 degrees Celsius, while pursuing efforts to limit the increase to 1.5 degrees”.

Last year, the IPCC special report Global Warming of 1.5 °C (in short SR15) detailed strong reasons for why limiting to 1.5 °C would be much more sensible than to 2 °C.

Step 2: The global CO2 budget

Once the temperature limit has been agreed, we need to know the corresponding CO2 budget. That is a question for science, and the IPCC SR15 answers that, including the uncertainties as always is a hallmark of good science. The following shows the budget table from IPCC.

CO2 emission budget left from the beginning of 2018 in order to remain below a certain warming limit. Example: in order to remain below 1.5 degrees with a 67% probability, we can still blow 420 billion tons into the air from the beginning of 2018. From the beginning of 2019, that is only 380 billion tons, since around 40 billion tons are currently emitted annually. Source: IPCC SR15, Table 2.2

The uncertainties to a large extent result from the fact that CO2 is the main but not the only cause of human-caused climate change, so the CO2 budget depends on how we will deal with non-CO2 climate forcings such as aerosol pollution. There are also different methodologies to estimate the CO2 budget. A thorough analysis of the uncertainties is found in a recent paper by Rogelj et al. in Nature. The bottom line, as one of the co-authors (Elmar Kriegler) told me, is that the SR15 estimates in the table above are still the best we have.

Some have argued that the uncertainties make the budget approach a poor guidance for policy. I disagree. First of all, practically all of politics operates under high levels of uncertainty about the outcome of policy decisions; that is inevitable. In fact it is rare that politics has a clear guidance like the well-established linear relationship between cumulative emissions and global temperature. Those who criticise using this as policy guidance must come up with a better guidance providing less uncertainty, then we can discuss.

Second, some of the uncertainty is captured by the probabilities for reaching a certain temperature limit, shown in the table, so society can simply decide what level of risk of overshooting a temperature level they are willing to take.

And finally, all policy is to a large extent learning by doing. You start with the best scientific advice now (especially since we cannot afford to wait any longer), and if we know more in ten years time we can adjust policy then. Given that climate change is largely irreversible it is best to err on the safe side, i.e. the uncertainty, if anything, is a reason to apply the precautionary principle and reduce emissions fast.

Greta has argued in her speech to use 67% probability for staying below 1.5 °C, i.e. a 420 Gt budget from the start of 2018. Subtract 2 years of emissions, i.e. 80 Gt, then we’re left with 340 Gt from the start of next year. That is 8.5 years of current emissions – or 17 years until zero emissions in case of a linear rampdown.

If you translate the “efforts to limit the increase to 1.5 degrees” promised by all nations in the Paris Agreement as a policy that gives us 50:50 chance to actually achieve that goal, that’s 500 Gt from the start of next year. That’s 12.5 years of current emissions, or 25 years for a linear rampdown, i.e. halving emissions in 12.5 years to reach zero by the end of 2044.

But beware of using those end dates instead of budgets, because it is not the end date but the cumulative emissions that count! A simple illustration: if you don’t achieve reductions in the next ten years but keep emissions constant, and reduce linearly after that, the result is that you have to reach zero ten years earlier! See the next figure.

Detrimental effect of wait-and-see policy. The blue emissions path stays within a 500 Gt budget, but the solid red path emits 700 Gt. To stick to the 500 Gt budget despite ten years of waiting, emissions need to reach zero by 2035 rather than 2045 (dashed line).

This is why one should not attach much value to politicians setting targets like “zero emissions in 2050”. It is immediate actions for fast reductions which count, such as actually halving emissions by 2030. Many politicians either do not understand this – or they do not want to understand this, because it is so much simpler to promise things for the distant future rather than to act now. Greta asked the pertinent question in her Paris speech:

”What I would like to ask all of those who question our so called ‘opinions’, or think that we are extreme, is: Do you have a different budget for at least a reasonable chance of staying below a 1,5° of warming? Is there another, secret Intergovernmental Panel on Climate Change?”

Step 3 Computing a budget for your country

How do you divide up the remaining budget amongst humankind? This is a crucial step since most climate policy is made at the national level. Yet, this is not a scientific question but one of climate justice. Who gets how much?

I can’t solve this question but I am going to propose a starting point, based on the idea that a principle of fair distribution needs to be universal and simple. The most simple one clearly is an equal per capita distribution. Anyone who wants more of the budget than someone else would need to provide a good reason. There could be many reasons – cold countries might claim they need more emissions for heating, hot countries for air conditioning, large countries for transport over long distances, developing countries to eradicate poverty, rich countries because they are already developed.

A tricky question is: at what point in time do you distribute the budget? This is important because rich countries are eating up the remaining CO2 cake much faster than poor countries. I would propose: from the time of the Paris Agreement, i.e. from the start of 2016. Of course developing nations will argue (and have argued) for a much earlier start date, to account for the historic emissions of developed nations. That may be justified but has the practical problem that the remaining budget for countries with large per-capita emissions is then already zero or rather: overdrawn.

So just to be practical, let’s take 2016. So you compute the remaining global budget at the start of 2016 by adding 80 Gt to the IPCC budget table numbers shown above. Then you multiply that number by the population of your country, divide by the global population, and then subtract the emissions of your country from the start of 2016 until now. I have done this for Germany (in a German blog post) using a global budget of 800 Gt from the table, just to be generous, for a 67% chance to stay below 1.75 °C (my interpretation of “well below 2 °C”). The result was a remaining emissions budget of 7.3 Gt from the start of 2019 or 6.5 Gt from the start of 2020. That is 8 more years at current emissions. The next figure shows a linear reduction trajectory compatible with this budget.

Emissions budget example for Germany

I’m not so concerned about the exact numbers, given the uncertainties discussed above. But there are at least three important conclusions from the budget approach.

First of all, nations with high per-capita emissions need to reduce faster than others, based on the limited budget and simple justice considerations. If some reduce faster and some slower, even if every nation reduces linearly global emissions will not decline linearly, but more rapidly at first from the reductions of wealthy nations, with a longer tail of emissions from developing nations reaching zero later.

Second, even with generous assumptions (like an 800 rather than 420 Gt global budget and a 2016 start date for dividing up the cake) emissions from developed nations need to drop much faster than almost all politicians think, in order to honour the Paris agreement.

Third, it is not some end date that counts but rather very rapid reductions starting right now. The end date is a moving target – every year we wait we lose two years: the year we waited, and a year at the end because the required end year moves towards us.

Finally, unprecedented global cooperation is needed to tackle the climate crisis. This may involve deals that make the tight budgets more palatable to countries with high per-capita emissions – for example they might find partners with low emissions and negotiate to use some of their budget in exchange for technological and financial support in climate adaptation and mitigation.

p.s. (7 August): I have posted a spreadsheet where you can look at this budget estimate and the budget reach in years for any country. Someone suggested on twitter I should provide a site which automatically produces the figure above for any country – I don’t have the time to do this but it is not a bad suggestion, perhaps there is a volunteer?


Messner et al. 2010: The budget approach: A framework for a global transformation toward a low-carbon economy (PDF)

For a more complex formula to share the budget: Raupach et al. 2014, Sharing a quota on cumulative carbon emissions.

117 Responses to “How much CO2 your country can still emit, in three simple steps”

  1. 101
    Mal Adapted says:


    KIA 85: please post the steps you’ve taken to switch to renewables:

    BPL: I’m getting 100% of my electricity from wind and solar. Your turn.

    Voluntary efforts to reduce one’s private carbon footprint shouldn’t be disparaged as mere virtue signalling, if they inspire competitive virtue in enough others to make a difference. They won’t drive fossil carbon emissions to zero on their own, however. Yet again: AGW is a drama of the Commons, i.e. a phenomenon of the global ‘free’ market, which socializes every private cost it can get away with. For one thing, voluntary internalization of socialized costs runs into the ‘free-rider’ problem, wherein your coal-rolling Trumpist neighbor enjoys the benefit of your Prius’s relatively low emissions for free. For another, bringing one’s personal carbon footprint to zero currently entails living wholly outside the global economy, which calls for (IMHO) uncommon virtue. Collective intervention in the free (of targeted collective intervention, that is) market for energy is what’s required, to internalize the marginal climate-change costs of every fossil carbon transaction in the price, thereby harnessing consumer thrift and the profit motive to build out the carbon-neutral economy with desired alacrity.

    Leading economists recommend revenue-neutral carbon taxes (‘This is not controversial’: Bipartisan group of economists calls for carbon tax) for the purpose. It’s close to a minimum collective intervention: it’s not an intrusive command-and-control measure, it’s just a fee (i.e. tax or tariff) per tonne of actual or embodied carbon, efficiently collected from domestic energy producers and importers of manufactured goods, who are left to decide how much of it they can pass on to buyers and stay profitable. ‘Revenue-neutrality’ means the money stays in the economy rather than, in a pseudo-skeptic’s imaginings, disappearing into a bureaucratic black hole. Your neighbor is still free to roll as much coal as his denying heart desires or his budget affords, whichever is less; OTOH, under Carbon Fee and Dividend proposals, he winds up paying you for your fuel-sippin’ virtue. That makes Prius ownership a market and a ‘Booyah’ signal in one!

    Yes, in democratic societies, every collective action is taken on a slippery slope. But if AGW-deniers think democratically requiring everyone to pay for their own marginal climate-change costs whenever they buy fossil energy directly or as embodied, is ‘socialism’, then the Koch brothers’ plan to reshape America has succeeded. Dang.

  2. 102
    Mr. Know It All says:

    92 – BPL
    “BPL: I’m getting 100% of my electricity from wind and solar. Your turn.”

    Good job! What steps did you take to achieve it? Where does your power come from when it’s dark and the wind isn’t blowing?

    My turn? OK – I get mine from renewables too. Only steps I took were to pay a small extra fee on electric bill here in the PNW and they “claim” the power is from new wind generators and from old hydro in the Columbia River. Don’t think we get any from FFs but I’m not sure. I will say the windmills are not a positive addition to the landscape, and they claim that the dams kill the fish – I’d believe it.

  3. 103
    Mr. Know It All says:

    92 – BPL
    In my reply (still awaiting moderation), I forgot one minor detail: our heat is from natural gas. Our local electricity may be fairly good from a carbon emissions standpoint, but our heat isn’t – although our house is reasonably well insulated and does get considerable solar gain in winter which helps – as does keeping T-stat set fairly cool.

    Your turn on heat source. :)

  4. 104

    …then the Koch brothers’ plan to reshape America has succeeded.

    It has, for the moment.

    The promotion of fossil fuel is the single most important focus of the Maladministration, with the possible exception of promoting racism and xenophobia.

    Moreover, Kochist framings of social problems are quite pervasive, both in an out of media.

    That’s what you get–or can get, anyway–when you spend billions of dollars, decades of effort and a whole lot of good quality brainpower on social engineering.

    And that’s maybe the biggest irony, right? That putative devotees of liberty, free thought, and non-intervention have staged one of the most successful examples of social engineering in history? It makes a mockery of their supposed Libertarianism, really, in a pretty deep way. But that’s how it looks to me, at least.

    I think the pendulum is about to swing. But the effects they’ve brought about won’t just disappear with the collapse of Trumpism, sadly. We’ll be trying to deal with their destructive legacy for decades. At best.

  5. 105
    Mr. Know It All says:

    104 – Kevin
    “…then the Koch brothers’ plan to reshape America has succeeded.” Wrong.

    Leftists have had controlover much of this country for decades. That’s why we have Trump now. People are sick of leftist failed policies.. Like Sam Elliot said after the election: “The fact that there are riots in the streets because Donald Trump was elected president… is proof Donald Trump needed to be elected!”

    “The promotion of fossil fuel is the single most important focus of the Maladministration, with the possible exception of promoting racism and xenophobia.”

    Nope. The most important focus is America First. He has never promoted racism or xenophobia. Keep lying; it helps him.

    “We’ll be trying to deal with their destructive legacy for decades. At best.”

    Nope. AOC said the world will end in 12 years, and that was several months ago! Wasn’t that vote on the Green New Deal amazing? Not ONE US Senator voted for it – not even the sponsors of the bill!!!!! The evil Koch brothers made ’em do it, right?

    Hey, I read that Greta’s team was flying back and forth over the Atlantic to pick up the yacht, etc. I read that it would have put less CO2 in the atmosphere if she had just bought tickets and flown.

  6. 106

    KIA 105: He [Trump] has never promoted racism or xenophobia.

    BPL: The Department of Housing and Urban Development sued him in the 1970s because his apartments were excluding black people. He pressed to execute the Central Park Five long after they were proven innocent. He was elected by calling Mexicans rapists and criminals and insists that they are a terrible threat to the US, responding by putting would-be immigrants in concentration camps. To say Donald Trump has never promoted racism or xenophobia bespeaks a terrible blindness to reality.

    KIA: Wasn’t that vote on the Green New Deal amazing? Not ONE US Senator voted for it – not even the sponsors of the bill!!!!!

    BPL: And they made the reason why clear at the time–because all the Republicans in the Senate were going to vote No, so there was no chance of passage even if the Democrats had all voted for it. It was called a “sham vote” and that’s what it was. Propaganda for useful idiots like you.

  7. 107
    Dan says:

    106. In addition, to say Trump has never promoted racism and xenophobia in light of countless examples that he has is enabling thinly disguised hate/racism/xenophobia/bigotry. Per KIA.

  8. 108
    Dan says:

    106. In addition, to say Trump has never promoted racism and xenophobia in light of countless examples that he has is enabling thinly disguised hate/racism/xenophobia/bigotry. Exhibit A: KIA.

  9. 109

    KIA, #105–

    Trump never promoted racism or xenophobia?

    Exhibit A: Bannon. His whole career is about xenophobia.
    Exhibit B: Miller. Notoriously racist.
    Exhibit C: His contention that Congresswomen of color have no right to an opinion about how the country should be run, and that for the ‘crime’ of nevertheless having one, they should be deported (even though three of four are native-born Americans).
    Exhibit D: “Rapists and murderers.”
    Exhibit E: “Shithole countries.”
    Exhibit F: “Very fine people on both sides.”
    Exhibit G: Promoting white supremacist ideology in verbal and graphic form, as here:

    I could go on… but the evidence is already sufficiently nauseating.

  10. 110
    save_ecosystems says:

    #100, K.McKinney:

    “How would you suggest that this be changed?”

    Perhaps by creative usage of several media and PR? Are regulations by state organizations that reward renuciation and small ecological footprints enough? Goal 8 of the 17 SDG’s of the agenda 2030 should contain degrowth instead of “economical growth”. CSR (corporate social responsibility) is another approach. The actual sustainability measurements, clean development mechanisms, UNFCCC, Rio+20, Kyoto Protocol, Green Climate Fund, the Social Contract for Sustainability, the Climate Summit 2014, the Paris Agreement and COP 24 were not sufficient.

  11. 111
    Aurel Wünsch says:

    Just a minor point: it is less ambiguous to use “tonne/tonnes” instead of “ton/tons”. a “tonne” is always a 1000kg. while a “ton” can understood as a metric ton (1000kg), a short ton (907kg, primarily used in US) or a long ton (1016kg, primarily used in UK). I’m aware that the difference is smaller than the uncertainty of the budget anyways, but if someone uses the numbers here and calculates something based on them the errors can multiply.

  12. 112
    Al Bundy says:

    KIA quotes:#3
    “Because I am a long distance sailor too and know about those starlit nights, inspiring all sorts of discussions, I am wondering whether little Greta’s ideas are being debated on board: For instance the obvious question how the little girl with the big ego who rarely goes to school has come across the knowledge necessary to decide whether CO2 really influences world climate. I bet nobody on the boat even dares to touch the topic!”

    AB: Your [quote’s] question makes sense, at least based on your personal experience. After all, you’ve spent ever so long not-in-school-but-here and haven’t learned anything.

    zebra: And you are also correct that this doesn’t mean we shouldn’t be trying as hard as possible to reduce emissions as rapidly as possible.

    AB: The rest of your comment sang, but this? No. The fastest way to reduce emissions as rapidly as possible is to develop CH4 resources as fast as possible, to convert vehicles to CH4, to convert everything to CH4.

    The result of this insanity? Catastrophe, because emissions aren’t terribly relevant. The relevant metric is built infrastructure’s inherent emissions through its life. As you noted, current CH4 is best left intact. That’s true especially because the future will have some percentage of energy provided by biofuel, and CH4 will be a large fraction of that. Perhaps many of those apartments and houses heated with gas need zero conversion at all. But to build more CH4 infrastructure is dumb as dirt.

  13. 113
    Al Bundy says:


    You should think about reality instead of Scoring Points. You literally said [implied] that if your child had a chance at having Greta’s experience you’d fight tooth and nail to have your child NOT experience what Greta’s experiencing [please ignore your political belief system when analyzing this; that Greta’s views ain’t yours is irrelevant].

    Yeah, doing homework and keeping up with studies while addressing the UN is such a limited education. MUCH better to be chained to a desk.

    What I find amazing is how factproof you are. Like water off a duck.

  14. 114
    Al Bundy says:

    KIA quotes:#3
    “Because I am a long distance sailor too and know about those starlit nights, inspiring all sorts of discussions,”

    AB: Seriously, your selected logic (not yours, but your admiration) is amazing. Think about WHO the folks who would ride that sled ARE. Surely they are World Class. Who else would get to run such a cutting edge system? (And you poo-pooed it as 1600AD technology; as if crossing the Atlantic faster than motorized transport can keep up was available 400 years ago)

    Greta got to have conversations with some of the best, the brightest, those on the cutting edge. AND YOU DISS IT!!!!!!!

    Self-made moron, thou art. Go ahead, say something to defend your position. I dare you. MUCH better would be to open your eyes and ADMIT that you noticed something that wasn’t in accord with your pre-conceived ideas.

  15. 115
    Mr. Know It All says:

    112, 113, 114 – Al Bundy

    Greta is playing the politics game. Have to have thick skin to play.

  16. 116

    Hey everybody,

    I took on the gentle challenge, and developed an interactive version of the dataset from Prof. Rahmstorf. It can be viewed at

    and the code is accessible on

    It was my first python/dash/plotly coding project, so excuses if I used onorthodox coding principles. But I tried to document the code as good as possible in the readme file, so it should not be too difficult to find out what is calculated where. Ideas, suggestions, corrections, extentions, … are welcome!

  17. 117

    So KIA (115) admires Putin. Why am I not surprised that a Trumper thinks Putin is worth listening to.

    Putin puts forth the old fallacy that you can’t develop the Third World without fossil fuels. This is, of course, garbage, which Greta Thunberg knows and Vladimir V. “I have oil and gas to sell you if you play along” Putin does not.