22 years till we blow the 2°C Carbon Budget

If global carbon emissions continue to grow as they have in the last decade we will burn through the 2°C carbon budget by 2035.  If we don’t begin aggressive reduction immediately, we will burn through the budget at some point soon enough.

That is the grim reality of extending historical emissions growth into the IPCC’s cumulative carbon budgets.

In its new report the IPCC stated that to have an even chance of limiting warming to less than 2°C (since the period 1861–1880) it will require keeping cumulative CO2 emissions from all anthropogenic sources to less than 840 GtC.

By 2011 mankind had already emitted 531 GtC.  (See our carbon emissions and sinks piece)

If global carbon emissions continue to grow at 2% each year, as they have done over the last decade, we will blow through the 840 GtC carbon budget at the start of 2035.

Global carbon budget

The more stringent target of 800 GtC, that gives us a 66% chance of limiting warming to 2°C, is exhausted in 2032.  The more lax goal of 880 GtC, that gives us a 33% of limiting warming to 2°C, follows shortly afterwards in 2037.  If non-CO2 greenhouse gas concentrations increase, aerosols are reduced or the permafrost begins to melt these dates will be dragged forward.  The reverse will push them back.

Our current emissions path will leave us committed to more than  2°C of warming in just 22 years.  It would also commit us to much more warming beyond that given the economic inertia of global carbon emissions.

In fact the 2°C carbon budget is so stringent that even if global carbon emissions stopped growing and remained flat for the coming decades we would still break the 2°C budget in 2041, less than 30 years from now.

Emissions growth rates

In the graphic above we show the speed at which we exhaust the 2°C  budget based on different annual emissions growth rate scenarios.

The first one is the same as our initial chart and shows that if emissions grow at 2% each year we break the 2°C budget in 2035.  In the second we see that if annual emissions remain constant at a 2011 level we break the 2°C budget in 2041.  The third shows that if annual emissions decline at 2% per year we will break the 2°C budget in 2058.

To reach 2100 within the 840 GtC budget (>50%) emissions need to decline at 3.5% per year, beginning immediately.  If action is delayed until 2020 annual reductions of  6%/year are required.  Such reductions would be largely dependent on the deployment of negative emission technologies.

The gap between where we are and where we need to be is enormous.

This is the nature of our problem:

Carbon Emissions Sources

We have a coal problem.  We have an oil problem.  We have a gas problem.  We have a deforestation problem.


And our lack of ambition in dealing with it is quite astonishing.

  • CelloMom on Cars

    Could you clarify: does the data you show include the contributions from methane (in a carbon-equivalent way) at all? My recent back-of-the-envelope estimate is that, on a 20-year scale, the contribution of methane to global warming is already about a third that of carbon dioxide. If we get the positive-feedback loop going on methane, we may have a lot less than 22 years. [bit.ly/GAfrJ6]

    • Lindsay Wilson

      It uses the non CO2 forcings based on the representative concentration pathway 2.6 (RCP 2.6) from the IPCC. That includes all the other forcings at a relatively low level. The forcing rise from methane over the last three decades has been quite small compared to that of CO2, even when you include the ozone it causes. As you note the major worry with methane is the permafrost feedbacks. There is no exact answer on dates of commitment, as everything is probabilities. If sensitivity is high then we are well on our way already.

  • RGignac

    I have a clarifying question about this passage from the IPCC report :

    “Limiting the warming caused by anthropogenic CO2 emissions alone with a probability of >33%, >50%, and >66% to less than 2°C since the period 1861–188022, will require cumulative CO2 emissions from all anthropogenic sources to stay between 0 and about 1560 GtC, 0 and about 1210 GtC, and 0 and about 1000 GtC since that period respectively23. These upper amounts are reduced to about 880 GtC, 840 GtC, and 800 GtC respectively, when accounting for non-CO2 forcings as in RCP2.6. An amount of 531 [446 to 616] GtC, was already emitted by 2011. {12.5}” http://www.climatechange2013.org/images/uploads/WGIAR5-SPM_Approved27Sep2013.pdf

    In your analysis, you interpreted the passage “An amount of 531 GtC was already emitted by 2011” by not including the 531 GtC in the carbon budget of 800 GtC that we have left. In interpreted it differently : don’t we in fact have only 269 GtC left to emit by 2100 (not 800 GtC)?

    Grad econ student, Montreal QC

    • Lindsay Wilson

      That isn’t what I’ve done at all. If you look at the first graph you’ll see that I’ve accounted for the 531 Gt up to 2011 in the yellow. The following light orange is the 269 Gt (>66%), the darker orange goes to (>50%) and the red to (>33%). I also think I was quite clear by stating that: ‘By 2011 mankind had already emitted 531 GtC.’ in the text.

      Best, Lindsay

      • RGignac

        But then how come the area under the light orange curve (269 GtC) seems equivalent – or larger – than the area under the yellow curve (531 GtC)?

        Another question : I have annual world emissions not around 10 GtC but more like 50 GtC. Are you sure about 10 GtC?
        See World Bank : http://wdi.worldbank.org/table/3.9Line “World” (data from 2009 and 2010)

        • RGignac
        • Lindsay Wilson

          The yellow area isn’t 531. That is the total from 1750 to 2011. (you can see most of them in the bottom graph, from 1960). Total GHGs were about are 50 Gt CO2e in 2011. CO2 was about 37 Gt, which equals about 10.2 GtC. Don’t confuse the carbon metric with CO2. Scientists tend to use C, whereas policy people use CO2

          • RGignac

            Thanks very much for the clarification.

          • Lindsay Wilson


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  • RGignac

    Hi, me again.
    Thanks again for the clarifications, this is very helpful. (I work at a small research institute in Montreal, QC)
    One more question : in your simulations, you “assume limited further non-CO2 forcings as per RCP 2.6”. Does the IPCC report explains the reasons why this RCP2.6 scenario should be preferred over the higher-end carbon budget estimates? Why exactly do the other scenarios do not include these non-CO2 forcings?
    In other words, how do you reply to people who say we should use the numbers 1560, 1210 and 1000 GtC rather than 880, 840 and 800 GtC?
    Thank you,

    • Lindsay Wilson

      If you are looking at the “C limit I think it makes sense to look at RCP 2.6, as this is the only one that involves strong mitigation. All the other RCPs have higher non-CO2 forcing. Using the carbon only budgets assumes away the other forcings, which makes little sense to me. The IPCC does not give preferences, it simply presents the data for policy people

  • Isabel Evans

    Hey- just a clarification, what is the y axis on the graphs? And how did you calculate when we would surpass the 2 degree carbon budget in the different scenarios? Thank you :)

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