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22 Years Till We Blow the 2°C Carbon Budget

Lindsay Wilson's picture
Shrink That Footprint
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  • Oct 7, 2013 11:00 pm GMT

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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.

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.

Lindsay Wilson's picture
Thank Lindsay for the Post!
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Steve K9's picture
Steve K9 on Oct 7, 2013


Agreed.  But, if your answer is put on a hair shirt and live in a grass hut eating fish heads … well forget it.  Humans want more energy, not less.  The way to have abundant, cheap, limitless energy without CO2 is to burn uranium not coal.  

Hopefully enough people do and will get this to prevent the catastrophe you fear.

Bob Meinetz's picture
Bob Meinetz on Oct 7, 2013

Lindsay, can you give me a specific reference in AR5 where I can find the following conclusion?

“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.”


Max Kennedy's picture
Max Kennedy on Oct 8, 2013

From my readings, such as and several others I would characterise this 840GtC as being somewhat optimistic.  I’d expect +ve feedbacks to mean we hit this sooner than that number indicates.

Lindsay Wilson's picture
Lindsay Wilson on Oct 8, 2013

Yep, that is a genuine risk.  The calculation above assume non-GHG forcings as per RCP 2.6, which is very successful mitigation.  If permafrost methane leaks accelerate dramatically it will be worse

Lindsay Wilson's picture
Lindsay Wilson on Oct 8, 2013

Hey Bob, Summary for Policymakers page 20:

“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 1861–1880, 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 respectively. 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}”

My calculations assume the non-CO2 forcings from RCP 2.6, which is pretty conservative given the current emissions trajectory.

Best, Lindsay

Lindsay Wilson's picture
Lindsay Wilson on Oct 8, 2013

I don’t really care which technologies solve the carbon problem.  That said it is worth remembering that the power sector is only 30% of total carbon emissions

Bob Meinetz's picture
Bob Meinetz on Oct 8, 2013

Thanks again.

One observation, and a point which can’t be emphasized enough (and which your graph makes clear): fossil fuels are responsible for 7x as much excess carbon in the atmosphere as all other causes combined.

We have to stop pulling carbon out of the ground yesterday.

Robert Bernal's picture
Robert Bernal on Oct 11, 2013

Looks like we really need to focus on the least expensive, most abundant low carbon source for global power needs!

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