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Study: our Paris carbon budget may be 40% smaller than thought

Posted on 24 July 2017 by dana1981

In the Paris climate treaty, nearly every world country agreed to try and limit global warming to no more than 2°C above pre-industrial temperatures, and preferably closer to 1.5°C. But a new study published in Nature Climate Change notes that the agreement didn’t define when “pre-industrial” begins.

Our instrumental measurements of the Earth’s average surface temperature begin in the late-1800s, but the Industrial Revolution began in the mid-1700s. There’s also a theory that human agriculture has been influencing the global climate for thousands of years, but the mass burning of fossil fuels kicked the human influence into high gear.

We may be at 1°C or 1.2°C warming since “pre-industrial”

We know that since the late-1800s, humans have caused global surface temperatures to rise by about 1°C. But what about the human influence in the centuries before that, which are technically still “pre-industrial”? The new study used climate model simulations from 1401 to 1800, during which time we know the climate influences of natural effects like solar and volcanic activity fairly well. They found that depending on the starting point, global surface temperatures during that period were 0 to 0.2°C cooler than the late-1800s.

According to the last IPCC report, to have a 50% chance of staying below the 2°C target, when accounting for non-carbon greenhouse gases, we have a remaining budget of about 300bn tons of carbon dioxide. But that was for 2°C warming above late-1800 temperatures. If we add another 0.1°C of pre-industrial warming, the study authors estimated that the budget shrinks by 60bn tons (20%), and if there was an additional 0.2°C pre-industrial warming, the 2°C carbon budget shrinks by 40%. As one of the study authors Michael Mann put it:

Either the Paris targets have to be revised, or alternatively, we decide that the existing targets really were meant to describe only the warming since the late 19th century.

It’s an important point if we want to measure whether we’ve succeeded or failed in meeting the Paris climate targets. And it’s important to know if our budget should be set at no more than 300bn tons, or more like 200bn tons of carbon dioxide pollution.

We’re moving in the wrong direction

However, we’re not yet on track to meet the Paris climate target budget. Based on current national pledges, humans will cause around 3 to 3.5°C warming above late-1800 temperatures by 2100. However, the Paris treaty included a ratcheting mechanism through which countries can gradually make their carbon pollution targets more aggressive. If successful, that ratcheting could limit global warming to 1.8°C above late-1800 temperatures, which is likely less than 2°C above pre-industrial temperatures.


Global greenhouse gas emissions and 2100 temperatures under no action, current pledges (INDCs), and successful ratcheting scenarios. Illustration: Climate Interactive

To accomplish that goal, the US would have to ratchet its carbon pollution down to 45% below 2005 levels by 2030, for example. But at the moment, America is moving in the wrong direction, shamefully becoming the only nation announcing withdrawal from the Paris treaty, aiming to join Nicaragua (which declined to sign due to objections that the agreement was too weak) and Syria (which did not participate due to a civil war) as the only non-signatory countries. Fortunately, other countries like China and the EU are stepping up to fill the global leadership role vacated by America under the Trump administration.

Regardless, we need to cut carbon pollution ASAP

It’s also important to remember that 2°C isn’t a red line – that if we cause 2.1°C the world will end or that at 1.9°C everything will be fine and dandy. The 2°C target is a reasonable one for two reasons:

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Comments 1 to 11:

  1. Dana,

    Can you confirm, from your point of view, if you see us being able to saty below 2 deg?  In this article you say with Ratcheting we could achieve 1.8 deg but I have heard, over and over, that the warming in the system already will get us above that.  Kevin Andersons Emperors new clothes presentation shows how absurd reaching 2 deg is even if you believe in tech not invented yet that gets us negative emmissions.

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  2. The scientific investigation of what the real pre-industrial temperature was is a dangerous, and unnecessary, 'debate' to open up.

    At the time of the Paris Agreement the global average of the late-1800's was understood to be the starting point for the 2.0 C and 1.5 C limits.

    The warming imposed by human activity prior to the late-1800s is not relevant even if it can be considered to also be pre-industrial. It is a purely scientific exercise. If there was 0.1 C before the late-1800s then the limits become 2.1 C and 1.6 C above that lower starting point.

    The danger is that some smart delayers will claim that this is just more proof that climate scientists are still debating the science. They will be able to gather popular support by claiming that world leaders (who all need regional popularity to remain leaders) would be irresponsible if they acted on understanding that was still not well understood/agreed to. And each region of the developed and developing world has a large potentially easily infuenced portion of its population, a portion that perceives the required changes to their way of living/benefiting to be a personal negative that they will not 'vote for' (and many of them are correct because they currently live in ways that have developed very far in incorrect/unsustainable/damaging directions or they perceive opportunities for personal benefit from the pursuit of activity that is incorrect/unsustainable/damaging).

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  3. I totally had the same reaction as OPOF. Focussing too much on pre-industrial temperatures wont help.

    Pre-industrial temperatures are of some scientific interest, and the work of Rudiman is worth reading in this regard, but were not that much different anyway so of no huge practical use to the discussions about reducing emisssions.

    It's of deep  scientific interest, but will only confuse the Paris issue and sidetrack the more practical discussions on emissions targets and reductions, in unhelpul energy wasting directions, and will play into the hands of the denialists.

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  4. There is this theory that human agriculture and deforestation, starting when farming first emerged which is approximately 12,000 years ago caused some warming. I think it's a plausible theory, but was clearly a modest increase in temperature over many thousands of years. This has no comparison to the more rapid, and clearly unsustainable, damaging, warming from fossil fuels, so should not be used as some form of baseline point.

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  5. Agreed with the others here.  This feels too much like moving the goalposts and realistically we've only ever worked from the basic late-1800's starting point.  Moreover, it feels foolish to me, to be specifying over a tenth of a degree when we can't know the sensitivity that well or actually get any indication that we are going to stop before we hit 4 or 5 degrees.   We have  not really even slowed down and adding more to the target will not I think, help us to change course.   

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  6. I agree in part and disagree in part.

    To the extent that the 1.5 and 2C warming limits are social conventions, I agree.

    However there is an objective component to the amount of warming since pre-industrial. If climate model simulations reliably show a particular impact at 1.5C vs pre-industrial, then we should probably work on the hypothsis that that impact will appear at that level of warming compared to pre-industrial. The key is then to define 'vs pre-industrial' in the same way between the models and observations. That's not a trivial step, and requires an understanding of the forcings used in both historical and control runs - I would need to look into that further.

    I like the paper. The implications, which dominate the media coverage, are something to which I need to give more thought.

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  7. In a summary of the global temperature in 2016, James Hansen et al start with a discussion of what the term "preindustrial" really means and argue that the period 1880-1920 is appropriate. They then present a global temperature graph with that baseline, and conclude that the best estimate of global warming since "preindustrial" time is 1.07°C based on the linear trend since 1970.

    Global temp vs 1880-1920

    When I did the same with the Berkeley Earth data, but used the linear trend since 1975 instead of 1970, my "end-of trend" result was 1.14°C. With the 1880-1920 baseline the BE temperature in 2016 was 1.34°C, so it seems that the 2016 El Niño boosted the global temperature by 0.2°C.
    Therefore it’s not necessary to move the "preindustrial" back several hundred years to reach the conclusion that the global warming has already crossed the 1°C threshold.

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  8. Agreed. The important message, as stated in Dana's last section heading, is "We need to cut carbon pollution ASAP."

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  9. A good starting point would be the time when fossil fuel usage surpassed the use of charcoal/firewood. First commercial mining of coal started back in 1680 (England), 1740 (USA) but the use of coal became significant after we could produce a better from the coal than charcoal (around 1850). I would pick that point as the start time: we put more long stored carbon into the air than from the short storage period. 

    Best option to me would be creating a second -closed loop- carbon cycle, capturing all carbon dioxide from power production. No need for sequestering on a large scale if at the same time we use all available solar/wind power produced in excess to convert CO2 back to methane (Power to gas) and inject the gas into existing pipelines/resevoirs until needed. Solar power received is large enough to convert a 10,000 time over all energy need so even a 2% coverage of all land mass (roof tops/desserts/forest/water bodies) with 0.5% efficient overall technology would give about 2 to 3 times the amount of energy we use today. The larger part of that excess can be used to remove CO2 from the natural loop and inject into the new technical loop. 

    If carbon capture can be done for a $45/ton ( $135/MWh produced) than, on top of the production price of $70/MWh, reducing distribution costs by local distributed generation (tie lines with capacity of 10% of total volume) to a $30/MWh, we are looking at a power price $235/MWh or US$ 0.235/kWh at the moment. 

    Currently the price I pay (non-industrial use) is a 16 cents/kWh (Philippines, Manila area) but know of enough areas here where the actual price is 22 cents, areas in Cambodia where the price is 1700 Riels (consumer, 40 cents) to 2000 Riels (industrial, 45 cents). Imagine a good distributed power to gas generating system in such sunshine countries with constant 'natural' carbon capture storing natural carbon in a separte second loop. 

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  10. 3rd sentence first paragraph: a better COKE from the coal than from the charcoal..

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  11. The panic has set in (as readily observed by increasing market demand being met by increasing market supply): the truth is that a journey of a thousand miles doesn't begin with the first step because we are already on the path. We are already on the journey.

    "Where am/are I/we going again?", becomes the individual/collective question as it always has been.

    Who am/are I/we?

    The game is always being played... we are on the journey as we speak.

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