Young People’s Burden: Requirement of Negative CO2 Emissions

In a paper authored by Jim Hansen and a number of other climate scientists[1], the concept of “climate debt” is raised. This is the amount of carbon dioxide that will have be removed from the atmosphere at a future date due to a lack of emission reductions in the present. This can be seen as an intergenerational debt, run up by the present adult generations but to be paid out by the future ones. Global temperatures averaged 1.10C above preindustrial levels in 2016 (excluding the short-term warming impact of the 2015/16 El Nino)[2]. An extra 0.50C of delayed warming is baked in through the thermal inertia of the oceans, and up to another 0.50C may also be as the dimming effect of aerosols (produced by burning fossil fuels, especially coal, and land use changes) is reduced. Therefore an above 20C temperature rise may already be baked in at current CO2 levels.

The safety of the 20C global temperature rise target (relative to preindustrial levels) is questioned by the paper’s authors, given that temperatures during the Eemian period may have been as little at 10C-1.50C above pre-industrial levels. The Eemian inter-glacial period began about 130,000 years ago and ended about 115,000 years ago. It had sea levels that were between 6 to 9 metres higher than at present. The paper raises the probability that any extended period at such temperatures may trigger the major slow feedbacks of ice-sheet disintegration (raising sea levels), the release of soil and tundra carbon stores, and a reduction in the capacity of carbon sinks such as the ocean and forests. The current global temperature level is already at the level of the Eemian, with up to an extra 1-degree of warming possible without any further increase in CO2 levels.

Recent academic research has pointed to the triggering of slow feedbacks at current temperature levels[3] [4] [5]. With the speed of temperature rise, multi-meter sea level rise may be with us within a few decades rather than a century or so. Another dangerous factor is the possibility of a greatly reduced level of Arctic albedo given the rapid reductions in Arctic sea ice volume[6] [7]. Once started, such feedbacks may become unstoppable and remove the ability for human civilization to return to the Holocene environment within which it developed and flourished. Given this, the paper argues that the United Nations IPCC targets of 450ppm CO2 and 20C are far too high. The target must be to reduce atmospheric CO2 to 350ppm to maintain the safe Holocene environment, from the current level of over 400ppm. The longer the Earth stays within the higher temperature levels, the greater the probability of self-reinforcing feedbacks overwhelming any human mitigation attempts.

The inter-generational climate debt is already over 50ppm, rising each year that emissions are not drastically cut. Hansen proposed previously that cuts of 6% per year in carbon emissions, starting in 2013, together with the extraction of 100 petagrams of carbon (about 47 ppm) from the atmosphere, would be required to reduce CO2 levels to 350ppm by 2100. 100 petagrams of carbon is seen as a realistic limit for a “concerted global-scale effort to improve agricultural and forestry practices with carbon drawdown as a prime objective”. Hansen’s proposal took into account the fact that as atmospheric CO2 levels fall some CO2 will be released into the atmosphere by the oceans and plants.

As 6% annual emission reductions did not begin in 2013, greater amounts of atmospheric carbon removal will be required than can be achieved through improved agricultural and forestry practices alone. If emissions are reduced by 6% annually from 2021 onwards, an additional 53 petagrams of atmospheric carbon removal is required. At a 3% emissions reduction rate the required additional carbon removal increases to 137 petagrams. Spread over an 80-year timeframe, the annual cost would be up to $230 billion for 53 petagrams and up to $595 billion for 137 petagrams. The paper’s estimates do not take into account the effect of any feedbacks, such as releases of soil or permafrost carbon nor reduced Arctic albedo. Any such feedbacks would require increased levels of atmospheric carbon extraction, possibly very large increases.

The other two major greenhouse gases, methane and nitrous oxide, have been increasing at levels higher than assumed in the UN IPCC scenarios. Without changes in framing practices and reductions in fossil fuel extraction (especially coal mining and shale gas extraction) these gases may continue to increase, requiring even greater levels of atmospheric carbon extraction. Reductions would help reduce the amount of atmospheric carbon dioxide reductions.

Further delays in reducing emissions, and any delays in starting the negative emission activities, would rapidly increase the annual costs by increasing the amount of carbon and reducing the time available to remove it. Current country commitments do not envisage global carbon emissions peaking before 2030, let alone falling by 3% or 6% from 2021 onwards. The current international policy community assumption is of an overshoot of 450ppm followed by atmospheric carbon removal to return to the 450ppm level. If Hansen et. al. are correct, and the real safe level is 350ppm, there is the probability of a very late realization of this reality by the international community.

The costs and risks of the drastic measures that would then be required would be a severe burden to those alive at the time. This is a quite horrendous debt to be taken on by those in the present, requiring a very painful repayment by those in the future. That is, if the debt will be fully repayable before catastrophic climate change takes hold. Extremely risky emergency actions, such as large-scale albedo reduction via increased sulfate aerosol levels may then have to be taken as a last ditch option to avert the worst outcomes.

Perhaps there should be emissions debt “clock” located prominently in every capital city, stating the debt being rung up by the current generations for the future ones to pay. Each year it would increase by the amount that the required emission reduction rate had been missed.


[1] James Hansen et. al. (2017), Young People’s Burden: Requirement of Negative CO2 Emissions, Accessible at

[2] James Hansen et. al. (2017), Global Temperature in 2016, Columbia University. Accessible at

[3] American Geophysical Union (2014), NEW STUDY INDICATES LOSS OF WEST ANTARCTIC GLACIERS APPEARS UNSTOPPABLE, American Geophysical Union. Accessible at

[4] Kevin dennehy (2016), Losses of soil carbon under global warming might equal U.S. emissions, Yale News. Accessible at

[5] Lawrence Berkeley National Laboratory (2017), Soils could release much more carbon than expected as climate warms, Accessible at

[6] Wipneus (2017), PIOMAS Monthly Average Ice Volume, Wipneus. Accessible at

[7] Peter Wadhams (2016), The Global Impacts of Rapidly Disappearing Arctic Sea Ice, Yale Environment 360. Accessible at


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4 Responses to Young People’s Burden: Requirement of Negative CO2 Emissions

  1. Joe says:

    Rapid reductions in CO2 emissions will have the same consequences as rapid economic collapse from other causes, such as financial crisis, pandemic or war. The future generations you envision won't need to worry about the cost of negative emission activities, since that generation will not exist (except in tiny numbers).

    We are going to have economic collapse soon enough, whatever we do or don't do about our CO2 emissions, simply because there will soon come a time when the global economy cannot continue growing exponentially. When that happens, capitalism will collapse in financial disarray. Rapid reductions in fossil fuel use would accelerate the arrival of negative growth, and I'm all for it, but it will not save civilization nor the vast majority of the fathers and mothers of the future generation you are so concerned about.

    Just take a look at the exponential curves for population, resource consumption, and just about any other parameter of modern civilization on a chart with an x-axis of a few hundred years or so. The upward slope of this year's part of the curve is very close to vertical. When these curves roll over, the decline will be almost straight down. The chance for a soft landing was lost many years ago.

    CO2 concentration may rise for a few more years, but it will never reach 450 ppm from fossil fuel emissions; civilization won't last that long.

    • rboyd says:

      Capitalism has enough fossil fuels to keep going for a while yet, and it will keep going right up to the point that it no longer can. At the current rate we will hit 450ppm in the early 2030's, possibly earlier if we get natural emissions/reduced sink feedbacks kicking in. With an ice-free Arctic we could be in the runaway version of climate change within a couple of decades.

      Societies tend not to collapse in one big crisis, but go down in a step-fashion from one crisis to another with intervening periods of stability. I can see this happening, especially in the richer and "luckier" countries. People are good at getting used to a new lesser reality and then coping with it.

      There is a lot of fat in society that can be given up before full collapse sets in, so the quality of government is also very important. Do we give up the fat that is not needed, or defend it at the expense of long-term survival? Do we get "disaster capitalism" living off the decaying flesh of society or a managed descent?

      The mixture of local energy, climate and political dynamics will shape how well each country/region does.

      • Joe says:

        If there is indeed a period of fat-cutting-stairstep-descent after growth stops, your fears will likely be realized. I think, I hope, that the financial stresses caused by continuous recession will be too much for the market economy to cope with and will not allow such a "gradual" collapse.

        Coping with those financial stresses would require a world-wide debt reset, or jubilee, so that mass bankruptcy would not cause the "supply chain contagion" that David Korowicz describes so well. I doubt that there will be enough international cooperation to facilitate such a thing. I think that international conflict is more likely than careful management of an international financial crisis that would make 2008 look like a minor stumble.

        • rboyd says:

          Currently CO2e (including methane, nitrous oxide etc.) is increasing at 4 ppm per year. Even if a global crash (which is quite possible given the astonishing levels of debt) cut this in half, we would still be increasing at 2ppm per year.
          If the crash significantly reduced aerosols there would be a pretty much immediate warming (sulfate aerosols only stay in the atmosphere for a few days). Add in albedo, increased natural emissions, and we are still rapidly warming.

          A financial crash would also cripple the financing of new energy initiatives and focus the government on the short-term issues of unemployment, collapsing tax revenues etc.
          We would end up at a lower level of output (like in the 1930's) but still with enough activity to drive warming. Some form of short-term recovery may be triggered as fossil fuel prices will have crashed.

          We are already so far along, above 400ppm (close to 500ppm Co2e) that even an economic crash would only slow things down a bit.


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