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The Critical Decade - Part 3: Implications for Emissions Reductions

Posted on 11 June 2011 by dana1981

The Australian government established a Climate Commission which recently released a three chapter report entitled The Critical Decade.  In Part 1, we examined Chapter 1 of the report, which summarizes the current state of climate science observational data.  In Part 2, we examined Chapter 2, which discussed the risks associated with a changing climate.  In Part 3, we will examine Chapter 3, which looks at the implications of the science on carbon emissions reductions.  The quotes and bullets below come directly from the report, while the remainder is our commentary.

The Budget Approach

Because of the long atmospheric lifetime of carbon dioxide (CO2), the total amount of carbon emitted matters more than when it is emitted.  Thus the report recommends examining the issue by using a budget approach, wherein a certain budget of CO2 emissions corresponds to a certain amount of eventual global warming.

  • The budget approach directly links the projected rise in temperature to the aggregated global emissions in Gt CO2 or Gt C for a specified period, usually 2000 to 2050 or 2100. For example, humanity can emit not more than 1 trillion tonnes of CO2 between 2000 and 2050 to have a probability of about 75% of limiting temperature rise to 2°C or less.
  • Given an overall carbon budget between 2000 and 2050, the approach does not stipulate any particular trajectory, so long as the overall budget is respected.  This allows a strategy that delivers least cost to the economy over time in making the transition to a low- or no-carbon economy.

According to the latest data, between 2000 and 2010 we emitted approximately 300 billion tons (gigatons, or Gt) CO2, so after 20% of the allotted timeframe, we're already over 30% of the way through the allotted emissions.  Not a good start.  However, although we're running out of time to reduce our emissions, the good news is that we're not out of time  yet. 

Once nice aspect of the budget approach is that as long as we're still below the allotted emissions, we still have a chance to achieve the budgetary goal.  The figure below, taken from the report, shows that if we implement serious carbon emissions reductions policies soon and achieve a global emissions peak by about 2020, we can realistically meet the 1 trillion ton emissions budget by 2050.  However, in a scenario without serious carbon reduction policies in place, we're looking at a potentially catastrophic warming of 4°C or more by 2100.

Fig 36

Implications for Emissions Reductions Trajectories

The report proceeds to discuss the fact that since we have already burned through over 30% of our allotted emissions by 2050, we're running out of wiggle room and need to act immediately.

  • Reducing emissions of CO2 does not reduce or stabilise its concentrations in the atmosphere; it slows the rate of increase of CO2 concentration.  To stabilise the concentration of CO2 requires emissions to be reduced to very near zero.
  • The peaking year for emissions is very important for the rate of reduction thereafter.  The decade between now and 2020 is critical.
  • Targets and timetables are, in principle, less important in the budget approach, but the urgency of bending emission trajectories downwards this decade implies that more ambitious targets for 2020 are critical in preventing delays in the transition to a low- or no-carbon economy.

The chapter discusses the fact that although the budgetary approach gives us a good degree of flexibility, the longer we wait to take serious emissions reductions steps, the steeper the global carbon emissions cuts will have to be:

Fig 37

Eventually if we wait too long, we will reach a point where the necessary annual emissions cuts are simply beyond our political and technological capabilities.  This point is fast approaching, which is why it's so critical to start implementing serious climate policy immediately.

Relationship Between Fossil and Biological Carbon Emissions and Uptake

The report goes on to discuss the nature of different types of carbon offsets.  Some offsets are sold as an equivalent amount of carbon uptake by ecological systems (i.e. funding the planting of trees, which absorb a certain amount of carbon).  However, the report discusses that in the long run, these ecological systems are not as effective as direct emissions reductions because they don't represent permanent sequestration, and "the offset approach, if poorly implemented, has the potential to lock in more severe climate change for the future."

  • About 15-20% of net CO2 emissions globally have originated from land ecosystems, primarily from deforestation. This represents the removal of carbon from a stock in the active atmosphere-land-ocean carbon cycle. It does not introduce any additional carbon into the atmosphere-land-ocean system, but simply redistributes it.
  • The combustion of fossil fuels represents the injection of additional carbon from an inert, underground stock into the active atmosphere-land-ocean cycle. This additional carbon is redistributed among the three main stocks in the active carbon cycle, thus adding to the amount of atmospheric CO2.
  • Avoiding emissions by protecting ecosystem carbon stocks is a necessary part of a comprehensive approach to mitigation. Sequestering CO2 into degraded ecosystems is also an important mitigation activity because it reverses an earlier emission. However, sequestering CO2 into land ecosystems does not remove it from the active atmosphere-land-ocean cycle. Therefore, the sequestered carbon is vulnerable to human land use and management, which can rapidly deplete carbon stocks, and to major changes in environmental conditions, which can change the amount of carbon stored in the long term.
  • The only way that CO2 sequestered into land ecosystems can permanently “offset” fossil fuel combustion is if the sequestered carbon is subsequently removed from the land ecosystem and stored in an inert state or in a stable geological formation, thus locked away from the active atmosphere-land-ocean cycle. Another approach to offsetting is to replace fossil fuels with biofuels.

The key message here is that the most effective way to reduce CO2 emissions is to leave fossil fuels in the ground.  While reforestation is very important, using it as an excuse to reduce fossil fuel-related emissions less quickly is a mistake.  We need to do both.


In short, the scientific evidence discussed in the report indicates that we need to take significant steps to reduce global carbon emissions immediately.  One decade into the 21st Century, we're already one-third of the way to the carbon emissions we're allotted by mid-century if we're to be confident we can limit global warming to 2°C, and as has recently been in the news, even that level of warming may be too high. Yet instead of cutting emissions, last year saw a new record high in human CO2 emissions.  We're headed in the wrong direction, and need to reverse course immediately.

I'll leave the last word for the Climate Commission, because I think they did an excellent job summarizing the state of affairs in the report's final paragraph:

"As you’ve read in this report, we know beyond reasonable doubt that the world is warming and that human emissions of greenhouse gases are the primary cause. The impacts of climate change are already being felt in Australia and around the world with less than 1 degree of warming globally. The risks of future climate change – to our economy, society and environment – are serious, and grow rapidly with each degree of further temperature rise. Minimising these risks requires rapid, deep and ongoing reductions to global greenhouse gas emissions. We must begin now if we are to decarbonise our economy and move to clean energy sources by 2050. This decade is the critical decade."

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Comments 1 to 10:

  1. Important data, in a form that is easy to communicate. Great post, Dana.
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  2. One thing that perplexes me about the second diagram is the elevated end point for the 2011 start. By eye, each curve has the same area underneath it. That means each strategy uses the full permissible Carbon budget by 2050, but that in turn will mean the early start/ slower reduction approach will need to cease all remaining production instantly in 2050. Presumably a better approach would to be to have slightly higher initial reductions and to reach zero emissions some time after 2050. In that case the rate of reduction for a 2011 start will be higher than 3.7%, but still less than 5.3%.
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  3. There is an extremely simple way of reaching the goals of a budget policy : it is to forbid the exploitation of all non-conventional resources, deep off-shore, tar sands , shale oils and gas, methane hydrates, liquefied coal, and so forth...., and even the search and exploitation of new conventional resources.

    There is absolutely nothing to do : just forbid companies to go there. No drilling, no administrative permits - just - forbidden, like in Antarctica. Don't go there .

    It is absolutely impossible to extract them without extremely sophisticated techniques , mastered only by western companies, and many of these resources are located in democratic, industrialized countries : US, Canada, Japan, Europe ... no real political difficulty in applying these interdictions.

    and there are only very weak economic consequences, since most of these resources have hardly begun to be exploited - and for most of them not at all. Only Athabasca tar sands are really extracted, with a modest rate (less than 2 Mbl/j) that does not really contribute to GHG emissions - not a problem to lower gradually their extraction and close them in some decades.

    Forbidding the extraction would avoid to do ANY effort to persuade people to lower their consumption. It is much more, infinitely more simple to control a handful of companies than billions of people. The law of supply and demand would assure a growing price of fossil fuels and a natural switch to other alternatives - quite naturally. There is no need for sequestration, carbon market, and other awful sophisticated things. And contrary to demand policies, the result is 100 % certain.

    The only question is : why does nobody claim for such a simple measure ?
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  4. #3: Being a scientist and not a politician, I can't answer your last question, but I like the proposal otherwise! I suspect that there are savoury and unsavoury political reasons why this happens, as well as insufficient political pressure to move away from fossil fuels (see Obama's flip-flopping on it). As we move into the first significant decade of climate consequences, maybe those pressures will change. We're already seeing some renewables prices lower towards some FF prices, so maybe part of the solution is undeway.
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  5. okatiniko #3, that is a worthwhile thought exercise. The simple answer comes from the history of the oil industry (wikipedia). Oil and gas were exploited relatively extensively in the far east 1000 or more years ago. That spread to Asia, particularly Russia. The U.S. took over in the 20th century but various countries that we once dominated have now nationalized their industries. We still have varying degrees of geopolitical influence in oil and energy although that is increasing challenged by China and other countries.

    The question you raise is not technological. You imply that we should not invent new techniques, but it is impossible to not invent or uninvent when the market demands the product. You also point out the great expense involved, but even with the government "subsidies" (which are mostly just a temporary alleviation of high taxes), the market has no problem providing the financing. I would point out that China has oodles of money, strong science and technology, and a large manufacturing sector to feed the energy to.

    The answer is therefore, geopolitical, but also very much dependent on the economic policies of various countries independent of the environmental considerations. My suggestion is to start here because it is in the context of trade agreements where your suggestions have the best chance of being implemented.
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  6. I understand the point that it's not too late yet. However, given the economic growth rates in developing countries and community expectations that goes with that, it's difficult to conceive of them being able to cut emissions and maintain civil order. Even in developed countries where carbon emissions aren't increasing to the same extent (but still increasing) it will be very difficult politically to stabilise let alone reduce emissions.

    I remain hopeful but not optimistic. And I'm generally an optimist. I see very difficult times ahead for the world as a whole.
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  7. "I remain hopeful but not optimistic. And I'm generally an optimist. I see very difficult times ahead for the world as a whole."
    I feel exactly the same way, sout.
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  8. sout and dana... The most encouraging news that I hear is always in relation to the cost of solar. If projections hold true and they can get the cost of solar below the cost of coal... we have a fighting chance. That could easily tip the scales in a very significant way.

    If the solar industry can prove they can bring cost down like this, with the possibility of driving costs even below that... it's literally a game changer. Investment dollars are not going to go into new coal, gas or any other fossil fuel related energy. Who wants to put money into the old technology that is likely to not be anywhere close to competitive once the plants are built? The same could easily play out for nuclear as well.

    Once we get the two cost curves to cross (rising FF, falling solar) that will be the tipping point where big changes start taking place.

    Just hoping it happens soon!
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  9. Evidently my last has been "moderated". Here is the actual letter I have sent to Prof. Steffen:
    Dear Professor Steffen
    There is a basic fallacy throughout the discussion in Chapter Three of The Critical Decade of the so-called carbon budget, and that is the

    (-imputation of fraud and scientific misconduct snipped-)

    confusion there between gross emissions of CO2 and net additions to the atmospheric concentration of CO2. This procedure enabled your report to claim that “In the first nine years of the period (2000 through 2008), humanity emitted 305 Gt of CO2, over 30% of the total budget in less than 20% of the time period.” Your budget to 2050 of one trillion tonnes of CO2 apparently assumes that as has since 1958 been the case, on average only 45% or so of gross emissions remain aloft (Knorr, GRL, 2009). Thus in truth less than 15% of your “budget” had been used up by 2008, which is less than the 20% of the time period.
    I hope you and the Climate Commission will correct this gross error with as much publicity as in its original release of The Critical Decade.
    By the way, I note your report cites Meinshausen et al 2009 as the source for this very misleading budget approach. My attached published Note showed how they

    (-imputation of fraud and scientific misconduct snipped-)

    assumed 100% retention of emissions in the atmosphere.

    [Tim Curtin]
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    [DB] Please note that posting comments here at SkS is a privilege, not a right.  This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Please take the time to review the policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter.

  10. @#3 - There is enough capacity in coal alone to send us well over the budget. While I'm actually a fan of your suggestion, it would need to be complemented by some very strict controls on how much coal we could exploit. Oil and gas are ultimately more useful than coal, so it would be best to leave the vast majority of the remaining coal and non-conventionals (which often have lower EROEI anyway) in the ground while still being able to use quite a lot of oil and gas.

    @#8 - Yes, getting the costs of renewables below those of coal is a crucial goal, which can be helped with a decent price on carbon (as well as other means) that reflects something of the true costs associated with burning fossil fuels.
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