What 2 Degrees Looks Like

November 17, 2019

Robbie Andrew at CICERO:

We have a big challenge ahead of us if we are to hold global warming to under 2°C. This is largely because we have already used up most of our collective ‘carbon budget’.

The amount that global temperatures rise under global warming is very closely related to how much carbon dioxide (CO2) and other greenhouse gases we emit to the atmosphere, and this defines our ‘budget’, or the limit of much we can emit.

In the animation above, our CO2 emissions are shown in red, while the accumulated total emissions since 1850 are shown in grey. While reducing our annual emissions is critical, it is insufficient: we must in fact reduce annual emissions to zero so that the accumulated emissions stop increasing.

You might think of annual emissions as drops of water (or your favourite liquid fossil fuel) falling into a glass, and accumulated emissions as the amount that’s in the glass. What we’ve been doing for most of history is increasing the rate at which those drops fall into the glass, filling it up faster: accelerating. If we simply stop accelerating, and add drops at a steady rate, then we’re still going to fill up that glass. We actually have to stop adding water for the water level to stabilise.

Likewise, stabilising global emissions doesn’t solve the climate problem. We actually have to stop emitting.

In the future I have represented above – one that might hold temperature rise below 2°C – our annual emissions drop to zero in the year 2069, and at that point we finally see a peak in the accumulated emissions, which thereafter decline as we actually remove more CO2 from the atmosphere than we add to it.

But of course our annual emissions don’t drop to zero in this future: they drop substantially, but not to zero, and the remaining, intransigent emissions must be offset by so-called ‘negative’ emissions. This recognises the likelihood that there will be many sources of emissions that we will not be able to turn off before the end of the century, especially in developing countries and in agriculture.

Because of these residual emissions, we will need to introduce substantial negative emissions: removing CO2from the atmosphere. When we reach net-zero in this scenario, there will be emissions of CO2 in some parts of the world and removals of CO2 in others, and at some point the two will balance out so that our ‘net’ emissions across the globe are zero.

At that point of balance between positive and negative emissions, the accumulated emissions will stop rising. If we continue to mitigate positive emissions and to increase negative emissions then we will turn the accumulation curve around and go into reverse: we may actually start to reduce global warming rather than ‘merely’ putting a stop to its rise.

Why would we want to go into reverse? One reason is that we may not be able to reduce our emissions fast enough, and we may overshoot our target of 2°C, in which case we have to back up. Another reason is that we may decide that 2°C, while a useful target through the 21st century, isn’t necessary where we want to remain, and that less warming is better.

14 Responses to “What 2 Degrees Looks Like”

  1. MorinMoss Says:

    Pretty much what I’ve been telling anyone who’ll listen – and more than a few who won’t – since the turn of this century.

    Except whatever happened to the 1.5 degree target?
    We’ve moved the goalposts and will STILL fail.

  2. indy222 Says:

    …just another overly mild-i-fied accounting. Those IPCC AR5 carbon budgets are missing vast new science showing things are MUCH worse. Everybody loves carbon budgets because they make your agenda easy to compute if your a policy guy or a get-rich-off-environmental-disaster greenwashing guy. So without any exception I can find, all these econ-types use them, knowing as they professionally must, just how politically manipulated by the UN IPCC process they were from the start, and how scientifically indefensible they are today. ECS is 5C, not 3C, the permafrost DOES melt, soil carbon loss DOES go up with temperature, etc etc etc.

    “We have to stop adding water for the water to stabilize” this CICERO guy says… HA! Even if we stopped ALL human CO2 emissions, temperatures would STILL continue to go up because of the indirect sources we’ve now triggered. And are global CO2 emissions even staying just level? NO, they’re going UP 2% a year the past 3 years now, matching their prior levels before the ’16 China and global almost-recession period. Look at EIA data – only global recessions lead to year-over-year CO2 emissions reductions. https://www.iea.org/statistics/co2emissions/

    Energy use per capita continues to relentlessly rise https://data.worldbank.org/indicator/EG.USE.PCAP.KG.OE averaging 1.1%/year with no bending in sight.

    • doldrom Says:

      The IPCC tends to ignore the possibilities of positive feed backs. Negative emissions are premised on energy abundance (if releasing CO² is exothermic, binding it is going to be endothermic). But there is every possibility that the impacts of climate change (and other aspects of resource depletion) might actually impinge on our possibilities to ramp up renewable energy sources. Futurists almost always assume that we will magically have cheap and abundant energy in the future.

      • indy222 Says:

        Economics has mostly been a field developed during the times of vast cheap energy and it doesn’t even enter their most important (supposedly) equations (Cobb-Douglas). It’s utterly taken for granted. As if there some “substitution” possible for energy! Econo-physics people and Tim Garrett especially, are showing more insightful reformulations of economics. Speaking of the ludicrous nature of economicsts … did you see this from conservative economist William Nordhaus


        “+4C is optimum for global economies” ??!! At his Nobel acceptance speech, no less (!). Words fail to express the Monty Python’esque denial we’re being subjected to. Why wasn’t he yanked from the stage and his ill-gotten Nobel Prize (economics Nobel’s are decided not by the Swedish Academy of Sciences – they generally do a good job for the sciences and Peac), but by the notorious Swedish Central Bank. The real question is – why does the Nobel foundation allow their name to be associated with these prizes? There must be a lotta money changing hands under the table to get that prestige. Money talks, truth takes the short end of the stick.

        • jimbills Says:

          I saw the Nordhaus thing. Just amazing. It shows a real weakness in the sciences (allowing a generous view that economics is a science) that the highly specialized have little to no knowledge of the areas beyond their own expertise. It allows someone like Nordhaus to believe something so insane as a +4C optimum.

          • Keith Omelvena Says:

            Insane? Absolutely. Economics has evolved from a simple measurement of human activity, in order to benefit those living in the human community, to some sort of hideous, all consuming monster, that humans must serve and the natural world must be sacrificed for. Repeat the mantra. Grooowth, grooooowth. Now go shopping and forget the approaching Mad Max future.

        • rhymeswithgoalie Says:

          In a world where Donald J. Trump is President of the United States, the Nordhaus nonsense seems to fit.

  3. It is certainly much easier and cheaper to avoid emitting than it is to achieve negative emissions, so we shouldn’t bank too much on negative emissions technologies (NETs). Here’s a summary of 2018 National Academy of Sciences report on NETs, which helps identify the promising avenues for removing CO2 from the air:

    Click to access Negative%20Emissions%20Technologies.pdf

    It puts the lie to those like Bill Gates who say that we just aren’t funding enough R&D to solve the problem. There’s a ton of research effort going into making these and other low-emissions technologies work. But they aren’t being practiced at the scale needed, since they’re pretty much guaranteed losers from a financial perspective, or at least they’re relative losers to just continuing business as usual.

    So finding a way to bring the best of these technologies to scale, where they make sense, is where the effort is needed. A tax on fossil-based carbon would definitely help get things moving.

    • rhymeswithgoalie Says:

      Based on corporate and oil-producer politics, implementing the economic penalty mechanism of a carbon tax/tariff will be resisted and slowed at every step of the way.

      My only hope is that the technical race for better grid-level storage and control standards, which are positive incentives economically, will accelerate the adoption of green energy sources worldwide. That is, I’m betting on that aspect of competitive greed which is in alignment with our ecological interests will overtake the interests in perpetuating the war-promoting petroleum industry.

      Keep a lookout for the response to the Aramco IPO.

  4. J4Zonian Says:

    Of course it’s much more serious than this, and we need to convince people of that or there will be no revolution, which is the only way to change our direction and speed.

    The first 5 of at least 20 reasons:

    1. Underestimation of damage at each temperature level;
    2. The pipeline—the approximately 40 years that GHGs already emitted take to reach their full warming effect;
    3. Aerosols—pollutants hiding 0.5 to 1°C warming already built in, ie, unavoidable;
    4. The carbon cost of necessary new infrastructure;
    5. Tipping points, both internal to processes like ice melt, and external ones, like ice melt. Both include some that can cause abrupt shifts in the state of what’s changing.

    See more at this comment and the one above it: https://grist.org/article/600-environmental-orgs-say-this-is-what-they-want-in-a-green-new-deal/#comment-4289641621

    • rhymeswithgoalie Says:

      8. diversion of resources to adaptation and increasing disasters, eroding our ability to deploy solutions;

      This is not only a money problem, but a news cycle distraction problem: Disasters are much sexier than discussing funding and buildout of new infrastructure.

  5. rhymeswithgoalie Says:

    There is a temperature threshold for overall global temperature increase, yet we know that the arctic is warming much faster. So, if Dr. Anton Vaks says 1.5°C warming is the approximate tipping point for runaway permafrost melt, does that mean the local arctic temperature increase or the total atmosphere temperature increase?

    If the former, then we should be past that tipping point in the arctic. In any case, there are now permafrost-melt-triggered avalanches in the Alps.

  6. rabiddoomsayer Says:

    So if we hold CO2 to today’s level then we will get Eemian temperatures. But the Eemian CO2 topped out at about 300 ppm, that would suggest our budget was reached over 100 years ago.

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