Gaius Publius: New Study Evaluates Climate Models — Best Ones Also Show the Most Global Warming

By Gaius Publius, a professional writer living on the West Coast of the United States and frequent contributor to DownWithTyranny, digby, Truthout, and Naked Capitalism. Follow him on Twitter @Gaius_Publius, Tumblr and Facebook. GP article archive here. Originally published at DownWithTyranny

“Climate models that simulate the current climate the best [also] tend to project the most global warming.” See text below for explanation of the chart.

This is a climate story with two pieces.

The first piece is the by-now-obvious “Everything’s happening faster than anyone thought it would” observation, of which the immediate corollary is, “OMG we’re still screwed.”

It’s true that everything is happening faster than anyone thought it would (anyone who had a prominent public voice, that is). This part of the story is, as noted above, “by now obvious.” Changes are happening a lot faster — big storms are more frequent than anticipated, even by those who anticipated them; wildfires are burning hotter and later in the season (December?!) than even those who predicted more and hotter wildfires; and the cost to insurance companies of climate-caused damage is rising faster than insurance companies anticipated— and anticipating increasing costs is their whole business model.

But those of us without power have already gotten that message. The real resistance to that message is among people who do have power, but also have money to protect from that message as well.

The second piece of this story is much more interesting — it’s about how the message we all understand to be true is now supported. A group of climate scientists have published a paper (subscription required) that puts statistical data round the observation that things are happening faster than most models predict.

In other words, they’re analyzing the models statistically in order to see which models are making the best predictions. Instead of waiting for events to prove which climate models (projections) ended up being right because events proved them right, this study looks at models and figures out ahead of time which ones are most likely to “get it right” in advance of the observational data.

In other other words, all models are not created equal, so taking the average of a large set of models tells us less that looking at the best models first. The study attempts to identify those models.

How did the researchers test which models were best? They looked for models that made the most accurate statements in the past about the earth’s energy imbalance — models that most correctly anticipated the difference between energy-in (from the sun) and energy-out (radiation of that energy back into space).

Our whole problem is that difference — too much energy-in relative to energy-out, and the planet heats. So models that made predictions about the energy imbalance that turned out to be right are likely to be right about the effects of that imbalance, such as the amount of increased global warming.

From the website of the lead researcher, Patrick Brown:

The study addresses one of the key questions in climate science: How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases?

One strategy for attempting to answer this question is to use mathematical models of the global climate system called global climate models. Basically, you can simulate an increase in greenhouse gas concentrations in a climate model and have it calculate, based on our best physical understanding of the climate system, how much the planet should warm. There are somewhere between 30 and 40 prominent global climate models and they all project different amounts of global warming for given change in greenhouse gas concentrations. Different models project different amounts of warming primarily because there is not a consensus on how to best model many key aspects of the climate system.

To be more specific, if we were to assume that humans will continue to increases greenhouse gas emissions substantially throughout the 21st century (the RCP8.5 future emissions scenario), climate models tell us that we can expect anywhere from about 3.2°C to 5.9°C (5.8°F to 10.6°F) of global warming above pre-industrial levels by 2100. This means that for identical changes in greenhouse gas concentrations (more technically, identical changes in radiative forcing), climate models simulate a range of global warming that differs by almost a factor of 2.

The primary goal of our study was to narrow this range of model uncertainty and to assess whether the upper or lower end of the range is more likely.

RCP8.5 is the IPCC’s worst-case climate scenario; it’s roughly the same as “business as usual” forever with respect to emissions. It’s the red line in the chart below:

The IPCC’s four “representative concentration pathways” or RCP (source). The red line is RCP8.5. These four scenarios represent four “stories” of future concentration of greenhouse gases in the atmosphere, not outcomes or results in the form of warming itself. That’s what the models do.

Back to Brown (my emphasis):

So, what variables are most appropriate to use to evaluate climate models in this context? Global warming is fundamentally a result of a global energy imbalance at the top of the atmosphere so we chose to assess models in their ability to simulate various aspects of the Earth’s top-of-atmosphere energy budget. We used three variables in particular: reflected solar radiation, outgoing infrared radiation, and the net energy balance. Also, we used three attributes of these variables: their average (AKA climatological) values, the average magnitude of their seasonal variability and the average magnitude of their month-to-month variability. These three variables and three attributes combine to make nine features of the climate system that we used to evaluate the climate models (see below for more information on our decision to use these nine features).

And the finding:

We found that that there is indeed a relationship between the way that climate models simulate these nine features over the recent past, and how much warming they simulate in the future. Importantly, models that match observations the best over the recent past, tend to simulate more 21st-century warming than the average model. This indicates that we should expect greater warming than previously calculated for any given emissions scenario, or it means that we need to reduce greenhouse gas emissions more than previously thought to achieve any given temperature stabilization target.

In even plainer English, those models that best represented the energy imbalance were also the models that projected the greatest future warming.

The RCP8.5 Example

Brown has an extended discussion of the models that use RCP8.5 as a base from which to predict warming, which is explained by the chart above, taken from the paper linked earlier. So let’s take a look at that chart and what it tells us.

First, note the “envelope” starting around 2015 that surrounds the red line and the blue dashed line. Together these show the range of predictions for the RCP8.5 emissions scenario for every model studied. Quite a range.

Next, ignore the difference between the blue part of the data envelope and the purple part. That’s not relevant to the point made here. Look instead at the very thin pink sliver that sits on top of the entire envelope; it’s labeled “Observationally-informed projections.” Models in this sliver “got it right” in the past with respect to the earth’s energy imbalance.

What this paper is saying is that, if we stay on the RCP8.5 business-as-usual emissions path, the best models predict (a) a very narrow rangeof warming outcomes, and (b) the worst warming outcomes.

Why This Matters

This matters for two reasons. One, it adds to the certainty that we’re cooking the planet — a truly serious matter. But two, it also gives a science answer to the warming deniers’ and delayers’ counter charge, “But look at the uncertainty. Look at the range of predictions. These models are all over the place. How can you trust them?”

This important paper shows that that “range of predictions” can be narrowed considerable, from a broad fat funnel of outcomes to a tiny, toothpick-wide sliver of them. Goodbye “uncertainty.”

Print Friendly, PDF & Email


  1. The Rev Kev

    Those forecast are grim for where we live and it looks like that my area will be copping a flogging. If I was young, I would be considering building something like a southwest adobe home with real thick walls and thick tile floors or, if push came to shove, something along the lines of a hobbit house. If you are wondering about such outlandish choices, it is because they will be proof against extreme heat but without requiring energy to do so which may or may not be available down the track at a reasonable price. Passive designs in other words.
    However much we have the same ratbags denying global warming, I am willing to bet that when it come to cold harsh cash, that corporations tend to be true believers. Here I am thinking of the insurance industry who would find it critical for their profits to get the forecasts right. Somebody will have to underwrite the increasing costs of damaging events caused by global warming and no government will be able to afford all the sky high costs involved. How much real estate is tied up in a canal home development for example as the warming, expanding oceans rise? You can bet that the people there will demand either massive flood mitigation projects or to be bought out at full value of their soon-to-be-submerged homes.
    I would expect governments to come up with some multi-billion dollar schemes to protect poor people near the coast but whose resources will instead be directed to places like the Hamptons. If this sounds unlikely, remember then that after 9/11 the US government put billions of dollars into rebuilding what had been destroyed but that a big chunk of this cash was diverted elsewhere to luxury developments. On a local front – I have family members who think that climate change is some sort of ‘lefty plot’ but the evidence is there now if you want to see it and it is damning. I, for one, refuse to listen to the deniers. Not this little black duck!

    1. Samuel Conner

      Tangentially related — passive-solar “stabilised earth” structures with thick high thermal inertia walls are attractive even now from the perspective of heating/cooling costs. They can be constructed by teams of medium skilled people overseen by a competent builder, or even by a hardy solitary DIY-er with lots of time on his hands. This looks to me like a no-brainer two-fer to employ under-utilized labor and provide housing, sort of an alternative-materials Habitat for Humanity concept.

      Does anyone know of anything like this anywhere in US? I’m guessing that there are local regulatory hurdles to implementation of unfamiliar construction methods.

      1. Adam Eran

        Building standards will depend on the locals. There are plenty of straw bale predecessors to inform even regulators that want to authorize only “experimental” building.

        As someone who has lived in a passive solar house in California’s central valley, I can testify that a) they are very comfortable and quiet. The whooshing of central heating / air conditioning is gone. b) the cheapest way to build one costs roughly 20% more than standard California construction. This can be anything from straw bale to styrofoam to standard insulation more thickly applied (try blown in cellulose in the walls with 2 x 6 studs).

        Cheapest: Even adding to current insulation in your current dwelling is often an added comfort.

        Water conservation is next.

        I’d also recommend checking out permaculture. Geoff Lawton’s positively inspiring Greening the Desert is a nice intro.

  2. Paul P

    What I don’t understand is the purported ability to stabilize the
    climate with carbon reducing interventions. With the arctic and antarctic melting at 400 ppm of carbon in the atmosphere at present, how can stabilization occur without removing carbon from the atmosphere? The carbon now in the atmosphere is going to be there for a long time, even were we to bring human emissions to zero. And, nature will soon, if it hasn’t already, start adding carbon to the atmosphere outside the normal carbon cycle.

    1. tony

      Wishful thinking, I suppose. Carbon removal is in no way economically viable in the scale needed. We can pretend we intend to reduce carbon emissions and the recessions can be used as evidence that we are doing something.

    2. Jabawocky

      Man made carbon emissions account for roughly 10% of carbon added to the atmosphere every year. The flux of carbon to and from the atmosphere is large, even in the absence of man made emissions. Thus stopping emissions can still help, although I’m not clear exactly how much.

      1. pretzelattack

        but the climate was in balance, it’s the extra emissions that are causing it to change, from what i understand. we should be cooling, slightly.

  3. paul

    As agnostic in this area, do these models explain ice ages?

    I grew up cowed by that idea returning.

    The mere fact that the fate of the planet was entrusted to an oil made man (maurice strong) and an indian railway economist who, while not providing hands on advice to his female staff, found time to write a few soft porn novels and create for profit organisations while the fireball was accelerating, suggests a wonder pill to occlude the chemical degradation of the planet is not going to work.

    1. Jim Haygood

      Do these models explain ice ages?

      Nope, they’re one-way linear, with no provision for reversals, and moreover fitted to very recent data.

      It’s rather like fitting the Dow Industrials index for the past 12 months (it rose in every one), and concluding that its 25% annual rise is likely to accelerate to 30 or 35% in coming years.

      Global warming of the markets is creating new billionaires as we speak. :-)

      1. paul

        surely that’s not possible?
        A ski slope on one side and rubble behind?
        mmm. that’s good scientifying

      2. DJG

        Nice try, Jim, but you didn’t read the article. First, the article quotes Patrick Brown mentioning pre-industrial levels. Researchers make estimates, which then go into modeling, based on ice cores, trapped air, and other samples. Typically, the research on CO2 levels includes data that go back into the nineteenth century.

        There was even a study that showed CO2 rises due to the amount of industrialization and burning of wood during the Roman Empire.

        Second, all of these models and studies are by scientists fully aware of the atmospheric parts-per-million data out of Hawaii. These data go back to the mid-1940s.

        Science isn’t the stock market.

        1. paul

          What do the ice cores tell us about ice ages and their causes?
          Was there a drought of co2?
          What do the ice cores tell us about the temperate period and its causes?
          I am not being glib, but while I am asked to accept AGW, I would like to know about NAGW as described in the ice cores.

          1. SKM

            Read Peter Wadhams”Farewell to Ice” (a must read) Then read David Wasdell`s work based on empirical data about how the planet has behaved in the deep past (easy to find on the net)
            What staggers me is that people referred to as climate scientists end up relying on results from computer generated models that to be useful would have to be fed with exhaustive, accurate data about how the atmosphere behaves (yet no-one claims we have a full understanding of this latter). Prof Wadhams actually shows how data he acquired through direct measurements and field studies are deliberately ignored by the modellers. This when field observations diverge from model predictions,and by large factors. The other mystery to me is how any climate scientist can maintain that with already c400 ppm in the atmosphere, there can be any hope left of keeping to EVEN 2 degrees C above pre-ind levels, when the planet has NOT YET by any means come to the equilibrium corresponding to 400ppm – data based on past planetary behavior suggest average surface temperatures that correspond to 400ppm are likely to be way higher than 2 degrees above pre-industrial levels

            It looks as if we should have started reducing emissions rapidly in the 1980s to have had any hope of stopping the now beginning to run out of control positive feedback mechanisms that as a non-climate scientist I started to really worry about before that decade was out…..

            I just wish the science community wouldn`t behave like our political leaders and get real about where we`ve collectively got ourselves. They need to stop talking about the end of the century and stop pretending that even if we held the C in the air at current levels, the planet WILL WARM more than 2 degrees. We`re on a PLANET for God`s sake, so huge inertia, but once it gets rolling in bad (ie incompatible with human civilisation) direction humans cannot stop it in a handful of years, if ever……

            1. pretzelattack

              the science isn’t based on models. we can’t stop the warming already in the system, but we can mitigate it.

        2. Paul P

          The carbon in the atmosphere is from measurement, not modeling. See, the Keeling Curve. Older measurements come from ice and sediment cores. That carbon traps heat energy is basic physics or chemistry and his been known since the 19th Century. Pre-industrial levels of carbon are known from measurements as are current levels.

          With regard to the accuracy of modeling:

          There is a consensus among the world’s climate scientists, the Academy of Sciences of numerous nations, and numerous scientific organizations that the earth is warming.

          The scientific debate about whether burning of fossil fuels is
          changing the climate is over and has been for over 20 years.
          That this is not known widely is do to MSM and energy industry
          propaganda and influence.

      3. Jabawocky

        This is nonsense, they can describe any ice age as long as the driving variables can be appropriately measured or reasonably estimated.

    2. Jeremy Grimm

      I recall reading that past climate shifts like the ice ages resulted from ‘stochastic resonance’ where a small signal — the increasing or decreasing insolation due to the eccentricity of the Earth’s orbit as well as internal cycles in the sun slowly accumulated heat to or shed heat from the Earth. Denialists often point out that the increases in CO2 lagged the increases in temperature. I believe the change in temperatures resulted in changes in the CO2 cycles which locked in the small increments or decrements in temperature. Humans have been dumping large quantities of CO2 into the atmosphere in their own CO2 cycle resulting in an increase in temperature independent of the stochastic resonance effects.

      Ice age? Yes we could see an ice age result from the increased temperature of the Earth. It depends on the gulf stream. There are indications that the gulf stream is slowing. However, the rate of change is small and we know too little to determine whether the gulf stream will shut down.

      The models in this post can only model known effects. Much remains unknown. I view the models of past climate change combined with models of what we know as the best predictor for future climate. In the past changes occurred extremely rapidly — on the order of a few years and the sea level rose much more than current models predict. So you can remain agnostic about particular predictions for the Climte Disruption coming to an area near you but remaining agnostic that a major Climate Disruption is coming and coming soon is not a good idea.

    3. Kilgore Trout

      Very long term climate change–into and out of ice ages–is the result of changes in our planet’s orbital path (eccentricity), wobble, and tilt, collectively known as the Milankovitch Cycles, after the Russian mathematician who figured them out. These changes coincide and reinforce each other in different ways over cycles of from 20,000 to 100,000 years, and can kick-start the planet into or out of a cooling phase. The current man-made warming is over-riding what otherwise would be an interglacial period of gradual cooling leading (it is thought) to a relatively sudden shift (2 decades?) to a new ice age within one or two thousand (?) years.

      1. drumlin woodchuckles

        That has been my understanding of “why weren’t the returning-Ice-Age predictions correct”? People say that and laugh and say, those predictions were wrong, so are these predictions.

        But the predictions weren’t “wrong”. They were overtaken by events. Enough airborne CO2, nitrogen oxides, methane, have been added to the atmosphere to trap enough heat to overbalance the predicted cooling.

        Here is an interview from a climatologist from those days predicting the upcoming Frosty Chill Age.

        1. Kilgore Trout

          Even in the 1970s, I think Bryson was something of an outlier. Though the mainstream media caught the buzz, as a famous Newsweek cover hyping a new ice age is now an article of faith among deniers. But there was already recognition (Charles Keeling and Roger Revelle for example) that increasing atmospheric greenhouse gas levels would likely bode ill for the future. And going back further still, to Guy Callendar in 1938. And the theoretical basis for the warming was done in the 19th century.

          1. drumlin woodchuckles

            I did not know that about Bryson’s standing and regard at the time. Thanks.

            So the sensation-hyping MSM of that time did a real disservice with its Coming Ice Age reportage.

            How many millions of lay citizens remember the Next Ice Age hype and still think: “if they were so wrong then, how can they be any righter now?”

            1. Monte Davis

              I was a science writer/editor for national magazines in the 1970s-80s, and the “Next Ice Age hype” was neither very widespread nor sustained for very long. Most of what is now said about it reflects active, deliberate cherry-picking since the 1990s by denialists, promoting it from “a few breathless magazine articles” to “in the 1970s the whole climate-science establishment was DEAD CERTAIN that…”

              At a DoE-sponsored conference on CO2 and climate in 1979 I remember a long lunch conversation with Revelle, Syukuro Manabe (an early GCM leader), Steve Schneider (NCAR Boulder, and one of the unhappy sources for the Newsweek story) and others. There were still a lot of unanswered questions about actual and potential cooling episodes from sulfates/particulates, and about scenarios of positive/negative feedback from clouds and ice — but nobody doubted at all that CO2 was the most unidirectional, persistent, and hard-to-reverse driver. That will remain *my* take on the 1970s consensus, thankyouverymuch.

    4. UserFriendlyyy

      Over the course of the history of the planet there have been tons of different things that have affected the climate. The three big ones have been:

  4. funemployed

    The RCP8.5 model assumes that business as usual will continue for another 83 years. At this point, I have an awfully hard time imagining how that could be possible. I’m an admittedly pessimistic person, but I seriously doubt there will be anywhere close to 7.6 bill people alive on the planet come 2100, let alone the 9.5-10ish demographers estimate.

    It’s horrible to say, but very long term, I think the sooner our whole way of life ceases to support most of our lives, the better off humanity will be come, say 2300.

    1. paul

      What about the completely embedded model,historically ignorant, that consumer choice will use its roar to restore equilibrium?

      When that bubble pops, we might get somewhere

  5. Mike R.

    Human nature what it is, little will be done until things get particularly bad. It is hard to turn down convenience and comfort; particularly when that is all you’ve known.

    Insurance losses will mount; already evident. This will be handled mainly through even more inflation of the dollar. Notice how Congress simply appropriated “money” for the hurricane and wildfire damage. Any kind of “budget” today is a joke.

    The only countering balance I see in the future is that cheap energy will be running out; certainly oil and all its derivatives. So the economy will slow through higher costs (inflation). Slowly and gradually, more work will be done with human power and less work will be done overall.

    1. paul

      It is particularly bad for most people right now, survival tends to eat reflective time, human predators like that.

    2. tony

      The US relatively OK. It’s North Africa and the Middle East that are going to be the worst hit. They already import half their food, their food production will take a large hit and food in the world market is likely to be a lot more expensive. And Europe will not take hundreds of millions of Arabs.

  6. Wukchumni

    When I saw green vibrant ferns all over in an area where they should’ve died back months ago, I wanted to tell them the reason was climate change, but it’s forbidden to mention it in the National Park.

    1. drumlin woodchuckles

      It is not illegal for you or any citizen to talk about global warming in a National Park. It is only illegal for the Park employees to do so. One could even have some fun with that difference in who has what freedom.

      Citizen: ” Look at how global warming has kept all these ferns alive months after they used to die back for
      the winter. Isn’t that right, Mister Ranger Sir?”

      Mister Ranger Sir: ” No comment, Citizen.”

  7. Catsick

    The whole system is just too chaotic to extrapolate what has been a very small move over a very short period of time, there are many things on the verge of happening that could have massive effects with major feedback loops, The reversal of the gulf stream, the melting of the tundra and very reflective ice caps can kick off all kinds of chaos, I think the possibility that we just follow this linear path of higher temperatures is very unlikely, what we will have is going to be hugely unpredictable and our hope of reducing already set in motion feedback loops without some massive new AI are currently unknowable …..

Comments are closed.