How Climate Change Became Apocalyptic

Part 2: Digging deeper into the IPCC's most consequential error

ROGER PIELKE JR., the Honest Broker 10/17/23

Over the past 6 years I have spent a lot of time documenting and explaining how an implausible scenario of the future moved to the center of climate research and policy — our old friend RCP8.5. Today, RCP8.5 is so woven into the fabric of climate research, policy and advocacy that it has developed it own constituency among climate influencers who not only defend its continued use, but assert falsely that the scenario remains a plausible future.1

Today, I provide some additional background on errors made by the Intergovernmental Panel on Climate Change (IPCC) that led to the emphasis on RCP8.5.

Some readers have asked me whether these errors were mistakes or instead, tactical decisions to present climate change as more extreme than the evidence warranted. I have no evidence on the intent of IPCC participants. To be perfectly clear, I believe it unlikely that RCP8.5 was the result of tactical decisions — but I do have evidence of a hugely consequential scientific error made by the IPCC, one that continues to negatively influence research and policy.

Let’s take a closer look at how the cock up actually happened.

One aspect of the IPCC that is not widely appreciated — and is sometimes outright denied — is that the organization oversaw and directed the creation of the scenarios that underpin much of climate research. The IPCC thus served not simply as an assessor of the scientific literature, but also a coordinator and director of the research that it assesses.

The IPCC argued more than 15 years ago that its coordinating role in scenario development was a feature, as it “would probably lead to more homogeneity in the literature that is to be assessed later,” thus making the IPCC’s job of assessment much easier. After all, if everyone is using the exact same scenarios, then summarizing research results would be much easier.

The expectation of homogeneity was certainty fulfilled and it has indeed made assessment much easier — note the central role of IPCC scenarios, especially RCP8.5, in its reports. However, the expected feature turned out instead to be a huge flaw as it reduced research diversity, created a single point of failure, and concentrated climate research and applications in a misleading direction.

Here is the error — In the IPCC AR5, for whatever reason, the organization fundamentally mischaracterized the scenario literature, which elevated RCP8.5 and eliminated other baseline scenarios that were far less extreme. Whether you today believe RCP8.5 to be plausible or not is completely independent from the error documented below, which is obvious and undeniable.

Let’s take a quick trip back in time to document exactly how this happened.

In 2000, the IPCC presented its SRES Scenarios, which were a set of baseline scenarios designed to project where we thought the world might be headed in the long-term future. They were apportioned into four scenario families and designated as A1, A2, B1, B2 and no likelihoods or probabilities were associated with any of the families or individual scenarios.2

You can see the carbon dioxide emissions trajectories of these scenarios in the figure below. I added the CO2 range on the vertical axis in red and sketched in the 10% and 90% scenario range with the blue lines, which will be important in the discussion below. For 2100 this range spanned ~25 gigatons (Gt) CO2 to ~130GtCO2.3

IPCC SRES 2000

The SRES Scenarios were controversial for a number of reasons, including that they were all baseline scenarios and also because they projected some very low carbon futures in the absence of climate policy, which climate advocates strongly objected to. Calls for new scenarios came immediately.

In 2006, the IPCC requested that its task group on scenarios develop an updated set of scenarios that spanned the “full range” of scenarios found in the literature:4

 “benchmark concentration scenarios should be compatible with the full range of stabilization, mitigation and baseline emission scenarios available in the current scientific literature”

The new scenarios were to be informed by the work of the IPCC’s Fourth Assessment Report (AR4 in 2007) which surveyed the literature on scenarios that had been published since the SRES scenarios. These newer scenarios were called post-SRES scenarios. The AR4 concluded of the new scenarios:

[T]he scenario range has remained almost the same since the SRES. There seems to have been an upwards shift on the high and low end, but careful consideration of the data shows that this is caused by only very few scenarios and the change is therefore not significant. The median of the recent scenario distribution has shifted downwards slightly, from 75 GtCO2 by 2100 (pre-SRES and SRES) to about 60 GtCO2 (post SRES).

With this information, the IPCC group charged with developing new scenarios to underly work to be assessed in the IPCC Fifth Assessment (AR5 in 2013 and 2014), held a workshop in the Netherlands in September 2007. When published, that report included the following figure, showing the range of emissions associated with the post-SRES scenarios, and indicating baseline scenarios and policy scenarios in blue, as well as their overlap in the hatched region.

IPCC scenarios workshop report 2007

You can see that the baseline range spanned from ~20 GtCO2 to ~100 GtCO2, with a median a bit less than 60 GtCO2. As we would expect, these values were just about the same as those reported in the 2007 AR4 report.

The workshop report recommended four scenarios that would later become known as the RCPs. You can see those four scenarios, with their original names in the figure below.

You can clearly see that the baseline range is fully bracketed by MES-AR2 8.5 (RCP8.5) and MiniCAM 4.5 (RCP4.5). This is consistent with the request of the IPCC leadership for new scenarios that encompassed the “full range” of baseline scenarios in the literature. It is also how the creators of the new scenarios later introduced them to the world — RCPs 4.5, 6.0 and 8.5 were to be considered low, medium and high baselines, as you can see from the table below.

重點在自然資源與維持人口數目所需的資源是否相當。


Influential Ecologist Predicts Human Population Will Collapse This Century

We've heard this argument before.

Ross Pomeroy, 10/30/23

* Esteemed ecologist William Rees argues that humanity is in a state of ecological overshoot, using far more resources than the Earth can sustainably provide over the long term. When this happens to other species, there is a population "correction." 
* Mainstream opinion disagrees with his take. Demographers at the UN predict that — due to a combination of higher standards of living, birth control, and shifting perspectives on sustainability — the human population will peak in the mid-2080s and then decline slowly. 
* Others before him, notably Thomas Malthus in 1798 and Paul Ehrlich in 1968, made similar predictions. Reality proved them wrong.

For 99.9% of Homo sapiens‘ 250,000 years on planet Earth, our population has remained below one billion individuals, and for much of that time, our species’ growth curve was relatively flat. Since 1800, however, the human population has exponentially ballooned to 8.1 billion from just under one billion. We now occupy almost all parts of the globe and ravenously consume resources beyond what Earth can sustainably provide for the long term.

As eminent ecologist William E. Rees argues in an ominous new paper, this is a recipe for impending disaster.

Boom and bust cycles

For 40 years, Rees taught at the University of British Columbia, focusing on planning related to global environmental trends and sustainable socioeconomic development. His most notable academic contribution is the concept of the “ecological footprint,” the “amount of environmental resources needed to produce the goods and services that support an individual’s lifestyle.”

As an ecologist, Rees is well aware that all sorts of species frequently go through boom and bust cycles. When resources are plentiful and threats are low, they reproduce and multiply. But when resources dry up, perhaps from over-consumption or environmental change, species’ populations will precipitously fall.

Rees’ painfully simple proposition in his new paper is that humans are no different from any other species. Thus, we are just as vulnerable to population busts as we are prone to booms. “Homo sapiens is an evolving species, a product of natural selection and still subject to the same natural laws and forces affecting the evolution of all living organisms,” he wrote.

And make no mistake, we are at the peak of a boom on the precipice of a bust, he says. Human population’s 700% rise, along with a 100-fold expansion of real world product, over the last two centuries are anomalies unlocked by rampant use of fossil fuels, deforestation, mining, and arable land destruction. This has propelled us into an ecological state of “overshoot,” where we are consuming more resources than can be replenished and producing more waste than can be handled by ecosystems. The only question is when humanity’s bubble will collapse. Rees portends it will happen in our lifetimes.

“The global economy will inevitably contract and humanity will suffer a major population ‘correction’ in this century,” he wrote.

A population “correction”

How bad will it be? Rees cites estimates suggesting that the number of humans that Earth can support for the long term is between 100 million and 3 billion people. So, the population and civilization collapse he forecasts will be quite bad, indeed. He even briefly painted a bleak picture of how it might happen.

“As parts of the planet become uninhabitable, we should expect faltering agriculture, food shortages, and possibly extended famines. Rising sea levels over the next century will flood many coastal cities; with the breakdown of national highway and marine transportation networks other cities are likely to be cut off from food-lands, energy, and other essential resources. Some large metropolitan areas will become unsupportable and not survive the century.”

After the population correction, Rees portends a more primitive future.

“It may well be that the best-case future will, in fact, be powered by renewable energy, but in the form of human muscle, draft horses, mules, and oxen supplemented by mechanical water-wheels and wind-mills.”

A false prophet of doom?

Rees’ opinion is not destiny, of course. If it sounds familiar, it’s because much of it is simply a rehashed version of what Paul Ehrlich wrote in 1968 in his book The Population Bomb. Thomas Malthus made the same argument in 1798. For the past 225 years, reality has proven them wrong. There is no convincing evidence to suggest that conditions on Earth have changed so much that a human population collapse is inevitable or even likely. Indeed, as productivity has increased and technology has advanced, we are creating more things but using fewer resources.

Besides, demographers at the United Nations forecast that the human population will peak in the mid-2080s at around 10.4 billion people, after which it will level off and decline. Rather than due to a catastrophic collapse, this natural slow-down will be the result of higher standards of living, birth control, and shifting perspectives on sustainability, among other reasons. In short, the UN, along with most other scientists, predict that humans will effectively choose to dwindle in number rather than have the choice made for us in dramatic and deadly fashion.

In places, Rees’ paper reads like the rantings of a dour old ecologist, understandably angered by the damage humanity has done to the natural world. Sprinkled throughout the article are opinionated barbs aimed at various targets: short-sighted politicians, naive techno-optimists, and overly hopeful scientists. He also reserves a fair amount of irritation for those who insist that climate change is the greatest problem that humanity faces, when the real problem is us — or rather too many of us.

Still, Rees’ arguments should not be ignored entirely. The accomplished ecologist has distinguished himself through decades of scholarship. He also draws on history to correctly note that many major civilizations throughout human history have collapsed and suffered die-offs, often stemming from ecological overshoot within their respective habitats. He believes that, if we aren’t careful, the same will happen again. Let’s be sure to prove him wrong.