Archive for the ‘climate effects’ Category

Climate change as a matter of risk management requires different choices in communication

June 11, 2018

Rowan Sutton just published a very short article (an “idea”) in ESDD entitled “a simple proposal to improve the contribution of IPCC WG1 to the assessment and communication of climate change risks”. From a risk management point of view a focus solely on the most likely outcome is not recommended, especially when the impacts increase sharply towards one end of the scale.


A common measure of risk is likelihood x impact (Fig 1). It is standard practice in risk assessment to highlight both the most likely impacts and low likelihood high impact scenarios. Such scenarios merit specific attention because the associated costs can be extremely high, so decision makers need to know about them. It follows that WGI has a responsibility to assess and communicate explicitly the scientific evidence concerning potential high impact scenarios, even when the likelihood of occurrence is assessed to be small. In past reports the assessment of key parameters by WG1 has focussed overwhelmingly on likely ranges only. When information has been provided about the tails of distributions only likelihoods have been communicated using terms – following the IPCC’s uncertainty guidance (Mastrandrea et al, 2010) – such as “very unlikely” or “extremely unlikely”: a clear steer that policy makers should largely ignore such possibilities. But this is wrong. Policy makers care about risk not likelihood alone. The IPCC’s uncertainty guidance ignores impact and is symmetric with respect to high or low impact scenarios; this is inappropriate for the communication of risk (Fig 1).

Figure 1: A schematic representation of how climate change risk depends on equilibrium climate sensitivity (ECS).

Some will argue that the WGII report is needed to provide information on impacts. For detailed information this is certainly the case, but the general shape of the damage function for a large basket of impacts (Fig 1) is insensitive to such details, and is all that is needed to justify WGI providing a much more thorough assessment of relevant scenarios. Other critics will suggest that for WGI to identify high impact scenarios explicitly would constitute scaremongering; this concern is no doubt one reason why previous WGI reports have focused so much on the likely range. But it is misguided. Policy makers need to know about high impact scenarios and WGI has a responsibility to contribute its considerable expertise to making the appropriate assessments.

A very similar point has been made by Kerry Emanuel in his post “Tail risk vs Alarmism” on CCNF:

In assessing the event risk component of climate change, we have, I would argue, a strong professional obligation to estimate and portray the entire probability distribution to the best of our ability. This means talking not just about the most probable middle of the distribution, but also the lower probability high-end risk tail, because the outcome function is very high there.


But there are strong cultural biases running against any discussion of this kind of tail risk, at least in the realm of climate science. The legitimate fear that the public will interpret any discussion whatsoever of tail risk as a deliberate attempt to scare people into action, or to achieve some other ulterior or nefarious goal, is enough to make almost all scientists shy away from any talk of tail risk and stick to the safe high ground of the middle of the probability distribution. The accusation of “alarmism” is quite effective in making scientists skittish in conveying tail risk, and talking about the tail of the distribution is a sure recipe to be so labelled.

Hans Custers schreef een kort Nederlandstalig blog over Sutton’s artikel.


There once was a polar bear – science vs the blogosphere

November 29, 2017

Blogs on which man-made climate change and its impacts are downplayed are far removed from the scientific literature. That is the conclusion of a new article in Bioscience in which a variety of blogs was compared with the scientific literature regarding the shrinking Arctic sea ice and the impact on polar bears.

Although there is strong agreement within the scientific community about anthropogenic causation of recent climate change, a large segment of the general public has doubts about these conclusions. This is sometimes referred to as the ‘consensus gap’. Blogs and other social media play an important role in spreading misinformation, which fuels the distrust in science.

Jeff Harvey, a Canadian ecologist working at the Netherlands Institute for Ecology (NIOO-KNAW) and the Free University of Amsterdam (VU), set out to investigate how the information on blogs relates to the scientific literature. The focus was on conclusions about Arctic sea ice and polar bears. The results have been published in the article “Internet Blogs, Polar Bears, and Climate-Change Denial by Proxy” in the journal Bioscience. Disclaimer: I’m a co-author of said article.

So what did we find? There is a clear separation amongst blogs, where approximately half of the 90 blogs investigated agree with the majority of the scientific literature, whereas other blogs took a position that is diametrically opposed to the scientific conclusions. Most of the blogs in the latter group based their opinions on one and the same source: Susan Crockford.

90 blogs and 92 scientific articles were classified according to six statements about Arctic sea ice and polar bears and the citation of Crockford. The figure shows the results of a principal component analysis (PCA) of the results. PCA is a technique to show the maximum amount of variation in a dataset with a minimum of newly defined parameters, the so-called principal components. The score on PC1 shows a separation between on the one hand the position that Arctic sea ice extent is shrinking and that this poses a threat to polar bears (most scientific articles and science-based blogs) and on the other side the position that Arctic sea ice is not shrinking or that it’s due to natural variability and that polar bears are not threatened (pseudo-skeptical blogs).

Arctic Sea ice

Arctic sea ice has shrunk dramatically in the past few decades, both in surface area and in thickness. This trend is expected to continue with ongoing global warming as a result of greenhouse gas emissions. Of course the decrease in sea ice doesn’t happen monotonically, but rather with ups and downs as a result of natural variability. When it happens to fit their perspective, such short term fluctuations are framed as a ‘recovery’ on certain blogs, or the decrease in Arctic sea ice is downplayed in other ways.

Polar bears

Polar bears depend on sea ice for catching their main prey, seals. So their habitat literally melts away as temperatures rise. Over time, polar bears have become iconic symbols of the negative effects of global warming. The population has been relatively stable so far, but you can’t just extrapolate that to the future. Biological impacts are often non-linear, and their dependence on sea ice means that in the future polar bears will likely face difficulties from continuing warming trend. Indeed, they have been classified as ‘vulnerable’ by the International Union for the Conservation of Nature (IUCN) and as ‘threatened’ under the US Endangered Species Act.

“No climate report is complete without an obligatory photo of a polar bear balancing on a piece of ice”, John Oliver said in the famous 97% episode of “Last Week Tonight”.

But what about the previous interglacial?

The polar bear species has survived the previous interglacial ~125,000 years ago. Some deduce from that that the polar bear will be fine. However, if CO2 emissions aren’t drastically reduced temperatures will get a lot warmer over the coming centuries and even millennia than during the previous interglacial. Moreover, during the previous interglacial summers were probably not completely ice-free, as is expected to happen  later this century as a consequence of continuing warming (which of course depends on how global emissions evolve). The current warming trend is many times faster than back then, making potential adaptation to new conditions more difficult. Besides shrinking sea ice there are currently also other factors that negatively affect polar bears, such as human settlements, industrial activities, hunting, bio-accumulation of toxins, and smaller seal populations.


A future with ‘business as usual’ emissions doesn’t look bright for the polar bear. Blogs appear to fall into two camps in how they write about this topic. On pseudo-skeptical blogs scientific uncertainty is twisted into ignorance, or the current situation is extrapolated into the future without taking into account the available knowledge of polar bear ecology. They usually don’t base themselves on the scientific literature, but rather on the statements of one person. These rather unfounded opinions are consequently recycled via the blogosphere, which in this respect acts as an echo-chamber. Susan Crockford writes a lot about polar bears, but does so mostly on her own website and for anti-mitigation thinktanks such as the Heartland Institute and the Global Warming Policy Foundation (GWPF); not in the scientific literature.

The gap between scientific conclusions and pseudo-skeptical blogs will not be a great surprise to those who closely follow both the scientific and the public debate about climate change. After all, this tendency is more generally visible than only on the topic of Arctic sea ice and polar bears. This is however the first time that this has been demonstrated on the basis of a systematic comparison between the scientific literature and blogs. To close the consensus gap the authors call on their fellow scientists to actively participate in the public debate.

Zie de Nederlandse versie op ons klimaatverandering blog.


The Supplementary Information that was part of the paper submission is still not available on the OUP website despite our repeated request to do so asap. In the meantime you may download the SI here. The data (scores per blog and per scientific article) are available via Dryad.

There has been quite some media attention for this study. Below an incomplete listing (for Dutch pieces see the abovementioned link to my Dutch sister-blog).

Polarised debate: polar bear blogs reveal dangerous gap between climate-change facts and opinions (NIOO press release) (reposted at several other places)

New study uncovers the ‘keystone domino’ strategy of climate denial (The Guardian)

Writers behind climate-change denial blogs ignore science, study finds (Toronto Star and many other Canadian newspaper outlets)

Polar Bear Blogs Denying Climate Change Are Being Used to Spread Conspiracy Theories Around the Globe (Newsweek)

Revealing the Methods of Climate-Doubting Blogs – Study shows that climate-skeptic bloggers often use limited disagreements to cast doubt on the big picture. (InsideScience)

Climate Change & Anthropocene Extinction 37: If the sea ice goes, so does the Arctic ecosystem (Bits of Science)

80 Percent of Climate Denier Blogs Reference This One Canadian Zoologist (Vice Motherboard)

How do you Spot a Climate Science Denial Blog? Check the Polar Bears (DeSmogUK)

Polar Bears Chosen as a Bizarre Symbol to Deny Climate Change, Scientists Say (DeSmogCanada)

Nearly all climate-change denial blogs quote exactly the same dubious research (International Business Times)

Unsurprisingly, the article gave rise to very different reactions, which easily fell into two camps (sounds familiar?): “insightful overview” vs “stupidest paper ever”…

Biodiversity, extinction and climate change

February 19, 2011

The previous thread turned into a discussion on how climate change might affect biodiversity. It started with Jeff Id’s taunt:

A warmer world will produce more food, biodiversity and a nice place for people and critters to live. Polar bears might be mad, but life is hard.

Aftersome back and forth’s, with e.g. Dave H noting the apparent disconnect between a strong focus on uncertainty and such a strong statement about positive effects, ecologist Jeff Harvey chimed in:

high temperatures are not a pre-requisite for high biodiversity

He points out that an important factor for maintaining high genetic and species richness is

stability – that is, that conditions in a region are not altered frequently by some important extrinsic challenge, such as rapid local climatic changes. (…)

the current rate of warming threatens to seriously undermine the functioning of biomes and ecosystems through uneven effects on species within tightly interacting food webs. (…)

Our species has simplified the planet biologically through the combined effects of paving, ploughing, damming, dredging. logging. slashing and burning, mining, dousing in synthetic pesticides, biologically homogenizing (e.g. through invasive species), altering the chemical composition of the air and water, and through various other forms of pollution. We know that genetic diversity is being lost at rates unseen in 65 million years, and against this background we are challenging an already impoverished fauna and flora to respond to climate changes that are unprecedented in perhaps tens of thousands of years.

Jeff Id replies:

I think like so many tied up in the eco-sciences you have blended too many causes and effects together to attribute the micro-warming to anything damaging to the ecosystem. (…)

my point is that over the next hundred years of warm weather, it would certainly result in higher planetary biomass all other effects unconsidered. Higher biomass eventually results in higher diversity. Warm in general is good for the planet, if you do it slowly enough and not too much of it.

How fast and how much, we could argue all day.

I tried condensing Harvey’s points thus:

– Biodiversity depends more strongly on the rate of change of climate than on the actual climatic state (i.e. whether “warm” or “cold”).

– That is consistent both with evidence from the past and with theoretical considerations

– Biodiversity is already being stressed (by multiple anthopogenic stressors, of which climate change is one), and this stress is likely to increase as (the rate of) climate change will increase. (i.e. future projected biodiversity loss is much stronger than current biodiversity loss)

Of course, it’s a bit more cpmplicated than that, as Harvey aludes to in his reply. Later on he notes that

The IUCN (…) does not classify a species as being ‘formally’ extinct until it has not been recorded in the wild for at least 50 years.

And on the current rate of extionction:

We KNOW that between 10 and 40% of well-known species (vascular plants and vertebrates) are threatened with extinction.

This is an area that don’t know much about, so I don’t have much to add. It’s a very important aspect though, especially when taking into account that projected future (rates of) warming are much stronger than what we’ve seen so far. Not to mention that once a species is lost, it’s lost practically forever. I would think that the rate of species loss can be much greater than the maximum rate of new species development (or creation if you wish ;-).  

References on biodiversity, extinction and climate change:

Extinction risks from climate change

Coral decline threatens fish biodiversity

Papers on ecosystem response to past climate change

Kate at Climatesight on extinction and climate

Association between global temperature and biodiversity, origination and extinction in the fossile record

Recommended reading by Jeff Harvey

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