Posts Tagged ‘Arctic sea ice’

How blogs convey and distort scientific information about polar bears and Arctic sea ice

December 22, 2017

Our article on sea ice and polar bears proved to be a hot-button issue in the blogosphere. This was not entirely unexpected, of course. What is striking though, is that amidst all the criticism nobody has challenged our core finding: blogs on which man-made climate change and its impacts are downplayed are far removed from the scientific literature, at least regarding the topic of shrinking Arctic sea ice and the resulting future threat to polar bears.

Even more so, alternative figures that have been prepared by some critics basically underscore this same message (see examples below). That’s not so strange of course, since the signal is so clear: there is hardly any overlap between contrarian blogs and the scientific literature on this topic. Take a look at the pie-charts below for the three statements on sea ice and those on polar bears, for the two different groups of blogs (termed denier and science-based blogs, respectively), and the peer-reviewed scientific articles that investigate both polar bears and Arctic sea ice. This is basically an extension of figure 1 in the paper, in which only the two blog categories were shown. Most scientific articles as well as science-based blogs assess Arctic sea ice extent to be shrinking and polar bears to be threatened as a result, and most denier blogs take a contrary view on both sea ice and polar bears. They are poles apart.

You may argue that it was overkill to use an elaborate statistical analysis such as PCA on this dataset. It was used mainly to visualize our results in one figure. All the criticism on the PCA and the details of how data were analyzed misses the forest for the trees: there is a clear distinction between blogs, where the group that accepts AGW appears to base their claims on peer-reviewed science, and the group that doesn’t accept AGW does not. The latter group appear to base their claims to a large extent on blogs written by one particular biologist, Susan Crockford, whose views run counter to the relevant ecological literature.

Our paper is first and foremost a characterization of the blogosphere, and how it compares to the scientific literature. We restricted our literature search to scientific articles that investigate both polar bears and sea ice, and that shed light on polar bear ecology and how it may or may not depend on the presence of sea ice. An article such as “Evolutionary roots of iodine and thyroid hormones in cell signaling” does not fit that bill, to name just one example of Crockford’s scientific articles that has been pointed out as evidence of her having published on polar bear ecology. She has not.

Even though it is not the main scope of our paper, we described the scientific context of polar bear ecology and explained how and why polar bears depend on their sea ice habitat (summarized in my previous blog post). As such, we argued that the scientific understanding of arctic sea ice decline and polar bear ecology is more credible than the viewpoints put forward on contrarian blogs. However, providing new ecological evidence was not the point of this paper. The point was to investigate how our current ecological understanding is conveyed and distorted in the blogosphere.

If some people think that our conclusion is wildly wrong, then they could at least show some evidence to prove their point, right? They probably realize that our conclusion is robust, so instead they try to nitpick on details and make it appear as if that undermines our conclusion. It does not.


Appendix: A collection of PCA graphs depicting our results, all basically underscoring the main conclusion that one group of blogs correctly conveys our current scientific understanding, while another group of blogs distort this understanding and promotes a very different viewpoint regarding sea ice and polar bears.

From top to bottom the following PCA figures are shown:

  • As published in the Bioscience paper, in which missing values are replaced by zero after scaling the data
  • List-wise deletion of all records with missing values, considerably reducing overall sample size
  • Using multiple imputation with logistic regression (5 rounds of 40 iterations each)
  • PCA figure of the same data as produced by Richard Tol, where sample size of each location in the graphs is depicted by symbol size
  • PCA figure of the same data as produced by RomanM at ClimateAudit, without information on sample size

As mentioned in the supplemental information with our paper, jittering was applied to our PCA figure to gently offset data with the exact same entries from each other for graphical purposes. Tol uses an alternative method to provide information on sample size for specific data entries, namely via the size of the symbol used in the figure. Whatever your preference, the conclusion drawn from these figures is the same: there is a clear gap between the consensus in the scientific literature and science-based blogs on the one hand, and contrarian blogs on the other hand. We thank Roman Mureika and Richard Tol for underscoring the validity of our conclusion.


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”…

EGU General Assembly: The Arctic, Models, and Data

June 7, 2013

Guest post by Heleen van Soest

In April, the annual European Geosciences Union conference was held in Vienna, Austria. Heleen van Soest, MSc student Climate Studies at Wageningen University, attended the conference, and shares some thoughts and tweets (@Hel1vs).

The opening reception, April 7, reveals that geoscientists are fond of beer. I get to talk to some nice people and hand out my first business cards. Yay! I talk with Walter Schmidt,  President of the Division on Geosciences Instrumentation and Data Systems, about observations and data. Lesson learned: data are important, but never take them for granted. Especially from satellites: they basically measure counts and voltages. To interpret the numbers and get something useful, we already need models, i.e. algorithms. Usually, model skill is tested against data. Disagreement between them is often blamed on model errors, assumptions, etc. Keep in mind that data might be wrong, too. Fortunately, raw data is increasingly archived as such, together with the algorithms used to interpret them. In that way, data can still be used if the algorithms are updated. I dedicate my first #egu2013 tweet to this conversation and go home. I am happy to find a Va Piano (Italian restaurant) in ‘my’ street. Together with Sherlock Holmes (the book, that is), I eat my pasta.

Tweet At #egu2013 opening reception, interesting conversation about models and data: “important, but never take them for granted” (Walter Schmidt)

Monday, 8 April

Permafrost day. An important issue, as permafrost contains about half of the world’s soil carbon. If permafrost thaws, the organic carbon becomes available for microbes to degrade. Greenhouse gas (methane) emissions are a result, further increasing temperatures. This positive feedback is sometimes compared to a time bomb. Modelling studies of permafrost do show it will degrade under further warming. For example, Greenland permafrost south of 76°N will disintegrate this century. However, see RealClimate before you start to worry that this bomb is about to explode.

But today is not only permafrost; I’ve also got something on ice observations.


Melting of the Arctic sea ice

March 25, 2013

Guest post by Jos Hagelaars. Dutch version is here.

This was the title of a discussion that was held on the recently launched website ClimateDialogue regarding the possible causes of the decline in Arctic sea ice over the past decades. Three experts participated in this discussion: Walt Meier, Research Scientist at the NSIDC, Judith Curry, professor at Georgia Institute of Technology and Ron Lindsay, Senior Principal Physicist at the Polar Science Center of the University of Washington.

In this blog post I will start off with a description of the observations of the Arctic region, followed by a short overview of the potential causes of the decline in Arctic sea ice, incorporating the views of the three experts as they were expressed on ClimateDialogue. The final parts concern the uniqueness of this decline in a historical perspective and the possibility of having an ice-free Arctic in the summer in the not too distant future.

Observations of the Arctic region since 1979

Since 1979 the Arctic region has been extensively monitored by satellites. They detect e.g. the ice surface area, the extent of the area covered with ice and also the total amount or volume of ice. The results of these observations are startling. For example, sea ice area and the amount of perennial (multi-year) ice has decreased dramatically over the past 3 decades, as is visualized by the images in figure 1 and 2, generated by NASA (see here and here).


Arctic sea ice was higher in 1989 cherrypicking by Harrison Schmitt and Heartland Institute

February 8, 2011

How could someone possibly claim that

Arctic sea ice has returned to 1989 levels of coverage

Easy. The proof is in the data, of course:

See: The red line is clearly higher than the blue one in april. 

Is this a joke? I wish. This was said by ex-astronaut and New Mexico’s energy secretary Harrison Schmitt. The Heartland Institute had carefully picked april of 1989 and 2009 as the basis for comparison.

As regular readers here know, I’m very open to different opinions and to reconciliation efforts. But this has of course nothing to do with true skepticism. Look at those two lines! This is definitely not the kind of “skepticism” that we should be taking more seriously. I hope everybody (including Judith Curry) can at least agree to that. I’m all for bridge building, but let’s at least make sure that reality remains somewhat in view while standing on the bridge.

See also Scott Mandia, Chris Mooney, Charlie Petit, Lou Grinzo, Richard LittlemoreTim Lambert (suitable title: “Now THAT’s cherrypicking”), Peter Sinclair and Peter Gleick at the HuffPo.

Graph via Tim Lambert and Peter Gleick. Pictur here.

Tipping points in the climate: Melting ice

January 7, 2009

(Dutch version here)


James Hansen has put the concept of ‘tipping points’ on the agenda. It is not a strictly defined term, but at a tipping point, a relatively small change has a relatively large consequence, and the climate could end up in a different equilibrium state than before. (Compare it with the concept of meta-stability, with the classical example of a ball on a hill, which needs only a minor push to end up in the valley – the new equilibrium state.)


Ice-albedo feedback

Large scale melting of ice could cause such a tipping point. Ice reflects a much larger part of the incoming solar radiation (i.e. it has a higher albedo) than land or water surfaces do. Therefore, when ice melts and the underlying land or water surfaces become exposed, much more sunlight will be absorbed than was previously the case. This causes more warming, which causes more melting, and the circle is closed.


Sea ice

The amount of Arctic sea ice at the end of summer has dramatically decreased over the last 30 years. The last two summers (2007 and 2008) ended with even smaller amounts of ice than would be expected based on the long term downward trend. It is too early to tell whether this means that the trend has changed (i.e. having passed a ‘tipping point’). Melting sea ice has no direct consequence for sea level, and if the warming trend is halted or reversed, the sea ice is expected to return to its ‘normal’ state. It is therefore a reversible tipping point.



Decrease of Arctic sea ice extent over the last 30 years. Data are for September, when the ice extent reaches its minimum. Source: NSIDC


Land ice

The melting of land ice, on the other hand, does lead to sea level rise, and is practically irreversible on human time scales. The melting of Greenland would lead to a globally averaged sea level rise of about 6 meters. The West Antarctic ice sheet is good for about 7 meters, whereas the remainder of Antarctica has enough ice for over 50 meters global sea level rise. But that’s not gonna happen any time soon, is the expectation. No major changes are happening in the Antarctic, and in some places in the interior ice mass even seems to be increasing, due to increased snowfall. This is a predicted consequence of slight warming, because it leads to more water vapor in the air. As warming continues, melting will at some point start to outperform the effects of increased snowfall.


Sea level rise

According to Hansen et al, “equilibrium sea level rise for today’s 385 ppm CO2 is at least several meters, judging from paleoclimate history.” This seems predominantly based on the fact that in the previous interglacial, 125,000 years ago, sea level was about 6 metres higher than now, while the average temperature was about 1 degree higher. Even when the CO2 concentration would stop increasing, the Earth would still continue to warm up by another 0.5 degrees, mainly due to the thermal inertia of the oceans. So we’ll approach the same global average temperature of 125,000 years ago, even with current CO2 levels.


It’s not evident to what extent the relation between temperature and sea level is linear. Over ‘short’ timescales, when thermal expansion is the main influencing factor, it is probably close to linear. Several equilibrium situations from the distant past also show a strong relation over longer timescales, mainly influenced by the amount of land ice. The whole idea of ‘tipping points’ is of course that changes happen stepwise, rather than smoothly.



Relation between sea level (relative to today) and global average temperature based on different epochs. LGM stands for Last Glacial Maximum, Eocene is also known as PETM (Pleitocene-Eocene thermal maximum), Eemian is the previous interglacial. YBP stands for years before present. Numbers are from multiple sources and are associated with a ‘certain’ degree of uncertainty.


To what extent can we translate relations between climate variables from the past to the current situation? Melting of polar ice mainly depends on the regional temperature, and its relation with the global average temperature is not necessarily constant. We know relatively little about dynamical processes that influence the breaking up and melting of land ice. But apparently large changes in sea level are possible if the temperature remains long enough above (or below) a certain value. The examples from the past may give a sense of what order of magnitude sea level rise we could eventually expect for a given temperature increase. The rate of sea level rise is the most uncertain. Most scientific literature concludes that sea level rise won’t be more than one or at most two meters by 2100 (but it will continue to rise thereafter). That is quite a strong increase for large parts of the world to adapt to, and uncertainty in the rate and level of the rise is not really comforting. The examples from the past are even less so.


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