2010-09-25 23:46:53Basic rebuttal: "Polar bear numbers are increasing"
Anne-Marie Blackburn
Anne-Marie Blackburn
bioluminescence@hotmail.co...
80.42.215.97

Alright, my first attempt at this. Any feedback welcome.

 

Polar bears are found in the Arctic circle and surrounding land masses. There are 19 recognised subpopulations, and estimates place their numbers at about 20,000 to 25,000. Polar bears are classed as vulnerable by the World Conservation Union (IUCN) and listed as a threatened species under the US Endangered Species Act. Yet some claim that polar bear numbers have increased since the 1950s and are now stable. So what is the situation for this species?

First of all, a few points need to be made about polar bear numbers:

  • Nobody really knows how many bears there were in the 1950s and 1960s. Estimates then were based on anecdotal evidence provided by hunters or explorers and not by scientific surveys.
  • Polar bears are affected by several factors, including hunting, pollution and oil extraction. Most notably, hunting, particularly following the introduction of snowmobiles, airplanes and ice breakers, led to a huge decline in certain subpopulations. The introduction of the International Agreement on the Conservation of Polar Bears in 1973, which restricted or even banned hunting in some circumstances, consequently resulted in an increase in polar bear numbers.
  • Not all subpopulations are affected to the same degree by climate change, and while some subpopulations are well studied, for others there is insufficient data to make broad statements about current and past numbers.

With this caveat in mind, what do the figures actually say? According to a 2009 report by the IUCN Polar Bear Specialist Group, of the 19 recognised subpopulations of polar bears, 8 are in decline, 1 is increasing, 3 are stable and 7 don’t have enough data to draw any conclusions. Figure 1 below compares the data for 2005 and 2009.

 

Figure 1: Subpopulation status of polar bears for 2005 and 2009 (Source: Polar Bear Specialist Group)

 

Both habitat degradation and over-harvesting are responsible for the decline in some subpopulations. To understand why the IUCN and US Endangered Species Act consider polar bears to be at risk, it is important to look at how rising temperatures are likely to affect their habitat in the future. Polar bears are highly specialised mammals which rely heavily on sea ice for food and other aspects of their life cycle. Satellite data show that Arctic sea ice has been decreasing for the past 30 years, and projections show that this trend will continue as temperatures carry on rising. The changes in sea ice affect polar bears in several ways:

  • The early retreat of summer sea ice means that bears have less time to hunt and therefore less time to build up fat reserves.
  • The fragmentation and reduction in sea ice has several impacts. It forces the bears to swim longer distances, using up some of their fat reserves. It also reduces the number of seals, which are the bears’ main source of food, and impedes travelling and den making. And it also forces the bears to spend more time on land, with increased interactions with humans potentially leading to higher mortality.

To get an idea of the potential impacts of future climate change on polar bears, we can look at subpopulations found at the bears’ southern range, where habitat changes have been most noticeable so far. A good example is the western Hudson Bay subpopulation, which is one of the best studied. Here, ice floe break-up is taking place earlier than 30 years ago, effectively reducing the feeding period by about three weeks. As a result, the average weight of female polar bears has dropped by about 21% between 1980 and 2004, and the population declined by 22% between 1987 and 2004. In Alaska, there is evidence of increased cub mortality caused by a decline in sea ice.

In conclusion, the reason polar bears have been classed as threatened comes from the impacts of future climate change on the bears’ habitat. Current analysis of subpopulations where data is sufficient clearly shows that those subpopulations are mainly in decline. Further habitat degradation will increase the threats to polar bears.

2010-09-25 23:48:42
Anne-Marie Blackburn
Anne-Marie Blackburn
bioluminescence@hotmail.co...
80.42.215.97

Or I could use this graph:

 

2010-09-26 06:01:38Some suggestions:
nealjking

nealjking@gmail...
84.151.40.47


  • "Not all subpopulations are affected to the same degree by climate change, and while some subpopulations are well studied, others have insufficient data to make broad statements about current and past numbers."
=>

 

  • Not all subpopulations are affected to the same degree by climate change, and while some subpopulations are well studied, for others there are insufficient data to make broad statements about current and past numbers.

 

 

"Satellite data shows that Arctic sea ice has been decreasing for the past 30 years"

=>

"Satellite data show that Arctic sea ice has been decreasing for the past 30 years"

["data" is a plural noun]

 

"Here, ice floe break-up is taking place earlier than 30 years ago, effectively reducing the feeding period by about three weeks. As a result, the average weight of female polar bears has dropped by about 60 kilograms between 1980 and 2004, and the population declined by 22% between 1987 and 2004. In Alaska, there is evidence of increased cub mortality caused by a decline in sea ice."

=>

"Here, ice floe break-up is taking place earlier in the year than 30 years ago, effectively reducing the feeding period by about three weeks. As a result, the average weight of female polar bears has dropped by about 60 kilograms (about X%) between 1980 and 2004 and the population declined by 22% between 1987 and 2004. In Alaska, there is evidence of increased cub mortality caused by a decline in sea ice."

 

Also: It might be worthwhile to deconstruct the numbers by which the conclusion that "the polar bears are alright" has been drawn. By what numerical prestidigitation do they do this?

2010-09-26 07:10:05
Anne-Marie Blackburn
Anne-Marie Blackburn
bioluminescence@hotmail.co...
80.42.215.97

Thanks Neal. I've taken your suggestions on board and made some changes.

As for numbers, I've based my rebuttal on the intermediate rebuttal and the quote from Mitchell Taylor - no numbers are given, and often numbers aren't given when this argument is made. I did think to include a sentence along the lines 'The perception of increasing numbers could be explained by polar bears having to extend their range and therefore coming into contact with humans more often' but wasn't sure it was needed - I may change that.

2010-09-26 08:24:09
nealjking

nealjking@gmail...
84.151.40.47

Anne-Marie,

My interpretation of "basic" does not mean completely non-numerical, but rather non-complicated in logic. Sometimes a number or two makes the point more clearly.

In this case, the question is, Why do they think they can say this without having egg on their faces?

 

2010-09-26 08:24:11
nealjking

nealjking@gmail...
84.151.40.47

Anne-Marie,

My interpretation of "basic" does not mean completely non-numerical, but rather non-complicated in logic. Sometimes a number or two makes the point more clearly.

In this case, the question is, Why do they think they can say this without having egg on their faces?

 

2010-09-26 21:43:45
doug_bostrom

dbostrom@clearwire...
184.77.83.151

Forthright, conciliatory of what we don't know, should be tractable for most people.

I suppose it's extrapolation spin, but if most of the groups for which we have good data are in decline with a minority in increase, it seems reasonable to imagine the same proportions will extend to the groups with insufficient data.

I agree w/Neal about numbers; surely if we peel -all- numbers from explanations we're going a little too far?

Might be useful to make the first mention of the polar bear specialist group into a link.

 

 

 

2010-09-26 22:19:11
Anne-Marie Blackburn
Anne-Marie Blackburn
bioluminescence@hotmail.co...
80.42.215.97

Thanks for the input, Doug. My question would be: which numbers should I use? The intermediate rebuttal makes no reference to specific numbers and I can't find consistent figures out there, just vague statements (and I even made myself read material from James Delingpole, The Heartland Institute and Taylor's original article). And to be honest, either I'm missing your point or I simply don't agree that number crunching adds much here - people are making statements which don't appear to be substantiated in any way, well certainly not according to the polar bear specialist group.

I do need to make the polar bear specialist group into a link, and add a source to the graph I included.

2010-09-27 00:04:03
doug_bostrom

dbostrom@clearwire...
184.77.83.151
Anne, my point was that I hope you would not find yourself encouraged to remove the numbers in the post as they stand now.
2010-09-27 01:57:05
Anne-Marie Blackburn
Anne-Marie Blackburn
bioluminescence@hotmail.co...
80.42.215.97

So I was missing the point again - sorry. I wasn't planning on removing anything from my post but thought I could add some text as to why there is a perception that the numbers are increasing.

I don't seem to be understanding anyone's points today - I might just call it a day and start again tomorrow :)

2010-09-27 08:07:30
Riccardo

riccardoreitano@tiscali...
93.147.82.165
I'm open to the possibility of adding the reason of the wrong perception, your (tomorrow? :)) choice. 
2010-09-27 18:21:06
nealjking

nealjking@gmail...
84.151.57.191
All I was thinking about was the claim, "The polar bear population is stable/growing." Surely they must point to some numbers when they say that? In that case, there must be something missing: Is that the population of one small subset? Are they counting zoo bears? What's the catch?
2010-09-27 18:42:20
Anne-Marie Blackburn
Anne-Marie Blackburn
bioluminescence@hotmail.co...
80.42.215.97

Thanks Riccardo, I will think about how to best include it. I was a bit worried that my post was getting long but a sentence or two won't hurt :)

Thanks for the clarification Neal. I think that particular claim is down to the fact that some subpopulations are increasing, mainly because of restrictions on hunting from what I've read (though these sources weren't over-reliable sources, I'd have to look into it more carefully). Though their figures don't seem to tally with those put forward by the polar bear specialist group, and part of it must be down to the disinformation campaign against climate change (in my humble opinion). Also there's a perception that numbers are increasing because polar bears are having to extend their range due to habitat changes. This means they are more likely to come into contact with humans. Finally, I believe that the fact that polar bears are important economically for some native communities - as sport hunters use locals to guide them to the bears - is behind some of the claims that polar bears are just fine. I was thinking of working on the intermediate version to include these different aspects and add details to the narrative. I just didn't want this version to be too long.

2010-09-27 18:56:50
nealjking

nealjking@gmail...
84.151.57.191
Probably just a sentence to the effect that this perception is likely based on incomplete information (or a "selection effect") could be useful even at the Basic level. Probably need to find a throwaway line that expresses that point. Maybe something like: "If bears have to go looking for garbage, people will see more bears."
2010-09-28 06:34:52
Paul D

chillcast@googlemail...
82.18.130.183

I think the 1973 agreement is conveniently ignored by skeptics.

2010-09-29 06:36:27
doug_bostrom

dbostrom@clearwire...
184.77.83.151

Are they counting zoo bears? What's the catch?

CGI polar bears in commercials. "Huggy Bear." 

2010-09-29 16:43:01numbers
gpwayne
Graham Wayne
graham@gpwayne...
81.132.179.253

On the number issue, while I don't believe we should be shy of using good data, I'm not sure we have any that is sufficiently robust to build a better case than has already been stated here. I suppose the only thing I might have emphasised more is that most of the arguments I've come across conflate the popular news stories of recovery after the hunting ban, with putative habitat degradation in the future. If we extrapolate the current declines we know about, and introduce further pressure on habitat, these numbers will simply get worse.

Anyway, I'm nit-picking amongst the fur now. Nice work Anne-Marie, and a green thumb from me...

2010-09-29 20:18:50
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.132.222
Thumbs up from me. 
2010-09-29 20:20:05
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.132.222
Doh!, forgot to tick the icon. 
2010-09-30 07:12:00
Riccardo

riccardoreitano@tiscali...
93.147.82.100

Partly OT, a new video from Peter Sinclair

http://climatecrocks.com/2010/09/27/extinction-its-not-just-for-polar-bears-anymore/

 

2010-09-30 20:03:09Published
John Cook

john@skepticalscience...
124.186.160.198
Thanks Anne-Marie. I axed my intermediate version as it was rubbish compared to yours (let's face it, it was a horrible rush job). So the Intermediate Version is unclaimed if anyone is keen for the job. :-)
2010-09-30 21:25:09
Shirley_Rocks
Shirley Pulawski
missfabulous@verizon...
96.243.52.109
It is a bit long, but it's all easily digestible, I think. I personally like the pie charts better than the graphs. I think they have more visual impact and require less thinking.