Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.


Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Support

Twitter Facebook YouTube Pinterest MeWe

RSS Posts RSS Comments Email Subscribe

Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...

New? Register here
Forgot your password?

Latest Posts


Explaining Arctic sea ice loss

Posted on 13 October 2010 by Doug Bostrom

Arctic sea ice has aptly been termed a "canary in the global warming coal mine," a sensitive indicator of climate change; because of its importance as a diagnostic of global warming, climate change skeptics struggle to explain the decline of Arctic sea ice as a natural phenomenon. 

Satellite measurements of Arctic sea ice extent reveal a rapid decline over the past 30 years, particularly at the end of each year's annual melt season.  The downward trend and the increasing difference between seasons are in keeping with predictions of the effects of global warming. As the Arctic warms, the volume of ice in the region gradually declines, making it less likely ice will survive more than one year and thus exposing more open water at the end of each melt season (Maslanik et al).

(from National Snow and Ice Data Center )

As an explanation for the decline of Arctic sea ice, skeptics hypothesize we're seeing the effects of natural cycles causing deep, decades-long swings in Arctic ice coverage and volume. Lending observational support for such cycles is much more difficult than relying on direct observations of ice extent with contemporary instruments. Still, thanks to ocean sediment cores and some other physical clues left by past climate regimes we have reasonable insight into past Arctic sea ice extent. Combining various information about past climate behavior, we can better understand why changes in ice coverage have occurred in past times, whether those natural variations are happening today, and how those changes compare to today's sea ice trend. 

While it's true that natural variations of the climate have caused significant changes in Arctic ice extent in the past, it's important to note that such such changes are not airtight arguments against anthropogenic global warming causing today's loss of ice. After all, events of the past do not describe newly identified influences by human culture on today's climate. Indeed, comparisons between past and present Arctic climate reveal different reasons for yesterday's and today's Arctic sea ice changes and strongly suggest that today's changes are largely anthropogenic (Overpeck et al).  Meanwhile, analysis of several hundred indicators of past Arctic sea ice extent tells us that recent losses appear to have no parallel in records going back many thousands of years (Polyak et al).

The past 200 years offers an example of how natural and anthropogenic influences on Arctic sea ice can be distinguished.  The Arctic appears to have undergone an unusually cool period in the early 19th century, certainly natural, with recovery to more normal conditions extending into the 20th century leading to the warming we see today. Referring to the graph above, we can see that after the earlier cool period sea ice extent in the Arctic appears to have largely stabilized, later to begin a steady decline in chorus with other emerging observations of global warming such as increasing air and ocean temperatures. This decline in ice extent is happening even though the causes for natural recovery from the unusual cold of the 19th century are no longer in play, while research strongly suggests these recent reductions in Arctic sea ice are are caused by a new, anthropogenic mechanism (Johannessen et al).  

In sum, although natural factors have always influenced the state of Arctic sea ice, research strongly suggests that today's decline is driven by the novel influence of anthropogenic C02 we've added to the atmosphere and thus is unique in Earth's history.

This post is the Basic Version (written by Doug Bostrom) of the skeptic argument "Arctic ice melt is a natural cycle".

0 0

Printable Version  |  Link to this page


Prev  1  2  

Comments 51 to 60 out of 60:

  1. Sorry, better links to the above references: MPG animation of Arctic sea ice PDF of the published research paper
    0 0
  2. Chris G #47 "Please put a thermometer in a glass of ice water, stir continually, and record the temperature every minute. Plot the temperature over time. The temperature will stay right at freezing, neither cooling nor warming, until the ice is gone. I'm not sure that I'm here to teach you basic physics." Where is your glass? In a steam room? In the oven? Definitely not in the freezer. If the ice is melting, the "system" is not in equilibrium, and therefore ambient heat must be entering the glass, the liquid water (a fluid) provides a path for convective heat exchange. Just for fun, lets turn the problem around and ask what conditions would be necessary to allow the ice in your glass to never melt as you are stirring it? Is this even possible? And as far as how this relates to the Artic... moving water should not help ice formation, even if that water is near freezing.
    0 0
  3. @Inconvenient Skeptic I followed your link and found "The All Natural Cause of Global Warming". Here's my critique on your AMO - Global Warming post. Since you are commenting on this site, I thought that other Skeptical Science readers would like to comment on your AMO - Global Warming conclusions. Kelly O'Day
    0 0
  4. The Inconvenient Skeptic at 01:49 AM on 14 October, 2010 It seems I may have pre-empted your potential comments on Arctic temperature here. I also responded to a comment you made on AMO there. To add to what D Kelly O'Day has done I will re-post the chart below for readers of this post, to save some effort for once. The AMO is de-trended North Atlantic SST from NOAA ESRL and I have de-trended the HadCRUT3 surface temperatures also to allow comparison. It is easy to see correlation, as we might expect from coupled Sea Surface Temperature (SST) and Surface Air Temperature (SAT), but causation (sea to air) is not evident from the relative phases.
    0 0
  5. Peter Can you tell me how you made your detrended HADCRUT series. I looks like AMO leads HADCRUT in some cases, lags in others. I'd like to reproduce your chart and take a look at how they vary.
    0 0
  6. THe difficulty I find is that there are lots of predictions of tipping points such an ice free Arctic in the summer which will be the thing that convinces everyone that the models of climate change are correct. The problem with this is that when year after year it does not happen, the warning begin to look like one of these chaps walking around with a billboard saying "the end is nigh" and it has the opposite effect on peoples perceptions. The other issue is that although the long term trend is obviously down, the short term trend is up from the 97 low. If this continues for another year or two the graph will start to look curiously like a hockey stick.
    0 0
  7. garethman #56: "The problem with this is that when year after year it does not happen, the warning begin to look like one of these chaps walking around with a billboard saying "the end is nigh" and it has the opposite effect on peoples perceptions." To my knowledge NO ONE has predicted an ice free Arctic ocean in the Summer prior to 2012 at the earliest. Most projections are closer to 2050... or 2100 if you go back about four years. Thus, I can't agree with the 'year after year' bit... it hasn't been projected to happen YET. So the fact that it actually hasn't in several years when no one thought it would doesn't seem particularly 'damaging'. "The other issue is that although the long term trend is obviously down, the short term trend is up from the 97 low. If this continues for another year or two the graph will start to look curiously like a hockey stick." Since we are now far below 1997 ice levels I assume you mean the 2007 low in ice extent... which was only a tiny amount lower than the 2008 and 2010 values. Claiming an 'upward' (barely) trend of three years is like claiming that Summer is going to be below zero because June 2-4 were one degree cooler than June 1. In any case, that's ice extent... which is largely determined by how spread out the ice is. The ice volume, the actual AMOUNT of ice, hit new all time lows of 5800 km^3 in 2009 and 4000 km^3 in 2010. If that trend continues nearly all the Arctic sea ice will be gone within a few years.
    0 0
  8. Hi, garethman. There are numerous "periods of recovery" visible in the graph since it began showing an extended decline ca 1970. These have all swiftly ended, to be overwhelmed by subsequent declines. The graph in this article ends in 2009; a look at a graph including 2010's melt season shows another "period of recovery" appearing to draw to a close. This particular article is more about attribution. Peter Hogarth has done a fine job of covering "recovery" here on Skeptical Science.
    0 0
  9. Garethman, The problem with AGW is that it is a very, very slow train wreck. The changes from one year to the next are not noticable. Even most of the changes from one decade to the next are difficult to observe: sea ice is an exception. It takes careful observations over 20 or more years to see most of the effects of AGW. People like you who expect sea levels one meter higher tomorrow will always be able to say there is no change. You do not pay attention to the record heat in Russia or the record floods in Pakistan. They are not in your backyard. That does not mean that the changes will not be substantial, expensive and difficult to adapt to. As time goes on the changes are accelerating. Only 20 years ago Lindzen testified in the US Congress that the climate was not changing. Now it is common on this web site for deniers to say everyone knows it is getting warmer, they dispute the cause. If you care about what the world will be like in 30 to 50 years then you need to pay careful attention now. Starting in 30 years to mitigate will be much more expensive than starting now.
    0 0
  10. D Kelly O'Day at 09:40 AM on 19 October, 2010 Sorry about the delay in responding. I fitted a linear trend to the HadCRUT series, then worked out the exact monthly increment for that trend, then generated a monthly cumulative time series and subtracted these values from the corresponding original monthly data values, (then back-checked the result!). This is crude but effective. Hope that makes sense.
    0 0

Prev  1  2  

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.

The Consensus Project Website


(free to republish)

© Copyright 2022 John Cook
Home | Translations | About Us | Privacy | Contact Us