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Climate Hustle

A Swift Kick in the Ice

Posted on 19 February 2011 by Rob Honeycutt

Commenting in the trenches of the climate change blogosphere I find a large number of people who lack very basic understanding about Arctic Ice.  While I'm not an expert in the field I have managed to learn a few things with regards to why Arctic ice is an important issue.  There are a few misconceptions that require a "swift kick in the ice."

When learning about these issues myself I came upon a question that I could not immediately answer.  We know that water vapor is a strong greenhouse gas.  We know that warmer air holds more moisture than cold air, in fact, to the point where the Antarctic is one of the driest deserts on the planet.  So, how does this jibe with the idea of polar amplification, the idea that the poles will warm faster than the rest of the planet on average?  The climate models tell us that the poles will warm faster, and the model results are proving true now. Why would the poles warm faster if there is so little water vapor in the air?

Fig 1  -  Surface Temperature Map for Jan 2011 (Source: GISS)

The first answer comes by way of looking at a surface temperature map (Fig 1).  What we find is that the north and south poles are not warming equally.  In fact, the term "polar amplification" is better described by saying "Arctic amplification."  If we look out to the end of the century there is anticipated to be amplification in the south as well but most of the warming will take place in the north.

But that still leaves us with, why?  The Arctic gets cold too, therefore is drier than the equator.  Why would the equator not warm faster?  

Fig 2  -  Orbital tilt through the year

Pretty much everyone knows that these basic very important facts about the north pole:

  1. The ice at the pole is covering the Arctic ocean.  It's sea ice.
  2. Both poles are mostly dark half the year and mostly light half the year.

These two very basic aspects of the Arctic make it special in terms of climate change form the reason why Arctic Amplification is happens and is so important.

Each year the ice of the Arctic thaws back to a minimum extent during the late summer, usually some time in September.  Then it freezes back each winter.  This is obviously because summer months are warmer and winter months are colder.  

The Battle of Albedo

Now I'll beat you up with the concept of "albedo."  Albedo is the effect where light colored surfaces reflect light and dark colored surfaces absorb light. Think of it as white pavement or black pavement.  Black pavement is always going to scorch your bare feet more than white pavement in the noontime sun.  Dark surfaces absorb more heat from the sun.  Light surfaces reflect more light away and absorb less heat.  

Fig 3  -  Albedo effects (source: wikipedia)

As you can see from Figure 3, the albedo of fresh snow is dramatically different from water - it's much more reflective.

In the winter the Arctic sea is almost completely frozen over but this doesn't matter a lot because there is little sun shine for half the winter and even no sun shine at all for several months of the year.  There is no albedo effect at all during this part of the year.

In the summer months, though, the story is the opposite.  If the Arctic Sea is covered with ice in the summer - as it has been dating back perhaps thousands, to millions of years - the incoming sunlight is mostly reflected back to space without adding any heat to the Earth.  But, as ice melts back, as is happening today, the summer sun is absorbed by the darker open sea exposed by the disappearing ice.  

The open water absorbs more and more heat during the extended daylight of the summer months until winter comes again, when the Arctic Sea freezes.  But because of warming the ice is also losing its capacity to freeze back to previous levels.  This is what is meant by a feedback.  Less ice makes warmer water, which makes thinner ice, which melts easier, which makes warmer water… and so on.

 Fig 4  -  2007 Summer sea ice minimum (source: NSIDC)

This also points out why the sea ice in the Antarctic is less important and generates less warming.  The Antarctic is a land mass 1.5 times the size of the United States.  Each winter sea ice develops around the Antarctic continent but thaws back mostly to the coast each summer.  There it can go no further.  The continent is almost completely covered in snow year round so the south pole maintains its high reflectivity during the summer months.

Something to be wary of is people who point to very select years or short time periods to say the ice is not melting.  You have to look at all the data to see the full picture.  The full picture of the Arctic clearly shows a rapid decline of ice both in extent (area) and volume (total ice).  Some people will also tell you that ice is growing in Antarctica.  That's true and false.  Winter sea ice extent is increasing slightly, but the land based ice, on the whole, is melting.  And as we understand above, winter sea ice extent is not going to have any effect because there is little or no sun in the winter.

When you take a moment to step back from the dusty battle taking place on climate issues sometimes you gain a little perspective.  I've actually learned quite a lot doing battle in the blogosphere trenches.  On occasion I get a boot on the derriere that forces me to try to better understand the arguments on both sides of the issue and learn more about what scientists are trying to tell us. 

It's not a pretty battle, and you have to bust ice to really get down to the truth.

-  -  -  -  -  -  

For the most up to date and accurate information about snow and ice issues you can visit the NSIDC, the National Snow and Ice Data Center.

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Comments 1 to 50 out of 221:

  1. Grammatical mistake in the first sentence: understand
    Spulling mistake in the second paragraph: warm faster 'that' the rest...
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  2. Nice clear explanation. [:thumbs up smilie:]
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  3. Thanks, The Ville. Fixeded...ed it. :-)
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  4. You ask "Why would the poles warm faster if there is so little water vapor in the air?" The answer is in part the changing albedo, as you note, but there is another part to the answer: Rising CO2 matters most when water vapor is lowest. This is because the absorption bands of H2O and CO2 overlap to some extent. The effects of CO2 tend to get swamped out when water vapor concentration is high, but in cold, dry places, CO2 accounts for most of the greenhouse effect. The change in water vapor concentration with temperature is exponential: At 15C and 50% humidity, water vapor is 0.84% of the atmosphere at sea level (by volume or by molar fraction); at -15C water vapor is only 0.08%. And at -40C, 0.006%.
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  5. Another reason is the warm Atlantic Water entering the Arctic Ocean from the Gulf Stream. There is a recent article in Science on this subject. Speilhagen, et al. "Enhanced Modern Heat Transfer to the Arctic by Warm Atlantic Water" by Spielhagen et al. Science (2011) vol 331, pp 450-452
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  6. Thank you Peter... That's a really valuable point!
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  7. Does any of what you describe occur in the parallel world of the climate deniers?
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  8. Badgersouth... You know, I find the ice issue really interesting exactly for that reason. It's quite clear that the planet is losing ice at an accelerated rate by any number of measurements. But it's an issue that climate deniers tenaciously hang on to for dear life. Many of the arguments are listed here on SkS, of course. But when I'm on other sites arguing I'm amazed at how they hang on to these ideas.

    These people are utterly convinced that the ice is now starting to come back. They're as sure as they are that the sun will come up tomorrow. I'm really curious how much summer ice needs to disappear before finally acknowledge that it's disappearing. I fairly certain that all of it will need to be gone before they say "maybe." It's like a parallel reality.

    I like to point out that, after 2007, Arctic sea ice only "rebounded" to the accelerating declining trend. I suggest that, maybe if we were seeing a few years popping up past the 2 standard deviation trend on the positive side... then they might have something. But such comments seem to go unnoticed.
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  9. "fairly certain that all of it will need to be gone before they say "maybe."" - dunno Rob, I think you will find that when it is all gone they will be more firmly insisting that the Chinese sailed over the north pole in 1423, and that of course there wasn't any ice there 100 million (choose figure at random) years ago, and that polar bears have only just evolved. I have long concluded that there is absolutely no point at which the deniers will recognise the error of their ways. No point at all. Every step along the road to the year 2100, every shift in climate, every catastrophic event, every species extinction, every loss of coral reefs, will be explained away, rationalised, dismissed as having been seen some time on the past, or as too expensive to fix (except, if you insist, by a combination of nuclear power and DDT).
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  10. David... There are many for which I think what you say is exactly true. But I also think there are different extremes of denial.

    Ice is a pretty clear, visible signal. It's there or it's not. There's no quibbling about degree or missing heat or other issues. Ice has this way of drawing a line in the sand (or sea). As more and more ice disappears incrementally more and more people are going to sit up and take notice.

    The ice is going away, that's clear. With thermal inertia we have several more decades of warming no matter what. Arctic summer ice is going to be gone before that. Hopefully the far extreme deniers will become more and more marginalized during the process.
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  11. An excellent article, and very clear.

    It may be of interest that Arrhenius first calculated the increased warming at higher latitudes in 1898.

    He wrote:

    "... I have calculated the mean alteration of temperature that would follow if the quantity of carbonic acid [CO2] varied from its present mean value (K=1) to another, viz. to K=0.67, 1.5, 2, 2.5, and 3 respectively. This calculation is made for every 10th parallel and seperately for the four seasons of the year. The variation is given in Table VII.

    A glance at this Table shows that the influence is nearly the same over the whole Earth. The influence has a minimum at the equator and rises to a flat maximum that lies further from the equator the higher the quantity of carbonic acid in the air. For K=0.67, the maximum effect lies about the 40th parallel, for K=1.5 on the 50th, for K=2 on the 60th, and for higher values above the 70th parallel. The influence is generally greater in winter than in summer, except in the part that lies between the maximum and the pole. The influence will also be greater the higher the value of [absorptivity], that is in general somewhat greater for land than for ocean. On account of the nebulosity [cloudiness] of the Southern hemisphere, the effect will be less than in the Northern hemisphere. An increase in the quantity of carbonic acid will of course diminish the diference in temperature between day and night. A very important secondary elevation of the effect will be produced in those areas that alter their albedo by the extension and regression of snow-covering, and this secondary effect will probably remove the maximum from lower parallels to the poles."

    So, the current polar amplification was predicted over 110 years ago on the presumption of the greenhouse effect, while it so confounds denialist theories that they have to assert, against the evidence, that it is not hapening.

    Arrhenius' prediction was made without considering the effects of changes in water vapour levels due to change in temperature. I do not think that those changes suggest a stronger heating at the equator. It is true that the greatest greenhouse effect due to water vapour is found in the very humid tropics, but the change in humidity is due to the change in temperature, and that is not automatically stronger at the equator. In fact, the change in temperature is weakest at the equator, though because of the high temperatures, the change in humidity may be slightly higher there.
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  12. David Horton @9, I strongly suspect that what you say is true about the hard core deniers. What will change when yachts can regularly sail to the north pole in summer is that the hard core deniers will no longer have any credence with the general public. They will be viewed, and rightly so, with the same mental condescension that is reserved for flat earthers and geocentrists.
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  13. Tom @12,

    But Tom, the models, those hopeless models!!

    I jest, that was a very interesting post, and not a model in sight, probably not even in his wildest imagination...just hard physics. Very cool.

    And despite what Lindzen thinks, as shown by Ari's recent post on ocean levels (which I highly recommend) and the two recent seminal nature papers on extreme events, models can be incredibly useful tools.
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  14. Albatross, there was a model in sight. It was just simple enough to be implemented by pen and paper. This is one of the biggest confusions about models, which are in fact just mathematical equations which are worked through to find out what they actually predict.

    As some deniers rightly claim, models are not evidence. But they are the predictions of physical theory. As it happens, no plausible physical theory using only natural forcings predicts the warming in the late 20th century, nor the greater warming in the arctic, nor the decrease in the difference between day and night temperatures, nor the cooling stratosphere combined with a warming troposphere. All plausible physical theories including natural and anthropogenic forcings predict these.

    In this circumstance, rational people prefer the theories that actually predict what is actually happening. Deniers just obfusticate.
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  15. ... and very few people realise an important fact about Antarctica: it has an avergage elevation of 2,286 m.

    As a consequence, it is naturally colder than the Arctic, by about 20°C (calculated from the lapse rate), and so most Antarctic ice will be very slow to melt to a significant extent. Glaciers sliding into the ocean faster because of melting near the coast is another matter.
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  16. Rob,

    "If the Arctic Sea is covered with ice in the summer - as it has been dating back perhaps thousands, to millions of years - the incoming sunlight is mostly reflected back to space without adding any heat to the Earth. But, as ice melts back, as is happening today, the summer sun is absorbed by the darker open sea exposed by the disappearing ice."

    This couplet of sentances seems to allow for mis-interpretation. The wording seems to suggest that todays conditions represent a departure from conditions that have persisted for thousands or millions of years. This of course is not true. Evidence exists for possible ice free summers on thousands of years time scale.

    11 Tom Curtis

    Just for completedness, amplification isn't a feature specific to the greenhouse effect. It occurs in the history of the arctic during warming phases attributed to other forcings.

    For general interest there are two extensive science reviews here and here from a long list of eminent authors. My guess this would be the concensus view heading for AR5.
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  17. I am seriously trying to follow you guys without physics a subject I always wanted to learn but could not grasp, I am left with basic logic and observation.

    Can someone please explain the importance of why losing ice is and seems (to me) to be a bit of scaremongering. From what I can see and knowledge of history, like everything else on this planet it goes in cycles. One minute we are hot another cold. One minute theres ice and the next there is not. I can remember as a child rivers (salt) freezing over in southern England that you could walk on.

    We also know that the arctic regions were once fertile and that Mammoths were frozen in situ as they grazed these areas. In Roman times grapes tropically grown fruit was being farmed in Scotland and CO2 level were supposedly higher then than now as well as temperatures higher than now.

    Also why are sea levels not rising as high and as fast as some models predict with the big melt?

    Now I have tried to find out how true this is but supposedly oil companies as they pump the oil out of the ground is floated up by injecting sea water. If true how many millions of gallons of sea water is used, which is lost forever if the case is provable?
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  18. HR @16:

    1) There may have been ice free summers in the Holocene Climactic Optimum, but there certainly have been none since then. In view of the very large difference in Milankovitch forcing between now and then, that is no reason to suppose the current decline in arctic summer sea ice is natural.

    2) Arctic sea ice will melt for any warming, but warmings due to increased insolation or reduced cloud cover will have a strongest primary effect at the tropics. The net effect should be that the primary warming at the tropics and the secondary warming in the arctic should be of similar magnitude. In contrast, warming due to a strengthened greenhouse effect has a stronger effect at high latitudes than at the equator, which are then reinforced by the arctic amplification, resulting in much higher arctic warming than that seen in the tropics. It is the later we in fact observe, not the former.

    Changes due to orbital mechanics have a different pattern, with net incoming energy remaining essentially unchanged, but with large variations of insolation at high latitudes. Consequently polar amplification can reinforce an effect which preferentially warms NH summers. However, we know from astronomical observation that we are currently approaching a minimum in NH summer insolation. Hence, if that were the only influence, we would expect the arctic amplification to be increasing a reduction in summer temperatures, not an increase.

    Pretending that because High summer insolation coupled with polar amplification has lead to an ice free arctic summers in the past, that therefore our rapid approach to ice free arctic when we have low summer insolation is because of natural causes is disenginuous at best.
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  19. @17 HGP:

    1) Grapes are not a tropical fruit, they are a temperate climate fruit. They were grown as far north as Yorkshire in the Medieval Warm Period, and in Southern England in roman times, but never in Scotland. They are now grown in Yorkshire once more, and indeed are now grown in Sweden commercially outside of greenhouses, which has never happened before.

    One essential difference between now and the past is the relative cost of transport. High costs of transport during Roman and medieval times made it sensible to grow grapes to the limit of their cultivation. That is why grape growing survived in Southern England right through the LIA, but died early in the 20th century. However, even though transport is now cheap, growing grapes is sufficiently easy to make local commercial grape growing even in Yorkshire.

    2) During the summer months, the Earth receives more energy from the sun at the poles than at the equator. This is because the poles have 24 hour sunlight, even though the sunlight is much weaker because of the high latitude. The essential difference between ice and water in this context is that ice reflects approximately 90% of incoming sunlight, while water absorbs approximately 90% of incoming sunlight. In the summer months, that vast change in albedo, which coupled with the high summer insolation will make a significant change to overall global temperatures.

    That is quite apart from any ecological concerns about several species of seal and fish which are entirely dependent on sea ice for birthing (seals) or food (fish), or an even larger number of species including polar bears that are primarily dependent on sea ice.

    3) Sea levels are currently rising faster than is predicted by the models. This does not make sea levels a matter of significant concern for the next 50 odd years, but after that sea levels will have risen high enough to impose significant adaption costs.

    You obviously draw your information primarily from denier sites (either directly or indirectly). You should avoid that. They lie to you. They lie frequently, and with breath taking bravado. It is impossible to form a rational opinion based on deliberate falsehoods, so if you want to learn about global warming, avoid denier sites like the plague. At the very least, never believe anything you read on one of those sites until you have confirmed it on at least to genuine science sites like Skeptical Science and Real Climate.
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  20. hi guys, first post mid-2020s-releasing-100-billion-tons-of-carbon-by-2100/
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    Moderator Response: Welcome! In future please provide context for links, or your comment will be deleted. For this one, please post an additional comment with context such as a question.
  21. Rob Honeycutt,

    What percentage of the average global albedo is the Artic?
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  22. HumanityRules @ 16... I believe there is still considerable debate on that very point.

    See this lecture by Dr Barber.
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  23. RW1... I don't believe that is relevant to the article. I'm talking about polar amplification, not global temperature.
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  24. RW1: Surely you know the issue is not Arctic albedo as a percentage of the whole, the issue is added forcing due to the decreased Arctic albedo. See the Flanner thread for that discussion.
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  25. That's what I'm trying to quantify.

    How many W/m^2 of the roughly 102 W/m^2 total albedo comes from the Artic?
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  26. RW1... Again, we're talking about polar amplification, not the entire planet. Do you have a comment relative to the article?
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  27. That's what I'm trying to quantify - potential polar amplification. Without knowing the actual quantification of the polar albedo, how do you know it's of any real significance?

    How many W/m^2 of additional post albedo solar power are we going to get into the system from Artic melting? Without knowing how many W/m^2 are currently being reflected away, how can you know?
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    Moderator Response: [muoncounter] See the Flanner thread linked above.
  28. thankyou moderator


    how about oh bugger!!

    the quote i heard in a interview on abc radio was that the greenhouse gas from the expected permafrost release will be the equivalent of the GHG releases from the USA at their current level for the next 80 years
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    Moderator Response: [Daniel Bailey] One other thing about the permafrost release paper is that the authors used the most conservative estimates based upon the IPCC medium emissions scenario. Note that actual emissions are following the high-emissions scenario, so the outlook taint as optimistic as portrayed in the linked paper you kindly provide.
  29. RW1... I do not know the actual W/m2 without doing some research. But what I would suggest is that we know very clearly that there will be an increase in the Arctic when there is less ice. Correct?

    What I challenge you to do is not conflate the global change in albedo to the change of albedo in the Arctic. That would be an act of searching for a way to falsely downplay the effect.

    Be sure to also read Peter Offenhartz post at #4 so you understand that albedo is not the only mechanism behind polar amplification.

    Rather that beating around the bush I suggest you just give us the point you're wanting to make. Everyone here is open to hearing all perspectives. Point in case, Peter Offenhartz taught me something new I didn't know.
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  30. muoncounter,

    From Flanner thread article:

    "i.e. for each degree of global warming, the loss of snow and ice means that another 0.25 W of sunlight is absorbed per square metre of the Northern Hemisphere. Globally, and in the long run it’s expected to be 0.2 because there’s less snow in the south and you eventually run out of summer snow to melt."

    So about 0.2-0.25 W/m^2 per 1 degree of global warming?
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  31. **Case in point** Not point in case... It's getting late and I have the flu. blah.
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  32. Rob Honeycutt (RE: 29),

    "Rather that beating around the bush I suggest you just give us the point you're wanting to make."

    My point is this: +16.6 W/m^2 is needed at the surface for a 3 C rise. 2xCO2 only gives you about +6 W/m^2 (assuming all the additional absorbed energy affects the surface). What percentage of the additional 10 W/m^2 will come from 'polar amplification' from ice melting?
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  33. If it's only about 0.2 W/m^2 - that's only about 2% of the difference needed, or only about 0.03 degrees C of warming.
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  34. RW1... Again, you are conflating global temperature with polar amplification.
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  35. The issue at hand ultimately is what effect polar amplification may or may not have on global average temperatures, is it not?
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  36. RW1... No, it's not. Polar amplification just mean that. Global warming is amplified at the poles. Nothing more nothing less.
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  37. Rob: Better to say 'Arctic amplification' than 'polar' for the current context, as the South seems to respond dramatically differently.

    Serreze et al 2009 is a key paper describing what's happening in the Arctic.

    As the climate warms, the summer melt season lengthens and intensifies, leading to less sea ice at summer’s end. Summertime absorption of solar energy in open water areas increases the sensible heat content of the ocean. Ice formation in autumn and winter, important for insulating the warm ocean from the cooling atmosphere, is delayed. This promotes enhanced upward heat fluxes, seen as strong warming at the surface and in the lower troposphere. This vertical structure of temperature change is enhanced by strong low-level stability which inhibits vertical mixing.

    Peter Hogarth did an excellent post on this as well.
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  38. Grammatical mistake in the first sentence: understand
    Spulling mistake in the second paragraph: warm faster 'that' the rest.

    Also, it's "jibe," not "jive." Nitpicky, I know, but that typo has always bugged me, since the words basically mean opposite things.
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  39. Phila... I happen to like nitpicky. Fixed.
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  40. Tom @14,

    You are right, the framework which he used to make those calculations was in fact a simple model. In my original post I was thinking more in terms of the sophisticated and complex models (i.e., AOGCMs) that we are familiar with today, and not communicating very eloquently (my own lapse) that in fact there are some very basic (yet solid) physics are at play.

    Fascinating that Arrhenius predicted current events so very long ago.
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  41. RW1 @33, in 30 you quoted 0.2 w/m^2 per degree centigrade of global warming. That would mean the effect of polar amplification is 0.6 w/m^2 at 3 degrees of global warming, or 3.6% of the total effect.

    Of course, the figure you quoted is that derived from models which are underestimating the extent of sea ice loss in the arctic. Based on observation, the net forcing for the ice and snow loss to date is 0.62 w/m^2, and we have not yet experienced a full degree of global warming. That suggests the total effect could result in 7 to 10% additional warming, or up to an additional degree centigrade by the end of the century.
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  42. Albatross @40, yes, I love the fact that Arrhenius got it so right so long ago.

    The one area in which he slipped up was Antarctica, which was a virtual unknown at the time. The first attempt to reach the South Pole did not even set out until four years after his paper.

    SFAIK, there are three crucial distinctions about Antarctica.

    The first is that rather than sea ice, it has ice sheets which cannot melt to bedrock in a season, or even in a hundred years; thus side stepping the mechanism of polar amplification.

    The second is the uninterrupted ocean of the Antarctic ocean allows circumpolar currents and winds that drastically reduce heat transfer between the tropics and the antarctic. The original mechanism identified by Arrhenius only works because the polar regions recieve a significant amount of heat from the tropics, and as the Antarctic receives much less than the Arctic, the effect is much weaker there.

    The third is the unusual fact that due to the extreme cold of Antarctica, especially in winter, sometimes there is an inverted lapse rate over the continent. The surface temperature in these circumstances is actually colder than the tropopause. When that happens, the effect of increased greenhouse gases is to cool the continent rather than to warm it.

    It is uncertain what the net effect of this is. I believe most models predict much reduced warming, though at least one has predicted cooling for Antarctica.
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  43. Thanks for going to all the trouble to ensure that the public are as well informed as possible. A prodigious output for a one man site.

    Unfortunately, for every day that action is delayed because the public is presented with conflicting information, a lot of it unsupported, or supported in a misleading way, vote-seeking politicians have an immediate need to hang fire. As things stand, to quote Bob Dylan, the 'sceptics' are 'winning the war while losing every battle' (Bob Dylan).
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  44. One pretty strong argument you can use in the discussion with the deniers is that even gas and oil companies believe that the arctic ice is disappearing (although it is still unclear whether this means that they endorse AGW). In every case they are in full battle for the rights to drill for oil and gas in the Arctic Sea.
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    Moderator Response: [Daniel Bailey] Even Shell Oil Company, to their credit, is on record as accepting the findings of the IPCC AR4.
  45. @17 HPB
    “From what I can see and knowledge of history, like everything else on this planet it goes in cycles. One minute we are hot another cold. One minute theres ice and the next there is not. I can remember as a child rivers (salt) freezing over in southern England that you could walk on.”

    We have had some slight variations in the climate in historical times, for instance the Medieval Warming Period and the Little Ice age, but you shouldn’t compare f.i. a time in which it was possible to ice skate on the Thames in Winter (the little ice age) with a time in which the whole of Europe was covered in an ice layer 2 kilometers thick (a genuine Ice Age). Likewise, the worst case scenario: triggering a runaway greenhouse effect would have consequences that cannot in the least be compared to the medieval warming period.

    It is true that drastic climate changes have taken place in a more distant past due to natural causes so strictly speaking the current warming is not unprecedented in the entire history of the earth. But you have to understand that these past climate changes have led to mass extinctions, and a virtual standstill of the evolution for millions of years (look up for instance “snowball earth” or the “perm-trias mass extinction event”). The argument that sea ice melt or temperature trends have occurred in the past is in itself not comforting at all.

    I think this is a major problem with most people. They still think that climate change means we’re going to have a climate comparable to the south of France (at least that’s what people in Belgium think ). They even welcome the thought.

    We also know that the arctic regions were once fertile and that Mammoths were frozen in situ as they grazed these areas. In Roman times grapes tropically grown fruit was being farmed in Scotland and CO2 level were supposedly higher then than now as well as temperatures higher than now.

    Average global temperatures are currently higher than during the MWP, and still rising. CO2 levels have never been this high in historical times. They are the highest in 800000 years and very likely the highest since the origin of mankind, 3 million years ago. We are creating conditions on this planet that have not prevailed since the dawn of mankind. The consequences are difficult to predict, but knowing from the past how strong the earth’t climate may react to different conditions, we should prepare for the worst.
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  46. Tom Curtis (RE: 41),

    "RW1 @33, in 30 you quoted 0.2 w/m^2 per degree centigrade of global warming. That would mean the effect of polar amplification is 0.6 w/m^2 at 3 degrees of global warming, or 3.6% of the total effect.

    Of course, the figure you quoted is that derived from models which are underestimating the extent of sea ice loss in the arctic. Based on observation, the net forcing for the ice and snow loss to date is 0.62 w/m^2, and we have not yet experienced a full degree of global warming. That suggests the total effect could result in 7 to 10% additional warming, or up to an additional degree centigrade by the end of the century."

    Not really. There becomes less and less ice to melt, and you'll never melt it all because half of the year the Artic is dark and the ice grows back. Also, as more ice melts, you get closer and closer to North Pole, which means lower and lower insolation.

    Furthermore, increasing temperatures can lead to increases in evaporation, which can lead to increasing snow accumulations, which in turn increase the earth's surface albedo and have a cooling effect, which in turn can cause more ice to grow back.
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  47. As someone else has eluded to, for the last 4 years the arcitc sea ice level has been well below 2SD deviations from the 1979-2000 mean. This means all things being natural variation that there has been a 1:100 year at least event in the arctic every summer for the last 4 which would be a rarity I'd of thought.

    It is most likely from sea ice extent estimates and arctic temperature reconstructions that the arctic hasn't had this little ice in the summer and this high a temperatures since the thermal maximum if not longer and the trend for temeprature change in keeping with the Northern hemisphere insolation averages was for a slow cooling until 100ppm of CO2 was dumped into the atmosphere in a very short period, when the arctic temperature suddenly started to rise again. The arctic really should be cooling all things natural!

    Due to natural variation 2010 should have been on the cold side, unless of course the recent paper in nature saying the solar max and heat in put min. is correct. However if it is correct then there is no accounting for the LIA cooling other than the very slight drop in CO2 at the that time, which would mean CS to CO2 is very significant, so lets maintain that low sunspot activity means lower general earth temperatures, thus the none activity from 2008-2010 should have been a signifcant cooling effect of about 0.1-0.15C from the mean, La Nina (which was strong) and El-Nino (which wasn't strong in early 2010 until May) somewhat cancle each other out but still overall a cooling effect!

    Do wonder if the earth has slipped into a new phase with a higher median temperature with 2010 representing a low year in the natural variance?

    Would be in keeping with chaos for the climate to start to do jumps or leaps from one phase of being to the next.

    Anyway it is more likely that despite being much warmer in the pliocene and previous inter-glacials that the arctic ocean was still only free of ice in the summer. Virtually ice free summers do seem inevitable by 2050 at the latest, this is sobering stuff, for it will accelerate warming locally as water will warm up alot more than it did basking in the long summer sun and will release this heat in the Autumn.

    Lots of amplification potential and less latent heat exchanges which mean the artic winter to summer temperature differential will be amplified.

    Interesting times, new weather patterns to emerge, extreme events to witness and new arctic tourist industry to set up.

    Swim with the, ?who knows?

    Lets face it CO2 emissions aren't seriously going down any time soon so what were does leave us?
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  48. The interesting thing about the GISS anomaly map above is the choise of base=line (1951-1980). This was a relatively cooler period of time and to use that to show Arctic warming may distort what has recently been going on.

    I went to the GISS page (At this time I do not know how to paste a map on a post so I can only send a link) and put in this last decade for the baseline. The Global temp for January is lower than the last decade and the Arctic warming does not look too severe except around Greenland. Going to the Arctic sea ice page this is explaine by a negative Arctic Oscillation: Quote from the page "Arctic sea ice extent for January 2011 was the lowest in the satellite record for that month. The Arctic oscillation persisted in its strong negative phase for most of the month, keeping ice extent low."

    The negative phase kept parts of the Arctic warmer but created much colder weather in other areas as this cold air was able to move much further south.

    GISS Arctic temp map using 2000-2010 as the baseline.
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  49. Norman: Don't you think a comparison of what happened last month to what happened in the last 10 years has a major sample bias issue? Like comparing what happened yesterday with what happened last week?

    For further discussion of recent surface temperatures, go to Global warming stopped in ...
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  50. Norman... Remember, we're trying to look at climate, not weather. Your choice of the most recent 10 years as a base line is wrong on many levels. 1) It's not statistically significant (too few years). 2) Comparing the past year to the most recent decade tells you absolutely nothing.

    Stick with a 30 year baseline.
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