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The inevitability of sea level rise

Small numbers can imply big things. Global sea level rose by a little less than 0.2 metres during the 20th century – mainly in response to the 0.8 °C of warming humans have caused through greenhouse gas…

Miami, New York City… who’s next? Allstar/Fox 2000/Sportsphoto Ltd

Small numbers can imply big things. Global sea level rose by a little less than 0.2 metres during the 20th century – mainly in response to the 0.8 °C of warming humans have caused through greenhouse gas emissions. That might not look like something to worry about. But there is no doubt that for the next century, sea level will continue to rise substantially. The multi-billion-dollar question is: by how much?

The upper limit of two metres that is currently available in the scientific literature would be extremely difficult and costly to adapt to for many coastal regions. But the sea level will not stop rising at the end of the 21st century. Historical climate records show that sea levels have been higher whenever Earth’s climate was warmer – and not by a couple of centimetres, but by several metres. This inevitability is due to the inertia in the ocean and ice masses on the planet. There are two major reasons for the perpetual response of sea level to human perturbations.

One is due to the long lifetime and warming effect of carbon dioxide in the atmosphere. Once emitted carbon dioxide causes warming in the atmosphere over many centuries which can only be reduced significantly by actively taking the greenhouse gas out again. This is because both the amount of heat and carbon dioxide the ocean can absorb is reduced, and so the temperature stays up for centuries or even millennia. Of course, not cutting emissions would exacerbate the problem even further.

The other reason is that both the ocean and the ice masses are very big and a warming of the surrounding atmosphere will only penetrate slowly, but inevitably, into them. As a consequence their sea level contribution continues even if the warming does not increase. Sea level rise over the last century has been dominated by ocean warming and loss of glaciers. Our recent study indicates that the future sea level rise will be dominated by ice loss from the two major ice sheets on Greenland and Antarctica – slumbering giants that we’re about to wake.

Sea level rise contributions over 2000 years from: ocean warming (a), mountain glaciers (b), Greenland © and Antarctic (d) ice sheets. The total sea level commitment (e) is about 2.3m per degree of warming above pre-industrial.

It is easier to understand a future world that has adjusted to a new equilibrium of higher temperatures than it is to understand the dynamic (perhaps rapid) transition from today’s world to a warmer one. That is why we used physical models for the ocean, the mountain glaciers and the big ice sheets to compute how the systems would be different if the world was warmer.

What we found was that for each degree of global warming above pre-industrial levels the ocean warming will contribute about 0.4 metres to global mean sea-level rise while Antarctica will contribute about 1.2 metres. The mountain glaciers have a limited amount of water stored and thus their contribution levels off with higher temperatures. This is over-compensated for by the ice loss from Greenland, so that in total sea level rises quasi-linearly by about 2.3 metres for each degree of global warming (see figure).

How fast this will come about, we do not know. All we can say is that it will take no longer than 2,000 years. Thus the 2.3 metres per degree of warming are not for this century. They need to be considered as our sea level commitment - the sea level rise that cannot be avoided after we have elevated global temperatures to a certain level.

Ben Strauss of Climate Central has considered the different possible future pathways that society might take and computed which US cities are at risk in the long-term. He poses the question as to what year, if we continue with greenhouse emissions at current rates, we will have caused an inevitable sea level rise that puts certain cities at risk.

According to his analysis, within the next few years Miami in Florida will be committed to eventually lie below sea level, while our future actions can still decide on whether we want to one day give up cities such as Virginia Beach, Sacramento, Boston, Jacksonville or New York City.

This is a decision society has to take for future generations. We will need to adapt to climate change in any case, but some things we will not be able to adapt to. Society needs to decide whether we want to give up, for example, the Tower of London, or to put the breaks on climate change so that we don’t have to.

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80 Comments sorted by

  1. Mark McGuire

    climate consensus rebel

    Quote #1: "How fast this will come about, we do not know."

    This is known:

    "James Hansen, director of NASA's Goddard Institute, is arguably the world authority on climate change.
    He predicts we have just a decade to avert 25-metre rise of the sea.
    Picture an eight-storey building by the beach, then imagine waves lapping at it's roof.
    That's what a 25-metre rise in sea level looks like."

    http://newsstore.smh.com.au/apps/viewDocument.ac?page=1&sy=smh&kw=tim+flannery&pb=all_ffx&dt=selectRange&dr=entire&sd=12%2F02%2F2009&ed=12%2F02%2F2009&so=date&sf=author&rc=10&rm=200&sp=adv&clsPage=1&docID=AGE061028V15G63KM0OC

    Quote #2: "Global sea level rose by a little less than 0.2 metres during the 20th century – mainly in response to the 0.8 °C of warming humans have caused through greenhouse gas emissions."

    No link?

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    1. Greg North

      Retired Engineer

      In reply to Mark McGuire

      " He predicts we have just a decade to avert 25-metre rise of the sea.
      Some cientists think we may have already passed a tipping point, the 400 club for instance but if Hansen is saying that we have a decade to avert a 25M rise, that does not really say how fast it will come about and I doubt anyone could accurately predict that.

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    2. Alice Kelly
      Alice Kelly is a Friend of The Conversation.

      sole parent

      In reply to Mark McGuire

      Thats a pretty old document greg, at the moment the sea level rise seems to be 3.16 mm per year.
      http://climate.nasa.gov/key_indicators
      Anders, thank-you for the article. I'm most interested in the west antarctic ice sheet which is bedded on the ocean floor. Is anyone trying to determine how much greater the ocean has to heat, for its faster demise. I know predictions are hairy beasts, but how fast is its disintegration, also does this happen by temperature from below (known), and summer storms, does wind and current strength play a role?

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    3. Mike Hansen

      Mr.

      In reply to Mark McGuire

      James Hansen's assessment is not from models but is based on the geological evidence.

      "Two degrees Celsius of warming would make Earth much warmer than during the Eemian, and would move Earth closer to Pliocene-like conditions, when sea level was in the range of 25 meters higher than today, Hansen said. In using Earth's climate history to learn more about the level of sensitivity that governs our planet's response to warming today, Hansen said the paleoclimate record suggests that every degree…

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    4. Mike Hansen

      Mr.

      In reply to Mark McGuire

      Mark. While the 2006 article from Tim Flannery that you linked to provides a good explanation of the processes at work, he does underestimate the pace of melting of the Arctic sea ice.

      He also does not explain explicitly why the next decade is relevant to sea level rise over the next 2000 years.

      Anders explains it in his article.

      "One is due to the long lifetime and warming effect of carbon dioxide in the atmosphere. Once emitted carbon dioxide causes warming in the atmosphere over many centuries which can only be reduced significantly by actively taking the greenhouse gas out again."

      "actively taking the greenhouse gas out again." Good luck with that.

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    5. Mark McGuire

      climate consensus rebel

      In reply to Mark McGuire

      Greetings Mr. Levermann. Thank you for your response.

      Considering James Hansen announced co2 AGW in 1988, and consequently leads a world wide war on carbon (sic) energy to save the planet, to insinuate that Hansen DID NOT do a detailed look into the process is an astounding charge.

      Was it incompetence? Lack of data? GiGO IPCC computer climate models?
      What details did Hansen miss to reach a conclusion of a 25-metres sea level rise by 2016?

      No offence but why should I believe you and your…

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    6. Mark McGuire

      climate consensus rebel

      In reply to Mark McGuire

      Thanks for the links Mike, but they don't make Hansen's 25-metre SLR by 2016 any more accurate.

      28 months & 25-metres to go until where I live, surfing mecca, Kirra Point, will be a memory.

      Or Hansen was wrong & Anders is correct.
      But therein is the conundrum for me, as Anders assumptions are based on Hansen's original thesis.

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    7. Mark McGuire

      climate consensus rebel

      In reply to Mark McGuire

      Mike,
      Your statement that Flannery in 2006 " does underestimate the pace of melting of the Arctic sea ice" is an understatement to say the least.

      Quote Flannery 2006: "At the trajectory set by the new rate of melt, however, there will be no Arctic icecap in the next five to 15 years."

      No Arctic Ice cap by 2011/2021.

      15 years to "pin the tail on the donkey" is a pretty wide & forgiving target.
      First 3 years have been 'misses' from Flannery.

      Personally I would like a more accurate and provable KPI before I hand over my hard earned for a carbon (sic) tax or ETS.

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    8. Mark McGuire

      climate consensus rebel

      In reply to Mark McGuire

      Quote: "Personally I would like a more accurate and provable KPI before I hand over my hard earned for a carbon (sic) tax or ETS."

      Edit: Personally I would like a more accurate and provable KPI before I hand over my hard earned for a carbon (sic) tax, ETS or LNP Direct Action..

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    9. Mike Hansen

      Mr.

      In reply to Mark McGuire

      "Hansen's 25-metre SLR by 2016 "

      Now I understand what you are on about Mark. I thought your first comment sounded too coherent for a climate science denier.

      Here is a sanity test on that claim for you Mark.

      It is fair to say that the climate crank blogs hate James Hansen almost as much as they hate Michael Mann. To the extent that they analyse every punctuation mark in his publications and speeches. Yet this is the first time that I have ever heard the claim that Hansen predicted "25 metres of sea level rise by 2016".

      Don't you think that there is a slight chance that your chronic scientific illiteracy has left you completely bamboozled.

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    10. Mike Hansen

      Mr.

      In reply to Mark McGuire

      "Incompetence" ?

      Would that not apply to someone who confuses cause and effect?

      Now here is your opportunity Mark to show readers at TC that you are not in fact scientifically clueless.

      Find that quote from James Hansen where he predicts 25 metre sea level by 2016 and copy and paste it here.

      Should only take you a second.

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    11. Gary Murphy

      Independent Thinker

      In reply to Mark McGuire

      "...but they don't make Hansen's 25-metre SLR by 2016 any more accurate."

      I thought that was the misinterpretation you were going for. He never said sea levels would rise by 25m in ten years. He meant we had a decade to cut emissions to prevent an eventual rise in sea levels by 25m.

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    12. Andrew Vincent

      Marketing . Communications . Multimedia

      In reply to Mark McGuire

      You're mis-quoting, or misunderstanding. Hansen is not saying the actual sea level will rise by that amount by 2016.

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    13. Mark McGuire

      climate consensus rebel

      In reply to Mark McGuire

      Mike,
      The original comment above at top has the link and quote:
      "He predicts that we have just a decade to avert a 25-metre rise of the sea. "

      Hansen even describes the photo heading this article:
      "Picture an eight-storey building by a beach, then imagine waves lapping its roof. That's what a 25-metre rise in sea level looks like."

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    14. Mike Hansen

      Mr.

      In reply to Mark McGuire

      "when do the sea levels start to rise 25 metres?"

      They are rising now. Do you read the articles that you comment on?

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    15. Mike Hansen

      Mr.

      In reply to Mark McGuire

      The article that you linked to was from Flannery, not Hansen. He was discussing the Kyoto protocol and the need to reduce CO2 emissions.

      As Gary Murphy noted, Hansen was warning that we had a decade to reduce emissions before we committed the globe to a 2C+ temp rise - temperatures last seen on Earth during the Eemian and Pliocene.

      Read the NASA link I provided earlier. Hansen was pointing to the evidence provided by geologists and paleoclimatologists that during the Pliocene sea levels were 25 metres higher.

      You could have read the link before embarrassing yourself.

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    16. Chris O'Neill

      Victim of Tony Abbotts Great Big New Tax

      In reply to Mark McGuire

      "Hansen's 25-metre SLR by 2016"

      That's not what he said.

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    17. Chris O'Neill

      Victim of Tony Abbotts Great Big New Tax

      In reply to Mark McGuire

      "15 years to "pin the tail on the donkey" is a pretty wide & forgiving target."

      Let's see how forgiving all Arctic sea ice gone in 15 years will be.

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  2. Greg North

    Retired Engineer

    " This is a decision society has to take for future generations. We will need to adapt to climate change in any case, but some things we will not be able to adapt to. Society needs to decide whether we want to give up, for example, the Tower of London, or to put the breaks on climate change so that we don’t have to. "
    It could well be that the societal masses of India, China and elsewhere do not give two hoots about the Tower of London and more on their Taj Mahal or the Great Wall, both considerably inland.

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  3. Christopher Seymour

    Business owner

    "Once emitted carbon dioxide causes warming in the atmosphere over many centuries". This statement is quite simply not true, and its repetition hides some real options for solving the problem of global warming.
    According to the IPCC (http://www.nasa.gov/centers/langley/images/content/174212main_rn_berrien2.jpg) the atmosphere contains about 750 Gigatonnes of carbon in the form of carbon dioxide. And according to the same diagram the land and sea exchange about 210 Gigatonnes of carbon with the atmosphere…

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    1. Mike Hansen

      Mr.

      In reply to Christopher Seymour

      Christopher's argument is based on a misunderstanding of the carbon cycle.

      Not surprisingly this argument and variations of it surface often and it has a standard rebuttal here.
      http://www.skepticalscience.com/co2-residence-time.htm

      It is not the lifetime of an individual carbon atom that is at issue. It is the lifetime of the extra carbon that is accumulating in the atmosphere.

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    2. Alice Kelly
      Alice Kelly is a Friend of The Conversation.

      sole parent

      In reply to Christopher Seymour

      "Individual carbon dioxide molecules have a short life span of around 5 years in the atmosphere. However when they leave the atmosphere, they're simply swapping places with carbon dioxide in the ocean. The final amount of extra CO2 that remains in the atmosphere stays there on a time scale of centuries."
      http://www.skepticalscience.com/co2-residence-time.htm
      We are putting too much CO2 into the atmosphere for it to disappear to 0.01 grams. It is only removed by biological uptake and dissolving into the ocean. That's why current charts look like this.
      http://climate.nasa.gov/key_indicators
      There's no magic disappearing trick, "implied" by your post.

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    3. Christopher Seymour

      Business owner

      In reply to Christopher Seymour

      I think I understand the carbon cycle far better than you.

      Your reference isn't a rebuttal at all. It states as true that the average residence time in the atmosphere is only five years. Apart from the fact that whoever wrote this can't do the maths and apparently thinks that 750/215 = 5 when the answer is actually 3.52 the reference supports my comment. Don't you read your own references?

      The fact that the atmospheric carbon sink is so small is a very important and often obscured point. Partly it poses a serious risk because there are other much larger sinks, such as the deep oceans (38,000 Gt). A very small release from the deep oceans could cause a huge increase in atmospheric carbon.

      On the other hand the fact that there is so little carbon dioxide in the atmosphere represents an opportunity. If we were serious about averting global warming we would be considering ways to reduce carbon dioxide in the atmosphere. Cutting emissions - even to zero - can't do that.

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    4. Mike Hansen

      Mr.

      In reply to Christopher Seymour

      Again Christopher - you completely miss the point. The residence time of an individual CO2 molecule is largely irrelevant.

      The concentration of CO2 in the atmosphere has increased from approx 290 ppm pre industrial to around 400 ppm now. So CO2 is accumulating in the atmosphere despite the fact that individual molecules are circulating between the different carbon stores.

      And 750 Gigatonnes is not small by any measure.

      Assuming that we cease emitting ALL CO2 now, it would still take thousands of years to restore the CO2 levels in the atmosphere back to their pre-industrial levels.

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    5. Alice Kelly
      Alice Kelly is a Friend of The Conversation.

      sole parent

      In reply to Christopher Seymour

      I find these sort of letters embarrassing, you state, "the fact that there is so little carbon dioxide in the atmosphere represents an opportunity " (If you don't understand why scientific immaturity of this kind could be seen as embarrassing and painfully boring for a real scientist like Anders , I can't help you.)
      For what? destruction of the food chain in the ocean? Acidification of the worlds ocean means that minute calcareous organisms, shellfish, crabs, and corals can't form the calcareous structures designed for them to live. larger fish can't breath due to less oxygen so they become smaller. Habitat is lost due to the loss of coral. The food chain is damaged from the smallest to the largest. How is any of this an opportunity????
      http://oceanacidification.net/docs/Acid%20Test%20-%20Second%20Edition_June2009.pdf
      http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F
      http://www.gg.mq.edu.au/rep/websites/docs/paper.pdf

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    6. Christopher Seymour

      Business owner

      In reply to Christopher Seymour

      Once again my issue is the statement:
      "One is due to the long lifetime and warming effect of carbon dioxide in the atmosphere. "
      Whether or not this relevant the "long lifetime" is clearly wrong and the author should be embarrassed.
      750 Gt (actually the real number at a concentration of 400 ppm is 878 Gt) is a small number compared to the 31,000 Gt stored in the deep ocean or even the 1,600 Gt stored in the soil.

      Where do you get your "thousands of years" from. According to the Nasa chart…

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    7. Christopher Seymour

      Business owner

      In reply to Christopher Seymour

      Alice,
      The oceans are being acidified now. They will go on getting more acid for at least 50 years even if all human emissions stop. My discipline as an engineer rather than as a scientist tells me we should do something about it rather than just study it. Pouring more carbon into the atmosphere with international conferences isn't going to solve the problem.

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    8. Chris O'Neill

      Victim of Tony Abbotts Great Big New Tax

      In reply to Christopher Seymour

      "the "long lifetime" is clearly wrong"

      If you think the lifetime of the CO2 we put up there is so short then why is so much of it still up there after 200 years of opportunity for a lot of it to dissolve in the oceans?

      "if the 5.5 Gt of human emissions is removed there is a net imbalance of 2.1 Gt removed from the atmosphere. This would clear the human derived excess of 120 ppm in just 120 years."

      And what an insignificant time constant (for exponential decay) 120 years is!

      Even if you think a time constant of 120 years is insignificant (which it isn't), the other problem is that the oceans can only absorb 75% of the emitted CO2 in anything like that timescale (500 years). To get the level down more requires absorption by CaCO3 or igneous rocks, which takes many thousands of years: http://www.realclimate.org/index.php/archives/2005/03/how-long-will-global-warming-last/

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    9. Christopher Seymour

      Business owner

      In reply to Christopher Seymour

      Less than 30% of the carbon emitted by humans in the last 250 years is still up there. The 3.5 year average life of emitted carbon in the atmosphere is a mathematical fact.
      I have not disputed that bringing the carbon concentration back to pre-industrial levels under current policies will take a long time compared to human lifetimes. Nor to I dispute that current carbon levels pose a serious risk to humanity - most immediately those located in the many large cities just above current sea levels…

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    10. David Bindoff

      manager

      In reply to Christopher Seymour

      Chris, I need some clues, I just can't see how you can put a billion tons of water per day onto the driest and most inhospitable place.Where does the water come from and how does it get there? As far as I could see it's going to take more energy than current total world electricty production.
      (I think it is laudable to be engaging with the problem of sea level rise though)

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    11. Chris O'Neill

      Victim of Tony Abbotts Great Big New Tax

      In reply to Christopher Seymour

      "Less than 30% of the carbon emitted by humans in the last 250 years is still up there. The 3.5 year average life of emitted carbon in the atmosphere is a mathematical fact."

      If your 3.5 years figure is relevant then the anthropogenic part of CO2 in the atmosphere will equal 3.5 years of our emissions when it is actually way more than that.

      I think you need to brush up on your "mathematical facts".

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    12. Anders Levermann

      Professor of Dynamics of the Climate System at Potsdam Institute for Climate Impact Research

      In reply to Christopher Seymour

      Chris is making a very valid point. In addition please consider the link that I provide in the text. The temperature decline after the complete cessation of CO2 emission has been considered by a number of papers a lot of them appeared in 2009. The one I cite is by Susan Solomon and colleagues, but there are more. The decline of CO2 and temperatures is very slow.

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  4. Geoffrey Henley

    Research Associate

    "Global sea level rose by a little less than 0.2 metres during the 20th century – mainly in response to the 0.8 °C of warming humans have caused through greenhouse gas emissions. "

    Where is the irrefutable evidence that the 0.8 degree rise is almost entirely due to greenhouse gas emissions?

    Global temperatures have been rising and falling for time immemmorial. To completely ignore the fact that natural cycles could have at least, in part, contributed significantly to the 0.8 degree rise is a complete disregard for the scientific method. Evidence from ice core samples suggest that rises in global temperature precede rises in the CO2 concentration, not the other way around.

    The above statement sounds more like a political statement than a scientific one.

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    1. Alice Kelly
      Alice Kelly is a Friend of The Conversation.

      sole parent

      In reply to Geoffrey Henley

      http://climate.nasa.gov/key_indicators
      If you genuinely want answers, you can look at any of the information on the left hand side of the graphs for :Carbon dioxide concentrations, Global surface temperature, Arctic sea ice, Land ice, and Sea Level.
      The key words are Evidence, Causes, Effects, and lastly Consensus.

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    2. Mike Hansen

      Mr.

      In reply to Geoffrey Henley

      "irrefutable evidence"

      No such thing exists in science which is quite ironic as you are always quacking on about the "scientific method".

      Some of the evidence which is overwhelming (but not irrefutable) is here.
      http://climate.nasa.gov/evidence

      Interesting that you have the same misunderstanding of the scientific method as climate cranks Anthony Watts and Rich Trzupek when they rubbished Michael Mann's point that
      “Proof is for mathematical theorems and alcoholic beverages. It’s not for…

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    3. Alice Kelly
      Alice Kelly is a Friend of The Conversation.

      sole parent

      In reply to Geoffrey Henley

      And another thing, " global temperatures have been rising and falling for time immemorial"........ "natural cycles"
      Well the chart you would note shows historic CO2 levels moving between 300 ppm and 180 ppm for the last 400,000 years, this would be the sort of time your talking about, and the sort of variation. Since 1950 the line goes up dramatically to 400 ppm. Natural variation can't explain this.

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    4. Geoffrey Henley

      Research Associate

      In reply to Geoffrey Henley

      So logically, if there is no proof, then the claims that 'the science is settled' and 'there is no debate' must be false.

      So, therefore Professor Levermanns statement that "mainly in response to the 0.8 °C of warming humans have caused through greenhouse gas emissions" must be false because it implies proof rather than evidence.

      But of course, the Potsdam Institute has shown it self to under the control of alarmist zealots rather than objective scientists.

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    5. Geoffrey Henley

      Research Associate

      In reply to Geoffrey Henley

      Quite frankly, one has to question the objectivity of an organisation that displays the nonsensical 97% consensus statement on their website.

      Apart from the fact that consensus has nothing to do with science, the studies referenced to support this statement are methodologically flawed and do not distinguish between scientists who think that humans have some effect on the climate, but that that effect is relatively minor (sceptics) and those that think that humans activities could lead to catastrophic consequences and all those in between. They are practically useless.

      It appears that NASA cherry picks data to suit the alarmist theme and ignores any research that contradicts this theme.

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    6. Alice Kelly
      Alice Kelly is a Friend of The Conversation.

      sole parent

      In reply to Geoffrey Henley

      Geoffrey, did you ever submit your findings to John Cook that only 65 scientists were sure about climate science in the affirmative? for clarification?

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    7. Mike Hansen

      Mr.

      In reply to Geoffrey Henley

      We cannot "prove" the theory of gravity but I would not suggest jumping off a tall building.

      You continue to use the word "settled" as if it has mystical powers. It is just another English word that has meaning in context. In the strictest sense, nothing in science is ever "settled" (see Popper - scientific theories are “forever tentative”).

      But that does not imply the need to engage in extensive debate about the theory of gravity every time a plane takes off. In that sense the science is "settled".

      AGW is the scientific theory that best fits the evidence. The enhanced Greenhouse effect was first proposed in 1820 so there has been plenty of time for someone to come up with a better theory.

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    8. Mike Hansen

      Mr.

      In reply to Geoffrey Henley

      "consensus has nothing to do with science"

      We have already established that you do not understand the scientific method and the nature of scientific "proof".

      You do not understand the role of consensus in science either.

      From the Skeptical Science consensus project FAQ.
      http://theconsensusproject.com/#evidence
      "Consensus doesn’t prove human-caused global warming. Instead, the body of evidence supporting human-caused global warming has led to a scientific consensus."

      And from NASA
      "Consensus: 97% of climate scientists agree"
      http://climate.nasa.gov/scientific-consensus

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    9. Geoffrey Henley

      Research Associate

      In reply to Geoffrey Henley

      Your question implies a lack of understanding here. The 65 has nothing to do about 'climate science being in the affirmative'. I'm not sure what that even means since it is so vague. And it is not 65 scientists, it is 65 studies.

      65 is the number of studies that were given a rating that explicitly endorses the consensus that humans are responsible for most of the recent warming. It's pretty simple really.

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    10. Geoffrey Henley

      Research Associate

      In reply to Geoffrey Henley

      But the vast majority of sceptics acknowledge the greenhouse effect so that is not the issue. However, the relationship between C02 concentration and temperature is logarithmic, not linear, so as C02 increases in the atmosphere its effect is less and less.

      The theory of CAGW relies almost entirely on unproven positive feedback mechanisms

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    11. Geoffrey Henley

      Research Associate

      In reply to Geoffrey Henley

      I do understand that consensus has no place in science, which is about evidence, not opinion. History is littered with examples where the consensus view has proven to be wrong.

      Cook and others use deliberately vague definitions about what the consensus is even about. They use vague terminology such as 'humans cause global warming' or 'endorse AGW' which includes most sceptics. In this way, Cook conjures up his meaningless 97% figure.

      The definition used by NASA below is also poorly defined and is not supported by the references supplied, none of which possess a methodology which is capable of remotely estimating the true proportion of scientists who adopt a particular view re AGW.

      "Ninety-seven percent of climate scientists agree that climate-warming trends over the past century are very likely due to human activities"

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    12. Mike Hansen

      Mr.

      In reply to Geoffrey Henley

      "unproven positive feedback mechanisms"

      Water vapour is a strong greenhouse gas. This is not controversial.
      A warmer atmosphere can hold more water vapour. 7% per 1C. This is not controversial as anyone who has travelled to the tropics will attest.
      http://www.csiro.au/news/Climate-Change-Water-Vapour

      Snow and ice reflect sunlight back to space. (Ask any snow skier. This is not controversial.).
      The ocean has a lower albedo than sea ice.
      Melt ice (e.g. Arctic sea ice) and less sunlight is reflected back to space leaving more to warm the oceans.
      http://nsidc.org/cryosphere/seaice/processes/albedo.html

      Would you like me to keep going?

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    13. Mike Hansen

      Mr.

      In reply to Geoffrey Henley

      "I do understand that consensus has no place in science, which is about evidence, not opinion."

      You continue to knock down the same strawman. Are you hoping that no one will notice?
      "Consensus doesn’t prove human-caused global warming. Instead, the body of evidence supporting human-caused global warming has led to a scientific consensus."
      http://theconsensusproject.com/#evidence

      "History is littered with examples where the consensus view has proven to be wrong."

      What consensus view? You just said consensus was irrelevant. You appear confused.

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    14. Geoffrey Henley

      Research Associate

      In reply to Geoffrey Henley

      Once again you fail miserably to address my points.

      As I have pointed out time and again, John Cook and others continue to provide definitions of a consensus that are so vague, that they include the vast majority of sceptics. What you have is some form of an apparent consensus that human activities have some impact on the global climate. What you absolutely DO NOT have is any credible evidence for a consensus that human activities are causing the Earth's climate to heat dangerously because none of the cited studies address this issue.

      Is that so hard to understand?

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  5. David Bindoff

    manager

    "How fast this will come about, we do not know. All we can say is that it will take no longer than 2,000 years. Thus the 2.3 metres per degree of warming are not for this century."

    An upper time bound is placed but no lower time bound in the first statement. The 'Thus' does not necessarily follow, so are you saying it will take at least 90 years to achieve equilibrium level of a further 2 metres or so of sea level rise due to already emitted greenhouse gases?

    Is it possible that some dynamical…

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    1. Mike Hansen

      Mr.

      In reply to David Bindoff

      This article in today's New York Times covers the issue.

      As well as discussing Ander's paper, it also discusses a new paper from Michael O'Leary et al from Curtin University in WA.

      http://www.nytimes.com/2013/08/13/science/timing-a-rise-in-sea-level.html?_r=0

      " Dr. O’Leary’s group found what they consider to be compelling evidence that near the end of the Eemian, sea level jumped by another 17 feet or so, to settle at close to 30 feet above the modern level, before beginning to fall as the ice age set in.

      "In an interview, Dr. O’Leary told me he was confident that the 17-foot jump happened in less than a thousand years "

      " ...if the work does hold up, the implications are profound. The only possible explanation for such a large, rapid jump in sea level is the catastrophic collapse of a polar ice sheet, on either Greenland or Antarctica."

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    2. David Bindoff

      manager

      In reply to David Bindoff

      Thanks for that. It's hard to imagine 'catastrophic collapse' would occur any slower than a few months I guess, though warning signs would most likely be seen well before that.

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    3. Alice Kelly
      Alice Kelly is a Friend of The Conversation.

      sole parent

      In reply to David Bindoff

      Mike, just one more thing, I once read something about this very question and haven't been able to find it. Scientists were looking around for evidence that ice collapse could happened suddenly, and realised that the creation of the hudson bay was one place which seemed to have been created by a sudden event of ice movement over the space of days or weeks. If you ever find this in your googling please give me the link. I'll try again now, just incase it was my inexperience at the time.

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    4. Anders Levermann

      Professor of Dynamics of the Climate System at Potsdam Institute for Climate Impact Research

      In reply to David Bindoff

      Thank you for these questions. To answer them iin detail would require a lot of space and thought which I cannot provide here. I was a coauthor of the upcoming IPCC report which will be released September 30th. You will find some of your answers there, but one has to keep in mind that the IPCC is providing only the "best guess" of the future sea-level evolution and not the upper bound. It is asking the question "what is likely to happen" not "what could happen". That is very important to keep in…

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    5. Mike Hansen

      Mr.

      In reply to David Bindoff

      It is estimated that the deglaciation of the Hudson Bay took about 400 years.

      Decades, centuries and millennia, not weeks and months are the timescales for ice sheet collapse and sea level rise. The ice sheets are Kms thick - that takes a lot of energy to melt or even destabilise. But as New York discovered, even a small amount of sea level rise can overwhelm flood defences during storm surges.

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  6. James Gerard

    Climate and Energy Research at Transplan

    Anders, you say "The other reason is that both the ocean and the ice masses are very big and a warming of the surrounding atmosphere will only penetrate slowly, but inevitably, into them."

    However, it is my understanding that the WAIS (West Antarctic Ice Sheet) which is largely held in place by ice anchored to underwater rock, is under serious threat of rapid collapse, since warming ocean waters are causing accelerated melting of the underwater ice.

    While it is difficult, as in all such cases…

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    1. Anders Levermann

      Professor of Dynamics of the Climate System at Potsdam Institute for Climate Impact Research

      In reply to James Gerard

      I can only answer very briefly that the collapse of the WAIS is incorporated in the contribution of Antarctica in our simulations. The Antarctica contribution is based on simulation of the last 5 million years published by Pollard & DeConto in Nature in 2009. During this period temperatures varied significantly and so did the Antarctic ice volume. The simulation compares well with paleorecords of this period which was shown in a Twin paper in the same edition of Nature. Especially the WAIS collapse is captured by this model.

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    2. James Gerard

      Climate and Energy Research at Transplan

      In reply to James Gerard

      Still waiting for more from you.

      On further reflection, I would ask, how can you say that the collapse of the WAIS is incorporated when you speak only of 2 meters of ocean rise?

      Are you depending on the theory that only two meters of rise is possible by the end of this century including all sources, WAIS, EAIS, Greenland, and the smaller contribution from remaining large glaciers in South America and Asia? (Which, if allowed to melt, will leave major populated areas without consistent…

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    3. Anders Levermann

      Professor of Dynamics of the Climate System at Potsdam Institute for Climate Impact Research

      In reply to James Gerard

      The model simulation for Antarctica are exactly the on by David Pollard (coauthor of our study) and Robert De Conto from Penn State. They used paleorecords of temperature and alike to force their Antarctic ice sheet model. In response to the forcing of the past 5 million years the ice sheet responded by growing and shrinking. This was compared to independent paleorecords of the region (Naish et al. Nature 2009). The model is physically capable of a WAIS collapse because it incorporates the grounding-line…

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    4. Anders Levermann

      Professor of Dynamics of the Climate System at Potsdam Institute for Climate Impact Research

      In reply to James Gerard

      ...and there are other possible reasons why the threshold is not visible. One being that in the past the forcing was weaker than at present and thus the instability took longer than 2000 years. If the forcing "rushes by" an unstable regime you might not see the instability fully develop because the surrounding conditions have changed in a stabilizing way too quickly to see it.

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    5. Anders Levermann

      Professor of Dynamics of the Climate System at Potsdam Institute for Climate Impact Research

      In reply to James Gerard

      This is our current result of what the sea-level commitment will be. Science is a constant flow. While I think this is a good contribution respect of science demands to realize that it might not be the final answer... let s see and enjoy the path of understanding....

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    6. James Gerard

      Climate and Energy Research at Transplan

      In reply to James Gerard

      Very interesting reply and analysis. It will take me some time to digest this material, including expanding my research into some of the parameters.

      I very much appreciate you taking the time to answer this fully.

      "...let's see and enjoy the path of understanding" Yes! Most emphatically.

      However we analyse the present situation and make projections as to future changes, one thing is clear. The World must stop using fossil carbon as fuel as soon as possible.

      One of the best, if not…

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  7. John McKeown

    JRI Associate. Past: module leader, Gloucestershire University; and Assoc. Lecturer, Open University. PhD (Liverpool). Currently: IT support, Exeter University. Sector: at Higher Education.

    Thank you Anders Levermann for this informative article.

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  8. MItchell Lennard

    Researcher - Distributed Energy Systems

    Hi Anders,

    Thank-you for the article which explains your reasoning very clearly. The concept of looking at the longer term steady state conditions allows those of us who get lost in the dynamics to start to understand.

    And thank you to Alice and Mike for once again trying to explain issues. I admire your ongoing determination. Personally I gave up some years ago 'discussing' these issues with people who insist on gathering snippets of information and opinion from the web then using those factoids…

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    1. James Gerard

      Climate and Energy Research at Transplan

      In reply to MItchell Lennard

      Anders, Alice, Mike, Mitchell, it has been a great pleasure participating in this discussion. Thanks to all of you,

      Here is another excellent book, a major resource for understanding the best technology for using Nuclear Power as the major component of refocusing our energy production.

      Thorium in the LFTR is clearly the best way forward. I find the evidence overwhelming that solid fuel reactors have an extremely limited place, if any place, in our energy future. In particular, the IFR, with its exceedingly complicated fuel recycling procedures and the inherent and inescapable dangers of Sodium Cooling, needs to be reevaluated. I would like to see the great energy and knowledge of people now working on the IFR redirected into a vigorous LFTR program.

      Read "Thorium Energy Cheaper Than Coal" by Dr Robert Hargraves.

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    2. Anders Levermann

      Professor of Dynamics of the Climate System at Potsdam Institute for Climate Impact Research

      In reply to MItchell Lennard

      James,
      wrt the discussion of nuclear power, I find two aspects critical when considering it as a solution for the GLOBAL problem. 1. a global energy solution needs to be for everyone, so the question is can it be made a weapon and is it safe and 2. does it require the exploration of a finite resource?
      Anders

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