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Earth's Climate History: Implications for Tomorrow

Posted on 26 July 2011 by James Hansen

This a re-post of an article by James E. Hansen and Makiko Sato 

The past is the key to the future. Contrary to popular belief, climate models are not the principal basis for assessing human-made climate effects. Our most precise knowledge comes from Earth's paleoclimate, its ancient climate, and how it responded to past changes of climate forcings, including atmospheric composition. Our second essential source of information is provided by global observations today, especially satellite observations, which reveal how the climate system is responding to rapid human-made changes of atmospheric composition, especially atmospheric carbon dioxide (CO2). Models help us interpret past and present climate changes, and, in so far as they succeed in simulating past changes, they provide a tool to help evaluate the impacts of alternative policies that affect climate.


Hansen IllustrationHumans lived in a rather different world during the last ice age, which peaked 20,000 years ago. An ice sheet covered Canada and parts of the United States, including Seattle, Minneapolis and New York City. The ice sheet, more than a mile thick on average, would have towered over today's tallest buildings. Glacial-interglacial climate oscillations were driven by climate forcings much smaller than the human-made forcing due to increasing atmospheric CO2 -- but those weak natural forcings had a long time to operate, which allowed slow climate feedbacks such as melting or growing ice sheets to come into play.


Paleoclimate data yield our best assessment of climate sensitivity, which is the eventual global temperature change in response to a specified climate forcing. A climate forcing is an imposed change of Earth's energy balance, as may be caused, for example, by a change of the sun's brightness or a human-made change of atmospheric CO2. For convenience scientists often consider a standard forcing, doubled atmospheric CO2, because that is a level of forcing that humans will impose this century if fossil fuel use continues unabated.

We show from paleoclimate data that the eventual global warming due to doubled CO2 will be about 3°C (5.4°F) when only so-called fast feedbacks have responded to the forcing. Fast feedbacks are changes of quantities such as atmospheric water vapor and clouds, which change as climate changes, thus amplifying or diminishing climate change. Fast feedbacks come into play as global temperature changes, so their full effect is delayed several centuries by the thermal inertia of the ocean, which slows full climate response. However, about half of the fast-feedback climate response is expected to occur within a few decades. Climate response time is one of the important 'details' that climate models help to elucidate.

Hansen Fig 1
Fig. 1. Global temperature relative to peak Holocene temperature, based on ocean cores.

We also show that slow feedbacks amplify the global response to a climate forcing. The principal slow feedback is the area of Earth covered by ice sheets. It is easy to see why this feedback amplifies the climate change, because reduction of ice sheet size due to warming exposes a darker surface, which absorbs more sunlight, thus causing more warming. However, it is difficult for us to say how long it will take ice sheets to respond to human-made climate forcing because there are no documented past changes of atmospheric CO2 nearly as rapid as the current human-made change.

Ice sheet response to climate change is a problem where satellite observations may help. Also ice sheets models, as they become more realistic and are tested against observed ice sheet changes, may aid our understanding. But first let us obtain broad guidance from climate changes in the 'recent' past: the Pliocene and Pleistocene, the past 5.3 million years.

Figure 1 shows global surface temperature for the past 5.3 million years as inferred from cores of ocean sediments taken all around the global ocean. The last 800,000 years are expanded in the lower half of the figure. Assumptions are required to estimate global surface temperature change from deep ocean changes, but we argue and present evidence that the ocean core record yields a better measure of global mean change than that provided by polar ice cores.

Civilization developed during the Holocene, the interglacial period of the past 10,000 years during which global temperature and sea level have been unusually stable. Figure 1 shows two prior interglacial periods that were warmer than the Holocene: the Eemian (about 130,000 years ago) and the Holsteinian (about 400,000 years ago). In both periods sea level reached heights at least 4-6 meters (13-20 feet) greater than today. In the early Pliocene global temperature was no more than 1-2°C warmer than today, yet sea level was 15-25 meters (50-80 feet) higher.

The paleoclimate record makes it clear that a target to keep human made global warming less than 2°C, as proposed in some international discussions, is not sufficient – it is a prescription for disaster. Assessment of the dangerous level of CO2, and the dangerous level of warming, is made difficult by the inertia of the climate system. The inertia, especially of the ocean and ice sheets, allows us to introduce powerful climate forcings such as atmospheric CO2 with only moderate initial response. But that inertia is not our friend – it means that we are building in changes for future generations that will be difficult, if not impossible, to avoid.

Hansen Fig 2
Fig. 2. Greenland (a) and Antarctic (b) ice mass changes deduced from gravity field measurements by Velicogna (2009) and best-fits with 5-year and 10-year mass loss doubling times.

One big uncertainty is how fast ice sheets can respond to warming. Our best assessment will probably be from precise measurements of changes in the mass of the Greenland and Antarctic ice sheets, which can be monitored via measurements of Earth's gravitational field by satellites.

Figure 2 shows that both Greenland and Antarctic ice sheets are now losing mass at significant rates, as much as a few hundred cubic kilometers per year. We suggest that mass loss from disintegrating ice sheets probably can be approximated better by exponential mass loss than by linear mass loss. If either ice sheet were to lose mass at a rate with doubling time of 10 years or less, multi-meter sea level rise would occur this century.

The available record (Figure 2) is too brief to provide an indication of the shape of future ice mass loss, but the data will become extremely useful as the record lengthens. Continuation of these satellite measurements should have high priority.

A copy of this web page is also available as a PDF document.

References

Hansen, J., M. Sato, 2011: Paleoclimate implications for human-made climate change, Accepted for publication in "Climate Change at the Eve of the Second Decade of the Century: Inferences from Paleoclimate and Regional Aspects: Proceedings of Milutin Milankovitch 130th Anniversary Symposium" (A. Berger, F. Mesinger, and D. Šijači, Eds.)

Velicogna, I., 2009: Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE, Geophys. Res. Lett., 36, L19503, doi:10.1029/2009GL040222. 

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Comments 1 to 39:

  1. Worrying times unless we stop CO2 emissions.

    Peak 400pmm as a suggestion for safety?

    In figure 1 the early Pliocene (CO2 330-400ppm), is 2C hotter but I pressume it still had 20-25m higher seas, poles 19-21C hotter, warmer Eastern Pacific temperatures, wider tropical belt and generally different climatic zones when compared to the present as other researchers have reported. (Lunt D.J. et al, “Earth system sensitivity inferred from Pliocene modelling and data”, Nature Geoscience, VOL 3 , JANUARY 2010, Pagani M et al, “High Earth-system climate sensitivity determined from Pliocene carbon dioxide concentrations” Nature Geoscience VOL 3 , JANUARY 2010, Seki O. et al, “Alkenone and boron-based Pliocene pCO2 records” Earth Planet Sci Lett (2010), Schneider B. “Global warmth with little extra CO2”, Nature Geoscience, VOL 3, pg. 6-7, 2010, Csank, A.Z., et al., “Estimates of Arctic land surface temperatures during the early Pliocene from two novel proxies”, Earth Planet. Sci. Lett. (2011))


    The Early Pliocene is most often reproted to be 3-5C hotter (ref. above) than pre-industrustial times making the 100yr climate sensitivity for a doubling of CO2 to be alot higher at 4.5-7.5C (70ppm is 0.4 of a halving if the initial CO2 is 350ppm, 70/(350/2)), whereas if 2C is correct then CS 3C is correct as above.

    Basically though over the long term 350ppm gets you to the Pliocene whatever its temperature was and you gets about 60% along the way in 100years (unless there is a significant hystersic effect in the way which seems unlikely as Greenland is likely to melt and Antarctica has been a stable albedo for much longer) and if it was only 2C hotter, 1.4C is 100 years looks a lot more relevant and we've already gone ~0.7C.

    Wonder how much effect an summer ice free arctic will have on the rate melt of Greenland?

    Ignoring the possibility of at least 2m sea levels rise by 2100 would seem poor planning to me.
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  2. Hansen and Sato reiterating their paper from earlier this year. Good stuff all.
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  3. Clear and simple enough for even me to understand with an honest statement of what is still uncertain.

    Thankyou for a great article.
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  4. The issue of intertia in the climate system is an important one to consider, but what about the issue of inertia in the increased emissions of anthropogenic greenhouse gases?

    Even with the best will in the world - which simply doesn't exist anyway - it will take considerable time before we can transition from our current emission rates to a 'low carbon' culture. How far will CO2 rise in the interim?

    But - and here's the big but - the dual problem of rising energy demands from developing economies, and the lack of political will in almost every country in the world, means that emissions are alomst certain to rise by a considerable amount before we either can or will do anything about it. What will that mean for global temperature increases?

    I hate to sound pessimistic, but everything seems to be pointing towards a more than doubling of CO2 levels - and if a 2 degree rise is going to be problematic (and I agree with that assessment), what will a 3, 4 degree or more rise mean? (yes, I have seen the Nat Geo videos)
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  5. Mandas,

    Well, I'll risk sounding doom and gloom...

    But before I do, a heartfelt thanks to Jim for all his efforts.


    We are off the map. There be monsters here, and we don't know when or where they will strike, how hard they'll bite or how many of them there will be.

    To me, food supply is the most serious risk. If a poor man runs out of food, he starves, if a man with a gun runs out of food, bad things happen.
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  6. Crunching Velicogna's numbers, I make the annual sea level rise from melted polar land ice (assuming my abacus has all its beads) 0.65mm pa in 2003 & 1.5mm pa in 2008. Any rapid increases in those rates will soon show up in the sea level data which are running at +3mm pa (itself a modest ten times the average rise for the last 3,000 years!).
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  7. Hansen and Sato now say 2 degrees is going to be a disaster, as that 'inertia' begins to subside. In the meantime, its like a 'Faustian bargain' that inertia, it has put policy makers and the public into a complacency that in the end will bring hell.

    Yes extreme weather events are beginning to cause havoc everywhere. Here in Connecticut yesterday late, strong storms, 60pmh winds, massive power outages. Tornado warnings.

    These kind of events are increasing. The problem is; when will the public begin to take notice, and tie this together with AGW?

    Unfortunately that be be another 10-20 years. By then C02 will be way beyond 400ppm, and rising faster each year- approaching 3ppm annually.

    450ppm is now a forgone conclusion- 550 a doubling from pre industrial ti lagging inertia will finally begin to respond to these high levels of C02 on a scale that will be horrific- WE will likely reach 700ppm before emissions are reduced significantly, and by then feedback's will take over.

    All N all not good news for civilization.
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  8. I may add, that Hansen has said now, that an additional 1 degree rise C- is too much.
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  9. CO2 has risen at 3ppm pa momentarily but the average is still about the 2ppm level. (I will attempt to support this assertion with some graphical support. This will involve a web link which I have a bad history with.)
    See graph here.
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  10. Anyone know a ball park figure for the carbon footprint in switching our fossil fuel infrastructure to a sustainable one?
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  11. "To me, food supply is the most serious risk. If a poor man runs out of food, he starves, if a man with a gun runs out of food, bad things happen."

    Bad things.... survival of the fittest....
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  12. My background is health science not climate science. Thankyou to all the contributors to Skeptical Science for dedicated and heroic efforts in reporting and explaining the science. This nightmare is almost too difficult to comprehend, wakes me up at night in fear for my children's future and the future of millions of people in terms of food supply and wars - it is probably waking some of you up at night also. Up until now I had been telling people that 2 degree C was the guardrail - not so.
    Are we able to scientifically link the rise in extreme/severe weather events in terms of being attributable to climate change ? To me it seems like having a cohort of smokers and finding increased rates of cancer, stroke, heart attacks, peripheral vascular disease and emphysema as predicted by science.
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  13. "Anyone know a ball park figure for the carbon footprint in switching our fossil fuel infrastructure to a sustainable one? "

    Lets look at two things that would make most difference.

    1/ Stop building FF power stations. No immediate effect but once an aging power station has to be replaced, then the replacement generation needs to be non-FF type. Since you are only replacing stations that would be have to be built anyway, the carbon footprint of changing to sustainable is zero unless the carbon-footprint of renewable generation is significantly higher than than of construction FF power. Also, once you have around 50% of energy from non-FF, then carbon cost of construction would also start to drop off significantly. You do know that say windmills and solar very rapidly produce more energy than the cost of creating them?

    2/Electrification of transport. If vehicles are replaced with electric ones at end of life only, then again, the carbon footprint of change neutral, then decreasing if energy of construction is from non-FF.
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  14. Sally #12: "Are we able to scientifically link the rise in extreme/severe weather events in terms of being attributable to climate change ?"

    That's a hot button issue. Most people will respond with a cautious 'maybe'; statements like the probability of extreme events has increased due to global warming. See the prior extreme weather thread for cautious discussion of 2010's events.

    The frequency of extreme warm anomalies increases disproportionately as global temperature rises. "Were global temperature not increasing, the chance of an extreme heat wave such as the one Moscow experienced, though not impossible, would be small"

    See this recent Scientific American series for this year's version:

    Increasingly, the answer is yes. Scientists used to say, cautiously, that extreme weather events were "consistent" with the predictions of climate change. No more. "Now we can make the statement that particular events would not have happened the same way without global warming," says Kevin Trenberth, head of climate analysis at the National Center for Atmospheric Research (NCAR) in Boulder, Colo.

    Is it a good sign that the language used by the experts is changing? Sorry, didn't mean to give you another reason to lose sleep.
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  15. Dr. Hansen,

    Thank you for a very clear, succinct and sobering account of a complex and potentially alarming situation.

    I very much appreciate (and admire and respect) everything that you have done regarding the science behind both natural and anthropogenic climate change. Not to mention the great progress that your dedicated and hard work has fostered in this field. Your efforts are especially noteworthy considering the relentless attempts to undermine your credibility and interfere with your work by 'skeptics' and those in denial about anthropogenic climate change.

    History will reflect very favourably on your admirable, professional and principled approach to this issue-- the same will not be true for Lindzen, Spencer, McIntyre, Christy, Singer and Michaels and their ilk.
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  16. @15 i 2nd that.
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  17. Sally at 12
    When you look at the bottom portion of the graph what you see is a classic sawtooth graph. It shows business as usual - periodical and predictable changes in climate over a large scale.

    Neanderthals may have appeared as long ago as 650K years in Europe and Asia. They survived all those alternating periods of warming and cooling. Homo sapiens most likely left Africa 50K to 100K years ago. That means our direct ancestors survived an Ice Age by technologically adapting. Whether we have more warming, or begin to enter another ice age, humans will technologically adapt again. That doesn't mean times won't necessarily be difficult, but we will adapt and survive.

    That also does not mean the human race should not currently be developing new and more efficient/environmentally sound forms of energy. We definitely should.
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  18. Pirate#17: "our direct ancestors survived an Ice Age by technologically adapting. ... That doesn't mean times won't necessarily be difficult"

    That's starting to sound like discussions on the It's not bad thread, which may be a better spot for continued commentary.

    Sure, we can adapt, as long as the rate of environmental change is not too fast for our sluggish political, economic and public health systems.

    What's the downside of this form of forced adaptation? Some parts of the population (those who can't or don't adapt so easily) must fall by the wayside. So the tens of thousands who die each year of heatwave-related causes (chiefly the elderly, infirm, poverty-stricken, etc) are the new Neanderthals. Is this your version of natural selection?

    Difficult times, indeed.
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  19. Muon @ 18
    Don't forget about the tens of thousands who die from hypothermia. Whether hypo- or hyperthermia, weather extremes will kill living organisms. And, yes, some will die. Just as some will die from too much or not enough water. Too much or not enough food. That may sound callous, but that is life. Always been like that and always will.
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  20. apiratelooksat50.... You know, that is a very dangerous attitude to take. I hesitate to compare the points throughout history where dismissive comments like this have paved the way for tremendous human misery.

    When we have the data in front of us that tells us that a humanitarian crisis is looming and we choose to dismiss it... that makes us clearly responsible for the outcome.

    We stand at a similar precipice in human history now. How we respond today, the level of responsibility we take for future events, will determine the level of misery inflicted upon later generations.
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  21. Pirate, your attitude is a front. You wouldn't be here at SkS discussing anything with anyone if you didn't share a human concern. You have claimed to be a teacher. Is that attitude proper to your students?

    Note that the species went through two world wars in the span of thirty years. Are you saying that you could take-or-leave-whatever-shrug another world war? If your attitude is not a front, then you certainly don't have children nor are you a teacher (or, if you are, you must be desperately looking for another occupation, away from bleeding hearts and artists -- maternal and paternal instincts--pshaw!).

    Take this to the "it's not bad" thread.
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  22. pirate#19: "Too much or not enough food."

    See this comment and use It's not bad for replies.

    "That may sound callous, but that is life. Always been like that and always will. "

    Yes, it's a jungle out there. But for those who are top-of-the-food-chain, it's all good?
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  23. 20 - 22
    Please don't misunderstand me. I think as stewards of the earth, humans should be doing everything possible (within reason) to make the world a better place. That includes preserving nature, conserving natural resources, developing alternative forms of energy, etc...

    I teach my students that humans (animals) have 3 basic requirements: food, shelter and water. With the advent of the agricultural revolution human populations exploded. Every year we find better ways to coax even more food out of the same areas of land. Better living conditions are becoming more available around the world including shelter. Clean water resources have also become more available.

    That improved quality of life requires one important factor: energy. Right now we can't supply most of that energy without FF resources. Hopefully, one day we can.

    Still, human populations will one day outpace the ability of the earth to provide those 3 basic needs. At that point, there is only one result. It's simple biology.

    And, since humans have survived climate change before, we will survive whatever is in the pipeline. Populations do shrink and grow naturally.
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  24. @pirate #17:

    You state, "That doesn't mean times won't necessarily be difficult, but we (the human race) will adapt and survive."

    What if you are wrong?

    The Earth is littered with the fossils of life forms that have gone extinct.

    For the human race, there is no Planet B!
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  25. DSL @ 21
    This is OT and will probably be deleted. I am a parent of 2 and a teacher of about 180 this year. I volunteer at my local YMCA. I've been to Africa as part of a not-for-profit group installing wells and water filtration units in remote villages.

    Don't mistake my large scale pragmatism for an inhumane attitude.
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  26. Pirate: "Still, human populations will one day outpace the ability of the earth to provide those 3 basic needs. At that point, there is only one result. It's simple biology."

    Why did you install wells in Africa? Why not let "simple biology" take over?
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  27. Pirate, Sally, et al,

    For the sake of discussion, I put some thoughts down, but though there are ties to this thread, I found they fit better under the 'It's not bad' topic per MounCounter's suggestion.
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  28. Pirate, DSL,

    I would hazard a guess that even though Pirate knows that a lot of starfish are doomed, he still wants to save some. Personally, my main disagreement with Pirate is in that he treats global warming like the inevitable storm, and I still think there are things we can to do mitigate the severity of the storm.

    The Star Thrower
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  29. #13 scaddenp,

    An excellent point Phil. The cost of shifting can be managed by gradually replacing the infrastructure that goes offline anyway. I didn't rush out and buy a ground-source heat pump as soon as they became available, but I did make the investment when my AC died.

    A shift to a new energy infrastructure is bound to cause an increase in energy costs in the short term. The reason we use so much fossil fuels now is there is very little that can compete with the internal costs of getting energy from them. We have learned, and our knowledge is increasing, that the external costs are going to be difficult to live with.

    I very much like the idea of a phased-in carbon tax (+dividend) to give utilities incentive, and time, to shift from FF plants to alternatives. Let the market sort out which alternatives work better in different places.

    Any time you get more energy out of a system than you put into it, energy becomes cheap. So, there will be a increase in costs in the near term, but in the long run it will be fine. I believe that from now on, fossil fuels are going to be increasingly expensive, especially petroleum-based forms. So, we can use some of that energy now to shift to alternate ways of generating energy, or we can wait until fossil fuels are even more expensive, and we find our situation is even more dire and that we have to make the shift even quicker.
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  30. Pirate @25 etc

    I agree with many of your sentiments about the ultimate capacity of humanity to survive what is likely to be coming - probably. Consider a few things.

    Survival does not necesarily mean survival of civilisation. Early hunter/gather type societies might well survive in the world that is coming but possibly literate, knowledge rich civilisations.

    Will that future world be perhaps harsher than the world of our ancestors. Sure, Icy wastes may have been uninhabitable then while in the future it will be scorching deserts. But what will the still 'habitable' zones look like. What will the density of possible prey species for our descendent be for example. As the world crashes from a peak of 10 billion to way way lower due to a cornucopia of pressures, with hunger at the top of the list, James Lovelock's words may prove chillingly prophetic - "Forget Lions & Tigers. If it moved we ate it". And what state will the oceans be in as a food resource - acidification events and all that. Could our descendents face a much harder future than our primitive ancestors.

    And what of civilisation ever recovering? If we are driven down that far because of environmental circumstances essentially all our moder knowledge will be lost. Past civilisations grew and expanded their knowledge because they flourished in some key regions of biological bounty. If there are no such regions in the future, could our ancestors ever rise back up again.

    Look at the Aboriginal population here in Australia. They occupied the entire continent and lived successfully and innovatively here, even developing some very primitive agriculture, fish farming etc, as far as the local conditions permitted. But the climate never allowed them to rise to the level of the great Middle-Eastern civilisations - conditions restricted them to essentially hunter-gather societies over 60,000 years. Could that be our descendents fate, but with nothing bigger than small rodents to live on?

    Even if our descendent do eventually manage to start climbing back up, what resources will they have available? We have mined and or burned so much already, including virtiually all the easily accessable resources. They won't find surface coal, oil, etc like our ancestors did. Without these will they be able to make the leap back to electricity, nuclear physics etc. Could the atronauts on the space station be the last humans in space, ever?

    And what of the transition to this harsh future world. What will the lives of our descendents be like as they live through the 'crash'? How far off is it? Of those 182 children you spoke of; how many of them will dy terrible deaths during this decline.

    The harsh future world of 'just biology' will happen to anonymous future generations. The horros of the journey to that destination are likely to happen to those we know and love today.

    So every tiny thing we can do now to diminish this will be some measure of horror averted for our loved ones.
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  31. Chris G @ 28
    FYI - I do believe in doing those things that could help "all the starfish". Within reason, that is. And, that is probably a conversation for another time and place.

    Peace!
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  32. @pirate #31:

    Your qualifier, "within reason" does indeed merit further discussion.
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  33. "The past is the key to the future". Hansen and Sato 2011.

    This is a reversion of the classic statement that took decades in 18th and 19th centuries geological science to establish: "the present is the key to the past".

    It is not a simple idea, and has numerous political ramifications and subtleties. Historically, creationists were the ones fighting for the idea of the reverse, which is what Hansen and Sato are also doing: that the past is the key to the present, and the future, which is not valid. Just because A leads to B, does not mean that B leads to A.

    The reason it is not valid is we cannot determine the past as accuately as we can determine the present, neither can we determine the future as accurately as we can determine the present. Centuries of earth scientists fought hard to establish these basic truths, Hansen and Sato with one statement seek to sweep this history aside.

    The rest of the arctile has similar issues. Eg "However, about half of the fast-feedback climate response is expected to occur within a few decades." This 'fast-rate' cannot be determined from the past due to the inability to determine rates and feedback in sufficient resolution on geological time scales. In other words, the rate of the warming in the e.g. Eocene thermal event cannot be sufficiently determined below an error of at least 1000 years, which means the fast feedback rate as stated by Hansen above cannot be determined, nor the negative feedbacks which act to slow this rate etc.
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  34. Nice try at dismissing the entire field of paleoclimatology with a little semantic hand waving.
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  35. thingadonta#33: "Hansen and Sato with one statement seek to sweep this history aside."

    Hardly. Uniformitarianism is about consistency of process. The 'present is the key to the past' because the physical laws we see operating today also worked in the past. From the University of Oregon,

    Uniformitarianism posits that natural agents now at work on and within the Earth have operated with general uniformity through immensely long periods of time.

    There is nothing intrinsically special about the 'present.' Thus what we can take from the paleo record must be a result of the same processes, which will also operate into the forseeable future. James Hutton 1788:

    ... the progress of things upon this globe, that is, the course of nature, cannot be limited by time, which must proceed in a continual succession.

    A good example are floods on the scale of the Missoula Flood. Today's streams do not carry the requisite volume of water and types of sediment. We infer that unusually large volumes of water were involved and must find a source for that water (in this case, a glacial lake). Should those same conditions arise in the future, we would expect the same events. If you pond enough water behind some temporary dam, when the dam breaks, you'll get one heck of a flood (or if you melt enough ice, you'll get one heck of a sea level rise, for that matter).
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  36. Good point, mouncounter!
    Astronomers can also recognise the spectral fingerprint of elements in the light from distant galaxies millions or even billions of light years away, even if it is more or less redshiftet. That proves that the absorption and emission of light worked in the same way millions or billions of years ago, and that is relevant for the greenhouse effect.
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  37. More good news: Prehistoric glacial melting similar to concerns about Antarctica

    An analysis of prehistoric “Heinrich events” that happened many thousands of years ago, creating mass discharges of icebergs into the North Atlantic Ocean, make it clear that very small amounts of subsurface warming of water can trigger a rapid collapse of ice shelves.

    The findings, to be published this week in Proceedings of the National Academy of Sciences, provide historical evidence that warming of water by 3-4 degrees was enough to trigger these huge, episodic discharges of ice from the Laurentide Ice Sheet in what is now Canada.

    The results are important, researchers say, due to concerns that warmer water could cause a comparatively fast collapse of ice shelves in Antarctica or Greenland, increasing the flow of ice into the ocean and raising sea levels.


    Yes, the past may indeed be the key to the future. A very wet future, possibly coming soon to a coastal city near you.
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  38. Mandas is right. The possibility of persuading China, India, Russia and the US to actually cut carbon dioxide emissions is zilch. The economic problems in Europe and the well known difficulties they have had in carbon dioxide trading would indicate that they will be going nowhere fast, particularly if Germany continues with the threst to close down nuclear power - which I don't actually believe will happen once the flurry over Fukushima has faded out of memories.
    Obviosly what is really beeded is to maintain strong world economies which will be capapble of taking whatever appropriate action is necessary to prepare for any variations in the future, be they warming or as now apears more likely, a period of cooling. Adaptatation is the only sensible way to consider the future wihout needing to reduce the standard of living in these poorer countries. Australia's contibution from 5%, a mere 0.001 C as a worst case scenario is not going to help.
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  39. Getting serious action anywhere is mostly inhibited by an electorate on the US which is prepared to believe almost anything rather than the implications of the published science.
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