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How we know an ice age isn't just around the corner

Posted on 1 September 2010 by Anne-Marie Blackburn

According to ice cores from Antarctica, the past 400,000 years have been dominated by glacials, also known as ice ages, that last about 100,000 years. These glacials have been punctuated by interglacials, short warm periods which typically last 11,500 years. Figure 1 below shows how temperatures in Antarctica changed over this period. Because our current interglacial (the Holocene) has already lasted approximately 12,000 years, it has led some to claim that a new ice age is imminent. Is this a valid claim?

Figure 1: Temperature change at Vostok, Antarctica (Petit 2000). The timing of warmer interglacials is highlighted in green; our current interglacial, the Holocene, is the one on the far right of the graph.

To answer this question, it is necessary to understand what has caused the shifts between ice ages and interglacials during this period. The cycle appears to be a response to changes in the Earth’s orbit and tilt, which affect the amount of summer sunlight reaching the northern hemisphere. When this amount declines, the rate of summer melt declines and the ice sheets begin to grow. In turn, this increases the amount of sunlight reflected back into space, increasing (or amplifying) the cooling trend. Eventually a new ice age emerges and lasts for about 100,000 years.

So what are today’s conditions like? Changes in both the orbit and tilt of the Earth do indeed indicate that the Earth should be cooling. However, two reasons explain why an ice age is unlikely:

  1. These two factors, orbit and tilt, are weak and are not acting within the same timescale – they are out of phase by about 10,000 years. This means that their combined effect would probably be too weak to trigger an ice age. You have to go back 430,000 years to find an interglacial with similar conditions, and this interglacial lasted about 30,000 years.
  2. The warming effect from CO2 and other greenhouse gases is greater than the cooling effect expected from natural factors. Without human interference, the Earth’s orbit and tilt, a slight decline in solar output since the 1950s and volcanic activity would have led to global cooling. Yet global temperatures are definitely on the rise.

It can therefore be concluded that with CO2 concentrations set to continue to rise, a return to ice age conditions seems very unlikely. Instead, temperatures are increasing and this increase may come at a considerable cost with few or no benefits.

This post is the Basic version (written by Anne-Marie Blackburn) of the skeptic argument "We're heading into an ice age".

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Comments 1 to 50 out of 60:

  1. "(Petit 2000)" links straight back to the SkepticalScience homepage. Other than that, good explanation.
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  2. You omitted 'years' at the end of the first sentence. Good explanation.
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  3. A small nit: The title should either start with "How do ..." or omit the question mark. Also, following on to Tom_the_Bomb's comment, all the links point to the SkepticalScience homepage.
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    Response: Egad, a whole swag of grammatical and HTML errors. All fixed, thanks to the first 3 commenters for pointing these out.
  4. Anne-Marie: A small tip: When importing text from another editor into the Skeptical Science editor, links usually get reset to point at just the main Skeptical Science landing point. Check links you import via the preview before posting (I found I had to import them one at a time to create a post with links that worked as I had intended). Maybe the other contributors, who post much more frequently than I, can offer more sage advice. The Yooper
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    Response: Actually, Anne-Marie did it all correctly - it was when I tried to move her rebuttal into the blog post that things went awry. All my fault! :-(
  5. The reason we are not heading down that road is simple. Sea levels are not high enough yet. If they reach the height needed to shut off the Gulf Stream and we are still in a relatively weak position to the sun we will go back into an Icing time. If the sea levels rise too slowly to catch that we may not have one.
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  6. I have found this site very informative and helpful. Thanks for the explanation. One question: How does the rate of temperature increase between the glacial and interglacial periods compare to the current rate of increase and the predicted rate of increase for the next century? I ask because one of the things I (and millions of other people) am concerned about is the ability of ecosystems to adapt to the change. Thanks in advance.
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    Response: The change in global temperature between ice ages and interglacials is approximately 5 to 6°C (the change in temperature is greater in Antarctica, less in the tropics). If we went along business as usual, we might achieve warming of this order:



    However, the issue is the speed of change. The change from glacial to interglacial occurs over thousands of years. We're effecting this change over a century or two. It's the speed of change that's the issue here - if temperatures change too quickly, ecosystems are unable to adapt quickly enough. We know this from past history - all the mass extinctions in the past were associated with periods of dramatic climate change.
  7. While this is an interesting post, it lacks the grand vision of earlier posts. Let us not forget the truly breath taking predictions of David Archer: http://www.skepticalscience.com/upcoming-ice-age-postponed-indefinitely.html Take a look at Figure 3. Ice Ages will be a "thing of the past" thanks to CO2. Personally I see that as something wonderful (if only it was likely). No more glacial cycles that have so stressed hominids during the last million years. As Eliza Doolittle would say "Would'nt it be loverly?"
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  8. gallopingcamel: Yeah, but there are a few potential downsides to elevated temperatures. And as many others have pointed out many times before - it's possible, perhaps even probable, that Homo Sapiens will survive the worst global warming can throw at us. You may not be able to say the same of the civilisation that lets you sit in air-conditioned comfort typing your message on a PC...
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  9. Bern (#8), There may be plenty of problems arising out of sustained high global temperatures such as we had in past epochs when trees grew in Antarctica. However, a return of the Laurentide ice sheet extending all the way to where New York City stands is much more to be feared.
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  10. I want to make a prediction – not about the climate, that’s old stuff. I want to make a prediction about climate deniers. 20 years from now they will still tell us that global warming isn’t happening, and at the same time that global warming IS happening and isn’t it wonderful ? And all natural and human disasters that happen in the meanwhile will be either completely ignored by them or attributed to completely other causes.
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  11. cruzn246 wrote : "The reason we are not heading down that road is simple. Sea levels are not high enough yet. If they reach the height needed to shut off the Gulf Stream and we are still in a relatively weak position to the sun we will go back into an Icing time. If the sea levels rise too slowly to catch that we may not have one." Do you know what height that would be and how fast levels would have to rise to initiate all that ? Also, how do you believe that fits in with the Milankovitch cycles ?
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  12. gallopingcamel @ 9 Yes, replacing the climate cycles that crafted all life on earth with the most rapid rises in global temperature and ocean acidification ever seen, greater than during the PETM [IIRC] is to be celebrated, or perhaps not. We know that life managed to cope with past perturbations, but now we are in new territory. And while denialists often talk of 'adapting' and 'survival', they seem to have as much idea of the concept and mechanisms of evolution as they do of the climate.
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  13. gallopingcamel writes: However, a return of the Laurentide ice sheet extending all the way to where New York City stands is much more to be feared. Only if you make it a practice to worry about things that are not going to happen until after you've been dead for tens of thousands of years [with no AGW] or hundreds of thousands of years [with AGW].
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  14. "Today's comparatively warm climate has been the exception more than the rule during the last 500,000 years or more. If recent warm periods (or interglacials) are a guide, then we may soon slip into another glacial period. But Berger and Loutre argue in their Perspective that with or without human perturbations, the current warm climate may last another 50,000 years. The reason is a minimum in the eccentricity of Earth's orbit around the Sun." (Berger 2002)(PDF)
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  15. @ Ann #10. "or attributed to completely other causes" ... such as 'It is God's Will'. The move will be away from skepticism to fatalism.
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  16. For those who fear a return of the Laurentide ice sheet, why is it not obvious that the correct response would be something like this flowchart a) Be carbon neutral for thousands of years b) If ice sheets start growing, burn some carbon - maybe 5 to 10 ppm increase in CO2 c) Continue to monitor ice sheets, return to (b) In other words, with our capability to dig up fossil fuels and burn them, we can *easily* dominate the Milankovitch cycles. The danger is going too far the other way, which we are near to doing. Recall that the "normal" interglacial CO2 concentration is 280-300 ppm. We can hold off any natural cooling by keeping CO2 at some slightly higher level, probably 320-350 ppm. Note that the rate of burning fuel to hold that range of CO2 concentration would be very low, so conventional fossil fuel reserves would last darn near forever (and we could mine methane hydrates after that - probably a few million year's worth, after that, the sun is warmer ...) Our mad dash to higher CO2 levels (currently 390 +2/y) might be great for Jurassic flora and fauna (if we had any) but is likely to be a significant extinction event for current species.
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  17. GC - once again - RATE of change is what is more important. Maybe warmer would be better in long term but only if we get there slowly. I would like some explanation from you of why you think rate doesnt matter.
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  18. A scientist called Ruddiman has a book speculating we started altering the climate with early farming thousands of years ago. It appears humanity has been heading off an ice age thats going too far too fast as in #17. An unconscious deliberate experiment or just chance?
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  19. I think there is a bit o a misconception here in regards to rate o climate change.... coming outta the last glaciation, the rate o change was at times SEVERAL orders o magnitude above the current trends.... this is where the tipping point hypothesis have come from! http://www.chmi.cz/HK/OK/clivar-cz/PRA_posters/clivar_poster_pages2.pdf http://www.gisp2.sr.unh.edu/DATA/fancy.html http://math.ucr.edu/home/baez/temperature/
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  20. Joe Blog - as I understand it that high-rate temperature change was strictly a localised phenomenon - one of the candidates for cause is the release of meltwater from behind the ice sheet over North America, interrupting the flow of warm water to Europe. While this would have caused a dramatic drop in temperatures in Europe, it probably would have led to even *warmer* temperatures further south - after all, if that equatorial heat isn't ending up at northern Europe, it's gotta go somewhere! I imagine a good global reconstruction for that time period would show this effect quite well, while also showing that the global average temperature continued to change at a relatively slow rate.
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  21. Bern No, these rapid changes where counter hemispherical(as you say, as good as can be ascertained from the paleo reconstructions) And im not just talking about the younger dryas event.. the rise out of glaciation was punctuated with rapid shifts, several degrees a decade. This whole "most rapid warming" is referring to extremely recent geological record... the last 1-2kybp. The early Holocene was not a stable climate.
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  22. ScaredAmoeba (#12), Your comments make sense although I believe you are judging "Denialists" too harshly. Ned (#13), It may sound odd but I do care about what will be happen long after my demise. I plant trees and work to reduce river pollution in the hope that my children (and yours) will benefit. GFW (#16), You seem to buy David Archer's idea that rising CO2 concentrations will have a more powerful effect than Milankovitch cycles. I hope you are right. How do you explain the glacial periods that occurred when CO2 concentrations were ten times higher than today? scaddenp (#17). I agree that the rate of change is important. However, you cannot assume that the rapid warming that occurred from the 1975 to 1998 will be the norm. Global temperatures have drifted lower over the last decade and are likely to fall for at least another 10 years.
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    Response: "How do you explain the glacial periods that occurred when CO2 concentrations were ten times higher than today?"

    The sun was cooler back when CO2 was higher.

    "Global temperatures have drifted lower over the last decade"

    Global temperatures have not drifted lower over the last decade - the planet is still accumulating heat and the hottest 12 months on record are June 2009 to May 2010.

    NASA GISS global temperature - hottest 12 months on record June 2009 to May 2010
  23. GC - give me some science to support the "temperatures will drift lower over next decade or so". What will be your position if they dont? And also, the 100 year rate of change is still near order of magnitude higher than rate of change from Milankovich cycle.
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  24. It would also appear that the so-called skeptics' belief that last Winter in some parts of the Northern Hemisphere (AKA 'the world' in so-called skeptical speak) was a sign of things to come (i.e. the coming Ice Age), was a little premature : Northern Hemisphere winter snow anomalies: ENSO, NAO and the winter of 2009/10 Winter 2009/10 had anomalously large snowfall in the central parts of the United States and in northwestern Europe. Connections between seasonal snow anomalies and the large scale atmospheric circulation are explored. An El Niño state is associated with positive snowfall anomalies in the southern and central United States and along the eastern seaboard and negative anomalies to the north. A negative NAO causes positive snow anomalies across eastern North America and in northern Europe. It is argued that increased snowfall in the southern U.S. is contributed to by a southward displaced storm track but further north, in the eastern U.S. and northern Europe, positive snow anomalies arise from the cold temperature anomalies of a negative NAO. These relations are used with observed values of NINO3 and the NAO to conclude that the negative NAO and El Niño event were responsible for the northern hemisphere snow anomalies of winter 2009/10.
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  25. “The change from glacial to interglacial occurs over thousands of years.” present interglacial in exactly,(!) three years (a major change; the whole - seven years), probably even the Sahara became the Sahara (with green, thriving savannah to desert - as today) in less than 100 years (movie: Man on Earth). I can present hundreds of works that the former changes were equally dramatic - not just warming. “H” events occurred during the life of one man - the main changes sometimes within one of the winter. Richard Seager (The Gulf Stream, European climate and Abrupt Change, 2009) says: “These abrupt changes - the Dansgaard-Oeschger events of the last ice age and the Younger Dryas cold reversal of the last deglaciation - are well recorded in the Greenland ice core and Europe and involved changes in winter temperature of as much as thirty degrees C!” Changes have always been violent - even those much smaller than the “H” events, because: „In its place we need serious assessments of how changes in ocean circulation will impact climate change and a new look at the problem of abrupt climate change that gives the tropical climate system and the atmosphere their due as the primary drivers of regional climates around the world.” (Seager, 2009.) Again, the tropics ... I think that the AMOC - “two-pole swing” - it's just delayed in time - delayed warming in the SH to NH - as the globally is warmer - is less. And after a period of warming to the 2030s, waiting for us again but slightly weaker LIA ...
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  26. Arkasiusz - that graph shows a bunch of very abrupt climate changes that happened moving from glacial to interglacial. While we would certainly like to understand them more (because yes, that rate of change would really seriously threaten civilization - how would farm in the face of such change), there isnt evidence for them happening during interglacial period - while its warm. It isnt in disagreement with fact that the transition to glaciation (if our atmosphere would still permit it), is something that takes place extremely slowly.
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  27. John Cook, (Response to my #22), As Ronald Reagan would say, "There you go again". You keep quoting NASA/GISS and James Hansen. You need to check out some of the contrary data that can be found at UAH and RSS. Which data is wrong? The satellites or the ground stations? I don't pretend to know the answer but until someone can come up with a convincing explanation for the discrepancies, we should all try to keep our minds open.
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  28. John Cook, (Response to my #22), There was an Ice Age in the late Ordovician (~450 million years before present). At that time the CO2 concentration was ~20 times what it is today. You say that the sun was cooler back then. I can concede that you are right about the sun's output being lower but that only raises more questions. If the sun's output was low, why was it so hot in the Cambrian period that preceded the Ordovician and in the Silurian that followed it?
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  29. scaddenp (#23), You got me. It is just a gut feeling although some people have suggested that there is an oscillation (PDO and other ocean effects) with a ~30 year period. If I am right and temperatures trend down for the next ten years, it would not surprise me to find rising temperatures after that.
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  30. gallopingcamel the suns out put 450mybp would have been around 97% o the present irradiance.... The location of the continents plays a large role in climate, the current configuration weighs the climate towards ice house.. there is a land mass over the southern pole, preventing transport of heat over the pole via the oceans, and the land masses around the northern pole greatly inhibit the transport of heat. As well as the location of the other continents playing a role in oceanic heat transport by the way they influence ocean currents. GHGs are important, but the continents set the stage.
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  31. GC looked at Its the PDO? I am more interested in what you will think if temperatures trend up for next 10 years. Also, UAH and RSS dont measure ground temperature - they attempt to measure the lower troposphere (around 4000m from memory). However, they see the same 30-year TREND as GISS/HadCrut. Neither data set is wrong - just measuring something different.
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  32. GC writes: Global temperatures have drifted lower over the last decade and are likely to fall for at least another 10 years. No they have not. Here is the RSS satellite record: The pink line shows the trend through 2000. Note that from 2001 onward, most months have been above the pre-2001 trend line, with the notable exception of the 2008 La Nina.
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  33. GC writes: Which data is wrong? The satellites or the ground stations? I don't pretend to know the answer but until someone can come up with a convincing explanation for the discrepancies, we should all try to keep our minds open. What discrepancies? The RSS satellite record and all the major land+ocean temperature records currently agree to within 0.01C/decade. UAH is just slightly lower. When there were discrepancies in the past, they turned out to be due to errors in the processing of the satellite data, not due to errors in the surface data. For example, there was the famous case where UAH was accidentally applying the satellite-drift correction factor backwards. Also, FYI, contrary to your claim, none of the temperature records shows "temperatures have drifted lower over the last decade." Land surface, sea surface, and lower troposphere temperatures have all increased since 2000. Since these are measured using completely different -- and independent -- technologies, the agreement among them is quite convincing.
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  34. GC @ 29 - as Phil Scadden has pointed out, the PDO 30 yr cycle thing seems to be based on imagination, not the data:
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  35. GC #27, using the UAH temperature data we can calculate five year average global anomalies; 1990-1994: -0.04 1995-1999: 0.14 2000-2004: 0.18 2005-2009: 0.23 All other data sets show GREATER warming. So no, this is not a matter of 'which data you look at'. ALL data sets show warming and your claim of cooling the past ten years (the hottest decade on record in all data sets) is simply false. The years 2007-9 were relatively cool... but then 2010 thus far is at +0.55 C anomaly in the UAH data... which is higher than the 0.52 C record they have for 1998.
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  36. Not trying to pile on here, but here's a helpful comparison for GallopingCamel: Note that the blue line (Pacific Decadal Oscillation, or PDO) doesn't match the red and orange lines (temperatures, from surface [GISS] and satellite [RSS]) very well ... especially during the last three decades. In contrast, the green lines (log of CO2, from ice core [Law Dome] and direct measurement [Mauna Loa]) match the temperature record more closely. Adding in the effects of other greenhouse gases, and subtracting the effects of volcanic and anthropogenic aerosols, would make this match even closer. Bottom line, ocean oscillations can't explain the observed temperature trend. Greenhouse gases can. -------------- The fine print: PDO data from University of Washington. Surface temperatures from GISS land+ocean. Satellite temperatures from RSS. Law Dome CO2 from NOAA NCDC. Mauna Loa CO2 from NOAA ESRL. PDO and temperature data shown in monthly and 120-month LOESS smoothed versions. Law Dome CO2 dating based on "air age" with 20-year smoothing. Mauna Loa CO2 (monthly) are seasonally adjusted. Both CO2 data sets were log-transformed (base 2). Data sets with differing units (PDO, temperature, log[CO2]) have been scaled to fit on the same graph.
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  37. You know, I don't think there's enough information in the graph above. Here's an improved version, with some additional content -- I've added in total solar irradiance (TSI). Clearly, over the last 30 years, CO2 and temperature keep rising (green and red or dark-red lines), while PDO (blue) is fluctuating and solar irradiance (yellow) is stable or declining. It should be noted that this kind of visual correlation is not actually how scientists attribute climate change. This graph doesn't prove that CO2 causes the observed warming. But the graph is certainly consistent with the claim that CO2 causes the observed warming, and that solar and PDO are not the cause. So ... anything else we should add into this figure? There's still a little white space left in there.... :-) Apologies for straying off-topic. -------------- More fine print: See above for sources of PDO, temperature, and CO2 data. Solar irradiance data from University of Colorado, shown annually and with a 22-year LOESS smoothing function.
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  38. Ned (#32) Thanks for the RSS graph. It clearly shows that there is no temperature rise in the last decade in spite of the recent peak due to the summer of 2010. This thread was about the possibility of a plunge in temperature leading into a new Ice age. Let's stop drifting "Off Topic". The current era (Holocene) is technically an Ice Age but we live in a fool's paradise called an inter-glacial period. The Vostok ice cores show that inter-glacials are relatively short, so enjoy it while it lasts.
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  39. Joe Blog (#30), I don't doubt what you say about the importance of continental drift when it comes to the "big picture" of climate over hundreds of millions of years. However, global temperatures were high in the Ordovician but fell sharply toward the end of that era and then rose again in the Silurian. The time scale is too short for continental drift to be a factor and CO2 concentrations remained high throughout that period. So what caused that Ice Age? Shariv postulates that the Earth's movement into a region in one of our galaxy's spiral arms with a high stellar density could be responsible for the late Ordovician Ice Age. Do any of you have a better hypothesis?
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  40. gallopingcamel #38 Interglacials can last up to 30,000 years. Another glacial is unlikely to happen any time soon because orbital factors are currently too weak to trigger one. On top of that, we're seeing a rise in global temperatures when natural factors should be leading to a slight cooling. This strongly suggests that greenhouse gases are overwhelming the impact of other factors.
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  41. Anne-Marie Blackburn at 20:32 PM, given that about half the anthropogenic carbon emitted is sequestered by natural means it can also be claimed natural processes are as equally influential in determining the nett result. As to which is prevailing can only be judged by considering what the situation would be without the anthropogenic emissions. Would natural processes have continued to reduce CO2 levels leading to global cooling? Making an case supporting one scenario is biased unless the alternative is recognised and quantified.
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  42. johnd, I'm not sure I understand your point - what is the alternative scenario in this case? I have pointed out in my original post that natural factors would in all likelihood have led to global cooling, though the overall forcing would probably not have been strong enough to cause a new glacial period. Isn't this the alternative scenario you mention? Also I should mention that this is the basic explanation for this rebuttal - you can read a more detailed explanation here.
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  43. Anne-Marie Blackburn at 07:55 AM, yes, the alternative scenario is no anthropogenic emissions. Only then could a baseline be established for where natural processes would be heading. At the moment natural processes sequester about half of anthropogenic emissions so it is not valid to claim that the emissions are overwhelming the natural processes, as they, the natural processes are equally overwhelming the anthropogenic emissions.
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  44. johnd, I said that greenhouse gases were overwhelming the impact of other factors, which in context meant that their warming impact was greater than the cooling impact expected from other, natural factors. With regards to natural processes, I don't agree with you. If natural processes were overwhelming CO2 emissions, we'd see no increase or even a decrease in CO2 levels. But CO2 levels are rising, which means CO2 emissions from human activities are overwhelming the ability of natural processes to remove this additional CO2.
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  45. Anne-Marie Blackburn at 08:22 AM, you are missing the distinction, natural processes are removing half of the estimated anthropogenic emissions so it can't be said that one is overwhelming the other, each is only winning half the battle. It could be argued that CO2 levels would be falling by 2ppm each year in the absence of any anthropogenic emissions, so the 4ppm added annually is equally overwhelmed if a term such as overwhelmed is to be used at all. The nett global gain in CO2 concentration is less than the range in nett global seasonal fluctuation, and in turn the seasonal fluctuation in various regions in both hemispheres indicate values many times that of the annual emissions. This indicates that under normal seasonal conditions regionally there is a large capacity for natural processes to sequester many times more CO2 than what is being currently emitted. Thus understanding what drives those natural processes is vitally important especially given such natural processes also release about 30 times the CO2 into the atmosphere to that of anthropogenic emissions. If the processes are driven primarily by external factors related perhaps to solar emissions that may indicate what measures can be taken as counter measures. However if the processes are driven by other human related factors then perhaps action may be more effectively directed there. Given the relative magnitude of natural processes versus fossil fuel related emissions, a very little change in the natural processes, whether releasing or absorbing, whether driven by natural forces or by human action, would have perhaps greater impact than the huge change necessary to reduce emissions. At the end of the day it may be that if temperatures that rise as a result of increased emissions, the seasonal growth that already has a significant influence on the annual nett gain may accelerate to balance the emissions with overall nett positive benefits. However unfortunately the current understanding of all the processes involved is far from complete but studies that at least compare plant growth under deprived, ambient and enriched conditions are continually extending the current understanding of at least one aspect of the natural processes.
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  46. gallopingcamel at 15:32 Well for the earth to go into a full blown glaciation with a high GHG level, would mean it must be through increased albedo reducing SW, through which ever mechanism(from the hypothesis you stated, to greatly increased particulates from volcanism, or impact, biological? etc) One of those interesting questions we may never be able to answer with full confidence. But i for one dont know ;-)
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  47. Joe Blog (#46), Thanks for your comment. Let's hope that somebody will take the trouble to enlighten us.
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  48. Anne-Marie Blackburn (#40), I was nodding in agreement with your post until the end. I quote: "On top of that, we're seeing a rise in global temperatures when natural factors should be leading to a slight cooling. This strongly suggests that greenhouse gases are overwhelming the impact of other factors." CO2 concentrations in the atmosphere are rising and will continue to do so unless the burning of fossils fuels is sharply reduced. I think we are in agreement on this. I suspect that we also agree that the Earth has been warming since 1850 (it is so important to choose the right start date). When it comes to attributing how much of the recent warming results from CO2 concentrations and how much from other causes, we may disagree. I see plenty of evidence to suggest that CO2 is not a major climate driver. If you do not share my opinion I look forward to hearing your views.
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  49. JohnD - are you under the impression that CO2 would be dropping by the amount it currently sequesters of current emissions even we were werent emitting? Net CO2 losses from natural processes is extremely slow and obviously completely overwhelmed by human emissions as CO2 is rising.
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  50. Re: Joe Blog (46) and GC (47) "Full-blown glaciation with high GHG level" A more robust discussion of this issue can be found here. The post, reader comments and the NOTES section give valuable insights on this. The Yooper
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