Climate Science Glossary

Term Lookup

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

Settings

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

Term Lookup

Settings


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

Home Arguments Software Resources Comments The Consensus Project Translations About Donate

Twitter Facebook YouTube Pinterest

RSS Posts RSS Comments Email Subscribe


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



Username
Password
Keep me logged in
New? Register here
Forgot your password?

Latest Posts

Archives

Climate Hustle

Are we heading into a new Ice Age?

What the science says...

Select a level... Basic Intermediate

Worry about global warming impacts in the next 100 years, not an ice age in over 10,000 years.

Climate Myth...

We're heading into an ice age
"One day you'll wake up - or you won't wake up, rather - buried beneath nine stories of snow. It's all part of a dependable, predictable cycle, a natural cycle that returns like clockwork every 11,500 years.  And since the last ice age ended almost exactly 11,500 years ago…" (Ice Age Now)

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. 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.

Basic rebuttal written by Anne-Marie Blackburn


Update August 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial

 

Last updated on 7 August 2015 by MichaelK. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Further reading

Tamino discusses predictions of future solar activity in Solar Cycle 24.

Acknowledgements

Many thanks to Sami Solanki for his invaluable advice and feedback as well as John Cross for his very helpful comments.

Comments

Prev  1  2  3  4  5  6  7  8  Next

Comments 301 to 350 out of 389:

  1. Kevin @297, it is a shame that after the long wait you could only come up with a link to an article that I had previously linked to (@ 293, second link).  It would have been nice if you had come up with something new.  In this case the something new is a report of a new excavation of a late iron age, or possibly early Roman, vinyard (or possibly asparagus garden) in Hertfordshire.

    It should be noted that viticulture probably survived in England throughout the dark ages, and certainly survived in England throughout the Little Ice Age, only ceasing after WWI, due to the commercial inability to compete with cheap French imports.  It restarted in England following WWII.  Given that, why do you regard the presence of vinyards in Roman Enland as proof it was warmer at that time than now rather than simply proof that it was not colder than the LIA (when grapes were also grown in England to make commercial wines)?

    Also of interest is this study of modern viticulture in Baltic coastal regions.  It shows this interesting map which shows commercial viticulture in Denmark and Sweden:

    Again, given the northern distribution of commercial viticulture, which includes not only commerical vinyards in Denmark and Sweden, but vinyards being developed with the intention of becoming commercial in Scotland), why do you regard the presence of vinyards in more southerly regions in England as proof that the Roman Warm Period or Medieval Warm Period was warmer than current temperatures?


    And finally, why do you regard evidence that it was warmer then than now in just one region of the world (evidence you have so far failed to produce) as proof that it was warmer than globally rather then now?  

  2. And finally, why do you regard evidence that it was warmer then than now in just one region of the world (evidence you have so far failed to produce) as proof that it was warmer than globally rather then now?

    http://hockeyschtick.blogspot.com/2013/01/new-paper-finds-new-mexico-was-warmer.html

    This paper shows temps from New Mexico area.

  3. Your point?  Global temperature reconstructions are estimated from a network of proxies from locations around the globe. If you think this one place is significant, then why do you deny the significance of other proxies, or those places where ice retreat is exposing bare rock for first time since HCO ?

  4. Kevin @302, the first thing to notice is that the modern average is not necessarilly the average over the last few decades.  Indeed, by convenction, in paleographic studies the present is 1950 unless otherwise stated.  The article your denier propaganda site refers to is behind a paywall, so I am unable to determine which interval was used to determine the "modern average".  I am able, however, that they determine an annual average temperature as a function of the reconstructed July temperature, and that their modern annual average of 11 C corresponds to a July temperature of 22 C.  Further, the warmest temperature they show for July approximately 2000 years ago (see Table 2).  The NCDC shows the twentieth Century average of July temperatures in New Mexico to be just under 23 C, so it appears the "modern average" is below the average over the 20th century.  For comparison, the average over the last decade to be around 23.5 C (the equivalent of a mean annual temperature of 1.25 C above the twentieth century mean).   The peak modern July temperature is 25 C, the equivalent of 2.5 C above the "modern average". In other words, it appears that the reconstruction does not show temperatures higher than that of the late twentieth century at all.  (Treating studies showing warming greater than 1950, or in one case 1895 as being warmer than the late twentieth century has been a common denier trick.)

    Second, if you look at the following graph you will see that warm and cold periods at different locations do not coordinate in time.  Ergo simply picking out a location and saying it was warmer at some time in the past, and then a different location and saying it was warmer in the past does not tell you anything about whether the global average is warmer.  To do that you need a multiproxy reconstruction.  Oddly deniers have been unwilling to make multiproxy reconstruction despite all the purported examples of warmer temperatures in the past they claim to have found.  Note that I say purported because what deniers claim, and what was actually found in the scientific study often differ widely (as shown above).  I personally suspect that this unwillingness to make reconstructions is because the deniers know that any such attempt will give the game away.

    There is one exception to the rule about deniers and reconstructions.  Loehle (2007), and in particular as corrected by Loehle and McCulloch 2008 (Link for both papers).  There are a few oddities about that reconstruction.  First, many of the proxies used had previously been used by Moberg 2005, who Loehle cites as a source.  Not all of Moberg's non-treering proxies were used, however, as shown in the graph above.  One wonders why Loehle found it necessary to develop a methodology that excluded the Agassiz Ice Cap and Arabian Sea proxies, for example.

    Of greater concern is that Loehle simply takes the average of all proxies to determine his reconstruction.  The problem with that is found in this map of the location of his proxies (from Loehle and McCulloch 2008):

    A quick count shows that 10 of his 18 proxies come from around the North Atlantic; another 4 come from China, and two each from Indonesia and South Africa.  That is, they are heavily localized.  Simply taking a mean of the values treats the North Atlantic (including Europe and North America) as though it constituted 56% of the Earth's surface; China as though it were 22%; Indonesia and South Africa as though they were 11% each; and the entire rest of the globe as though it did not exist.

    What is even odder is that reconstructions using more widely dispersed proxies have shown where was warm, and where cool in the MWP.  Curiously the distribution of proxies used by Loehle gives most weight to the area that was warmest, the next most weight to the next warmest area, and zero weight to any area that was known to be cool.  It is an extraordinary coincidence.

    And despite all these biases, it turns out that Loehle's reconstruction still shows a RWP and MWP cooler than the late twentieth century (note the instrumental record shown as a dashed line):

    It is no wonder deniers don't like reconstructions.

    And it is also no wonder that people who are interested in science want to see them; because if you haven't made the effort of making a reconstruction, you have not analyzed which intervals are warmer or cooler than others.  At most you have attempted to pull wool over peoples eyes with an assortment of random facts.

  5. Tom, I have access to the paper. Let me know if interested though it doesnt seem that interesting to global temp proxies for reasons you have outlined. Their weather data is based in 34-130 year records from stations within 100km, though for that diagram, it appears to be based on closest station at Mountainair, 160m higher than the study area. I dont think the authors put much stock on the absolute values but are instead focussed on the patterns - hot/dry v cool/wet, and particularly in the speed and severity of local climate change in 2nd century.

  6. scaddenp @305, thankyou.  Allowing that the mean for a portion of the state may not match the mean of the state, but that the anomalies are likely to be close, we can shift the state anomalies down by 0.9 C to give them the same mean as the local stations.  In that cast, the 21st century average to date is 0.8 C greater than the mean for July, or an estimated 0.65 C greater for the annual average.  The peak July averages are 1.9 C greater than the mean, for an estimated annual average 1.6 C greater than the mean.

    On these figures, peak medieval warmth in a small part of New Mexico is may be just greater than the current warmth.  That is not certain, however, as the NCDC data represents only a 117 year record, and as the additional 17 years required to match are almost certainly cooler than the mean, the differentials are underestimated.

    I don't think anything else in my analysis requires correction. 

  7. On closer reading, the "current weather" in figure of (11degree) was chosen to be that of just the station at Mountainair, since the proxy record from C3 regression closely matched the values for that station.

  8. One further word. It is fortunate that this area isnt a global proxy because the authors present evidence for a temperature rise of over 2 degrees in just 59 years during 2nd century. That would have been bad on a global scale! I wonder if Kevin has actually read the paper and how he feels about the way that the paper has been represented on his "skeptic" site?

    The clear link between temperature and drought in the region doesnt bode well for its residents.

  9. You've all got this backwards on the planning & ethics front. We developed skills over centuries to know that climate will typically go into a very annoying cold state every few thousand years & found that it can be ameliorated simply by burning old rotted vegetables we've found. Instead of leaving most of them for future humans to regulate their climate for a pleasant life, we greedy pigs are taking the whole lot now when it isn't needed. That's an "intergenerational evil" involving very very old rotted vegetables. 

  10. Hi there grindup,

    I must be having a slow day... Could you spell out the argument for me?

    Thanks.

  11. Tzedakis et al. (2012), "Can We Predict the Duration of an Interglacial?" mentions the end of the current interglacial only insofar as saying "We should also be able to predict the duration of the current interglacial in the absence of anthropogenic interference," and "glacial inception is possible despite the subdued insolation forcing, if CO2 concentrations were 240±5ppmv (Tzedakis et al., 2012)."  [Emphasis is mine.]

    That latter citation is of "Determining the Natural Length of the Current Interglacial," which says "No glacial inception is projected to occur at the current atmospheric CO2 concentrations of 390 ppmv. ... The end of the current interglacial would occur within the next 1500 years, if atmospheric CO2 concentrations did not exceed 240±5 ppmv." [Emphasis is mine.]

    Of course there is no chance at all of CO2 falling that low for the next several hundreds and probably not for the next several thousands of years (see Figure A in another post), so we're not getting a new "Ice Age" for a really, really long time.

  12. jhnplmr (on an inappropriate thread) replied to my statement "your own calculations show only a 3 W/M^2 decrease of insolation in that one tiny region from the year 1950 to the year 3950--only .7%," with "0.7% of what?" 

    Insolation in the year 3950 is predicted to be .7% less than the insolation in 1950.

    You also replied "Do you think it helpful to suddenly introduce 1950 into the discussion? I based my year zero on the graph on 1950 as it made it easier to transfer the data to the spreadsheet. You seem to want to consider a nebulous point between 1BC and 1AD as year zero. Let us call the present day 1950 and call it year zero it will save a lot of confusion. The solar minimum will occur in 2000 years time, 3950AD using your scale."  Climatologists, among other scientists, use 1950 as the standard meaning of "present."  So the year 0 in your NOAA data source means 1950. If you did not know that already, you would learned it if you had bothered to read the readme file that accompanies those data files.

    You wrote you "also don't want us to slide into another glacial period."  There is no risk of that anytime soon; see the papers I linked to in my April 26 comment

  13. 312 Tom Dayton

    "So the year 0 in your NOAA data source means 1950. If you did not know that already, you would learned it if you had bothered to read the readme file that accompanies those data files."

    Which I had, I pointed out to you that I had used 1950 as my datum point for year zero. "I based my year zero on the graph on 1950 as it made it easier to transfer the data to the spreadsheet". It was you who introduced the 3950AD concept.

    "You wrote you "also don't want us to slide into another glacial period." There is no risk of that anytime soon;"

    I have pointed out this several times.  You have mentioned my comments on this point yourself.  You seem to have developed a habit of repeating my statements back to me as if I hadn't made them in the first place.

    The difference between my position and most contributors on this board is that I consider the contribution of man-made warming beneficial as it has stopped us sliding into a prolonged cooler period, we started to do this 10,000 years ago until AGW stopped it in its tracks and stabilised the temperature.  The other difference is that I consider trying to balance on the cusp of an interglacial period indefinitely is an impossible task but this is apparently what most of your contributors want!

    You call your opponents "climate change deniers" but try to keep a changing climate constant!

  14. jhnplmr,

    I don't know why you think contributors here want to keep the planet at a constant temperature.

    The future ice age (glacial, whatever you want to call it) is going to happen very slowly. The last one took tens of thousands of years from peak to trough, about 6 degrees average global temperature (more at the poles, less at the equator). The warm-up to the current interglacial took 5000 years.

    We may achieve 6 degrees warming in as little as 200 years.

    No one here wants to keep the global temperature constant. I think I can speak for most participants here by saying that we want change at the natural pace, not the rapid pace that may be caused by human activity.

    We have geological evidence of what happens when the global temperature changes quickly, and that evidence recommends against making it happen.

  15. jhnplmr@313

    you acknowledge that human activiety has forced a "hockey blade" onto what would otherwise be an overal,comparatively slow decline in average global temperature: But given this acknowlegment of AGW, how can you conclude humans have "stabilized the temperature"? Also, I don't think the issue is "trying to balance on the cusp". The issue is rather that we've stopped the comparatively gradual natural cycle towards colder termperatures ("in it's tracks" as you put it) and forced a much faster rate of change in the other direction that is not, as you indicate "stabilized". Finally, I'm doubtful that any/ many of those that accept AGW think it is feasible to try to control the climate as you imply they do.

  16. 314 Barry

    "The future ice age (glacial, whatever you want to call it) is going to happen very slowly. The last one took tens of thousands of years from peak to trough, about 6 degrees average global temperature (more at the poles, less at the equator). The warm-up to the current interglacial took 5000 years."

    Well it won't happen by the next Jul 65N solar minimum in 2000 years time, but I agree with your general point that there is a slow descent into a glacial period yet a sharp rise, a sawtooth waveform.  The Vostok temperatures took about 20,000 years to fall to a minimum in the last glacial period and about 5000 years to rise as you say.

    "No one here wants to keep the global temperature constant. I think I can speak for most participants here by saying that we want change at the natural pace, not the rapid pace that may be caused by human activity."

    You look upon the contribution of AGW as completely negative, I look upon AGW as stopping global temperatures from falling over the last 10,000 years.  They started to fall in line with the falling insolation but then recovered and stabilised under AGW forcing.  If you think that the present levels of CO2 are high at 393ppm then you should consider that in the age of dinosaurs they were 3000ppm.  It is possible that the present levels will melt the ice caps and we will come out of the current ice age but I believe that AGW will dwindle as we run out of fossil fuels and then the falling insolation will cause a fall in temperatures.

    We have already avoided the "natural pace", that happened some 6000 years ago when man started farming and keeping domestic animals.  Besides, who wants to slide into a prolonged cooling period with advancing ice caps?  Man's activities have stopped that scenario.

    Response:

    [DB] "If you think that the present levels of CO2 are high at 393ppm then you should consider that in the age of dinosaurs they were 3000ppm."

    In this venue this is an example of an unsupported assertion, typically employed as a rhetorical device.  Please avoid such in the future.  If you wish to defend this rhetoric, please do so on a more appropriate thread and provide links to substantive sources published in the reputable literation which you feels support your position.

    This is an evidence-based venue.  "Beliefs" and opinions carry little weight here.

  17. jhnplmr (from previous thread)... "My claims are not "fantastical", they are based on many sets of published data and the resultant graphs compiled from that data."

    Your claim is that Milakovitch cycles vastly overwhelm the radiative forcing of atmospheric CO2 (100w/m^2 vs 2.3w/m^2). That is a "fantastical claim" because it clearly does not square with the vast body of research.

    HK already pointed out that you're using an inappropriate metric that is not global. That is an elemental error, and when you present elemental errors that makes you look foolish. It's not meant as an insult. I make myself look foolish sometimes too. We all do. 

    You seem like a very nice person, John. All I'm saying is, stop believing you – as a non-expert – can disprove over a century of scientific research. Instead, you'd do yourself a greater service, if you're genuinely interested in this topic, to take the time to find out the answers to the questions you have.

  18. jhnplmr said: "[Global temps] then recovered and stabilised under AGW forcing."

    Um. I'm sorry but how do you come to the conclusion that global temperature has, in any way, stabilized?

  19. 315 Roger D

    "But given this acknowlegment of AGW, how can you conclude humans have "stabilized the temperature"?

    A glance at my graph, which Rob Honeycutt has promised to link for me, would convince you.  The Vostok temperatures started to fall in line with the falling insolation 10,000 years ago but then recovered and stabilised at present levels.  This recovery and stabilisation coincided with man clearing forests, starting farming and keeping domestic animals.

    "Also, I don't think the issue is "trying to balance on the cusp".

    Yet by trying to stop change that is precisely what you are trying to achieve, whether you realise it or not.  You are trying to resist coming out of the current ice age, yet hopefully, trying not to slide into a cooling phase.  That means that you want us to balance on the cusp of the current interglacial indefinitely.

    "Finally, I'm doubtful that any/ many of those that accept AGW think it is feasible to try to control the climate as you imply they do."

    I don't think that they are trying to control the climate, I think that the "climate control" that has occurred has been accidental, although beneficial to date.

    What I am trying to do is to make you realise that trying to stabilise temperatures at their present levels in the continual changing conditions of an ice age is impractical as well as unnatural.

  20. jhnplmr wrote "trying to stabilise temperatures at their present levels in the continual changing conditions of an ice age is impractical as well as unnatural."  He also wrote "This will require enormous amounts of energy which is becoming increasingly scarce and expensive."

    No, it is not at all impractical.  Preventing cooling is trivial, as is empirically obvious.  If by magic humans stopped all increases in greenhouse gases by ceasing use of fossil fuels, ceasing landscape changes, and so on, we could prevent a glacial period with a single chlorofluorocarbon factory for the entire world, as TonyW already told you.  But as other people already have told you, our greenhouse gas increases to date with just the next couple of decades will be sufficient to prevent cooling, let alone glaciation, for thousands of years.  Hare and Meinshausen produced a graph of the temperature consequence if we magically kept the greenhouse gas forcing at its 2005 level; it does not start going down.

  21. jhnplmr:

    I used data from the files bein1.dat and bein11.dat and created this graph showing the July insolation for 60oN and 70oN between 25,000 years ago and 25,000 years into the future. As you see, the insolation will decrease only marginally during the next 2-3000 years before it start increasing again.

    AGW has not only stopped the long-term cooling trend that culminated with the Little Ice Age, but has already brought the global temperature back to the level of Holocene optimum 5-8000 years ago. A popular denier argument is that northern Europe and Arctic was considerably warmer at that time than today, but that only proves that the reason for the warming was regional, not global, although some of the feedbacks had a global impact. As this graph on RealClimate shows, the global difference between Holocene optimum and LIA was not more than 0.6-0.7oC while the Medieval warm period was just a speed bump on the long-term cooling trend.

    So, the next ice age has been postponed for at least some tens of millennia, maybe several hundreds!

  22. jhnplmr

    "You look upon the contribution of AGW as completely negative"

    Here you have assigned to me a standard contrarian talking point that completely misses the point I actually made.

    No one is opposed to a slowly changing global climate. The concern is rooted in the pace of change. It wouldn't matter if the cause was anthorpogenic or natural. But it so happens that current human activity could cause a rapid change in global climate, the likes of which have caused massive disruptions to the biosphere in the gelological record.

    If AGW caused global climate to change at the same rate as glacial transitions, no one would care.

    I'm repeating this so you get it. It's not the change, it's the rate of change that is the concern. Our civilizations have flourished during a period of relative stability, the current interglacial. Now we are landlocked with huge populations dependent on hydrological and agriculatural infrastructure that are at risk from a changing climate. Large populations live and work near the coast and now the seas are rising. If they rose slowly we might be able to adapt with little pain. But if the climate changes rapidly, if extreme weather events become more numerous, if the sea eats into our coastlines displacing millions of people and destroying agricultural industries (the rice farms around the low-lying Mekong Delta feed millions in Asia), if floods drown our grain, drought starves our soil, more hurricanes wreck our homes and workplaces, and the changing climate uproots millians of people, we are in for a world of pain.

    We don't want to stop the climate changing, we'd just prefer it changed at a natural pace.

  23. Perhaps, jhnplmr, your gross overestimate of the effect of insolation decrease specifically at the 65N latitude is due to your misunderstanding of how glacial eras are started and ended.  You seem to think that the relative decrease in insolation at that latitude is the sole trigger for glaciation.  So you think glaciation will be triggered when the decrease from the previous insolation maximum nears the corresponding relative amount of decrease that happened at the initiation of the previous glaciation.  But that is not how it works.  Absolute, not just relative, temperature must be low enough to cause substantial increase in ice and snow cover, for the increased aledo to feed back, reducing the temperature, so the oceans start to absorb more CO2, feeding back to increase cooling, and so on. 

    If the temperature is high for any reason--hmmm, let's say high levels of CO2--ice and snow cannot increase enough to start that feedback.  And if the oceans already are pretty close to their capacity for absorbing CO2, decreasing their temperature a smidge will not pull enough CO2 out of the atmosphere to make enough of a cooling feedback.  And if there is a lot of CO2 in the atmosphere, the oceans will have to absorb far more than they did last time, for the absolute temperature to get low enough for the ice and snow to increase. 

    For some background, see the SkS post on Shakun's 2012 study of the CO2-temperature lag.

  24. #317 Rob Honeycutt

    "Your claim is that Milakovitch cycles vastly overwhelm the radiative forcing of atmospheric CO2 (100w/m^2 vs 2.3w/m^2). That is a "fantastical claim" because it clearly does not square with the vast body of research."

    I went on to say that the temperature had remained relatively constant over the last 6000 years so the comparatively large fall in solar insolation was balanced by the relatively small rise in CO2 forcing.  This implies that the two rates of forcing were equal despite their numerical inequality.

  25. #318 Rob Honeycutt

    "Um. I'm sorry but how do you come to the conclusion that global temperature has, in any way, stabilized?"

    I sent you my graph showing that ice core temperatures over the last 6000 years had remained relatively constant, naturally there have been oscillations during this period, you can see them on the graph but the long term mean temperature has remained constant.  This view is supported by this wikipedia extract Quaternary_glaciation:

    "The present interglacial period (the last 10,000 to 15,000 years) has been fairly stable and warm, but the previous one was interrupted by numerous frigid spells lasting hundreds of years. If the previous period was more typical than the present one, the period of stable climate in which humans flourished—inventing agriculture and thus civilization—may have been possible only because of a highly unusual period of stable temperature." 

    Wiki goes on to cite a scientific paper AgOrigins.pdf which postulated that the development of modern agriculture was only possible due to the relatively stable climate during the present interglacial.

    I might add that Vostok temperature over the last 50 years is only 0.2deg C warmer, last_50_yrs.html, a rise of 0.04deg C/decade.

  26. # 320 Tom Dayton

    "we could prevent a glacial period with a single chlorofluorocarbon factory for the entire world"

    You surely don't advocate such a method, it would have a catastrophic effect on the ozone layer.  The manufacture of such compounds has been phased out by the Montreal Protocol.

    "But as other people already have told you, our greenhouse gas increases to date with just the next couple of decades will be sufficient to prevent cooling, let alone glaciation, for thousands of years"

    This presupposes that present levels of GHG will be maintained, my contention is that they will decrease as the fossil fuel scarcity starts to bite in the next few decades.  Solar insolation will remain unchanged, the present level (426.76W/m2) was sufficient to reduce ice core temperatures 4 deg C below current levels at a similar point in the cycle 115,000 years ago.

  27. jhnplmr:

    "This presupposes that present levels of GHG will be maintained, my contention is that they will decrease as the fossil fuel scarcity starts to bite in the next few decades."

    What scarcity? According to this figure from James Hansen’s Climate Change and Intergenerational Justice (not yet published) the reserves are huge, particularly of coal and unconventional gas. If the estimates of recoverable resources (>12,000 gigatons of carbon) are approximately correct and half of that was released at once, it would raise the CO2 concentration by 3000 ppm. If it was released gradually and the airborne fraction remained close to 50% (not very likely) we are still talking about 1500 ppm in addition to the 400 we already have.

    If that happened, the CO2 level would remain above 600 ppm for 5000 years, enough for a complete melt-down of Greenland and West Antarctica and maybe East Antarctica as well.
    You can test it out for yourself with the GEOCARB model. If you set the transition CO2 spike to 3864 gigatons, the simulation will start with 1900 ppm CO2 in the atmosphere.

  28. jhnplmr wrote "This presupposes that present levels of GHG will be maintained, my contention is that they will decrease as the fossil fuel scarcity starts to bite in the next few decades."

    jhnplmr, you keep repeating that contention without responding to the factual counterpoints that a bunch of people have been making.  For example, I pointed you to a peer-reviewed study in the original post that this very thread is on, showing the tiny temperature consequence of a 1 W/M^2 drop in global (not just at 65N) insolation.  You could have gotten more details at the link provided in this original post, where you would have read that even in the optimistic greenhouse gas emissions reduction scenario A1B temperature would continue rising well past the year 2100.

    I and other people have given you data showing that just the quantity of greenhouse gases that already are in the atmosphere are sufficient to prevent cooling to pre-industrial levels for at least many decades, and that's if all emissions instantly went to zero, which has a probability of zero.  Reducing CO2 levels takes much, much longer than raising them (the "long tail"), so every single year that we keep increasing levels means we are delaying their dropping back by about ten years.  See the SkS post "Global Warming: Not Reversible, but Stoppable."

    You seem to be intentionally missing the point of the example that a single chlorofluorocarbon factory could delay the next glaciation indefinitely.  That example illustrates how little greenhouse gas emission is needed.  We don't have to use chlorofuorocarbons. We could use a larger amount of CO2, but an amount that still would be trivial to produce, even when fossil fuels become much scarcer.

    The bottom line is that your contention is factually incorrect, that preventing cooling would be expensive and difficult.

  29. jhnplmr, after you read the Global Warming: Not Reversible but Stoppable post, you should read A Glimpse at Our Possible Future Climate, Best to Worst Case Scenarios.  Skip past the first section.

  30. #321 HK

    "As you see, the insolation will decrease only marginally during the next 2-3000 years before it start increasing again"

    I agree, my graph shows the same, it should, we used the same data except that I calculated 65N as the mean of 60N and 70N to get one graph.  We also seem to agree now that the minimum will occur in 2000 years time.

    "AGW has not only stopped the long-term cooling trend that culminated with the Little Ice Age, but has already brought the global temperature back to the level of Holocene optimum 5-8000 years ago."

    This presupposes that present levels of GHG will be maintained, my contention is that they will decrease as the fossil fuel scarcity starts to bite in the next few decades. Solar insolation will continue to fall, albeit by not very much, dragging down the temperature with it.  After the minimum is passed temperatures will rise again, hopefully at GHG levels far below the present.

  31. jhnplmr, multiple people repeatedly have shown you data that the insolation decrease you are fixated on (and, bizarrely, you are hyper-fixated on 65N) will have a tiny effect on temperature--an effect too small to worry about for thousands of years, and one that can be offset by a trivial effort to put more greenhouse gases in the atmosphere.

    Your incessant repetition of your contentions without responses to factual counterpoints is sloganeering.  From the SkS Comments Policy: "No sloganeering. Comments consisting of simple assertion of a myth already debunked by one of the main articles, and which contain no relevant counter argument or evidence from the peer reviewed literature constitutes trolling rather than genuine discussion. As such they will be deleted. If you think our debunking of one of those myths is in error, you are welcome to discuss that on the relevant thread, provided you give substantial reasons for believing the debunking is in error. It is asked that you do not clutter up threads by responding to comments that consist just of slogans."

  32. 327 HK

    "What scarcity?"

    Fossil fuel depletion is as controversial as global warming!

    Here are some estimates:

    peak_oil.html

    Current estimates for the world wide peak production, not only for oil, but also for natural gas, and less traditional hydrocarbon sources range from the pessimistic (ASPO, 2007) to the less pessimistic (Edwards, 2001). The bottom line is that conventional oil and natural gas will probably peak sometime between 2010 and 2040.

    Predicting_the_timing_of_peak_oil

    In 2008, the IEA predicted a plateau by 2020 and a peak by 2030. The report called for a "global energy revolution" to prepare mitigations by 2020 and avoid "more difficult days" and large wealth transfers from OECD nations to oil producing nations.  This estimate was changed in 2009 to predict a peak by 2020, with severe supply-growth constraints beginning in 2010 (stemming from "patently unsustainable" energy use and a lack of production investment) leading to rapidly increasing oil prices and an "oil crunch" before the peak.

    It has been argued that even a "plateau oil" scenario may cause political and economic disruption due to increasing petroleum demand and price volatility

    A 2010 report by Oxford University researchers in the journal Energy Policy predicted that production will peak before 2015.  

    Nicol-André Berdellé adjusted world oil production by deducting the energy equivalent of investments, and concluded that a more than doubling of investment in oil exploration and development between 2005 and 2010, masked a decline in net oil production. He argued that in net energy terms, peak oil has alrady taken place.

    So most agree that peak oil will occur within the next decade, that is of course if the huge increases in reserves reported by most OPEC countries in the 1980's had any foundation in reality.  I think that when supply is unable to meet demand there will be a very rapid depletion as nations stockpile the remaining oil.  Unconventional sources such as shale oil take a lot of energy to extract and we will reach the point where we will put more energy into extraction that we gain from the product.  Fracking has proved successful in the short term but the wells deplete very quickly and it is expensive to drill more.  You point out the huge reserves left in the ground but most will never be extracted due to the energy requirement to extract them.

    We have already closed down the last coal mine in the UK and are trying to minimise our use of coal for power generation in line with international agreements.

    I think that all these factors will result in a decrease in GHG emissions during the next decades.

  33. #331 Tom Dayton

    "and, bizarrely, you are hyper-fixated on 65N"

    That is because in an ice age Jul 65N Milankovitch cycles have a close correlation with global temperatures.  there is nothing bizarre about it.

    "No sloganeering. Comments consisting of simple assertion of a myth already debunked by one of the main articles"

    The sources I have quoted are widely accepted, my interpretation of them differs from yours.  That doesn't make you right and me wrong, only time will tell.

    "It is asked that you do not clutter up threads by responding to comments that consist just of slogans"

    You are right, this debate is no longer productive.  I have stated my views that AGW has been beneficial in offsetting the falling Jul 65N solar insolation since the last peak 10,000 years ago.  This has served to prevent a fall in global temperatures and has extended the current interglacial period.  I have quoted scientific articles that support this view.  It is up to you to decide if these views have any validity.

    I don't like threats so this is my last post on the subject.

  34. jhnplmr claimed he is justified in using insolation at 65N latitude as the sole predictor of global temperature in the next few decades to 2,000 years, because "in an ice age Jul 65N Milankovitch cycles have a close correlation with global temperatures."

    No.  That correlation is "close" only in the orders of magnitude of time and temperature of glaciations, as illustrated by Figure 2 in a Climate Data Information page--even when that figure admittedly has been "tuned" to make the temperature and insolation match as closely as possible.  Just as CO2 is not the only driver of climate, neither is global insolation, let alone 65N insolation.  You don't need a complex climate model to see that, as multiple comments and posts here have made clear.  But you do need a climate model more complex than the single-predictor model that jhnplmr insists on using despite the overwhelming empirical evidence of its ineptitude for the application to which jhnplmr is putting it.

  35. jhnplr:

    Regarding peak oil
    Let’s assume that CO2 will peak at 450 ppm with zero emissions after that. This is a very optimistic scenario since it only takes 20-25 years of our present emissions (no further increase!) to bring us to that point. What will happen?

    In that scenario, according to the GEOCARB model, we will have 350 ppm of CO2 after 300 years and 300 ppm after 4000 years. 300 ppm is the highest level recorded in the ice cores during the last 800,000 years before the industrial revolution, so it’s safe to conclude that we have already cancelled the next ice age!

    And that doesn’t include other man-made GHGs or natural emissions of CO2 and methane from thawing permafrost or methane hydrates. Also keep in mind that in 4000 years the summer insolation in high northern latitudes will be slowly increasing!

  36. And further to peak oil, the climate problem is more about coal than oil, and we have an awful lot of coal available.

    "According to BGR there are 1038 billion tonnes of coal reserves left, equivalent to 132 years of global coal output in 2012. Coal reserves reported by WEC are much lower - 861 billion tonnes, equivalent to 109 years of coal output." Source

  37. jhnplmr...  When people challenge your assertions you have to be able to either defend them, showing why you are correctly interpreting the information, or you have to be willing to accept that the challenges are correct and then adjust your position accordingly. Just stating the same thing when others have presented evidence to show you're incorrect isn't a viable position.

  38. The thing that always gets me about fossil fuel reserves is that we know they can't sustain economic growth to 2100. Even if we take the higher figure of 132 years of continued coal use... that is at 2012 levels. Barring a massive decrease in population or economic collapse, electricity use is going to continue to skyrocket. By 2100 it will almost certainly be well over four times 2012 levels.

    One way or another, our fossil fuel use is going to plummet this century. Most children being born now will live to see a low fossil fuel world... which could mean either a transition to clean sustainable energy or a polluted hellscape and massive economic and population crash. Even without AGW and other pollution problems, the need to get off fossil fuels is blindingly obvious... yet somehow there is still fierce resistance.

    Fortunately, solar power is now becoming cheaper than coal for larger and larger portions of the planet. It seems likely that greed will save us from our own stupidity... but we're definitely cutting it close.

  39. #334 Tom Dayton

    "No. That correlation is "close" only in the orders of magnitude of time and temperature of glaciations, as illustrated by Figure 2 in a Climate Data Information page--even when that figure admittedly has been "tuned" to make the temperature and insolation match as closely as possible"

    Yes, the correlation is close as you can see from my graph, and it is from raw data, not tuned as you suggest.

    Effect of Solar Insolation on the last glacial period

    Look how the temperature rises in response the solar forcing at the start of the last interglacial.  Look how it follows the peaks and troughs until finally we are dragged out of the glacial period into the current interglacial.

    Notice after the peak, 10,000 years ago, temperatures (blue) start to fall in line with the solar insolation but then stop falling and start rising again before they level out and remain relatively constant.  What could have caused this rise and levelling out?  Could it be rising CO2 levels due to man clearing the forests (slash and burn) as he turned from hunting to farming and keeping domestic animals?  The times certainly coincide.  Could it be that the rising GHG from his activities are keeping the cooling at bay despite the falling solar insolation?  If so, then his activities have been beneficial not an unmitigated disaster as you would have us believe.

    If you don't believe that GHG emissions helped to counteract the falling insolation perhaps you can account for the rise and levelling out of the temperatures in some other way?

    "But you do need a climate model more complex than the single-predictor model that jhnplmr insists on using despite the overwhelming empirical evidence of its ineptitude for the application to which jhnplmr is putting it."

    Don't put words in my mouth, I have never said that solar insolation is the only forcing, my very first post on this forum said as much.

    Response:

    [RH] Fixed image width.

  40. #337

    Rob Honeycutt

    "Just stating the same thing when others have presented evidence to show you're incorrect isn't a viable position."

    Now you have given me the link to the graph I was referring to I have a new arrow for my bow.  A picture is worth a thousand words.  Thanks for that!

    I don't know why my post was duplicated, the only thing new is the image.  If this post is duplicated then something has gone wrong.

  41. #334 HK

    "300 ppm is the highest level recorded in the ice cores during the last 800,000 years before the industrial revolution, so it’s safe to conclude that we have already cancelled the next ice age"

    I agree, the next glacial period is not going to happen, as for the next ice age, we have to get out of this one first!

    By historic values the present levels of CO2 are low compared to those 500 million years ago when they were over 6000ppm Phanerozoic_Carbon_Dioxide.  Sea levels were much higher but life was thriving.  It has only fallen to current levels (393ppm) over the last few million years.

  42. jhnplmr 500 million years ago the sun was significantly dimmer than it is now, so higher levels of CO2 were required to avoid a snowball Earth so that life could be thriving.  You need to consider all of the forcings and consider the total energy budget.

    Also just because life was thriving 500M years ago with higher CO2, does not mean that rising CO2 now is not a problem.  The problem with climate change is a lot to do with the fact that it is a change from the climate to which we are heavily adapted (e.g. agricultural practices).

    Response:

    [TD] jhnplmr, for more information see the rebuttals to the myths "CO2 was higher in the past" and "CO2 was higher in the late Ordovician."  See also "It's Not Bad."  And if you want to argue with those posts, do so in the comments on those posts, not here.

  43. #336 scaddenp

    "And further to peak oil, the climate problem is more about coal than oil, and we have an awful lot of coal available."

    I agree, coal generates more CO2 than oil, but coal usage is falling.  We have closed down the last coal mine in the UK and we are trying to limit its use in power stations in line with our international committments.  These measures, coupled to oil shortages over the coming decade, should help to decrease GHG emissions.


  44. By historic values the present levels of CO2 are low compared to those 500 million years ago when they were over 6000ppm Phanerozoic_Carbon_Dioxide. Sea levels were much higher but life was thriving. It has only fallen to current levels (393ppm) over the last few million years.


    Fellas,

    I think it's time to stop feeding this particular troll. He can't possibly be unaware that cities containing millions of people live on the coast. Sure, 'life' will thrive after those cities drown, but that's a facile argument not worth your time, and I doubt even he takes it seriously. He's not here to learn or even think. When you prove him wrong he shrugs it off without acknowledgement and offers a new <snipped>.

    Happy for my comment to be modded out too.

    Leto.

    Response:

    [TD] I deleted one of jhnplmr's most recent responses, because it went too far into irrelevance and ridiculousness by invoking stellar evolutionary timescale as evidence that our current greenhouse gas emissions are nothing to worry about. 

  45. #344 Leto

    "and offers a new inaninty"

    Perhaps you should learn to spell before you start insulting contributors.  Why don't you start by telling me where I am wrong in the deductions I drew from my graph (#339)?

  46. Response:[RH] Fixed image width.

    What should I do next time I use an image?

    Response:

    [JH] Keep your graphic width to 500 pixels or less.

  47. "These measures, coupled to oil shortages over the coming decade, should help to decrease GHG emissions."

    Should and I certainly hope so. However, China and India are increasing coal use. Rising petrol prices will usher in electric vehicles, also good as far more efficient, but the electricity to drive them comes from what? The USA decrease in coal use is driven by shale gas. When that runs out, coal can increase in a perfectly free market. UK coal closures are driven by economics. My point was that there is no shortage of coal, plenty enough to create serious climate damage. If there is no limitation imposed on usage, and no alternative that is cheaper, then it will be burnt.

    Response:

    [JH] This discourse has gone off-topic. Please continue it elsewhere.

  48. 347 scaddenp

    "Rising petrol prices will usher in electric vehicles, also good as far more efficient, but the electricity to drive them comes from what? "

    Nuclear, wind, solar and tidal?

    I agree, while it takes less energy to get it out of the ground than you can get from it they (we) will continue to use it.  I'm afraid that it is very difficult to get people to stop heating their homes, using computers, electric lighting and their cars.  It isn't going to happen while fossil fuel supplies are available.  Any government that tried to ban their use would get voted out of office.

    Response:

    [JH] This discourse with scaddenp has gone off-topic. Please continue it elsewhere.

  49. This guy isn’t particularly worried about the next glaciation. He claims that it’s unlikely to start until the summer insolation at 65oN approaches the same level as the onset of the last glaciation. That means in 130,000 years at the earliest and maybe not until 620,000 years. Note that it takes a much lower insolation to start a glaciation than to sustain it as soon as the slow positive feedbacks have been set in motion. That’s why much of the last glaciation endured through higher insolation than today without ending.

    I adjusted his figure 3 to sum up his arguments:

    Response:

    [RH] Reinserted image to fix formatting error.

  50. @jhnplmr & scaddenp:

    I deleted your most recent exchange because it was completely off-topic.

Prev  1  2  3  4  5  6  7  8  Next

Post a Comment

Political, off-topic or ad hominem comments will be deleted. Comments Policy...

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

Link to this page



The Consensus Project Website

THE ESCALATOR

(free to republish)

Smartphone Apps

iPhone
Android
Nokia

© Copyright 2018 John Cook
Home | Links | Translations | About Us | Contact Us