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What does past climate change tell us about global warming?

What the science says...

Select a level... Basic Intermediate

Climate reacts to whatever forces it to change at the time; humans are now the dominant forcing.

Climate Myth...

Climate's changed before
Climate is always changing. We have had ice ages and warmer periods when alligators were found in Spitzbergen. Ice ages have occurred in a hundred thousand year cycle for the last 700 thousand years, and there have been previous periods that appear to have been warmer than the present despite CO2 levels being lower than they are now. More recently, we have had the medieval warm period and the little ice age. (Richard Lindzen)

A common skeptic argument is that climate has changed naturally in the past, long before SUVs and coal-fired power plants, and this somehow tells us that humans can't be the main cause of the current global warming. Peer-reviewed research and simple logic show this is not the case.

It's important to know there are a number of different forces acting on the Earth’s climate. When the sun gets brighter, the planet receives more energy and warms. When volcanoes erupt, they emit particles into the atmosphere which reflect sunlight, and the planet cools. When there are more greenhouse gases in the atmosphere, the planet warms. It's worth remembering that without some greenhouse gas  the Earth would be a ball of ice.

These forces are called "forcings" because they force changes in the global average temperature.

Looking at the past gives us insight into how our climate responds to such forcings. Using ice cores, for instance, we can work out past temperature changes, the level of solar activity, and the amount of greenhouse gases and volcanic dust in the atmosphere. Looking at many different periods and timescales including many thousands of years ago we've learned that when the Earth gains heat, glaciers and sea ice melt resulting in a positive feedbacks that amplify the warming. There are other positive feedbacks as well and this is why the planet has experienced such dramatic changes in temperature in the past.

In summary the past reveals our climate is sensitive to small changes in heat. 

What does that mean for today? Over the past 150 years greenhouse gas levels have increased 40 percent mainly from burning of fossil fuels. This additional "forcing" is warming the planet more than it has in thousands of years. From Earth's history, we know that positive feedbacks will amplify this additional warming.

The Earth's climate has changed in the past and ice cores and other measures tell us why. Based on this knowledge, and other types of evidence we know the human emissions of greenhouse gases are warming the climate.

The 'climate changed naturally in the past' argument is a logical fallacy known as non sequitur, in which the conclusion doesn't follow from the arguments.  It's equivalent to seeing a dead body with a knife sticking out the back, then arguing the death must be natural because people died naturally in the past.  It fails to even consider the available evidence.

Last updated on 4 February 2014 by dana1981. View Archives

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Comments 1 to 50 out of 309:

  1. Thanks for trying to answer science with science. Most sites on the subject are propaganda vs science or propaganda vs propaganda.
  2. A change or two in climate history has recently been revealed indicating change happens faster than thought:

    Fossils Found In Tibet Revise History Of Elevation, Climate
    ScienceDaily (June 12, 2008) — About 15,000 feet up on Tibet's desolate Himalayan-Tibetan Plateau, an international research team led by Florida State University geologist Yang Wang was surprised to find thick layers of ancient lake sediment filled with plant, fish and animal fossils typical of far lower elevations and warmer, wetter climates.

    Greenland Ice Core Analysis Shows Drastic Climate Change Near End Of Last Ice Age
    ScienceDaily (June 19, 2008) — Information gleaned from a Greenland ice core by an international science team shows that two huge Northern Hemisphere temperature spikes prior to the close of the last ice age some 11,500 years ago were tied to fundamental shifts in atmospheric circulation.
    Response: This would indicate that climate is more sensitive than realised which means the climate response to CO2 forcing will be greater than current estimations.
  3. Very interesting read here...haven't heard anything about water vapour feedback yet. Enlighten me if what i say is wrong but are the IPCC models flawed in that their water vapour feedback element is missing out on a rather unavoidable factor in gravity. Douglas Hoyt discusses here http://www.warwickhughes.com/hoyt/wvfeedback.htm about how overestimated the water vapour feedback is in the IPCC models. I take the side of the devil's advocate and say that it seems the IPCC has jumped on a bandwagon and is trying to make it work their way...but it isn't.
  4. That's a very odd notion. Odd in two respects. First the enhanced atmospheric water vapour that follows enhanced greenhouse atmospheric warming has been directly measured [*] and some of the consequences with respect to surface humidity and precipitation patterns are already identified in the real world [**].

    Secondly, because the "gravity" notion raised in the dodgy website you linked to is a nonsense. Water vapor that partitions in the atmosphere does so according to atmospheric pressure and temperature. As the temperature of the atmosphere rises so does the water vapour concentration. Is this effect countered by gravity? Not to any significant degree. Atmospheric water exists in the atmosphere in the form of individual water molecules. The gravitational force acting on these molecules is extremely small and is opposed by the kinetic energy of the water molecules provided by the ambient thermal energy.

    It's only if the atmosphere cools a bit and the water vapour concentration rises above the saturation point, that gravity takes a significant macroscopic hold. Then water molecules "aggregate", the water vapour condenses, and gravity then has an effect (it rains!).

    So not only is the website trying to sell a ludicrous notion, but it's premise is contradicted by real world measurements (see [*] and [**] below.

    [*] e.g.:

    Soden BJ et al. (2005) "The radiative signature of upper tropospheric moistening" Science 310, 841-844.

    Abstract: "Climate models predict that the concentration of water vapor in the upper troposphere could double by the end of the century as a result of increases in greenhouse gases. Such moistening plays a key role in amplifying the rate at which the climate warms in response to anthropogenic activities, but has been difficult to detect because of deficiencies in conventional observing systems. We use satellite measurements to highlight a distinct radiative signature of upper tropospheric moistening over the period 1982 to 2004. The observed moistening is accurately captured by climate model simulations and lends further credence to model projections of future global warming."


    Santer BD et al (2007) "Identification of human-induced changes in atmospheric moisture content" Proc. Natl. Acad. Sci. USA 104 15248-15253.

    Abstract: "Data from the satellite-based Special Sensor Microwave Imager (SSM/I) show that the total atmospheric moisture content over oceans has increased by 0.41 kg/m(2) per decade since 1988. Results from current climate models indicate that water vapor increases of this magnitude cannot be explained by climate noise alone. In a formal detection and attribution analysis using the pooled results from 22 different climate models, the simulated "fingerprint" pattern of anthropogenically caused changes in water vapor is identifiable with high statistical confidence in the SSM/I data. Experiments in which forcing factors are varied individually suggest that this fingerprint "match" is primarily due to human caused increases in greenhouse gases and not to solar forcing or recovery from the eruption of Mount Pinatubo. Our findings provide preliminary evidence of an emerging anthropogenic signal in the moisture content of earth's atmosphere."

    Rind D et al (1991) "Positive Water-Vapor Feedback In Climate Models Confirmed By Satellite Data" Nature 349, 500-503.

    Abstract: "Chief among the mechanisms thought to amplify the global climate response to increased concentrations of trace gases is the atmospheric water vapour feedback. As the oceans and atmosphere warm, there is increased evaporation, and it has been generally thought that the additional moisture then adds to the greenhouse effect by trapping more infrared radiation. Recently, it has been suggested that general circulation models used for evaluating climate change overestimate this response, and that increased convection in a warmer climate would actually dry the middle and upper troposphere by means of associated compensatory subsidence1. We use some new satellite-generated water vapour data to investigate this question. From a comparison of summer and winter moisture values in regions of the middle and upper troposphere that have previously been difficult to observe with confidence, we find that, as the hemispheres warm, increased convection leads to increased water vapour above 500 mbar in approximate quantitative agreement with the results from current climate models. The same conclusion is reached by comparing the tropical western and eastern Pacific regions. Thus, we conclude that the water vapour feedback is not overestimated in models and should amplify the climate response to increased trace-gas concentrations."

    [**] e.g.:

    Zhang XB (2007) "Detection of human influence on twentieth-century precipitation trends" Nature 448, 461-465.

    Abstract: "Human influence on climate has been detected in surface air temperature(1-5), sea level pressure(6), free atmospheric temperature(7), tropopause height(8) and ocean heat content(9). Human-induced changes have not, however, previously been detected in precipitation at the global scale(10-12), partly because changes in precipitation in different regions cancel each other out and thereby reduce the strength of the global average signal(13-19). Models suggest that anthropogenic forcing should have caused a small increase in global mean precipitation and a latitudinal redistribution of precipitation, increasing precipitation at high latitudes, decreasing precipitation at sub-tropical latitudes(15,18,19), and possibly changing the distribution of precipitation within the tropics by shifting the position of the Intertropical Convergence Zone(20). Here we compare observed changes in land precipitation during the twentieth century averaged over latitudinal bands with changes simulated by fourteen climate models. We show that anthropogenic forcing has had a detectable influence on observed changes in average precipitation within latitudinal bands, and that these changes cannot be explained by internal climate variability or natural forcing. We estimate that anthropogenic forcing contributed significantly to observed increases in precipitation in the Northern Hemisphere mid-latitudes, drying in the Northern Hemisphere subtropics and tropics, and moistening in the Southern Hemisphere subtropics and deep tropics. The observed changes, which are larger than estimated from model simulations, may have already had significant effects on ecosystems, agriculture and human health in regions that are sensitive to changes in precipitation, such as the Sahel."

    Allan, R P & Soden, B J (2008) Atmospheric warming and the amplification of precipitation extremes" Science 321, 1481-1484.

    Abstract: "Climate models suggest that extreme precipitation events will become more common in an anthropogenically warmed climate. However, observational limitations have hindered a direct evaluation of model- projected changes in extreme precipitation. We used satellite observations and model simulations to examine the response of tropical precipitation events to naturally driven changes in surface temperature and atmospheric moisture content. These observations reveal a distinct link between rainfall extremes and temperature, with heavy rain events increasing during warm periods and decreasing during cold periods. Furthermore, the observed amplification of rainfall extremes is found to be larger than that predicted by models, implying that projections of future changes in rainfall extremes in response to anthropogenic global warming may be underestimated."
  5. Has any research been done on just how much water vapour can be held in the atmosphere and the warmer temperatures before it reaches saturation point? And also explain to me why Douglas Hoyt's info is so dodgy. He's fairly knowledgeable in the field so why is his contribution so wrong? How do we know what's right or wrong? You can justify comments with 'scientific proof' but how do we know that it is correct? Are you prepared to take anyones word for it? Is there some corruption not only from the climate change skeptics but also from the IPCC and other anthropogenic climate change supporters?

    It's all very interesting but doesn't everyone within this current issue have an agenda?
  6. interesting questions; some are easily answered, some less so:

    [Has any research been done on just how much water vapour can be held in the atmosphere and the warmer temperatures before it reaches saturation point?]


    It depends where you are in the atmosphere since the saturation level varies with temperature and pressure. These data are known quite acurately 'though. You can see the variation of saturation of air with water vapour as a function of temperature here (scroll down the page to find the relevant graph):


    http://en.wikipedia.org/wiki/Water_vapor


    [And also explain to me why Douglas Hoyt's info is so dodgy. He's fairly knowledgeable in the field so why is his contribution so wrong? How do we know what's right or wrong?]


    One can compare Hoyt's assertions with reality. They don't match. Therefore in this instance we know Hoyt is wrong.

    A problem is that Hoyt hasn't published anything on this. he's just asserting stuff on a web site. Since he may well have written it in 2004, perhaps he thought it was correct then but doesn't realize that real world data now contradicts his assertion; perhaps he just hasn't bothered to update his web site. We'd have to ask him...

    Hoyt has made the assertion (on his website) that gravity effects will eliminate 90% of the warming-induced enhancement of water vapour concentrations. The Minschwaner and Dessler paper that Hoyt refers to indicates a possibility of a much smaller reduction in enhanced water vapour. So even in 2004, Hoyt's assertion didn't match reality. Now we have much better measures of atmospheric water vapour, and it's clear that the atmospheric water vapour concentrations rise pretty much as predicted by theory and modelling. As well as the articles whose abstracts are listed in my post above, more recent analyses (see [**] below) of direct tropospheric water vapour demonstrate that the water vapour concentrations are rising in response to warming pretty much as predicted. So Hoyt is demonstrably wrong.



    [You can justify comments with 'scientific proof' but how do we know that it is correct?]


    It's not really about "proof". It's about the evidence. In this case Hoyt is making assertions that are directly contradicted by the evidence. So in this instance Hoyt is demonstrably wrong. A lot of the efforts in dealing with so-called "skeptical" (!) "arguments" is in pointing out their inherent self-contradictions.

    Hoyt is also wrong (it seems to me) on straightforward theoretical/empirical grounds that relate to the competing effects of gravity and thermal kinetic energy on isolated molecules in a vapour as I outlined in my post just above.



    [are you prepared to take someone's word for it?]


    Yes and no. If someone has a habit of dishonesty of course one would be foolish to take their word. Likewise if someone is respected for their honesty and diligence, I'm more likely to take them at face value. I am always skeptical of stuff that is asserted on this or that web site, and if one investigates further and finds that the asserter hasn't published the relevant work (or in this case hasn't published anything for 10 years), makes assertions that are not supported by any evidence, and upon further investigation, finds that the assertions are actually directly contradicted by real world evidence, then it would be foolish not to discount the assertions.

    One should be skeptical about these things!



    [Is there some corruption not only from the climate change skeptics but also from the IPCC and other anthropogenic climate change supporters?]


    Corruption is usually identifiable. Can you identify any IPCC "corruption"? I haven't come across any. That doesn't mean the IPCC are paragons of perfection! If anything the IPCC presentations are somewhat conservative.



    [It's all very interesting but doesn't everyone within this current issue have an agenda?]


    I wouldn't have said so. There's clearly a strong agenda position to misrepresent the science amongst certain quarters (you see quite a lot of it from a cohort of posters on this web site). In my experience the only "agenda" the scientists have is to get to the bottom of whatever topic their researching, preferably making some good discoveries along the way and publishing some well-respected and highly-cited papers.



    [***]

    Gettelman A and Fu Q (2008) “Observed and simulated upper-tropospheric water vapor feedback” J. Climate 21, 3282-3289.

    Abstract: “Satellite measurements from the Atmospheric Infrared Sounder (AIRS) in the upper troposphere over 4.5 yr are used to assess the covariation of upper-tropospheric humidity and temperature with surface temperatures, which can be used to constrain the upper-tropospheric moistening due to the water vapor feedback. Results are compared to simulations from a general circulation model, the NCAR Community Atmosphere Model (CAM), to see if the model can reproduce the variations. Results indicate that the upper troposphere maintains nearly constant relative humidity for observed perturbations to ocean surface temperatures over the observed period, with increases in temperature similar to 1.5 times the changes at the surface, and corresponding increases in water vapor ( specific humidity) of 10% -25% degrees C-1. Increases in water vapor are largest at pressures below 400 hPa, but they have a double peak structure. Simulations reproduce these changes quantitatively and qualitatively. Agreement is best when the model is sorted for satellite sampling thresholds. This indicates that the model reproduces the moistening associated with the observed upper-tropospheric water vapor feedback. The results are not qualitatively sensitive to model resolution or model physics.”


    Brogniez H and Pierrehumbert RT (2007) “Intercomparison of tropical tropospheric humidity in GCMs with AMSU-B water vapor data” Geophys. Res. Lett. 34, Article Number: L17812

    Abstract: “We make use of microwave measurements of the tropical free tropospheric relative humidity (FTH) to evaluate the extent to which the water vapor distribution in four general circulation models is faithful to reality. The comparison is performed in the tropics by sorting the FTH in dynamical regimes defined upon the 500 hPa vertical velocity. Because microwave radiation penetrates non-rainy and warm clouds, we are able to estimate the FTH over most of the dynamical regimes that characterize the tropics. The comparisons reveal that two models simulate a free troposphere drier than observed (< 10%), while the others agree with the observations. Despite some differences, the level of agreement is good enough to lend confidence in the representation of atmospheric moistening processes. A climate change scenario, tested on two models, shows a tendency to maintain the FTH to an almost fixed value be it an ascending or a subsiding regime” ',
  7. Conspicously absent from consideration of what could have caused the warming for the 30 year period is ENSO and PDO. Here is a 58 year ENSO chart.

    http://www.cdc.noaa.gov/people/klaus.wolter/MEI/ts.gif

    Notice that prior to 1977 La Nina dominates the chart. After 1977 El Nino dominates the chart. The dominance of El Nino corresponds with the temperature rise of the last 30 years. Climate scientist Dr. Roy Spencer has calculated that up to 70% of the temperature rise that we have seen could be accounted for by ENSO and PDO patterns. There also seems to have been a flip in the PDO cycle in the last year or so that could well indicate another 20 years of flat or negative temperature trends.

    By the way, you may notice that the El Nino dominance in the chart was greatest from about 1977 to 1998. After that the distribution is a little more even. This corresponds well to the flatening of the temperature trend for the last decade. While that point is also challenged in this blog, I have proven it to be true in the relevant section.
    Response: ENSO has been considered as a possible driver of global warming. The El Nino Southern Oscillation does show close correlation to global temperatures over the short term. However, it is unable to explain the long term warming trend over the past few decades.
  8. Now THIS is interesting:
    Did Early Global Warming Divert A New Glacial Age?
    ScienceDaily (Dec. 18, 2008) — The common wisdom is that the invention of the steam engine and the advent of the coal-fueled industrial age marked the beginning of human influence on global climate.
    But gathering physical evidence, backed by powerful simulations on the world's most advanced computer climate models, is reshaping that view and lending strong support to the radical idea that human-induced climate change began not 200 years ago, but thousands of years ago with the onset of large-scale agriculture in Asia and extensive deforestation in Europe. ...

    http://www.sciencedaily.com/releases/2008/12/081217190433.htm
  9. And in follow up:

    "Nevle and Bird admit that volcanic activity and a decrease in the sun's intensity probably both played roles in triggering the Little Ice Age. Still, Bird said, human activity was undeniably important."

    http://www.msnbc.msn.com/id/28353083/
  10. This The_skeptic_who_came_in_from_the_cold.html is an attempt to answer, for a skeptic (not denialist) friend, his proposition that since climate had changed before there was nothing to either explain or worry about. It is an attempt to distinguish between genuine skepticism and malign, planet-hating, denialism.

    The comment from tommybar "even if C02 is contributing, which it may have/be, a lot has been shown that it's 'greenhouse' ability is a logarithmic function, and that it has already contributed as much as it can" is interesting because it has suddenly started cropping up, in blogs around the world almost simultaneously. Could it be the latest talking point provided for the denialist anti-environment lobby? Funny how they all sing to the same tune (ice caps on Mars, Antarctic ice growing, planet now cooling) at the same time with each new attempt to stack the card deck, shuffle the pea, while distracting the punters.
  11. David; the examples given of extinction events are interesting but not relevent. Sure there were changes in climate that caused species extinctions, but those changes were caused by massive physical forces -catastrophic in scale and duration far beyond what we can do by adding CO2 to the atmosphere.
    Bear in mind too, that the earth was a very different place then and so was the climate; in truth one could argue that if it wasn't for these events we would not have the climatic conditions we enjoy today.
  12. David
    I understand what you are saying but disagree that they caused the extinctions. The warming as the agent of extinction is simply false. Life on Earth has always adapted well to increases in heat, this quite clear from the fossil record. Climate changes can and do cause extinctions but from cooling, not warming.

    Every extinction cited as being caused by GHGs can be shown to have other causes. I agree with Mizimi on this.
    Name an extinction where warming is blamed and I will give you a more viable explanation for that extinction that has nothing to do with GHGs.

    This is a violent and dangerous planet. People that refuse to believe that are seriously deluded.
  13. ps
    Let me rephrase that. "this quite clear from the fossil record. Climate changes can and do cause extinctions but from cooling, not warming."

    I should have said: "this IS quite clear from the fossil record. Climate changes can and do cause MAJOR extinctions but from cooling, not warming. Minor extinctions happen all the time because some organisms have over specialized and are too sensitive. The small climate changes (which occur normally) weed out those species. It's called Natural Selection."
  14. Well, the Late Permian comes immediately to mind.

    The period which is my own research speciality is the late Pleistocene. The cold period (Europe) and relatively wet period (Australia) was a time when large mammals flourished. The change over to a warmer and drier time saw the loss of numerous species. This extinction event is going to be mirrored by what is going on now. But more so, because the change which took hundreds, perhaps thousands of years then (ie starting some 25,000 years ago), is going to be replayed in the space of a few decades in the 21st century.

    I swore I wasn't, on the basis that life, and an equable climate, is much too short, going to argue with denialists any more, but here I am, can't help myself I suppose.

    BY the way, does anyone still following this thread know what has happened to the owner of this blog? It feels like we are playing around in a deserted house, the owner curiously absent.
  15. David
    Someone essentially called John a liar (in a nice enough way) in the Arctic melt thread and he has been very quiet since. I side with John but I'm a liar too.

    The Permian extinction is obviously the most interesting. I'll assume that you have read "Gorgon" already since it is so pertinent.

    OK, the obvious factor is the Siberian traps. Large volcanic fields erupting for a very long time spewing all sorts of poisons into the atmosphere. But (from Gorgon) the sea extinctions (something like 90%) happened in a different time fram from the land extinctions (Somewhere around 75%). Sorry I don't remember the exact numbers.

    Well what caused the traps to erupt? In both the PT and KT extinctions we have evidence for very large impactors on the opposite side of the earth preceding the eruption of the traps. The reason for the extinctions is fairly obvious (two incidents and two extinction events, the second event caused by the first).

    BTW the same actually happened at the KT, Bakker points out that the dinosaurs were already in trouble by the KT event.
  16. ps
    I am not as familiar with the Pleistocene, I have been studying the Paleocene-Eocene-Oligocene periods recently but have not gotten as far as the Pleistocene.

    What do you have so far?
  17. pps
    Calling sceptics "deniers" is the same as calling you an alarmist. I am sure that you don't like it either.
  18. Just to refresh my memory you are talking about an interglacial within the Neogene-Holocene Ice Age?
    The Pleistocene was the last period prior to the Holocene and prior to H4, correct?
  19. Ok, I am getting caught up. It was a series of glacations and interglacials. Yes I did read about this period to some extent (I have a terrible memory). The chart at Wikipedia is a good refresher. I'll brush up on it.
  20. sorry, i screwed up the link:
    This should work.
  21. David
    I knew I had read a little about it. This is from my file. PLos One is down right now so I can't give you a link. But here is the Abstract.

    Neanderthal Extinction by Competitive Exclusion
    Banks,et.al
    Background:
    Despite a long history of investigation, considerable debate revolves around whether Neanderthals became extinct because of climate change or competition with anatomically modern humans (AMH).

    Methodology/Principal Findings:
    We apply a new methodology integrating archaeological and chronological data with high-resolution paleoclimatic simulations to define eco-cultural niches associated with Neanderthal and AMH adaptive systems during alternating cold and mild phases of Marine Isotope Stage 3. Our results indicate that Neanderthals and AMH exploited similar niches, and may have continued to do so in the absence of contact.

    Conclusions/Significance:
    The southerly contraction of Neanderthal range in southwestern Europe during Greenland Interstadial 8 was not due to climate change or a change in adaptation, but rather concurrent AMH geographic expansion appears to have produced competition that led to Neanderthal extinction.
  22. Um yes, the Neanderthals are an interesting case since they involve "creatures" with similar culture and lifestyle and bigger brain than us. Clearly the interaction between us and them was complex. Climate change may well have played a role in Neanderthal demise either directly or indirectly, as may interaction with H. sapiens sapiens. But I am talking about the extinction of the megafaunas - in Europe adapted to cold conditions (eg woolly mammoth), in Australia to cool wet conditions (eg Diprotodon).

    And extinctions due to strikes from space? Dunno. I was once reasonably happy with the dinosaur demise theory, but even that one I have my doubts about now. I reckon CO2 build up with methane release as the planet warms up is a better bet for all of them, but that is just me. But whatever the cause of the past great extinctions, they are really just cautionary tales about what can happen to this planet when something goes awry with the normal stabilising mechanisms. Makes a nonsense of the denialist view that us puny 6 billion humans spewing ever more CO2 into the air couldn't possibly alter the climate. I think we are in for a least the late Pleistocene (yes, pre-Holocene if you like) nastiness, and quite possibly much worse. And you will find that hot climate (plus dry in Australia) causes far more problems to water based life forms than cold climate.
  23. David
    You must mean the Berkeley paper:
    Climate Change Plus Human Pressure Caused Large Mammal Extinctions In Late Pleistocene
    ScienceDaily (Oct. 4, 2004) — Berkeley - A University of California, Berkeley, paleobiologist and his colleagues warn that the future of the Earth's mammals could be as dire as it was between 50,000 and 10,000 years ago, when a combination of climate change and human pressure resulted in the extinction of two-thirds of all large mammals on the planet.

    LOL - That's from Berkeley back in 2004! I don't know if I would trust them, but I can't access the original paper. That is a shame. There is also an ongoing argument about a couple of impacts right around then, one on land in the northern U.S. (I forget exactly where) and another in the Atlantic near Brasil (again I don't remember exactly where, I'll try to find the articles).

    I agree when something goes awry with the normal stabilising mechanisms things happen. But it's not something we have a lot of control over.

    But "causes far more problems to water based life forms than cold climate." I have to disagree with. Read that paper when PLos One comes back online (they are just doing maintenance) and look at the graphs. Both Neandertal and our ancestors took a real nose dive at H4, we were lucky to recover, neandertal wasn't so lucky.
  24. ps
    This link will take you to PLos One when they are back online. Then just type in "neandertal" in their site search for the paper.
  25. No, I don't mean the Berkeley paper, I mean my own work on Australian mammals, but I'm glad they agree. Seehttp://www.blognow.com.au/mrpickwick/History_Conquerors/ for an extended discussion on Australia and more generally. Whatever happened to the Neanderthals is a separate (though possibly related) issue to what happened to all these big mammals on all the continents except Africa.
  26. David
    Only the Australian mammals? I was not aware of particularly large mammals in Australia. As for all the continents except Africa, what about the Indian subcontinent?
  27. "I was not aware of particularly large mammals in Australia" - no they became extinct some 25,000 years ago. It was mainly mammals, but did include some giant emu-like birds, and some giant reptiles.

    India I'm not sure about. There were extinctions in South East Asia though, as well as the Americas of course. The equivalent large animals of Africa (elephant, rhino, giraffe, lion etc) all survived for reasons which are debated. I think it is because Africa straddles the equator and climate change therefore always left some refuge areas.
  28. David
    Re: "but did include some giant emu-like birds, and some giant reptiles."

    Yes I am familar with these and I recall a large carniverous "roo" as well. The reptiles are / were varinids and there are claims made to their survival.

    South East Asia and the Indian subcontinent still have their large species (elephants, bengals and 8 to 10 meter pythons (with claims to larger).

    North America and Eurasia definately did not fare well, I agree. South America lost some of it's megafauna but they were not truely giants and many survived (again with rumors of still more).

    So it seems that the most poleward areas were hit hardest, no?
  29. "So it seems that the most poleward areas were hit hardest, no?" Well no, the hardest hit were those where a shift in climate to hotter drier times led to environmental conditions that large species couldn't cope with. And in addition on the continents whose geography precluded the formation of refuge areas - which is where Africa, straddling the Equator, comes in - whichever way the climate zones move in Africa you are always left with areas that can support megafauna.

    I am really not sure why you think that cooling conditions causes extinctions unless you think that this means global warming is a good thing. If that is the case you are going to be sadly disappointed.
  30. David
    Climate changes ineither direction causes extinction events. But it is a matter of degree. Warming opens up new environments at the same time as it makes existing ines more harsh. What happens is that life follows the environment. If it gets warmer life shifts poleward and colder it shifts towards the equator. This paper might help:

    Long-Term Cycles in the History of Life: Periodic Biodiversity in the Paleobiology Database
    Adrian L. Melott*

    Department of Physics & Astronomy, University of Kansas, Lawrence, Kansas, United States of America

    Abstract
    Time series analysis of fossil biodiversity of marine invertebrates in the Paleobiology Database (PBDB) shows a significant periodicity at approximately 63 My, in agreement with previous analyses based on the Sepkoski database. I discuss how this result did not appear in a previous analysis of the PBDB. The existence of the 63 My periodicity, despite very different treatment of systematic error in both PBDB and Sepkoski databases strongly argues for consideration of its reality in the fossil record. Cross-spectral analysis of the two datasets finds that a 62 My periodicity coincides in phase by 1.6 My, equivalent to better than the errors in either measurement. Consequently, the two data sets not only contain the same strong periodicity, but its peaks and valleys closely correspond in time. Two other spectral peaks appear in the PBDB analysis, but appear to be artifacts associated with detrending and with the increased interval length. Sampling-standardization procedures implemented by the PBDB collaboration suggest that the signal is not an artifact of sampling bias. Further work should focus on finding the cause of the 62 My periodicity.
  31. ps
    This agrees with earlier work done at Berkeley, from a 2005 article in the San Francisco Chronicle:

    "Mass extinction comes every 62 million years, UC physicists discover"
    David Perlman, Chronicle Science Editor
    Thursday, March 10, 2005
  32. I did not copy the link but I did keep the article:

    With surprising and mysterious regularity, life on Earth has flourished and vanished in cycles of mass extinction every 62 million years, say two UC Berkeley scientists who discovered the pattern after a painstaking computer study of fossil records going back for more than 500 million years. Their findings are certain to generate a renewed burst of speculation among scientists who study the history and evolution of life. Each period of abundant life and each mass extinction has itself covered at least a few million years — and the trend of biodiversity has been rising steadily ever since the last mass extinction, when dinosaurs and millions of other life forms went extinct about 65 million years ago.

    The Berkeley researchers are physicists, not biologists or geologists or paleontologists, but they have analyzed the most exhaustive compendium of fossil records that exists — data that cover the first and last known appearances of no fewer than 36,380 separate marine genera, including millions of species that once thrived in the world’s seas, later virtually disappeared, and in many cases returned. Richard Muller and his graduate student, Robert Rohde, are publishing a report on their exhaustive study in the journal Nature today, and in interviews this week, the two men said they have been working on the surprising evidence for about four years. “We’ve tried everything we can think of to find an explanation for these weird cycles of biodiversity and extinction,” Muller said, “and so far, we’ve failed.” But the cycles are so clear that the evidence “simply jumps out of the data,” said James Kirchner, a professor of earth and planetary sciences on the Berkeley campus who was not involved in the research but who has written a commentary on the report that is also appearing in Nature today. “Their discovery is exciting, it’s unexpected and it’s unexplained,” Kirchner said. And it is certain, he added, to send other scientists in many disciplines seeking explanations for the strange cycles. “Everyone and his brother will be proposing an explanation — and eventually, at least one or two will turn out to be right while all the others will be wrong.”

    Muller and Rohde conceded that they have puzzled through every conceivable phenomenon in nature in search of an explanation: “We’ve had to think about solar system dynamics, about the causes of comet showers, about how the galaxy works, and how volcanoes work, but nothing explains what we’ve discovered,” Muller said. The evidence of strange extinction cycles that first drew Rohde’s attention emerged from an elaborate computer database he developed from the largest compendium of fossil data ever created. It was a 560-page list of marine organisms developed 14 years ago by the late J. John Sepkoski Jr., a famed paleobiologist at the University of Chicago who died at the age of 50 nearly five years ago. Sepkoski himself had suggested that marine life appeared to have its ups and downs in cycles every 26 million years, but to Rohde and Muller, the longer cycle is strikingly more evident, although they have also seen the suggestion of even longer cycles that seem to recur every 140 million years. Sepkoski’s fossil record of marine life extends back for 540 million years to the time of the great “Cambrian Explosion,” when almost all the ancestral forms of multicellular life emerged, and Muller and Rohde built on it for their computer version. Muller has long been known as an unconventional and imaginative physicist on the Berkeley campus and at the Lawrence Berkeley Laboratory. It was he, for example, who suggested more than 20 years ago that an undiscovered faraway dwarf star — which he named “Nemesis” — was orbiting the sun and might have steered a huge asteroid into the collision with Earth that drove the dinosaurs to extinction. “I’ve given up on Nemesis,” Muller said this week, “but then I thought there might be two stars somewhere out there, but I’ve given them both up now.” He and Rohde have considered many other possible causes for the 62- million-year cycles, they said. Perhaps, they suggested, there’s an unknown “Planet X” somewhere far out beyond the solar system that’s disturbing the comets in the distant region called the Oort Cloud — where they exist by the millions — to the point that they shower the Earth and cause extinctions in regular cycles. Daniel Whitmire and John Matese of the University of Louisiana at Lafayette proposed that idea as a cause of major comet showers in 1985, but no one except UFO believers has ever discovered a sign of it. Or perhaps there’s some kind of “natural timetable” deep inside the Earth that triggers cycles of massive volcanism, Rohde has thought. There’s even a bit of evidence: A huge slab of volcanic basalt known as the Deccan Traps in India has been dated to 65 million years ago — just when the dinosaurs died, he noted. And the similar basaltic Siberian Traps were formed by volcanism about 250 million years ago, at the end of the Permian period, when the greatest of all mass extinctions drove more than 70 percent of all the world’s marine life to death, Rohde said.

    The two scientists proposed more far-out ideas in their report in Nature, but only to indicate the possibilities they considered. Muller’s favorite explanation, he said informally, is that the solar system passes through an exceptionally massive arm of our own spiral Milky Way galaxy every 62 million years, and that that increase in galactic gravity might set off a hugely destructive comet shower that would drive cycles of mass extinction on Earth. Rohde, however, prefers periodic surges of volcanism on Earth as the least implausible explanation for the cycles, he said — although it’s only a tentative one, he conceded. Said Muller: “We’re getting frustrated and we need help. All I can say is that we’re confident the cycles exist, and I cannot come up with any possible explanation that won’t turn out to be fascinating. There’s something going on in the fossil record, and we just don’t know what it is.”
  33. So the point is that it is cyclic, regardless of cppling or heating, there is a causitive agent that does not include mankind and cold is much worse than warm (evidenced by our own near extinction at H4 in the neandertal paper).
  34. Sorry for all the typos, I'm diabetic so my eyesight is blurry after eating.
  35. Oh dear Quietman, you can find any kind of pattern you like, looking back at any kind of record (just as you can see apparently meaningful figures in melted cheese on toast), but that doesn't mean they are real or have a single "cause". The mentions of "Nemesis" and "Planet X" and UFO believers should give you some inkling that this stuff is suspect.

    Of course there are all kinds of causes of extinctions of the tens of thousands of species that have become extinct since life evolved on the planet. Volcanic eruptions might have played a role in some times and places, impact of an asteroid is possible I suppose, but for the vast bulk of species variations in climate are undoubtedly the cause. And for most water-based life forms hot and dry is more of a challenge than cool and wet. Dinosaurs may be an exception, but I doubt it. And then there are all the ocean life forms that have become extinct - not much prospect of asteroids and volcanoes affecting them (changes in temperature and acidity yes). Please, forget about Neanderthals, they are a red herring.

    You seem to be searching for something, anything, rather than accept that (a) CO2 concentrations are rapidly (in paleontological scales) increasing; (b) we know the physics and chemistry that causes the changes this will bring; and (c) the changes, not in models, but in the real world of glaciers and ice caps, droughts, heat records, storms, changes in species distribution and behavior, are already evident and rapidly accelerating. Talk about "natural timetables deep inside the Earth" is just whistling in the dark.
  36. David
    The Nemesis hypothesis, while nothing more than that, has been proposed serveral times in the past. Just because the crazies have picked up on it and made a cult centered around the concept does not invalidate the idea. But it has been largely abandoned by the scientific community. The mention is in the article, not a peer reviewed paper, by the reporter because of it's popular appeal. I don't have access to their paper as I did for the first reference at PLos One.

    Regardless of knowing the cause of this cyclicity, it does appear to exist.
  37. UW-Milwaukee Study Could Realign Climate Change Theory Scientists Claim Earth Is Undergoing Natural Climate Shift but like the telegraph said "Nobody listens to the real climate change experts".
  38. Anyone still following this thread will be interested in http://www.blognow.com.au/mrpickwick/131143/Wham_Bam_Climate_Spam.html. Comment number 94 suggests that it is much too mild and gentle and what is needed is a full blown offensive against denialists.
  39. Sort of a witch hunt? That is how ignorance always reacts to real science.
  40. Nah, witch hunts were against people who were merely imagined to be causing the community harm.
  41. Then it is the skeptics that should have a witch hunt. Ok, everyone, lock and load. :)
  42. One man's sceptic is another man's denialist.
  43. That IS a truism. One man's alarmist is another man's fundamentalist as well. Sorry, I'm agnostic. I see the greens as deniers of nature. CO2 is mans sin, pray for penance from the God Algore.
  44. Ah, why oh why couldn't I see it before. Yes, I have been a denier of nature, of course I have. All that concern about increasing CO2 and the destruction of habitats all around the globe, and the extinction of species, and rising pollution levels in sea and air, all because I, um, deny nature. And those who are happy to see giant corporations wreaking havoc on the planet, and who have absolutely no concern for the consequences, indeed, can see none, other than to mindlessly chant about climate always changing (gee, who knew, what an eye opener it was when I discovered THAT!), they are the what? True conservationists? Humanists? Libertarians? Rhetorical questions, I'm afraid, I really don't want to know how you label the delusions you are working under. Just go away. Learn something about the real world. Come back.
  45. Well Dave, I have been around long enough to have experienced warm winters before. Growing up on Long Island we had snowball fights wearing no more than jeans and t-shirts. You can fool the kids but you can't fool us old timers, sorry.
  46. ps
    I am retired on a healthy pension, I think I know about the real world, but you still have much to learn. Read my comments and links in the volcanos thread.
  47. Patrick
    These maps show the progression of the 3rd Ice Age (Carboniferous-Permian) beginning before it's onset in the Devonian through the End of the Permian.
    Devonian
    Early Carboniferous
    Late Carboniferous
    Permian

    These two maps show the 4th Ice Age (current) and the modern world (current interglacial):
    Current Ice Agea>
    Current Interglacial

    I already posted the Eocene and Miocene in the "It's the Sun" thread so I wont repeat them here.

    Compare the Ice Age maps to the earlier Ice Age and you can see easily how different the earth was and how unlikely another glacation actually is at this point. Think about it. What do you think caused the long extreme cycles in the late part of the this age?
  48. The changes in climate from changes in the Earth are not immediately obvious unless you realize that ocean currents have a much stronger effect than air currents.

    This is because the atmosphere is not efficient as a buffer, ie. GHGs are not as efficient as the ocean (or any body of water) at storing energy including heat.

    What is key to understanding how oceans drive climate is the convection currents (upwelling and downwelling currents). We know that ocean temperatures are not globally uniform. Some bodies of water are warmer or cooler than others. But what is more important is that the depths are different temperatures and the colder water sinks while the hotter water rises. Simple.

    Next comes the more complex part.
  49. The temperature of the ocean floor is variable. The depths have a thinner crust in general so transfer more heat and the volcanic active areas transfer heat from the magma directly to the water. The proximate temps change rapidly simply because the the amount of cold water available to sink this heat.

    But just like applying heat to the bottom of a pot of water, convection currents are created in both up and down directions. Some of these are fairly constant coming from the ocean depths but some are highly variable where volcanic activity exists and this can be at any depth along the ridges.

    At times of eruptions or even just increased plate movement the heat released into the water increases and either creates a new current or strengthens the existing current.

    As explained in the volcano thread, the ENSO is a real time example of this very driver. The subduction of the pacific plate under the Andes slows and speeds up in an irregular cycle.

    It's irregular because of the continental crust being uneven densiity and shape and made of materials of various ores with different melting points.
  50. This is why we get a warning when El Nino is beginning by volcanic eruptions in Chile. It's not the volcano that causes El Nino, it's just a symptom of the tectonic activity and it's accompanying vulcanism.

    And I have to stop for now since my grandson is having a tamtrum and I can't think straight with the noise.

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