Arguments
What does past climate change tell us about global warming?
What the science says...
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Scientific analysis of past climates shows that greenhouse gasses, principally CO2, have controlled most ancient climate changes. The evidence for that is spread throughout the geological record. This makes it clear that this time around humans are the cause, mainly by our CO2 emissions. |
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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)
Science has a good understanding of past climate changes and their causes, and that evidence makes the human cause of modern climate change all the more clear. Greenhouse gasses – mainly CO2, but also methane – have been implicated in most of the climate changes in Earth’s past. When they were reduced, the global climate became colder. When they were increased, the global climate became warmer. When changes were big and rapid (as they are today), the consequences for life on Earth were often dire – in some cases causing mass extinctions.
So why is the myth wrong?
The myth is wrong for two reasons:
- First, to infer that humans can't be behind today's climate change because climate changed before humans is bad reasoning (a non-sequitur). Humans are changing the climate today mainly via greenhouse gas emissions, the same mechanism that caused climate change before humans.
- Second, to imply we have nothing to fear from today's climate change is not borne out by the lessons from rapid climate changes in Earth's past.
Third rock from the Sun – why we’re not deep frozen.
A rocky planet this far from the sun should be frozen solid and lifeless at an average temperature of -18°C (0°F). The fact that it isn’t is due to greenhouse gasses in the atmosphere, mainly CO2. These atmospheric gasses have been in a delicate balance with the Earth’s oceans, the biosphere, and even the geosphere (all the rocks and sediments). Whether it was frigid ice ages or the steamy climates of the Eocene and the age of the dinosaurs, every change in the Earth (like a decrease in the rate of tectonic plate subduction or an increase in the rate of mountain building) caused a proportional change in CO2 in the atmosphere and in the oceans, and every change in atmospheric CO2 caused a proportional reaction in global temperatures, climate and ocean chemistry.
Ice ages
Scientists have shown that CO2 and climate moved in lock-step throughout the Pleistocene ice ages. The ice ages were actually many pulses of cold glacial phases interspersed with warmer interglacials. These pulses had a distinct regularity caused by wobbles in Earth’s orbit around the Sun (Milankovitch cycles). When Earth’s orbit reduced the intensity of sunlight in the northern hemisphere, the Earth went into a glacial phase. When the orbital cycle brought increased the intensity of insolation in the northern hemisphere, ice sheets melted and we went into a warm interglacial. Because warmer oceans can dissolve less CO2, the CO2 levels see-sawed extremely closely with Earth’s temperature. It was a slow pace of change, taking tens to hundreds of thousands of years, and yes as the myth states, in the last million years the biggest orbit-induced cycles were every 100,000 years.
But we know these orbital changes are not behind today's global warming. In fact our orbit dictates we should be cooling now, not warming.
The Earth was indeed cooling over the last 6,000 years due to Earth's orbit, heading into the next glacial phase scheduled for about the year 3500 AD. But all that changed when we got to the industrial era. Global temperatures departed from that cooling trend, and instead rose parallel with our greenhouse gas emissions.
Greenhouse gasses and Temperature moved in lock-step through the Pleistocene Ice Ages, controlled by Earth's orbit around the Sun (Centre for Ice and Climate, University of Copenhagen). Arrows show where levels were a few years ago, on the same scale.
CO2 doesn’t lag behind temperature
Until 2012, Antarctic ice core data suggested CO2 may have lagged behind the warming trend by hundreds of years. This was used by skeptics to question the link between CO2 and climate. More recent studies, with much more precise correlation between ice cores and global temperature records, have shown that temperature and CO2 changed synchronously in Antarctica during the end of the last ice age, and globally CO2 rose slightly before global temperatures.
Palm-fringed Arctic and balmy dinosaurs
It’s true that at times in Earth's past the climate has been as warm or even warmer than temperatures projected for the end of this century and beyond. Aside from some warm interglacials, the average climate was last as warm as we expect in 2100 during the Pliocene epoch – before the emergence of the genus Homo which includes you and me. In that time, summer Arctic temperatures were 3°C (5°F) warmer than today, with CO2 levels similar to today’s and sea levels were 15-25m (50-82ft) higher than today. Rain-drenched forests fringed the Arctic Ocean at the time.
Going further back to the Eocene, the world then was very warm and humid – on average 10°C (18°F) warmer than today. Lush swamp forests fringed the Arctic, inhabited by turtles, alligators, primates, tapirs, and the hippo-like Coryphodon (just as the myth claims). Lowland Antarctica was warm and covered in near-tropical vegetation, and London was a mangrove swamp as rainforests spread across much of the planet. Going back even further to the age of the dinosaurs, life flourished in a time of high CO2 and generally warm average temperatures with high sea levels. Even Antarctica was forested and supported a healthy population of dinosaurs.
CO2 and Climate Changes in the last 400+ million years (note all human existence fits under the right-hand vertical axis line). CO2 proxy data from Dan Breeker, U.Texas, originally published here. Greenhouse events in part from Kravchinsky 2012.
Sudden vs slow change
Life flourished in the Eocene, the Cretaceous and other times of high CO2 in the atmosphere because the greenhouse gasses were in balance with the carbon in the oceans and the weathering of rocks. Life, ocean chemistry, and atmospheric gasses had millions of years to adjust to those levels.
But there have been several times in Earth’s past when Earth's temperature jumped rapidly, in much the same way as they are doing today. Those times were caused by large and rapid greenhouse gas emissions, just like humans are causing today. In Earth's past the trigger for these greenhouse gas emissions was often unusually massive volcanic eruptions known as “Large Igneous Provinces,” with knock-on effects that included huge releases of CO2 and methane from organic-rich sediments. But there is no Large Igneous Province operating today, or anytime in the last 16 million years. Today’s volcanoes, in comparison, don’t even come close to emitting the levels of greenhouse gasses that humans do.
Those rapid global warming events were almost always highly destructive for life, causing mass extinctions such as at the end of the Permian, Triassic, or even mid-Cambrian periods. The symptoms from those events (huge and rapid carbon emissions, a big rapid jump in global temperatures, rising sea levels, ocean acidification, widespread oxygen-starved zones in the oceans) are all happening today with human-caused climate change. The outcomes for life on Earth were often dire. The end Permian extinction saw around 90% of species go extinct, and it left tropical regions on the planet lethally hot, too hot for complex life to survive. The Triassic extinction was another, one of the 5 biggest mass extinctions in the geological record. Even in the end Cretaceous extinction, in which dinosaurs were finally wiped out by an asteroid impact, a major global-warming extinction event was already underway causing a major extinction within 150,000 years of the impact. That global warming 66 million years ago was due to catastrophic eruptions in India, which emitted a pulse of CO2 that sent global temperatures soaring by 7°C (13°F).
So yes, the climate has changed before, and in most cases scientists know why. In all cases we see the same association between CO2 levels and global temperatures. And past examples of rapid carbon emissions offer no comfort at all for the likely outcome from today’s climate change.
Intermediate rebuttal written by howardlee
Update July 2015:
Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial
Additional video from the MOOC
Dana Nuccitelli: Adaptation takes time.
Last updated on 6 August 2015 by pattimer. View Archives
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.
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."
It's all very interesting but doesn't everyone within this current issue have an agenda?
[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” ',
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.
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
"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/
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.
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.
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.
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."
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.
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.
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?
Calling sceptics "deniers" is the same as calling you an alarmist. I am sure that you don't like it either.
The Pleistocene was the last period prior to the Holocene and prior to H4, correct?
This should work.
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.
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.
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.
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.
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?
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.
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?
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.
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.
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
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.”
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.
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.
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.
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?
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.
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.
And I have to stop for now since my grandson is having a tamtrum and I can't think straight with the noise.