Arguments
What does CO2 lagging temperature mean?
Posted on 12 October 2007 by John Cook
With a recent British court case critiquing An Inconvenient Truth and the news that Al Gore just won the Nobel Peace Prize, the attacks on Gore and his slideshow have stepped up in recent times. A common criticism is his use of the CO2/temperature record to show that in the past, CO2 caused temperature increase. A close look at ice core records finds that CO2 actually lags temperature. In fact, a study came out just a few weeks ago (Stott 2007) that confirms CO2 increases around 1000 years after temperature rise. This raises an important question - does temperature rise cause CO2 rise or the other way around? The answer is both.
The dominant signal in the temperature record (the white line in the above figure) is a 100,000 year cycle where long ice ages are broken by short warm periods called interglacials. This cycle coincides with a change in Earth's orbit as it evolves from a more circular orbit to a more elliptical orbit. When springtime insolation (incoming sunlight) increases in the southern hemisphere, this causes temperature to rise in the south. The warming is amplified as retreating Antarctic ice means less sunlight is reflected back into space.
As the southern oceans warm, they give up more CO2 to the atmosphere as the solubility of CO2 in water falls with rising temperature. The CO2 mixes through the atmosphere, amplifying and spreading the warming to the tropics and northern hemisphere. This is why warming in the southern hemisphere precedes warming in the northern hemisphere (Caillon 2003). This is confirmed by marine cores that show tropical temperatures lag southern warming by ~1000 years (Stott 2007). CO2 warming also explains how the relatively weak forcing from orbital cycles can bring the planet out of an ice age.
So where does that leave Al Gore? What he says in An Inconvenient Truth is this:
"The relationship is very complicated but there is one relationship that is far more powerful than all the others and it is this - when there is more carbon dioxide, the temperature gets warmer because it traps more heat from the sun inside."
This statement, while an oversimplification, is essentially correct. A more accurate and informative statement would've been
"A change in Earth's orbit warmed the southern oceans which released more CO2 into the atmosphere. The extra CO2 trapped more heat from the sun and amplified the warming. It also mixed through the atmosphere, spreading the warming to the tropics and northern hemisphere"
Of course, the audience may have dozed off by the end of the explanation and slept through all the pretty pictures of polar bears and glaciers.
Note - I've posted more info as well as links to many peer reviewed studies on this topic on our CO2 lags temperature page.
But, what I still want to know is what is currently happening with the Earth's orbit? What causes the sudden dramatic cool down and is it expected to happen soon? If not, why not? looks to me like the interglacial is due to end at least in terms of the last 4.
How do atmospheric scientists model solar flux and cloud formation in climate models? These are critical because only a 4% variation in cloud cover would account for climate change. They do not model it at all. Instead they assume an unknown mechanism by which carbon dioxide effects are amplified. The dominant green house gas is water vapor. CO2 is less than 5%, so of course some magic is required to make CO2 dominate.
That 4% variation would have to persist to trigger climate change. Look at the CERES and ERBE pages and see how many papers are there about clouds. There is nothing magic about CO2, the physics of it are very well known.
The CO2 temperature connection leaves much to be desired on any time scale I can find, 800 years wrong way over the last 600K years is only a bit of it. It is clear that temp increase can cause carbon dioxide to increase. The converse being true is your working hypothesis but it is questionable because it just doesn't fit the record. We have warm periods with low CO2 and ice ages with high CO2.
Maybe convection and cloud effects simply overwelm the supposed radiative issues.
However, the sun's effects are being subjected to far greater standards of proof than CO2's effects. When the former is used as a single variable cause of temperature change over the long term, little mention is made of the closeness of fit over most of the period; the focus seems to be on "it hasn't worked since 1975". Well if I was the sun I would be a little upset at that summary dismissal.
If I was CO2 looking to take plenty of credit for temperature change, I would feel very flattered by all the attention being lavished on me, especially as I had something of an inferiority complex on the matter of causality - was I the symptom or the cause, I had always wondered. Perhaps I had been appointed almost by default to fill the vacancy that has existed since 1975 (call it a change in the structure of the sun / temp relationship), rather than on my merits. My face happens to fit.
Cynics might say that it's the fact that CO2 levels incorporate some element of human behaviour and the various urges of governments (humans can be taxed and regulated whereas the sun can't) or human beings (we are powerful creatures who must be having an influence on the world around us) explain the focus on CO2 rather than on solar activity.
Get Your Nose Off The Canvas attitude....otherwise all you can see is the detail you are looking at and not how it fits into the overall picture. And that is un-scientific and potentially dangerous.
CO2 lags temperature increases mostly because a warming period releases the gas from oceans, increased CO2 levels further moderate the heat flow process ( to what extent nobody is sure), add a few (minor) complexities like forest fires and volcanic outgassing to the equation.
Ice starts melting ( latent heat of fusion) and cooling the biosphere, evaporation does the same, then biomass kicks in and CO2 starts getting locked up again further moderating the process.It all cools down and eventually the cycle repeats.
The whole debate is about long term trends not short term. The point I was trying to make is concentrating on one factor stops us getting the 'picture' in proper perspective. For example, global methane emissions from all known sources is (guess)estimated at around 500+ Mtonnes/annum and its' greenhouse effect is equal to about 1/3 to 1/2 of all CO2 emissions. Worse, it breaks down into water and CO2!
Now add a very recent discovery that green leaves ( on plants and in leaf litter) also produce methane but no empirical data is available. Factor in that methane emissions are rising faster than CO2 and in 10 years we may well forget about CO2 ...............
Research on CO2 influence on plant growth shows a 1/3 increase in rate of growth if the other moderating factores (temperature, water, nitrogen) remain the same.
If you maximise all these factors, growth rate increase can be as high as 85%.
As humans, we try and look for a few major factors that we can pin 'the problem' on; climate is hideously complex process with a lot of unknowns and simply will not bend to simplistic analysis.
http://hvo.wr.usgs.gov/volcanowatch/2006/06_02_23.html
The current estimate for manmade CO2 emissions is 75 million tonnes/day (27 billion tonnes/year)and forecasts suggest this may rise to 40 billion tonnes by 2030. Somewhat more than volcanic contributions.
In your response to Wondering Aloud in #5 above you said;-
"... But the overall assertion 'when there is more carbon dioxide, the temperature gets warmer' is correct."
The paleoclimatological evidence simply does not support that view. In the past, the Earth's atpospheric CO2 levels have been thousands of ppm higher than they are today, with no corresponding global warming. In fact, some periods that should have been excessively hot (such as the late Ordovician) were ice ages!
The paleoproxy graph WA.& you posted in the
"Does model uncertainty exagerate global warming projections?" thread is a beautiful example to show there IS a limit to which CO2 can effect temperature changes..the 'saturation argument'.
For most of the periods shown, temperature trundles along nicely at 22C despite massive changes in CO2 levels, which for me, indicates saturation is reached at quite low levels of CO2.
http://geology.geoscienceworld.org/cgi/content/abstract/33/2/109
There is evidence that increased carbon burial was a major contributing factor to the late ordovician glacial events.
Palaeos concurs with the overall sequence:
http://www.palaeos.com/Paleozoic/Ordovician/LateOrd.html
The USGS Hawaiian Volcano Observatory says exactly the opposite of you. I'll go with them, don't take it personally.
http://hvo.wr.usgs.gov/volcanowatch/2007/07_02_15.html
Here is a short excerpt:
"the global fossil fuel CO2 emissions for 2003 tipped the scales at 26.8 billion tonnes. Thus, not only does volcanic CO2 not dwarf that of human activity, it actually comprises less than 1 percent of that value."
Yet when Squidly blurts out an enormity like "volcanoes make more CO2" there isn't a peep from any of you to correct him. Why?
Try reading the posts. #14 would be a good start.
About accuracy: climate science is a remarkably inexact discipline in that it uses a curious mix of data: Proxies - which means we have no direct evidence and therefore use evaluation of causually connected processes to determine data. Yet logic tells us the farther we are away from an event ( both physically and temporally) the less we can dicriminate the underlying factors that caused the event.
Satellite data which are supposed to be more accurate than older data sources yet even these sources disagree with one another..
Older data sources are used when we don't have 'accurate' or long-term satellite sources.
We have no accurate data on biomass response to climate changes, only guesses because the numbers are too big and too diffuse.
We do not even have precise data on how much fossil fuel is being consumed...and so on.
Yet we are being told that the future of civilisation depends on ameliorating a warming trend calculated on these data and a remarkably precise figure it is- given the background data. So forgive us our desire for a bit more precision before we commit ourselves one way or the other.
Science does the best work possible with the best data that is available. Data are constantly sought, improved and correlated. Science is always a work in progress. If you want to talk about a really inexact science, we should start with economics.
I absolutely agree. And part of the process of improvement is to be open to valid critisism ( in the proper sense)and honest where data is sketchy or non-existent. Unfortunately for the scientists involved in this particular model, (I believe)it was high-jacked for other purposes and hence the current polarisation. Consequently resource which could be usefully addressing those 'iffy' areas are squandered on sawing sawdust.
You've been misled by a fundamental fallacy in some dodgy presentations of paleotemperature and paleoCO2 data that still appear on websites, unfortunately (Scotese's site is O.K., but he clearly needs to update/address his plaeodata that you and Dan Pangbourn on another thread have been confused by).
One cannot take the very sparse paleotemperature and paleoCO2 data points, draw lines betwen these, and then concluded that the temperatures (or CO2 levels) in the intervening periods (10's or even 100's of millions of years!) are thus defined! It's unlikely (and we know it to be untrue) that temperatures were a rock steady 22 oC for vast periods of the past, in much the same way that we know that the Earth's temperature was a rock steady 15 oC during the last million years, which is what a misguided individual in the future might conclude from two temperature proxies (say 1000 years before our present and 430,000 years before) with a straight line drawn between them!
It can be stated very succinctly:
"THE RELATIONSHIP BETWEEN ATMOSPHERIC CO2 LEVELS AND PALEOTEMPERATURE CAN ONLY BE ASSESSED AT THOSE SPECIFIC TIME POINTS WHERE PALEOTEMPERATURE AND PALEOCO2 DATA ARE CONTEMPORANEOUS"
Where we have data points for paleotemperatures and paleoCO2 levels that match in time, the evidence is rather strong for a CO2/temperature coupling. Where paleo temperatures are high paleoCO2 levels are high and cold/glacial periods are associated with low CO2 levels.
There's now extremely abundant information on this dating back many hundreds of millions of years.
A recent review compiles much of the data:
D.L. Royer (2006) "CO2-forced climate thresholds during the Phanerozoic" Geochim. Cosmochim. Acta 70, 5665-5675.
Even more recent studies supplement the information in Royers review/compilation and cover additional periods with new data sets right through the past several hundreds of millions of years:
R.E. Carne, J.M. Eiler, J. Veizer et al (2007) "Coupling of surface temperatures and atmospheric CO2 concentrations during the Palaeozoic era" Nature 449, 198-202
W. M. Kurschner et al (2008) “The impact of Miocene atmospheric carbon dioxide fluctuations on climate and the evolution of the terrestrial ecosystem” Proc. Natl. Acad. Sci. USA 105, 499-453.
D. L. Royer (2008) “Linkages between CO2, climate, and evolution in deep time” Proc. Natl Acad. Sci. USA 105, 407-408
Zachos JC (2008) “An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics” Nature 451, 279-283.
Doney SC et al (2007) “Carbon and climate system coupling on timescales from the Precambrian to the Anthropocene” Ann. Rev. Environ. Resources 32, 31-66.
Horton DE et al (2007) “Orbital and CO2 forcing of late Paleozoic continental ice sheets” Geophys. Res. Lett. L19708 (Oct. 11 2007).
B. J. Fletcher et al. (2008) “Atmospheric carbon dioxide linked with Mesozoic and early Cenozoic climate change” Nature Geoscience 1, 43-48.
And so on…..
What's the point of expressing a "desire for precision", when the rather precise data sets are ignored or overlooked in place of obviously fallacious presentations?
This bears on the very meaning of "skepticism". Skepticism is surely valid criticism or doubt about interpretations, on the basis of an honest and reasonably informed relationship with the evidence.
Skepticism is not piling on false arguments and trawling dodgy websites for stuff that suits a particular political/conspiracy/agenda position.
If we're going to be skeptical (I hope we all are!), then we should be skeptical. The temperature data on the Scotese site that is repeatedly referred to in preference to the science is surely something that a skeptic should be skeptical about. Here it is again:
http://www.geocraft.com/WVFossils/Carboniferous_climate.html
Doesn't it looks very odd? One might expect a skeptic to question 10's and even a 100 million year block of rock-steady temperatures, and to observe that the Earth's temperature apparently dropped smoothly from 22oC 30-ish million years ago to 12oC now. And yet surely we know that the last couple of millions of years the Earth's temperature has fluctuated back and forth over a temperature range of 5 - 6oC. Now one might say that Scotese's graph is too compact to show the recent ice age cycles. However the late Ordovician glacial period is represented in the scientific paleotemperature/glacial record by a period of around 2 million years. If that can be shown, why not the large temperature variations during the recent ice age cycles? And if we have observed these large swings in the Earth's temperature during recent ice age cycles, doesn't that make you think that perhaps the Earth's temperature in the deep past might not be well-represented by many 10's and even 100 million year blocks of rock-steady temperature?
...skepticism anyone?
What (little) can be deduced is that CO2 levels were considerably higher than todays and both plant and animal life flourished during the warmer periods
(however high the actual temperature might have been).
When presented with a ludicrous and blatantly incorrect paleotemperature "graph" of unknown provenance you consider it a "beautiful example to show there IS a limit to which CO2 can effect temperature changes.....(your post #16).
However when presented with copious scientific data on the straightforward relationship between atmospheric paleo CO2 levels and paleotemperature (see my post #25) you suddenly lose your enthusiasm. Apparently you prefer nonsense that supports some sort of agenda position in preference to the science...try re-reading my post #26 on the nature of skepticism.
Your "sub" point about paleo-warmth is unfortunately misplaced. In fact the evidence indicates that the warm periods in the past have been associated with lower biodiversity [***] and that it is the rapid increases in global warmth, largely associated in the past with tectonic events, that have been the drivers of major extinctions throughout Earth's history[*****]:
[***]PJ Mayhew et al. (2007) A long-term association between global temperature and biodiversity, origination and extinction in the fossil record Proceedings of The Royal Society B 275, 47–53.
Abstract: "The past relationship between global temperature and levels of biological diversity is of increasing concern due to anthropogenic climate warming. However, no consistent link between these variables has yet been demonstrated. We analysed the fossil record for the last 520Myr against estimates of low latitude sea surface temperature for the same period. We found that global biodiversity (the richness of families and genera) is related to temperature and has been relatively low during warm 'greenhouse' phases, while during the same phases extinction and origination rates of taxonomic lineages have been relatively high. These findings are consistent for terrestrial and marine environments and are robust to a number of alternative assumptions and potential biases. Our results provide the first clear evidence that global climate may explain substantial variation in the fossil record in a simple and consistent manner. Our findings may have implications for extinction and biodiversity change under future climate warming."
[*****]Major extinctions are associated with long lived perturbation of the climate system and the atmosphere. For example the early Jurassic extinction is associated with events (greenhouse gas induced warming) lasting 200,000 years:
Svensen H et al (2007) Hydrothermal venting of greenhouse gases triggering Early Jurassic global warming Earth Planetary Sci Lett 256 554-566
Abstract: "The climate change in the Toarcian (Early Jurassic) was characterized by a major perturbation of the global carbon cycle. The event lasted for approximately 200,000 years and was manifested by a global warming of similar to 6 degrees C, anoxic conditions in the oceans, and extinction of marine species. The triggering mechanisms for the perturbation and environmental change are however strongly debated. Here, we present evidence for a rapid formation and transport of greenhouse gases from the deep sedimentary reservoirs in the Karoo Basin, South Africa......."
likewise comprehensive analyses of the coincidence of major tectonic events, and resulting elevation of greenhouse gas levels, are associated with several of the major extinctions of the last 300 million years. Note that CO2 isn't the only player. Methane is implicated in several of these events (see especially the PETM below) and sulphurous oxides and their effects on ocean acidity and oxygen content are also implicated:
Wignall P (2005) The link between large igneous province eruptions and mass extinctions Elements 1, 293-297
Abstract: "In the past 300 million years, there has been a near-perfect association between extinction events and the eruption of large igneous provinces, but proving the nature of the causal links is far from resolved. The associated environmental changes often include global warming and the development of widespread oxygen-poor conditions in the oceans. This implicates a role for volcanic CO2 emissions, but other perturbations of the global carbon cycle, such as release of methane from gas hydrate reservoirs or shut-down of photosynthesis in the oceans, are probably required to achieve severe green-house warming. The best links between extinction and eruption are seen in the interval from 300 to 150 Ma. With the exception of the Deccan Trap eruptions (65 Ma), the emplacement of younger volcanic provinces has been generally associated with significant environmental changes but little or no increase in extinction rates above background levels."
R. J. Twitchett (2006) The palaeoclimatology, palaeoecology and palaeoenvironmental analysis of mass extinction events
Palaeogeog., Palaeoclimatol., Palaeoecol. 232, 190-213
concluding paragraph: "Mass extinction studies have enjoyed a surge in scientific interest of the past 30 years that shows no sign of abating. Recent areas of particular interest include the palaeoecological study of biotic crises, and analyses of patterns of post-extinction recovery. There is good evidence of rapid climate change affecting all of the major extinction events, while the ability of extraterrestrial impact to cause extinction remains debatable. There is growing evidence that food shortage and suppression of primary productivity, lasting several hundred thousand years, may be a proximate cause of many past extinction events. Selective extinction of suspension feeders and the prevalence of dwarfed organisms in the aftermath are palaeoecological consequences of these changes. The association with rapid global warming shows that study of mass extinction events is not just an esoteric intellectual exercise, but may have implications for the present day."
Notice that greenhouse environments are associated with the very delayed (millions of years) recovery of biota following these extinctions;
Fraiser ML et al. (2007) Elevated atmospheric CO2 and the delayed biotic recovery from the end-Permian mass extinction Palaeogeog. Palaeoclim. Paleoecol. 252, 164-175
Abstract: Excessive CO2 in the Earth ocean-atmosphere system may have been a significant factor in causing the end-Permian mass extinction. CO2 injected into the atmosphere by the Siberian Traps has been postulated as a major factor leading to the end-Permian mass extinction by facilitating global warming, widespread ocean stratification, and development of anoxic, euxinic and CO2-rich deep waters. A broad incursion of this toxic deep water into the surface ocean may have caused this mass extinction. Although previous studies of the role of excessive CO2 have focused on these "bottom-up" effects emanating from the deep ocean, "top-down" effects of increasing atmosphere CO2 concentrations on ocean-surface waters and biota have not previously been explored. Passive diffusion of atmospheric CO2 into ocean-surface waters decreases the pH and CaCO3 saturation state of seawater, causing a physiological and biocalcification crisis for many marine invertebrates. While both "bottom-up" and "top-down" mechanisms may have contributed to the relatively short-term biotic devastation of the end-Permian mass extinction, such a "top-down" physiological and biocalcification crisis would have had long-term effects and might have contributed to the protracted 5- to 6-million-year-long delay in biotic recovery following this mass extinction. Earth's Modern marine biota may experience similar "top-down" CO2 stresses if anthropogenic input of atmosphere/ocean CO2 continues to rise.
The lesser extinction associated with the Paleo-Eocene-Thermal Maximum (PETM)55 MYA is probably the best characterised (not surprisingly since it's the most recent!) example of massive tectonic processes (the opening up of the N. Atlantic as the plates seperated) associated with enhanced atmospheric greenhouse gases, ocean acidification etc.:
M. Storey et al. (2007)Paleocene-Eocene Thermal Maximum and the Opening of the Northeast Atlantic Science 316, 587 - 589
abstract: "The Paleocene-Eocene thermal maximum (PETM) has been attributed to a sudden release of carbon dioxide and/or methane. 40Ar/39Ar age determinations show that the Danish Ash-17 deposit, which overlies the PETM by about 450,000 years in the Atlantic, and the Skraenterne Formation Tuff, representing the end of 1 ± 0.5 million years of massive volcanism in East Greenland, are coeval. The relative age of Danish Ash-17 thus places the PETM onset after the beginning of massive flood basalt volcanism at 56.1 ± 0.4 million years ago but within error of the estimated continental breakup time of 55.5 ± 0.3 million years ago, marked by the eruption of mid-ocean ridge basalt–like flows. These correlations support the view that the PETM was triggered by greenhouse gas release during magma interaction with basin-filling carbon-rich sedimentary rocks proximal to the embryonic plate boundary between Greenland and Europe."
And even the end-Cretaceous extinction (that did for the dinosaurs) seems to have had at least a significant component from massive flood basalt events (that resulted in the Deccan Traps in what is now India). In fact there is increasing evidence that the impact that resulted in the Chicxulub crater in the Yucatan post-dates the onset of the extinction by several 100,000's of years, and the extinction is associated with global warming (including a sudden contribution from the impact into limestone-rich deposits that vapourized massive amounts of carbonate (limestone) back into CO2):
Keller G (2005) Impacts, volcanism and mass extinction: random coincidence or cause and effect? Austral. J. Earth Sci 52 725-757.
Abstract: "Large impacts are credited with the most devastating mass extinctions in Earth's history and the Cretaceous - Tertiary (K/T) boundary impact is the strongest and sole direct support for this view. A review of the five largest Phanerozoic mass extinctions provides no support that impacts with craters up to 180 km in diameter caused significant species extinctions. This includes the 170 km-diameter Chicxulub impact crater regarded as 0.3 million years older than the K/T mass extinction. A second, larger impact event may have been the ultimate cause of this mass extinction, as suggested by a global iridium anomaly at the K/T boundary, but no crater has been found to date. The current crater database suggests that multiple impacts, for example comet showers, were the norm, rather than the exception, during the Late Eocene, K/T transition, latest Triassic and the Devonian-Carboniferous transition, but did not cause significant species extinctions. Whether multiple impacts substantially contributed to greenhouse worming and associated environmental stresses is yet to be demonstrated. From the current database, it must be concluded that no known Phanerozoic impacts, including the Chicxulub impact (but excluding the K/T impact) caused mass extinctions or even significant. species extinctions. The K/T mass extinction may have been caused by the coincidence of a very large impact ( > 250 km) upon a highly stressed biotic environment as a result of volcanism. The consistent association of large magmatic provinces (large igneous provinces and continental flood-basalt provinces) with all but one (end-Ordovician) of the five major Phanerozoic mass extinctions suggests that volcanism played a major role. Faunal and geochemical evidence from the end-Permian, end-Devonian, end-Cretaceous and Triassic/Jurassic transition suggests that the biotic stress was due to a lethal combination of tectonically induced hydrothermal and volcanic processes, leading to eutrophication in the oceans, global warming, sea-level transgression and ocean anoxia. It must be concluded that major magmatic events and their long-term environmental consequences are major contributors, though not the sole causes of mass extinctions. Sudden mass extinctions, such as at the K/T boundary, may require the coincidence of major volcanism and a very large Impact."
Beerling DJ et al. (2002) An atmospheric pCO(2) reconstruction across the Cretaceous-Tertiary boundary from leaf megafossils Proc. Natl. Acad. Sci. USA 99 (12): 7836-7840
Abstract: "The end-Cretaceous mass extinctions, 65 million years ago, profoundly influenced the course of biotic evolution. These extinctions coincided with a major extraterrestrial impact event and massive volcanism in India. Determining the relative importance of each event as a driver of environmental and biotic change across the Cretaceous-Tertiary boundary (KTB) crucially depends on constraining the mass of CO2 injected into the atmospheric carbon reservoir. Using the inverse relationship between atmospheric CO2 and the stomatal index of land plant leaves, we reconstruct Late Cretaceous-Early Tertiary atmospheric CO2 concentration (pCO(2)) levels with special emphasis on providing a pCO(2) estimate directly above the KTB. Our record shows stable Late Cretaceous/ Early Tertiary background pCO(2) levels of 350-500 ppm by volume, but with a marked increase to at least 2,300 ppm by volume within 10,000 years of the KTB. Numerical simulations with a global biogeochemical carbon cycle model indicate that CO2 outgassing during the eruption of the Deccan Trap basalts fails to fully account for the inferred pCO(2) increase. Instead, we calculate that the postboundary pCO(2) rise is most consistent with the instantaneous transfer of approximate to 4,600 Gt C from the lithic to the atmospheric reservoir by a large extraterrestrial bolide impact. A resultant climatic forcing of +12 W(.)m(-2) would have been sufficient to warm the Earth's surface by approximate to7.5degreesC, in the absence of counter forcing by sulfate aerosols. This finding reinforces previous evidence for major climatic warming after the KTB impact and implies that severe and abrupt global warming during the earliest Paleocene was an important factor in biotic extinction at the KTB."
Well yes, they were profoundly catastrophic effects Mizimi...and they occurred infreqently.
And you might say that "in the scheme of things were relatively transient".
However the present massive return of long-sequested carbon into the atmosphere by anthropogenic oxidation of fossil fuels is also:
(i) infrequent (it hasn't happened at least for the last 20 million years)
(ii) "relatively transient" "in the scheme of things".
(ii) potentially catastrophic.
One needs to be careful to make a proper assessment of events in the deep past, particularly in telescoping" these into "transient" phenomena, when in many cases they certainly weren't. For example the Jurassic extinction (see Svensen et al, 2007, abstract in my post # 28), was likely the result of release of greenhouse gases over many 1000's of years to buils up atmospheric concentrations to catastrophic proportions. Likewise the extinctions associated with the opening up of the N Atlantic plate boundary at the Paleo-Eocene Thermal maximum (PETM) were probably due to a rather long-lived explusion of greenhouse gases into the atmosphere.
In fact (see Keller, 2005; abstract in my post #28) there isn't much evidence for impacts in extinctions outside of the end Cretaceous extinction. From the perspective of some time point in the deep future, a period of 2-300 years of pumping CO2 into the atmosphere at the rate of 2-4 ppm per year will look like an extremely "transient" event.
And notice that in the general case (see Mayhew et al. 2007; abstract in my post #28), low biodiversity in the fossil record is associated with warm periods. So it doesn't take "transient" catastrophies to warm the world to the extent of greatly reducing biodiversity
In other words, jut because human perception makes processes occurring within our lifetimes on the decadal/centennial time scale seem extremely slow (and seemingly innocuous), they are not necessarily any less "transient" or possibly less catastrophic, then events in the deep past. In fact the rate of enhancement of atmospheric greenhouse gases now is likely far higher than during many of the tectonic phenomena leading to massive extinctions in the deep past.
Of course where we have an advantage now, is that we know what is going on and are in a position to do something about it. We'd be extremly stupid to let events get too far out of control...
Some lifeforms will flourish under conditions which cause others to perish.
As an aside....we have the ability to conduct experiments at CO2 and temp levels intimated by the paleoproxy records....I wonder if anybody is??
In fact, it does not seem that low diversity is something that commonly happens in the natural world. What should be especially concerning is decreasing biodiversity in a biome where there used to be a lot of diversity.
and until cyanobacteria started putting O2 into the atmosphere remained so. Since then, as Chris has adequately pointed out, various catastrophes have severely affected life in terms of diversity and quantity.
Curiously,most of the life forms on earth seem hell-bent on overwhelming anything else ( particularly the smaller varieties) regardless of the consequencies?
And you final comment is in agreement with my view that life adapts to fill any and all possible vacuums, so that loss of one species is an opportunity for another to take over that niche.
http://www.co2science.org/subject/c/summaries/co2climatehistory.php
The fact that a hypothetical mechanism can be proposed that the CO2 increases the warming doesn't alter the underlying fact that the past record does not tell us that CO2 causes warming.
It may or may not cause warming, I had thought it certainly would, but the more I learn the less certain I am. In the past it was not a significant driver of climate despite much wilder concentration swings than we are likely to see.
I also can't see how one can look at the record and suggest warming if it happens and CO2 increase when it happens would not be a net benefit to the biosphere.
Yes it's interesting. It does quite a good job of pursuing a false argument and an excellent job of being fixed in time nearly 10 years out of date.
Most of the article is about the lag of CO2 changes relative to temperature changes during ice age transitions. That's fine except the authors pursue the fallacious argument that because CO2 was a feedback response to solar insolation changes during ice ages, that CO2 variations can't drive temperature variations. They present this quite slyly as a "cause/effect" dichotomy....paraphrasing: "since CO2 changes were an effect during the ice age cycles and in pre-industrial times, they cannot be a cause now"!
In fact some of the data they present merely reinforces the rather limited variation in atmospheric CO2 levels that occur under natural circumstances without catastrophic increases in CO2 (from massive tectonic events or terrestrial impacts, or massive burning of fossil fuels now), or very very slow drawdown of CO2 levels by weathering. E.g. they make a big play over the fact that the earth cooled a bit during the 2000 years from 7000-5000 years ago while atmospheric CO2 rose by 10 ppm.
But 10 ppm over 2000 years (0.005 ppm per year) is 4 years worth at present rates of greenhouse gas emissions. That's around 4-500 times slower than the current increase in atmospheric CO2. A 10 ppm change over 2000 years is hardly going to affect climate, and clearly in a world with little variation in atmospheric CO2 levels, any climate variations must be dominated by other things (a small residual Milankovitch cycle affecting N. hemispheric insolation in this case I believe).
It's unfortunate that the presentation is frozen in time around 2000. For example they present data by Pagani et al (1999) and Pearson and Palmer (1999) that appears to be "in conflict with greenhouse theories of climate change". But here's Pagani in 2005 showing that contrary to the assertions by the authors of your "article" that atmospheric CO2 was only 385 ppm in the middle Eocene, that the evidence indicates levels were actually 1000-1500 ppm, and in fact the slow, slow decline of CO2 levels through the Paleogene was likely the cause of ice sheet development and expansion in Antarctica.
Pagani M (2005) "Marked decline in atmospheric carbon dioxide concentrations during the Paleogene" Science 309, 600-603
Abstract: The relation between the partial pressure of atmospheric carbon dioxide (pCO(2)) and Paleogene climate is poorly resolved. We used stable carbon isotopic values of di-unsaturated alkenones extracted from deep sea cores to reconstruct pCO(2) from the middle Eocene to the late Oligocene (similar to 45 to 25 million years ago). Our results demonstrate that pCO(2) ranged between 1000 to 1500 parts per million by volume in the middle to late Eocene, then decreased in several steps during the Oligocene, and reached modern levels by the latest Oligocene. The fall in pCO(2) likely allowed for a critical expansion of ice sheets on Antarctica and promoted conditions that forced the onset of terrestrial C-4 photosynthesis.
Likewise Pagani has recently presented evidence that the ability of the Arctic and Antarctic to maintain ice sheets is effectively controlled by CO2 thresholds (< ~750 ppm for the Antarctic; <~ 280 ppm for the Arctic).
DeConto RM et al (2008) Thresholds for Cenozoic bipolar glaciation Nature 455 652-655.
and the role of CO2 levels in setting thresholds for glaciations is more widely suppoorted by the science:
e.g.: Lunt DJ et al (2008) Late Pliocene Greenland glaciation controlled by a decline in atmospheric CO2 levels. Nature 454, 1102-1104
likewise recent data indicate that the relationship between climate and atmospheric CO2 levels in the Miocene are not so "chaotic" as the authors of your article would like us to believe:
W. M. Kurschner et al (2008) “The impact of Miocene atmospheric carbon dioxide fluctuations on climate and the evolution of the terrestrial ecosystem” Proc. Natl. Acad. Sci. USA 105, 499-453.
...and so on….
It seems the site you linked to is a nice little family business (Dad chairman, two sons are President and vice President and Mum is the "Operations Manager"!). Every page has a "Donate" button and no doubt they have such a nice time with everyone's donations they just don't have time investigate the literature properly or to keep their "info" up to date.
I hope you left a donation Mizimi!
PS: It was not 'my' article - nor did I say it was anything other than an interesting read.
IF we are fortunate it will make life a little easier for us in the coming glacation, but it will not stop it, no matter how hard you pray.
CO2 can cause a large temperature rise. It depends on the atmospheric concentrations of course.
The evidence indicates that it can indeed prevent an Ice Age. The evidence from paleoproxies for temperature and atmospheric greenhouse gases indicates that Ice Ages in the deep past were associated with the reduction of atmospheric greenhouse gas levels below thresholds required to maintain the Earth in a non-ice age state. In other words atmospheric CO2 has prevented Ice Ages for long, long periods of the Earth's deep past.
(see for example: D.L. Royer (2006) "CO2-forced climate thresholds during the Phanerozoic" Geochim. Cosmochim. Acta 70, 5665-5675.)
It certainly can cause catastrophic global warming. Global warming can obviously be catastrophic even if it doesn't eliminate life in its entirety. If, for example, global warming was to occur to an extent that resulted in widespread breakdown of the structures of our societies, we'd consider that catastrophic. Or if mankind were to succumb while a denuded life on Earth went on without out us, that would be catastrophic, wouldn't it? The latter scenario is rather more consistent with those resulting from the extinctions associated with the Early Jurassic, the end Permian, the end Cretaceous, the Paleo-Eocene Thermal Maximum and so on.
P.S. what do you mean by "proposed tipping point"? No one has mentioned "tipping point" on this thread have they?
Not if you were one of the surviving life-forms!!