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Christy Crock #6: Climate Sensitivity

Posted on 7 June 2011 by dana1981, James Wight

Christy Crocks (200 x 70 pixels)In recent months, climate scientist "skeptic" John Christy seems to have grown an appetite for the limelight.  First he testified before U.S. Congress, then he appeared on an Australian radio talk show to discourage their country from implementing a carbon tax, and now he has appeared on a Canadian radio show to downplay the link between global warming and extreme weather.  In the process, he made one of the "skeptics" favorite arguments: climate sensitivity is low.

"We are finding that the climate is not very sensitive to CO2 and those kind of gases"

This statement is strikingly similar to one which we examined in Lindzen Illusion #4:

"If we doubled CO2, it's well accepted that you should get about 1 degree warming if nothing else what we've seen so far suggesting that you have more than that, and the answer is no."

We've also addressed the "low sensitivity" claims of Roy Spencer, David Evans, and Christopher Monckton.  It's not surprising that this is a favored "skeptic" argument, because low sensitivity is absolutely critical to arguing that global warming is of no concern, and opposing carbon emissions reductions.  I've previously even gone so far as to describe it as the "skeptic" endgame.

Christy and Lindzen's similar quotes are particularly puzzling because of their use of the term "we".  When I hear a climate scientist use the phrase "what we've seen" or "we are finding" when discussing a climate research issue like sensitivity, I assume they are referring to the body of climate science research.  But as we have discussed ad nauseam, the body of climate science research is in very strong agreement that climate sensitivity is not low, but rather likely between 2 and 4.5°C for doubled atmospheric CO2 (Figure 1).  In fact there are very few exceptions to this strong agreement, which are generally limited to fundamentally flawed papers by these same few "skeptics", like Lindzen and Choi (2009) or Roy Spencer's blunders and 'silver bullets'.

Various estimates of climate sensitivity

Figure 1: Various estimates of climate sensitivity (Knutti and Hegerl 2008).

It becomes a bit frustrating that these few "skeptics" continue to claim with such certainty that sensitivity is low, and in such a misleading fashion (i.e. saying "we" rather than "the work of a few like Lindzen and Spencer"), even though we have debunked this myth many times before.  But Christy's repetition of the  myth does give us the opportunity to discuss an interesting recent draft paper which examined the issue of climate sensitivity: Hansen and Sato's Paleoclimate Implications for Human-Made Climate Change.

Hansen and Sato (2011)

In the paper, Hansen and Sato evaluate fast-feedback climate sensitivity based on the radiative forcings in the last ice age (~20,000 years ago) compared to those during the Holocene prior to the Industrial Revolution (Figure 2), knowing that the planet was near equilibrium during these two periods:

"Climate, averaged over a few millennia, must be in near-equilibrium during the last ice age (~20 ky ago) and in the current interglacial period prior to introduction of substantial human-made climate forcings. Any planetary energy imbalance was at most a small fraction of 1 W/m2, as shown by considering the contrary: an imbalance approaching 1 W/m2 would be sufficient to melt all ice on Earth or change ocean temperature a large amount, contrary to numerous paleoclimate data records."

Fig 2

Figure 2: Climate forcings during the ice age 20 ky ago relative to the pre-industrial Holocene from Hansen and Sato (2011)

As you can see in Figure 1, the radiative forcing in the last ice age as compared to the pre-industrial Holocene is -6.5  +/- 1.5 W/m2.  The average global temperature was 5 +/- 1°C cooler during the past ice age, which means the climate sensitivity is 5°C/6.5 W/m2, or approximately 0.77°C per W/m2.  Since the radiative forcing associated with doubled CO2 is 3.7 W/m2, this implies a fast-feedback climate sensitivity of 2.8°C. Note that this is an empirical result based on real-world observations of climate change in the relatively recent past.

Hansen and Sato break down the approximate contributions of CO2 and feedbacks to this doubled CO2 warming:

"If Earth were a blackbody without climate feedbacks the equilibrium response to 4 W/m2 forcing would be about 1.2°C (Hansen et al., 1981, 1984). The water vapor increase and sea ice decrease that accompany global warming can be simulated reasonably well by climate models; together these two feedbacks approximately double the blackbody sensitivity. The further amplification is the net effect of all other processes, with aerosols, clouds, and their interactions probably being the most important of the remaining feedback processes."

The paper goes on to note that during the Pliocene, which was only 1-2°C hotter than current global temperatures, and also the last time CO2 levels were as high as today, average sea level was 25 meters higher (a subject which John Cook recently discussed). 

In another of Hansen’s draft papers, Earth’s Energy Imbalance and Implications, he concludes that slow feedbacks greatly amplify the 3°C sensitivity from fast feedbacks. The exact value depends on the climate state you start with, which feedbacks you include, what timescale you’re interested in, and what assumptions you make. Adding other greenhouse gases increases climate sensitivity to 4°C for doubled CO2, and adding ice albedo gives 8°C for doubled CO2 (as long as the Earth has ice sheets). These feedbacks have historically occurred over centuries to millennia, but could become significant this century. Including CO2 itself as a feedback would make climate sensitivity even higher, except for the weathering feedback which operates over hundreds of millennia.

To avoid kicking off slow feedbacks, Hansen advises that we return the Earth to energy balance by eventually reducing atmospheric CO2 levels to 350 ppm. Of course if we listen to the 'low sensitivity' crowd and buy into the wishful thinking that CO2 emissions are of little concern, we will blow post the 2°C danger limit (approximately 450 ppm CO2), let alone giving ourselves a reasonable chance to eventually reduce CO2 levels to 350 ppm.


Astute Skeptical Science readers may have noticed that "climate's changed before" recently supplanted "it's the Sun" as the #1 most used "skeptic" argument.  In the same radio interview, Christy made a similar argument, first specifically regarding extreme weather events:

"In looking at the best climate data through the past, these events are not outside the range that of what has already occurred"

But he then expanded the argument further:

"Extremes events are not the key that you look for, you look for a large global number in the heat storage of the atmosphere and ocean and that is rising slowly but it is not rising catastrophically or dramatically and certainly does not point to a high sensitivity of the climate to things like greenhouse gases."

This is simply wrong, because as we saw in Lindzen Illusion #1, the amount of warming we've observed is consistent with a climate sensitivity of approximately 3°C for doubled CO2.  With these two statements, Christy seems to be trying to weave several climate myths together to make an argument something like "climate has changed before, the current warming isn't very significant, it points to low climate sensitivity, and it could just be natural variability."  This sort of storyline is consistent with Christy's recent claims in the media and before US Congress, and similar to the alternative hypothesis to anthropogenic global warming that Lindzen put together.

The problem, aside from being wrong, is that it's self-contradictory.  The climate certainly has changed before, and by large amounts.  How can we explain the ~5°C increase in average global surface temperature between glacial and interglacial periods if climate sensitivity is low?  Natural variability can only account for fractions of a degree change, and the Milankovitch orbital forcing isn't that large, especially if sensitivity is low. 

As Hansen and Sato and many other studies have showed, these past climate changes are consistent with a climate sensitivity of 3°C.  The larger the past climate change, the larger sensitivity is required to explain them.  So arguing both for low sensitivity and large past climate changes is self-contradictory.

Misleading Christy

In short, Christy and the other "skeptics" who are claiming high certainty that climate sensitivity is low are not only contradicted by dozens of studies on the subject, including Hansen's empirically-based paleoclimate assessments, and by their own claims of large past climate changes, but they are advocating that we continue on an extremely risky path. 

It's particularly disturbing when these "skeptics" claim in the media that "we" are seeing evidence that climate sensitivity is low, implying that they are referring to the body of climate science research, when in fact the opposite is true.  In doing so they mislead the public about the actual state of the scientific research on climate sensitivity, which may lead people to the mistaken conclusion that urgent action is unnecessary.  In fact Christy seems to be going on an international public misinformation tour, having recently made similar misleading statements to the American, Australian, and Canadian public: a disturbing trend.

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Comments 51 to 78 out of 78:

  1. Eric the Red @45, Viezer et al 2000 did not allow for the change in uptake rate of O18 that results from changes in the pH of water. Royer et al 2004 correct for pH changes due to high levels of CO2, and show almost complete consistency between the temperature record and the CO2 record: A later paper by Dr Royer show that many of the apparent discrepancies are found to not be so once we find high resolution proxies for the relevant periods. He also shows that the combination of changes to solar forcing due to the "faint young sun" plus CO2 forcing correlate exceptionally well with temperatures throughout the phanerozoic: Even the remaining discrepancies detailed in Royer 2007 have now largely been closed, as noted by Dr Alley in his famous lecture.
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    Moderator Response: [Dikran Marsupial] sub tags fixed
  2. Tom, Thank you for the reference and subsequent graphic. I do not think we want to enter the dispute between Viezer, Royer, Shaviv, etc.
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  3. Eric the Red s/we/I/ ? ;o)
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  4. 51, Tom, Excellent work (did it take much, or did you know this off the top of your head?), and once again you've demonstrated the need for a database which makes it easy to realize which papers, while published, were later refuted or amended in some way. It's too easy for people to find a paper that says what they want, and then put 100% stock in it (and as I said, my reading of the original paper seemed like the authors were more raising questions, and admitting to gaps in knowledge themselves, and the need for further investigation, rather then putting a stake in the ground and making specific, hard claims).
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  5. 52, Eric the Red, You response sounds rather dismissive, as if you want to put all of your emphasis Viezer, and see no reason to be skeptical about it. This thread is about climate sensitivity. We're discussing climate sensitivity. Viezer, Royer, Shaviv, etc. are all about climate sensitivity. So suddenly someone doesn't like the idea of discussing the topic? Is it only fun to wander off topic, and bring up things that belong on other threads? WTF...
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  6. Eric the Red at 21:58 PM on 10 June, 2011 Eric, remeber that Veizer himself has reinterpreted the sea surface data you cite and concludes that his temperature reconstruction now indicates a coupling to CO2 concentrations, at least throughout the Paleozoic: R. E. Came, J. M. Eiler, Ján Veizer, K. Azmy, U. Brand & C. R. Weidman (2007) Coupling of surface temperatures and atmospheric CO2 concentrations during the Palaeozoic era Nature 449, 198-201
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  7. chris @56, thank you for the link. I was not previously aware of that paper, which is interesting. Sphaerica @54, I went through the rounds on his material some time last year. Luckily for me some of it stuck. Dikran Marsupial, thanks.
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  8. Re the top article, Hansen's interpretation that climate sensitivity might be amplified (as much as doubled) due to very slow feedbacks, especially associated with slow ice sheet responses in glacial periods (we're in a glacial period now), is supported by other recent analysis of greenhouse gas/temperature responses from the deep past: J. Park and D. L. Royer (2011) Geologic constraints on the glacial amplification of Phanerozoic climate sensitivity American Journal of Science, 311, 1-26 abstract M. Pagani, Z. Liu, J. LaRiviere & A. C. Ravelo (2010) High Earth-system climate sensitivity determined from Pliocene carbon dioxide concentrations Nature Geoscience 3, 27 – 30 abstract D. J. Lunt, A. M. Haywood, G. A. Schmidt, U. Salzmann, P. J. Valdes & H. J. Dowsett (2010) Earth system sensitivity inferred from Pliocene modelling and data Nature Geoscience 3, 60 - 64 abstract
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  9. Spaerica, Fine, this should satisfy both your requests.
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  10. Eric the Red at 02:29 AM on 11 June, 2011 Come on Eric, you've just been shown here and here that the evidence doesn't support that tentative hypothesis of Veizer and Shaviv. Veizer himself has reinterpreted the temperature part of the apparent correlation in the paper you cite and reinterpreted it. Veizer now considers that the temperature correlates with atmospheric [CO2] at least throught the Paleozoic part of the Phanerozoic. It's pretty desperate to base interpretations on an old paper that has been shown subsequently to have little scientiic merit, and which (at least one of) the authors now consider to be incorrect!
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  11. Eric_red, To be clear. Do you a) Support Christy's blatant misinformation and attempts to mislead, b) Do you recognize that his arguments are self-contradictory, c) Do you agree that his claims highlighted in the body post are not supported by the overwhelming body of scientific research and evidence?, d) Do you understand that the "we" he refers to actually means a few individuals? It blows my mind that people doggedly and uncritically defend Christy's lamentable actions, and choose to try and fabricate debate and doubt. You have been shown to be wrong numerous time son this thread...yet steadfastly refuse to change your position in the view of the evidence presented to you. In contrast, scientists like Veizer are open-minded enough to change their position in light of new evidence-- as they should. Give it up already...or are you in denial like Christy?
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  12. For those who think that Veizer has changed his position, you might want to read this: More recent statements by Veizer seems to show that he is standing by his original conclusions, and the merits of his original paper. Do not be swayed by misinformation. Actually, I do not see where I have been shown to be wrong, although I am open-minded enough to look back. Many people have told me that I am "in denial" recently to entertain the thought that climate sensitivity could be closer to 2 than 3. That number is not unreasonable, and does not contradict the science. It does not fall beyond any reported likely range, and in some cases is the most likely value. I have seen people applaud those who state that the climate sensitivity is 6 or above, yet that is above most likely ranges.
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  13. Eric the Red at 04:36 AM on 11 June, 2011 Really Eric? Veizer publishes a paper in Nature with a reinterpretation of his original sea surface temperature data, that negates the possibility that the tentative Shaviv/Veizer hypothesis could be correct when considered through the Paleozoic period...... ....and now we're supposed to believe what someone says on a blog about a conversation he had with Veizer that the latter doesn't actually believe the stuff he published in the Nature paper. No thanks Eric...I'm sticking to the science. Science is about evidence and the evidence simply doesn't support the tentative hypothesis of Veizer and Shaviv. Veizer's own data pretty much scuppers it. "do not be swayed by misinformation". Brilliant Eric! In your eyes Veizer's own work constitutes both the information and the misinformation on this topic. Truly anything and everything can be twisted into a misrepresenters "argument"!
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  14. Perhaps these are "dumb" questions, but nontheless... Because the enhanced greenhouse effect is all about the transfer of heat both within and between the various components of the Earth's climate system, why is only one metric, i.e., annual average mean global temperature of the troposphere" being used to define "Climate Sensitivity"? Doesn't this single metric mask all kinds of other things that are happening within and between the other components of the climate system?
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  15. Badgersouth at 05:20 AM on 11 June, 2011 There are (at least) three reasons why the Earth surface temperature is a useful and important metric. 1. Averaged over several years [i.e. averaging the effects of seasonal variation and short term ocean surface variability (El Nino/La Nina)] the Earth's surface temperature seems to remain relatively steady in the absence of external forcing. So the averaged Earth surface temperature seems to be a decent metric for the amount of energy in the climate system, despite the various energy fluxes through the system. And so the change in the Earth surface temperature is a good metric for the change in the energy in the climate system in response to a forcing (e.g. from enhanced greenhouse forcing in response to a change in [CO2] or changes in solar output). 2. From a terrestrial perspective the Earth surface is the location of the biosphere, and that's of fundamental interest to us. The Earth surface temperature is probably the most important metric for assessing potential effects of forcings on the biosphere. 3. Partly due to 2 [the response of elements of the geosphere and biosphere to temperature changes (plant leaf stomatal responses; isotopic composition of shells, wood and ice; the spectrum of species that thrive at a particular temperature, and so on), temperature changes leave a variety of signatures in the paleo-record that allow localized surface temperatures to be reconstructed. So this metric provides a means of assessing the relationship between changes in paleo[CO2] (which also leaves a variety of signatures in the paleo-record) and temperature (aka climate sensitivity), which informs us of contemporary and future temperature changes in response to massively enhancing the Earth's greenhouse effect...
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  16. Eric, Forgive me, but your position seems to be based entirely on a convenient form of cherry pick, but instead of cherry picking the data, you're cherry picking the one paper you want to use on which to base the all of the weight of your opinion. There are various and sundry studies, almost all pointing to high(er) climate sensitivity. You have picked one study, from 10 years ago, which is contradicted by a number of other studies, as well as the author himself, and you choose to put huge emphasis and weight on that one paper, to the point of declaring that "I disagree that the sensitivity has never been less than 2.5 or been as high as 5." Your defense of the paper comes from a blog post by someone who claims to have spoken to the author of the original and contravening studies, with hints of partisan politics pressuring him into "compromising" on the studies wording and conclusions. Is this really the skeptical approach to the science?
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  17. @Chris #65: Those are all good points and thank you for posting them. My frustration really stems from what I perceive to be an inconsistent use of the term "climate" among scientists. In the above discussion, the term really means "the temperature of the lower atmosphere as measured by a single metric." (Even that single metric masks all kinds of significant spatial and temporal variations within the lower atmospher during the course of a year.) If the basic definition of the Earth's "climate system" includes the atmosphere, the hydrosphere, the cyrosphere, etc., the word "climate" should not then be used to define one subcomponent of that system.
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  18. If Dr. James Hansen were not concerned about the negative consequences of climate change in the 21st century, he would not have written "Storms of My Grandchildren."
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  19. I suggest that every article in the Christy Crock series have a tab listing the titles of the other articles in the series with a link to each embedded in the title.
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  20. Eric @62, "Many people have told me that I am "in denial" recently to entertain the thought that climate sensitivity could be closer to 2 than 3." That would be completely at odds with what Christy and Lindzen believe. Also, keep in mind that on our current path we are easily going to double CO2 levels, and may quite easily treble them. So we are very likely looking at well over 2 C warming in an incredibly short time in geological terms, and that at a time when we will likely have over 10 billion mouths to feed.
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  21. Badgersouth at 06:22 AM on 11 June, 2011 Yes, OK; I think we have to recognise that words are shorthands for things, and that we sometimes need some informed knowledge about the meaning of a particular word or phrase in a specific context. That's a fundamental element of language - it would be cumbersome to communicate with each other if we didn't have shorthands to encapsulate more complex concepts! So yes "climate sensitivity " is a shorthand for something like "equilibrium response of the globally averaged near Earth surface temperature to a forcing equivalent to a doubling of atmospheric [CO2]". It doesn't really refer specifically to "climate" at all! However climate (which is a local property as you point out) is intimately related to the Earth's globally averaged surface temperature, and so a significant change in temperature is expected to lead to a change in temperature. So there is a connection. Obviously "climate" isn't amenable to definition with a single quantitative metric, as temperature is. So in order to usefully interpret "climate sensitivity" we need some information on the manner in which excess energy in the climate system in response to a forcing is spatially-distributed, and its consequences (on the hydrological cycles, weather systems, land ice and plant responses etc.), to assess the likely true climate responses to a change in globally averaged temperature...
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  22. my second paragraph I should say: "..and so a significant change in temperature is expected to lead to a change in climate"
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  23. Eric the Red @59 & 62: First, your second paper is Shaviz and Veizer, 2003. It still pre-dates Royer et al, 2004; and is refuted by it. Second, below is the crucial image from Came et al, 2007, of which Veizer was one of the co-authors. It compares the two temperature records from that paper with to previous reconstructions of Phanerozoic temperatures, that by Veizer et al, 2000 (light grey) and that by by the GEOCARBIII model (as shown in the second image in my 51). Also shown along the bottom is Scotese's division of the global climate into warm and cool periods. I have added a green line for easy alignment. It is very clear from this that Came et al, 2007 tends to confirm Royer et al's conclusions, and to disconfirm those of Veizer et al, 2000, and Shaviz and Veizer, 2003. Having said that, Came et al examine samples from just one location and one formation from the Silurian. The GEOCARBIII model has a resolution of 10 million year, and as the recent record of glacials and interglacials shows, temperatures can fluctuate a lot in such a short period. Therefore Came et al is neither a definitive confirmation of Royer et al, nor a definitive refutation of Veizer et al. Came et al in fact take refuge in that fact to say,
    "Our re-interpretation of the d18O values of Silurian and Pennsylvanian carbonate fossils also may apply to other parts of the Palaeozoic. However, there remain several marked discrepancies between climate reconstructions using the GEOCARB model versus those implied by the Scotese geological record and the Veizer et al. oxygen isotope record (which generally agree with each other, at least in timing of climate variations), and it is difficult to imagine that all time periods will be resolved in the same way as those examined in this study."
    So, Veizer does not think that Royer is right; but subsequent evidence which he has contributed has tended to confirm Royer's conclusions and disconfirm Veizer's. Disappointingly, Came et al do not discuss ocean pH even once. Considering the nature of Royer et al's critique of Veizer et al, that is a glaring oversight.
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  24. Eric, until a new paper with new data and/or methods can show an improvement on Royer, I dont see how its possible to stick with Veizer interpretation. Reality is not a matter of opinion. If Veizer thinks Royer wrong, then there has been ample time for a response. A conversation, interpreted and reported by a well-known denier, is hardly evidence.
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  25. scaddenp @74, being fair to Shaviv and Veizer, they did publish a comment on Royer et al, 2004. In it they claim that Royer et al failed to take into account changes in ice volume in their calculations, and that doing so largely obviates the effect of pH in interpreting temperatures. Disappointingly, they do not publish a reconstruction based on their estimate of the effects of ice volume, and continue to use the older reconstruction without pH correction. To an abbreviated version of that comment, Royer et al reply, saying that their result has good geological confirmation, and that the ice volume effect is only relevant during glacial periods, when their pH correction is small.
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  26. @chris #71: Or scientists could use the term, "troposphere temperature sensitivity" rather than "climate sensitivity." One of the reasons why scientists have such a difficult time effectively communicating their findings to the average person is what I call "scientific shorthand-speak."
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  27. This supercedes the Royer paper.
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  28. Eric the Red @77, did you even read the abstract?
    "Biospheric coupling of terrestrial water and carbon fluxes: Implications for the climate system Jan Veizer, University of Ottawa (Canada) Paul R. Ferguson, University of Ottawa (Canada) Terrestrial water and carbon fluxes represent one of the largest movements of mass and energy in the Earth's outer spheres, yet the relative contributions of abiotic water vapour fluxes and those that are regulated solely by the physiology of plants remain poorly constrained. By interpreting differences in the oxygen-18 and deuterium content of precipitation and river water, it is possible to partition plant transpiration from the evaporative flux that occurs directly from soils, water bodies and plant surfaces. The methodology was applied to fifteen large watersheds in North America, South America, Africa, Australia, and New Guinea, and results show that approximately two thirds of the annual water flux from the water-limited ecosystems that are typical of higher-latitude regions can be attributed to plant transpiration. In contrast to water-limited watersheds, transpiration in high-rainfall, densely vegetated regions of the tropics represents a smaller proportion of precipitation and is relatively constant, defining a plateau in response to incident solar radiation. Estimates of water transpiration behave similar to net primary productivity, confirming that, in agreement with small-scale measurements, the terrestrial water and carbon cycles are inherently coupled via the biosphere, offering a conceptual perspective on the dynamics of energy exchange between terrestrial systems and the atmosphere, where the carbon cycle is essentially driven by solar energy via the water cycle intermediary. Ferguson, P.R. and Veizer, J. 2007. Coupling of water and carbon fluxes via the terrestrial biosphere and its significance to the Earth's climate system. Journal of Geophysical Research - Atmospheres, Vol. 112, D24S06, doi:10.1029/2007JD008431, 2007"
    Now, can you explain how a study of isotope rations of oxygen and hydrogen in modern river water "supercedes" a study of temperatures through out the phanerozoic?
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