Paleo sea level and CO2

From the National Oceanography Centre, Southampton (UK)

New study documents the natural relationship between CO2 concentrations and sea level

By comparing reconstructions of atmospheric CO2 concentrations and sea level over the past 40 million years, researchers based at the National Oceanography Centre, Southampton have found that greenhouse gas concentrations similar to the present (almost 400 parts per million) were systematically associated with sea levels at least nine metres above current levels.

The study determined the ‘natural equilibrium’ sea level for CO2 concentrations ranging between ice-age values of 180 parts per million and ice-free values of more than 1,000 parts per million.

It takes many centuries for such an equilibrium to be reached, therefore whilst the study does not predict any sea level value for the coming century, it does illustrate what sea level might be expected if climate were stabilized at a certain CO2 level for several centuries.

Lead author Dr Gavin Foster, from Ocean and Earth Science at the University of Southampton which is based at the centre, said, “A specific case of interest is one in which CO2 levels are kept at 400 to 450 parts per million, because that is the requirement for the often mentioned target of a maximum of two degrees global warming.”

The researchers compiled more than two thousand pairs of CO2 and sea level data points, spanning critical periods within the last 40 million years. Some of these had climates warmer than present, some similar, and some colder. They also included periods during which global temperatures were increasing, as well as periods during which temperatures were decreasing.

“This way, we cover a wide variety of climate states, which puts us in the best position to detect systematic relationships and to have the potential for looking at future climate developments,” said co-author Professor Eelco Rohling, also from Ocean and Earth Science at the University of Southampton.

The researchers found that the natural relationship displays a strong rise in sea level for CO2 increase from 180 to 400 parts per million, peaking at CO2 levels close to present-day values, with sea level at 24 +7/-15 metres above the present, at 68 per cent confidence limits.

“This strong relationship reflects the climatic sensitivity of the great ice sheets of the ice ages,” said Dr Foster. “It continues above the present level because of the apparently similar sensitivity of the Greenland and West Antarctic ice sheets, plus possibly some coastal parts of East Antarctica.”

According to the study, sea level stays more or less constant for CO2 changes between 400 and 650 parts per million and it is only for CO2 levels above 650 parts per million that the researchers again saw a strong sea level response for a given CO2 change.

“This trend reflects the behaviour of the large East Antarctic ice sheet in response to climate changes at these very high CO2 levels. An ice-free planet, with sea level 65 metres above the present, occurred in the past when CO2 levels were around 1200 parts per million.”

Professor Rohling said, “Sea level rises to these high values will take many centuries, or even millennia, but the implications from the geological record are clear – for a future climate with maximum warming of about two degrees Centigrade, that is with CO2 stabilized at 400 to 450 parts per million, sea level is set to steadily rise for many centuries, towards its natural equilibrium position at around 24 +7/-15 metres, at 68 per cent confidence. In Intergovernmental Panel on Climate Change terms, this is a likely rise of at least nine metres above the present. Previous research indicates that such rises above present sea level may occur at rates of roughly one metre per century.”

Based on these results, which document how the Earth system has operated in the past, future stabilization of CO2 at 400-450 parts per million is unlikely to be sufficient to avoid a significant steady long-term sea level rise.




The study is published this week online ahead of print in Proceedings of the National Academy of Sciences of the United States of America (PNAS manuscript # 2012-16073R).



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And they did not even think about the possibility, that increased CO2 was the effect and not the cause of ocean temperature increase.


Well said Manfred.

Stephen Richards

and when cows lay down it’s going to rain. Ducks fly backwards to keep the wind out of their eyes and so on. Just utter BS


“This strong relationship reflects …”
Since when has relationship ever been causation, and why do I always have to start laughing when reading such wild guesses?

Disko Troop

1. Start with an assumption that CO2 causes sea level change.
2. Find suitable data points.
3. Ignore solar activity, sea temperature, plate tectonics, ocean circulation, air temperature, etc etc .
4. Assume cause and effect to be what you want it to be.
5. Keep a close watch on the closing date for AR5.
6. Conclude that 450 ppm will cause sea level rise. (See 1.)
Babies playing with lego bricks and my taxes are paying their wages. (expletive)
Ivor |Ward


Repeat until you accept the reality:
1) correlation does not equal causation….
2) we do not KNOW that proxies equal actual CO2 atmospheric concentrations of any precision versus comparative concentrations…
3) non-random, non-replicated samples with n = 1 or less than that required for statistical rigor are useful only for anecdotal conclusions and have unknown variance and error…

When my mother had children in December, it always snowed.

but the implications from the geological record are clear – for a future climate with maximum warming of about two degrees Centigrade, that is with CO2 stabilized at 400 to 450 parts per million, sea level is set to steadily rise for many centuries, towards its natural equilibrium position at around 24 +7/-15 metres, at 68 per cent confidence. In Intergovernmental Panel on Climate Change terms, this is a likely rise of at least nine metres above the present. Previous research indicates that such rises above present sea level may occur at rates of roughly one metre per century.”

I doubt we have “many centuries” left before we start seeing a significant increase in glacial ice. In fact, over the last 10 years the trend is sea level rise has reduced, not increased. I can not begin to explain how many ways this is wrong. The fundamental assumption here is that CO2 drives sea level with no proof of that given except that they have found periods in the past with higher sea level that also had higher CO2.
A sibling of mine was born in a snowstorm in December. Good thing my mother had only one in December because that storm was a real doozy and I don’t think people in the region would have appreciated a repeat of it.

Ken Hall

Manfred, I think you mean sea-level increase rather than temperature… But I was thinking the same thing. Changes in sea-levels of several meters would create different surface areas across the globe creating different weather patterns effecting plant life which would radically alter the balance of CO2 storage in the oceans and the amount of CO2 released into the atmosphere by the ocean and plant life on land.
Seems pretty obvious to me. And studying time-scales in the millions of years, would mean that the mere 800 year lag between temperature rise and then CO2 rise would not be as clear to show cause and effect, meaning it could be fudged.
Also did they did not take into account solar cycles from millions of years ago.
This is an incomplete study which presents fudged data designed to support a specific political narrative of “OMG WE ARE ALL GOING TO DIE!!!! So give us more taxes and stop using technology you serfs!”

Climate Ace

Who cares, really? It is going to be winner-take-all, whichever way the climate shakes loose.
Adaptation to rising sea levels is cheaper than stopping sea levels from rising. Everyone knows that. Go short property investment in higher elevations, do a bit of prepping on the side, and you can’t go wrong.

Mike McMillan

When sea levels rise and fall, that changes the volume of water available to dissolve the CO2. Colder water during ice ages can hold more gas, but there is much less of it. Interglacials have much more liquid water, but it’s warmer and can hold less per volume unit. I wonder if that trade off was taken into account.

“…sea level at 24 +7/-15 metres above the present, at 68 per cent confidence limits…”
“This remains to be seen,” said the cat after pissing into the sugar bowl.

As Manfred said, the CO2-level rises with temperature because the oceans can’t keep it as the get warmer. CO2 is a side effect, not the reason for higher tempertures. Don’t they have some real geologists and chemists in these research groups?


OK, so it takes 100’s of years, but should we be seeing the >10mm/year already?
If not, why not?


These are the games they have to play to keep the scare alive.
There is no sea level rise. There is no temperature rise.
But hey – come with us down this statistical garden path we’ve just made, and you can be reassured that the scare is still alive – rising CO2 will drown the world after all – so we can still have our eco-reich.


I am surprised by the results of this study. Next thing they will be saying that the earth’ts themperature was high at times when the CO2 concentration was high.

Colin Porter

I have to say I am ashamed to be British if all we can do is produce quality of work like this.
As with the carbon dioxide – temperature relationship, this astute professor makes the nieve assumption that sea level is a function of the carbon dioxide level concentration instead of the plainly obvious relationship that both sea level and carbon dioxide concentration are a function of long term temperature. At best, the only reasonable conclusion to be drawn, which is still somewhat tentative, is that the relationship has temporarily been disturbed away from natural equilibrium by our injecting extra carbon dioxide into the atmosphere which has not yet had the opportunity to equilibrate into the lower levels of the ocean. The professor even admits that his relationship mysteriously breaks down at a carbon dioxide concentration of between 400 and 650 ppm, which to my mind should have been resolved before making such a howler of a claim.
In short, this work is once more just a piece of pure alarmist propaganda.


I agree with Manfred on the cause/effect relationship which has been amply demonstrated over the past million years as we find that after inter-glacials it takes of the order of ten thousand years for CO2 levels to fall to lower levels after the beginning of a new glaciation thus demonstrating that CO2 does not cause global warming, as does most empirical data.
This means that if as warmists claim the increases we have seen over the past century in CO2 levels are indeed the result of human activity rather than a result of a warming world then the link as discussed in the above paper has been broken and sea levels will not rise as a result. Alternatively if the CO2 level increases are happening as a result of warming then we can expect sea levels to rise – and all shades of grey in between, i.e. depending on the relative fractions of human/natural CO2 in the atmosphere. This of course is a trend which can be reversed as seems to have happened over the past couple of centuries as measured CO2 levels were much higher in the late eighteenth century and early nineteenth century seeming to reach a low point roughly a hundred years ago when textbooks were reporting CO2 levels at 400ppm, presumably based on earlier work. In fact the atmospheric measurement history suggests that there are relatively high frequency components to atmospheric CO2 levels which would not show up in ice core data being averaged out.
It would be worth investigating the early measurement technologies to look for possible sources of systemic measurement error, calibrating old equipment against Mauna Loa. Obviously this should have been done…..

Ed Zuiderwijk

Warmer climate => warmer sea waters & less land ice => higher sea levels & less dissolved C02 => higher atmospheric CO2.
Not the other way around.

Claude Harvey

How many times must we go through this? We’ve known for a long time that global temperature and atmospheric CO2 concentrations have generally moved up or down in concert over the eons as we cycled from between Ice Ages and Warm Periods. The raging controversy has always been whether CO2 drove temperature (greenhouse argument) or temperature drove CO2 (gas solubility in sea water argument).

Peter Miller

Throughout the geological record, changes in temperature precede changes in CO2 levels, it is of those inconvenient facts that alarmists like to ignore.
So the study’s findings could well be correct, so the real question is what made the world warmer in the past?
1. Changes in the sun’s energy output?
2. Changes in the Earth’s orbit.
3. Changes in the ocean currents, triggered by tectonic plate movement, such as the emergence of the Isthmus of Panama?

David, UK

@ Manfred:Precisely. A warmer ocean fizzes out more CO2. Of COURSE they know this. Truth is not the aim.


Yep it’s worse than we thought. Great headlines for the MSM to pickup as usual. Surely they must have looked hard to make sure they had the cause & effect the right way round?

Kelvin Vaughan

So the IPCC are wasting their time trying to stop the inevitable. They should be concentrating on a program of teaching everyone how to build house boats and how to swim.


Nope this is an AGW study. They work from the answer down to the question. They need there global warming story’s but temperature is not rising so the make up other story’s like this.
This story works also that way. The answer is that sea levels rise because global worming and more CO2.
The question was probably like dos higher CO2 concentrations make sea level rise?
Then they look for a way to proof that CO2 and higher temperatures make sea levels rise.
This dos not mean it works that way but they found an likely correlation between the two just like whit CO2 and temperature. At some point they found that there could be a correlation between CO2 rise and temperature rise. And we all know where that whent.
In this case they found that 400 ppm CO2 what we have now is ideal. But there is a gap of 200 to 250 ppm to the point where the effect will be greater but to what site? Is there a increase of sea level rise or will the sea level go up much higher.

Alan the Brit

It is interesting what they don’t say. They do not appear to state that CO2 levels rise first followed by temperature, followed by sea-level rises!


How many of the known geocycles other than co2 and temperature did they compare with? In the little I understand I can name quite a few. This study should require peer review in a astrophysics journal.

…They are NOT paid for thinking that….


I thought it was well established that CO2 levels were a lagging indicator of temperature changes by about 600 years. I would also query ‘ice-age values of 180 ppm’. I understood that at this level there was insufficient CO2 for plant growth which would have caused a mass extinction.
In climate research scientific ignorance seems to be a boon – it seems to mean it is okay to just make it up rather than checking it out. As the sun is acknowledged to have a bigger impact on the climate I am just waiting for a paper saying that CO2 levels in the atmosphere affect the behavior of the sun!


Noah ! Noah ! Build an Ark …. collect the warmista Taliban and set them adrift.

“The researchers compiled more than two thousand pairs of CO2 and sea level data points”
Does anyone know the total number of possible pairs? Should the selection have been random instead of cherry picked? Briggs?


‘ CO2 stabilized at 400 to 450 parts per million, sea level is set to steadily rise for many centuries, towards its natural equilibrium position at around 24 +7/-15 metres, at 68 per cent confidence. ‘
Firstly a 68 confidence is no ‘confidence ‘ at all and secondly using massive time scales means that in effect they can never realistic be proved wrong , given that its impossible to rule out other factors and no one will ever remember the claims in the first place. So an unscientific ‘confidence’ level to back up claims that are not capable of being proved so are themselves not science. A normal day at the office for climate ‘science ‘

Chris Wright

As many have already pointed out, CO2 changes were usually driven by changes in ocean temperatures. In other words, CO2 levels tended to be a temperature indicator.
But of course the 20th century increase in CO2 is not a temperature indicator (probably) because it was caused by human emissions (probably).
Therefore it is completely false to draw comparisons between ancient CO2 levels and current CO2 levels.


@Alexander Feht
LOL That’s a funny one. I will put it on my famous quotes list.
And it’s so applicable for most AGW-science these days.

Henry Clark

CO2 does not correlate with temperature worth beans on timescales of seeing century-level variation like
and decade-level variation like
There is quite a reason more commonly posted plots are so zoomed out as to make a millenium close to a pixel: CO2 correlates with temperature well only when a view is zoomed out enough to hide the lag period, for oceans to warm to their depths and over a few centuries release CO2 (the temperature increase and then the CO2 as a consequence). Even then it doesn’t over the very longest timeframes (as well as short ones), though that’s another topic.


Temperature rise >>> Co2 rise >>> ice melts >>> sea level rise???

Claude Harvey says:
January 3, 2013 at 1:21 am
The raging controversy has always been whether CO2 drove temperature (greenhouse argument) or temperature drove CO2 (gas solubility in sea water argument).
1. the ice cores show that CO2 lags temperature by about 800 years. This establishes that temperature drives CO2, by a well accepted principle that cold water can hold more CO2 than warm water.
2. if CO2 ALSO drove temperature, then as more CO2 dissolved in the cold ocean during an ice age, and global CO2 levels fell, it would be impossible for the ice age.
3. similarly, if CO2 ALSO drove temperature, then as more CO2 came out of solution as the oceans warmed at the end of an ice age, it would be impossible for there to be a second ice age.
4. since we have been in a pretty regular series of ice ages every 100k years for a couple of million years, this is strong evidence that CO2 cannot be driving temperature. If it did, then we would either be stuck in a low CO2 ice age, or high CO2 warm age. Transition between the two would not be possible given the small irregularity in the earth’s orbit. Yet we see a regular transition in time with a beat frequency of the earth’s orbit.

Bill Illis

Sea Level has been falling for the last 94 million years as the Atlantic has opened up and deepened (it can take 50 to 100 Million years for a new ocean basin to widen, sink in the mantle and reach its mature depth of 5000 metres).
So here are all the reliable CO2 datapoints over the last 40 million years versus the sea level estimates of Haq Shutter 2008 (which is generally the most accepted sea level estimates). Sea level has been slowly falling while there is no way to match up the sea level datapoints to the CO2 datapoints since there is quite a different resolution.
Miller 2005 has higher sea level estimate resolution over the last 8 Million years which covers the ice age changes for example, but generally Miller’s estimates should have more of a decline over the last 8 Million years and are not consistent with other estimates. Again, the resolution is different in these two datastreams so it is not possible to tie these together the way the authors claim to do.
I don’t see CO2 in these numbers. I see Atlantic deepening and ice age/Milankovitch cycles.

knr says:
January 3, 2013 at 3:12 am
Firstly a 68 confidence is no ‘confidence ‘ at all
68% confidence is very close to 66.7%.
All too often we see things in terms of black and white or heads and tails. However in nature more often that not we are dealing with 3 states, with a 1/3 chance of each. When you look at things this way, you see that there is not a 50/50 chance that things will get warmer or colder. Rather there is a 2/3 chance (66.7%) that something else will happen.
Thus, there is a 66.7% chance things will not get warmer, a 66.7% chance things will not get colder, and a 66.7% chance things will not stay the same.
What the good professor has discovered is the law of probability as they apply to a 3 state system. (ice age, warm age, transition). Next week, the wheel.


68% is about 1 std deviation to get to 97% you need 2 std devitions this suggests that the error range for 97% confidence would be 24 -30/+14 which includes 0

According to the study, sea level stays more or less constant for CO2 changes between 400 and 650 parts per million
Since we are at 400, this study says it is OK to go up to 650 because it will not have much effect. Which will take us well into the next century, leaving lots of time to invent an alternative energy source. Without such an invention there is no way we can support present population levels without fossil fuels, let alone provide the benefits of industrialized society to the billions of people presently living in poverty.

Rob Boyd

A bit more on the 68% confidence level. One, you can’t do that. You are NOT allowed to adjust your confidence level to create significance. This violates EVERY principle of statistical hypothesis testing. What happened here was that the study FAILED to have significance, so the authors CHANGED the test level to the point where the F-test would show the desired result.
Imagine for a moment the design phase of the study. “Where shall we place our significance level? 90%, 95%?”.
“No, let’s put it at 68%”.
“Sixty-eight? Not 65 or 70?”
“No, 68. That will show real care and foresight in the design.”
Sarc off.

Ken Hall says: OMG WE ARE ALL GOING TO DIE!!!!
After 6.5 decades of observation, there seems to be strong evidence to support that theory.
I see they buy into our ability to control the climate by controlling atmospheric CO2 concentration. I keep being amazed that any scientist could believe that one and only one thing controls climatic temperature. I suppose if you buy into our ability to come up with mean global temperature as a meaningful statistic (to multiple decimal places, no less), then you could believe in only one driver of climate.


How many journals was this submitted to before going to PNAS?

Wearing short sleeves causes summer to come. Proofed.

As every scientist knows, correlation does not mean causation. The sea level changes obviously are the result of temperature changes, which also cause CO2 levels to rise. This study does nothing to enlighten anyone about anything.
No mention of whether those periods of CO2 rise but no sea level rise were also periods of no temperature rise, the most likely scenario, but one that would undercut the study’s logic to
a large extent.


So. When Noah had all the animals on the Ark….there was much water, and very little plant life to photosynthetically reduce whatever CO2 was produced by those nasty surviving humans…and their flatulent cattle. A data point from this time period would fit in with the conclusions of this study…without knowing the “rest of the story” as Paul Harvey was famous for saying. But then again, start with a conclusion, gather data that correlates, reaffirm original conclusion. That is called an endless do loop in programming terms.

Doug Huffman

PNAS difficulties with peer review allows arguing from conclusions to supporting premises to pass as logic.
[PNAS is Post Normal ?? Science? Mod]


Alan the Brit: Exactly. Has anyone looked at the full paper to see if they make any claims of causation and not only “association”?


68% is a 1 sigma range, that 68% of the data falls in 1 sigma. Now 2 sigma is I think 95% and 3 is 99%. So they are saying that there is a 1 sigma signifigance/deviation on this. >sigh< I personally have a few other questions, like how do they know that the sea level has fallen rather than land uplifted for some of the older peices, and by how much?
Also 24 +7/-15 meters? really so add 24 meters of sea level? or did I read that wrong? and from again what is 'zero point'. It all seems fuzzy. And 40 million years ago wasn't solar output higher? There seems to be some data missing here.
Maybe it is just me, but I suspect there isn't enough cross pollinization in PHD work anymore and thus people can make wags (like this statement) about their data without evaluating enough possible contaminates from other fields.