Guest Post by Bill Illis
This post is the first of what will likely be a series on the PaleoClimate.
In this part, we are just going to go through the various estimates for Temperature, CO2 and Sea Levels in the PaleoClimate. This post is also about making the data available to everyone so that others can use it. All of the data presented in this post is available for download at the end in easy to use Excel spreadsheets which also incorporates direct links to the actual data sources used.
PaleoClimate Temperature Estimates Over the Past 570 Million Years
There are various sources we can use for estimates of Temperatures in the PaleoClimate.
We have the ice core dO18 isotope data going back 800,000 years. James Zachos has a high resolution database of dO18 isotopes going back 67.0 million years. Jan Veizer has accumulated an isotope database that goes back 526.5 million years. Dana Royer and Robert Berner applied a ph-correction factor to Veizer’s database and Christopher Scotese has developed Temperature estimates that extend back into the pre-Cambrian.
For the most part, the Temperature estimates are based on dO18 isotopes and these have proven to be reasonably reliable, or more accurately, to be the most reliable temperature estimation method that is available.
The isotope data does require a number of different transformations and smoothing to make it useful as a Temperature proxy. Nobody is really sure what the proper way to carry this out is.
For one, it must be detrended as the data becomes older. The dO18 declines over time due to the radioactivity of the Earth. The above estimates are based on a simple linear detrending formula. The rationale is that the radioactive conditions would have remained reasonably constant over the last 530 million years. Others have used a second order polynomial but this does not result in much difference.
It has been noted that the dO18 isotope data should also be corrected for ice volume, sea level, the concentrations of CaCO3 in the oceans and -ph conditions of the oceans. Royer and Berner applied a ph-correction factor based on Berner’s GeoCarb III CO2 estimates. Again, this doesn’t make much difference except that Royer and Berner’s numbers are now lower than Veizer’s original database would point to.
Effectively, any transformation carried out has still got to match the record that we know about. It is still going to have to show a Carboniferous ice age, an Ordovician ice age, a hot Permian Pangea climate, a hot Cretaceous period, an Antarctic glaciation and the recent ice ages.
In other words, no matter what corrections are applied, one should just end up with something very similar to the above chart.
Detailed Temperature Estimates Over the Past 530 Million Years
Veizer’s database contains over 16,600 individual dO18 isotope data points extending back 526.5 million years. There is sufficient resolution throughout the database that we can be reasonably certain about any specific period.
The above chart has been constructed using Veizer’s data with two different smoothing parameters; a shorter one which preserves more detail and then one that emulates the Phanerozoic Climate Change chart by Robert Rohdes of Global Warming Art. It is likely that both are reasonably accurate and sometimes less smoothing is preferred to more smoothing so that more information can be extracted.
In this case, there really is more information available from the shorter Gaussian smooth. Immediately evident is that certain large temperature changes coincide with some of the large Mass Extinction events in the planet’s history.
The really unusual one is the Permian Extinction event in which 96% of marine species and 70% of large land animals died out in a very short period of time about 251.4 million years ago. Previously this was thought to be due to exceptionally hot conditions or even ocean chemistry changes.
But now one can see that temperatures actually declined by about 5.0C in a very short period of time (something that is that well-known). This temperature drop exactly coincides with the dating of the Siberian Traps volcanic events at 251 to 250 million years ago which is the largest series of volcanic events known in history. An area nearly the size of Australia may have been covered by volcanic magma flows hundreds of metres deep (some places have been measured at 4 kms deep). The volcanoes lasted for about 1 million years and, not surprisingly, temperatures fell.
The other event is the Ordovician extinction event of 443 million years ago in which 50% of the new Cambrian genera of life disappeared. This was always known to be caused by a cooling climate. But now, one can see that there is a very significant drop in the smoothed temperature estimates exactly at 443 million years ago.
The Devonian Extinction seems to be caused by a rapid increase in temperatures, as much as 10.0C in just a few million years.
Notice how the Cretaceous Period, 95 million years ago, is 2.0C to 3.0C higher than the Paleocene Eocene Thermal Maximum. The climate scientists are always talking about how unusual the PETM was but just a few million years earlier, temperatures were quite a bit higher. Dinosaurs even lived in Alaska at the time, and it was a little farther north in the period than it is now. The PETM event does not even look unusual enough in the record to spend much time on.
Notice that the timelines surrounding the Carboniferous Ice Age and the Ordovician-Silurian Ice Age are now clearly defined. These timelines match up very closely with the estimated alignment of the Continents during the periods. Even the short mid-Jurassic Ice Ages are now evident at a point in time when parts of EuroAsia were transiting the North Pole.
Detailed Temperature Estimates Over the Past 67 million Years
Zachos has developed another database of 14,800 individual estimates of dO18 isotopes that covers the past 67 million years with a resolution of less than 100,000 years in most cases.
The time period when Antarctica glaciated over (for the fourth time that is known about) is clearly evident. Temperatures reached as high as 6.0C during the PETM and the periods when Antarctica reglaciated and when Greenland’s glaciers started building occurred at 14 million years ago.
About 2.5 million years, the most recent cycle of ice ages began. In part II of the series, we may take a closer look at the ice ages in more detail.
PaleoCO2 Estimates
There are quite a few different estimates for CO2 in the PaleoClimate. We have the ice cores, we have Mark Pagani 2005 with high resolution estimates between 5.4 million years to 44.5 million years ago and we have Berner’s GeoCarb III estimates which go back to 570 million years ago.
There are others (and they have been included in the CO2 spreadsheet) but they are not as well-accepted as these. The other estimates come mainly from Stomata size (the cells that plants to use to absorb CO2), Paleosols (ancient soil deposits) and Phytoplankton among others.
Using the estimates that are most accepted and given the resolution is higher with the ice cores than with Pagani and then Pagani’s resolution is higher than Berner’s, they have been incorporated back-to-back-to-back as one series as follows.
As most of you are aware, CO2 goes as high as 7,069 ppm 520 million years ago and as low as 180 ppm during the height of the ice ages.
On the same timeline as the PaleoTemperatures Over 67 Million Years chart above, CO2 looks like this over the past 70 million years.
Paleo Sea Level Estimates
Sea level has also been included in the databases since it is not well-known that these high resolution estimates exist. In addition, sea level can certainly have an impact on the climate as well be an indicator for the climate.
There are many different sea level estimates and the most recent one covering the whole period, produced by the world-leading expert on sea level, Bilal Haq, is the most accepted version (Haq, Schutter, 2008).
Sea Level has varied by a large amount throughout history. Sea levels were as much as 265 metres higher than today 100 million years ago and have been as low as 120 metres lower than today during the Last Glacial Maximum.
Sea level seems to vary through three different mechanisms.
- Sea level falls when glaciers build up on land. Obvious enough.
- Sea level falls when continental land masses are concentrated together. Collisions and mountain building tend to squeeze the Earth’s landmasses together and there is less continental shelf area that can affect the average depth of the overall oceans. Related to the last reason, the ocean basins tend to be more mature and deeper in these situations. and,
- Sea level rises when new young ocean basins are opening. New ocean basins generally form at only 2,500 metres depth while mature ocean basins tend to deepen and reach a depth of about 6,000 metres after 100 million years. That means the overall average depth of the ocean is lower when new oceans are forming. This is particularly the case during the Cretaceous when the Atlantic Ocean was just opening up.
Sea levels rose so high during the Cretaceous as the Atlantic was just opening, that the ocean flooded North America from Texas to Inuvik, to Hudson Bay. Europe, the Middle East, North Africa and the central parts of Eurasia were also flooded by shallow oceans.
During the Carboniferous and the Jurassic, the land masses were collected together into the Supercontinent of Pangea. Sea levels fell in the earlier part as glaciers covered large parts of Gondwana, but then they stayed low as the glaciers melted and the continents moved together to form Pangea.
There are periods when there are rapid changes in sea level and these have been used by researchers to date the periods of glaciations. It appears Scotese has used earlier versions of the sea level data to date the glaciations used in his temperature reconstruction.
Conclusion
Putting all the best estimates together, here is a view of the Temperatures, CO2 and Sea Level throughout the past 526 to 570 million years.
In subsequent posts, we may look at the Milankovitch Cycles and the recent ice ages, Continental Drift through time and how that may have affected the climate and then the empirical evidence surrounding the CO2 doubling sensitivity in the PaleoClimate.
The main purpose of this post was to just make the data available to everyone. Others are free to use to use this data in any manner they see fit.
The data is available in three different easy-to-use Excel spreadsheets and can be downloaded at this link. The Paleo Temp Database is a very large file and may be a slow download.
[Paleo Temp CO2 Sea Level Data]
PaleoClimate Temperature, CO2 and Sea Level Estimates
Guest Post by Bill Illis
This post is the first of what will likely be a series on the PaleoClimate.
In this part, we are just going to go through the various estimates for Temperature, CO2 and Sea Levels in the PaleoClimate. This post is also about making the data available to everyone so that others can use it. All of the data presented in this post is available for download at the end in easy to use Excel spreadsheets which also incorporates direct links to the actual data sources used.
PaleoClimate Temperature Estimates Over the Past 570 Million Years
There are various sources we can use for estimates of Temperatures in the PaleoClimate.
We have the ice core dO18 
isotope data going back 800,000 years. James Zachos has a high resolution database of dO18 isotopes going back 67.0 million years. Jan Veizer has accumulated an isotope database that goes back 526.5 million years. Dana Royer and Robert Berner applied a ph-correction factor to Veizer’s database and Christopher Scotese has developed Temperature estimates that extend back into the pre-Cambrian.
For the most part, the Temperature estimates are based on dO18 isotopes and these have proven to be reasonably reliable, or more accurately, to be the most reliable temperature estimation method that is available.
The isotope data does require a number of different transformations and smoothing to make it useful as a Temperature proxy. Nobody is really sure what the proper way to carry this out is.
For one, it must be detrended as the data becomes older. The dO18 declines over time due to the radioactivity of the Earth. The above estimates are based on a simple linear detrending formula. The rationale is that the radioactive conditions would have remained reasonably constant over the last 530 million years. Others have used a second order polynomial but this does not result in much difference.
It has been noted that the dO18 isotope data should also be corrected for ice volume, sea level, the concentrations of CaCO3 in the oceans and -ph conditions of the oceans. Royer and Berner applied a ph-correction factor based on Berner’s GeoCarb III CO2 estimates. Again, this doesn’t make much difference except that Royer and Berner’s numbers are now lower than Veizer’s original database would point to.
Effectively, any transformation carried out has still got to match the record that we know about. It is still going to have to show a Carboniferous ice age, an Ordovician ice age, a hot Permian Pangea climate, a hot Cretaceous period, an Antarctic glaciation and the recent ice ages.
In other words, no matter what corrections are applied, one should just end up with something very similar to the above chart.
Detailed Temperature Estimates Over the Past 530 Million Years
Veizer’s database contains over 16,600 individual dO18 isotope data points extending back 526.5 million years. There is sufficient resolution throughout the database that we can be reasonably certain about any specific period.
The above chart has been constructed using Veizer’s data with two different smoothing parameters; a shorter one which preserves more detail and then one that emulates the Phanerozoic Climate Change chart by Robert Rohdes of Global Warming Art. It is likely that both are reasonably accurate and sometimes less smoothing is preferred to more smoothing so that more information can be extracted.
In this case, there really is more information available from the shorter Gaussian smooth. Immediately evident is that certain large temperature changes coincide with some of the large Mass Extinction events in the planet’s history.
The really unusual one is the Permian Extinction event in which 96% of marine species and 70% of large land animals died out in a very short period of time about 251.4 million years ago. Previously this was thought to be due to exceptionally hot conditions or even ocean chemistry changes.
But now one can see that temperatures actually declined by about 5.0C in a very short period of time (something that is that well-known). This temperature drop exactly coincides with the dating of the Siberian Traps volcanic events at 251 to 250 million years ago which is the largest series of volcanic events known in history. An area nearly the size of Australia may have been covered by volcanic magma flows hundreds of metres deep (some places have been measured at 4 kms deep). The volcanoes lasted for about 1 million years and, not surprisingly, temperatures fell.
The other event is the Ordovician extinction event of 443 million years ago in which 50% of the new Cambrian genera of life disappeared. This was always known to be caused by a cooling climate. But now, one can see that there is a very significant drop in the smoothed temperature estimates exactly at 443 million years ago.
The Devonian Extinction seems to be caused by a rapid increase in temperatures, as much as 10.0C in just a few million years.
Notice how the Cretaceous Period, 95 million years ago, is 2.0C to 3.0C higher than the Paleocene Eocene Thermal Maximum. The climate scientists are always talking about how unusual the PETM was but just a few million years earlier, temperatures were quite a bit higher. Dinosaurs even lived in Alaska at the time, and it was a little farther north in the period than it is now. The PETM event does not even look unusual enough in the record to spend much time on.
Notice that the timelines surrounding the Carboniferous Ice Age and the Ordovician-Silurian Ice Age are now clearly defined. These timelines match up very closely with the estimated alignment of the Continents during the periods. Even the short mid-Jurassic Ice Ages are now evident at a point in time when parts of EuroAsia were transiting the North Pole.
Detailed Temperature Estimates Over the Past 67 million Years
Zachos has developed another database of 14,800 individual estimates of dO18 isotopes that covers the past 67 million years with a resolution of less than 100,000 years in most cases.
The time period when Antarctica glaciated over (for the fourth time that is known about) is clearly evident. Temperatures reached as high as 6.0C during the PETM and the periods when Antarctica reglaciated and when Greenland’s glaciers started building occurred at 14 million years ago.
About 2.5 million years, the most recent cycle of ice ages began. In part II of the series, we may take a closer look at the ice ages in more detail.
PaleoCO2 Estimates
There are quite a few different estimates for CO2 in the PaleoClimate. We have the ice cores, we have Mark Pagani 2005 with high resolution estimates between 5.4 million years to 44.5 million years ago and we have Berner’s GeoCarb III estimates which go back to 570 million years ago.
There are others (and they have been included in the CO2 spreadsheet) but they are not as well-accepted as these. The other estimates come mainly from Stomata size (the cells that plants to use to absorb CO2), Paleosols (ancient soil deposits) and Phytoplankton among others.
Using the estimates that are most accepted and given the resolution is higher with the ice cores than with Pagani and then Pagani’s resolution is higher than Berner’s, they have been incorporated back-to-back-to-back as one series as follows.
As most of you are aware, CO2 goes as high as 7,069 ppm 520 million years ago and as low as 180 ppm during the height of the ice ages.
On the same timeline as the PaleoTemperatures Over 67 Million Years chart above, CO2 looks like this over the past 70 million years.
Paleo Sea Level Estimates
Sea level has also been included in the databases since it is not well-known that these high resolution estimates exist. In addition, sea level can certainly have an impact on the climate as well be an indicator for the climate.
There are many different sea level estimates and the most recent one covering the whole period, produced by the world-leading expert on sea level, Bilal Haq, is the most accepted version (Haq, Schutter, 2008).
Sea Level has varied by a large amount throughout history. Sea levels were as much as 265 metres higher than today 100 million years ago and have been as low as 120 metres lower than today during the Last Glacial Maximum.
Sea level seems to vary through three different mechanisms.
· Sea level falls when glaciers build up on land. Obvious enough.
· Sea level falls when continental land masses are concentrated together. Collisions and mountain building tend to squeeze the Earth’s landmasses together and there is less continental shelf area that can affect the average depth of the overall oceans. Related to the last reason, the ocean basins tend to be more mature and deeper in these situations. and,
· Sea level rises when new young ocean basins are opening. New ocean basins generally form at only 2,500 metres depth while mature ocean basins tend to deepen and reach a depth of about 6,000 metres after 100 million years. That means the overall average depth of the ocean is lower when new oceans are forming. This is particularly the case during the Cretaceous when the Atlantic Ocean was just opening up.
Sea levels rose so high during the Cretaceous as the Atlantic was just opening, that the ocean flooded North America from Texas to Inuvik, to Hudson Bay. Europe, the Middle East, North Africa and the central parts of Eurasia were also flooded by shallow oceans.
During the Carboniferous and the Jurassic, the land masses were collected together into the Supercontinent of Pangea. Sea levels fell in the earlier part as glaciers covered large parts of Gondwana, but then they stayed low as the glaciers melted and the continents moved together to form Pangea.
There are periods when there are rapid changes in sea level and these have been used by researchers to date the periods of glaciations. It appears Scotese has used earlier versions of the sea level data to date the glaciations used in his temperature reconstruction.
Conclusion
Putting all the best estimates together, here is a view of the Temperatures, CO2 and Sea Level throughout the past 526 to 570 million years.
In subsequent posts, we may look at the Milankovitch Cycles and the recent ice ages, Continental Drift through time and how that may have affected the climate and then the empirical evidence surrounding the CO2 doubling sensitivity in the PaleoClimate.
The main purpose of this post was to just make the data available to everyone. Others are free to use to use this data in any manner they see fit.
The data is available in three different easy-to-use Excel spreadsheets and can be downloaded at this link. The Paleo Temp Database is a very large file and may be a slow download.
[Paleo Temp CO2 Sea Level Data]
I hope this is somehow brought to the attention of the IPCC alarmists preparing to meet in Copenhagen, even though the CO2 data, in particular, doesn’t seem to agree with their “consensus.”
Great work, Bill!
Shaviv and Veizer specifically criticized Royer’s pH “correction”:
http://www.phys.huji.ac.il/~shaviv/ClimateDebate/RoyerReply.pdf
“The analysis of Royer et al. (2004) assumes an unrealistically high pH correction. First, it neglects the ice-volume effect, which changes the relation between 18O and T . Second, this large pH correction implies high
temperatures for seawater even during times of extensive glaciations. Moreover, the analysis of Royer et al. (2004) consists of bootstrapping, by introducing a correction to T that is an implicit function of RCO2. It is then not surprising that a correlation between T and RCO2 is obtained. This would be the case irrespective of the RCO2 model utilized.”
maybe this is conventional in the field, but to my eyes it looks like the time axis runs in reverse (greater x axis values represent negative years from now). This confuses my weak intellect :(. I’d prefer clearer labelling to make this easier to interpret correctly. Most other charts I see here have the present on the right edge.
The inconvenient truth is that none of these facts about past climate matter… we all must submit to the will of our masters and pay more taxes and give up our freedoms. That is the ultimate objective of the warmists.
Used to be that we worried about getting food. Of all people, my 16 year old son pointed out to me that abundance creates stupidity. Too much good leads to too much bad. And realist’s are subjected to praying for cold and the demise of society so that they can be proven right.
OT, but 11% of bugger all is still bugger all IMO. Also more examples of “assumption and modelling”…
http://www.smh.com.au/environment/sins-of-emissions-just-hot-air-says-think-tank-20091016-h150.html
Thanks for posting the data in excel! That’s a great habit and appreciated.
Is there any geomagnetic data over these time spans available by chance?
Sea level seems like a highly problematic measure to make, especially given the nature of tectonics, over time periods of even millions of years. In that time, lithified ocean deposits can be lifted 1,000’s of feet into the air. What is the defined by this study to be level 0?
Will this study take into account the different flora/fauna present during these periods? Life adapted to the conditions present on earth at the time. Any comparison of Cambrian life (and it’s CO2 and temp) with the present would be highly misleading.
red432 (20:09:02) : “maybe this is conventional in the field…”
There are certain conventions, which apparently do not pertain to blogs, yet. Ordinates and abscissas should be unambiguously labeled: units, parameter, numeric range, and any other necessary information should appear on the appropriate axis or in the legend.
The x-axes here all represent millions of years BP (before present). Some of the graphs say millions of years BP; other say just millions of years; and one says nothing at all. Zero years BP is often on the right, but can also be put on the left as a little prank to see if you’re paying attention.
The y-axes here are either meters, ppm* CO², or temperature anomaly, but (as is too often the case) the zero temperature anomaly is undefined in some of the graphs. Where this key datum is lacking, I guess you should assume the T anomaly is relative to the average global temperature at the founding of Rome, April 21, 753 BCE/BC, in degrees Caesar (°C). jk
Graphs should be dated and should show the source of the data or of the graph itself. Prior versions of new original graphs should be given recognition (e.g., “after Schnickelfritz.”)
* this is usually parts per million by weight if you’re looking at liquid solutions or parts per million by volume if you’re looking at gases, but there are industry-specific exceptions. If not stated, hey, just assume it’s ppmv. That will be close enough for jazz, astrophysics, dendrophrenology, and paleoclimatology.
It’s like throwing scraps to the dogs……
I think measuring sea level that far back is a pointless excercise. Techtonic Plate movment means that all sorts of assumptions have to be made to correct for it.
I`d like to see that last combined graph with just CO2 and Temperature.
Great work (which will of course go un-noticed by the warmists)
Bill Illis…..credibility going down here….just wait until Joe gets hold of this…if he even bothers….
Can someone explain how sea level over large time spans is estimated? Sea level relative to what? To land is what matters, but the land is in motion. Plate tectonics push land up and down, so do ice caps that go away and return. Mountains rise and get eroded. One can one measure sea level without a static reference point?
It would be interesting to compare phase in the d18O and d13C data in Cenozoic sediments. Zachos, et al. show the data for the Paleocene-Eocene Thermal Maximum in figure 5 of Science vol. 292, pp. 686-693. Lag of d13C behind d18O is evident if you give comparable scale to the anomalies. Even at the ocean bottom, temperature seems to control gaseous carbon. Science declined to publish this observation.
Of course, Mudelsee in Quaternary Science Reviews, vol. 20, pp. 583-589 observed that the best fit between temperature and carbon in the Vostok core indicates a 1300 year lag for carbon. When the warmists deny the significance of this, they are effectively saying that the CO2 level in 2000 AD influenced the temperature in 700 AD.
Of all those who would impose unscientific beliefs on their fellow humans, warmists are really perhaps the most harmful as they have been able to distort profoundly the economic status of the western world, and the worst may be yet to come.
Bill,
Nice post – I think you should add some additional details on the delta O18 paleothermometry – nowhere do you note that the ice core data comes from oxygen isotope ratios in the ice for the first 800,000 year record, whereas the older Phanerozoic record comes from the oxygen isotope ratios preserved in the shells of marine microfossils like forams. Where much of the recent debate over tree-rings temperature proxies focuses on whether trees really are thermometers, the physical basis for using isotopes for paleothermometry is well established and has strong theoretical and experimental support.
I think you were were wise to allocate your time and effort to bring this dataset to the public’s attention because it really is one of the most important constraints on the range of temperature and CO2 variability through geologic time – people should know these graphs and understand how they are produced and what the data means.
Very useful to give an overview and a broader picture. Puts things into perspective. Thanks, Bill.
There are certainly some questions and doubts which would probably need a closer look at the original publications.
What’s the”d” for (in “dO18”)? Thanks.
red432 (20:09:02) :
Download the data, on the graph in excel you can right click the x-axis, click format axis, select the scale tab and check the box at the bottom that says values in reverse order.
Although Red432, If you do that, all the labels added won’t be much good. But the data is there.
Ron House (23:39:11)
The d is for delta…read “delta-O-18”
Ben
nvw (22:40:49
“I think you were were wise to allocate your time and effort to bring this dataset to the public’s attention because it really is one of the most important constraints on the range of temperature and CO2 variability through geologic time – people should know these graphs and understand how they are produced and what the data means.”
I agree. This looks to me like a very important post. Too big for a rapid comment.
Bill, I’ve just quickly scanned this article and I commend you for making the data available. There are details missing however and some errors. For example the notion of a correction to d18O to account for the radioactivity of the earth is wrong. Similarly the pH correction to d18O is controversial. At equilibrium the d18O composition of a marine mollusc/foraminifera (which most of these data are based on) would be independent of pH.
These issues are complicated but if Anthony and you are in agreement then I’m more than happy to write a 101 primer to stable isotopes and palaeotemperature measurements for WUWT and readers.
Paul Dennis
Head of Stable Isotope and Noble Gas Laboratories
School of Environmental Sciences
UEA
UK
http://sites.google.com/site/silenvuea/people/pfd
Reply: I’ve emailed Anthony about this ~ charles the moderator
nvw (22:40:49)
“I think you were were wise to allocate your time and effort to bring this dataset to the public’s attention because it really is one of the most important constraints on the range of temperature and CO2 variability through geologic time – people should know these graphs and understand how they are produced and what the data means.”
It’s also important people try to keep their mind in a geologic time state when looking at this data. For some of the graphs presented, there is enough time between data points were 20 ice ages could come and go.
Climate operates on decadal scales and we are looking at scales in the millions of years.
Just to give you a sense, there are 100,000 decades in 1 million years. So for that 540 million years of data, lets think of that as 54 million decades (54,000,000 decades).
Hard to imagine geologic time, and this is only 1/9th of the history of the earth.
Ed (21:17:33) :
Is there any geomagnetic data over these time spans available by chance?
http://dragon.ngu.no/Palmag/paleomag.htm
Any chance of adding a history of sea-level atmospheric pressure as well?
Are there proxies for air density? ….. e.g. wing area/weight of flying creatures?