Study settles prehistoric puzzle, confirms modern link of carbon dioxide, global warming

November 14, 2017
Fossil leaves from prehistoric plants collected from the Ethiopian Highlands of Chilga and Mush River Valley tell scientists how much carbon dioxide was present in the atmosphere millions of years ago. Credit: SMU

Fossil leaves from Africa have resolved a prehistoric climate puzzle—and also confirm the link between carbon dioxide in the atmosphere and global warming.

Research until now has produced a variety of results and conflicting data that have cast doubt on the link between high levels and climate change for a time interval about 22 million years ago.

But a new study has found the link does indeed exist for that prehistoric time period, say researchers at Southern Methodist University, Dallas.

The finding will help scientists understand how recent and future increases in the concentration of atmospheric carbon dioxide may impact the future of our planet, say the SMU researchers.

The discovery comes from new biochemical analyses of from plants that grew on Earth 27 million years ago and 22 million years ago.

The new analyses confirm research about modern climate—that global temperatures rise and fall with increases and decreases in carbon dioxide in our atmosphere—but in this case even in prehistoric times, according to the SMU-led international research team.

Carbon dioxide is a gas that is normally present in the Earth's atmosphere, even millions of years ago. It's dubbed a greenhouse gas because greater concentrations cause the overall temperature of Earth's atmosphere to rise, as happens in a greenhouse with lots of sunlight.

Recently, greenhouse gas increases have caused , which is melting glaciers, sparking extreme weather variability and causing sea levels to rise.

The new SMU discovery that carbon dioxide behaved in the same manner millions of years ago that it does today has significant implications for the future. The finding suggests the pairing of carbon dioxide and global warming that is seen today also holds true for the future if carbon dioxide levels continue to rise as they have been, said geologist Tekie Tesfamichael, lead scientist on the research.

"The more we understand about the relationship between atmospheric and global temperature in the past, the more we can plan for changes ahead," said Tesfamichael, an SMU postdoctoral fellow in Earth Sciences.

"Previous work reported a variety of results and conflicting data about carbon dioxide concentrations at the two intervals of time that we studied," he said. "But tighter control on the age of our fossils helped us to address whether or not atmospheric carbon dioxide concentration corresponded to warming—which itself is independently well-documented in geochemical studies of marine fossils in ocean sediments."

The researchers reported their findings in Geology, the scientific journal of the Geological Society of America, in the article "Settling the issue of 'decoupling' between atmospheric carbon dioxide and global temperature: [CO2]atm reconstructions across the warming Paleogene-Neogene divide."

Co-authors from SMU's Roy M. Huffington Department of Earth Sciences are professors Bonnie Jacobs, an expert in paleobotany and paleoclimate, and Neil Tabor, an expert in sedimentology and sedimentary geochemistry.

Other co-authors are Lauren Michel, Tennessee Technological University; Ellen Currano, University of Wyoming; Mulugeta Feseha, Addis Ababa University; Richard Barclay, Smithsonian Institution; John Kappelman, University of Texas; and Mark Schmitz, Boise State University.

Researchers measured and counted the leaf pores and epidermal cells on well-preserved fossil leaves from the Highlands of Ethiopia to determine the concentration of carbon dioxide present in the Earth's atmosphere 22 million years ago and 27 million years ago. Credit: SMU

Discovery of rare, well-preserved fossil leaves enables finding

The findings were possible thanks to the rare discovery of two sites with extraordinarily well-preserved fossil leaves of flowering plants from the Ethiopian Highlands of eastern Africa.

Such well-preserved fossil leaves are a rarity, Tesfamichael said.

"Finding two sites with great preservation in the same geographic region from two important time intervals was very fortunate, as this enabled us to address the question we had about the relationship between atmospheric carbon dioxide concentration and global temperatures," he said.

Scientists know that variations in the concentration of atmospheric carbon dioxide affect carbon fixation in leaves during photosynthesis. This causes leaves to develop anatomical and physiological changes such as the frequency and size of stomata—the pores on the surface of a leaf through which carbon passes.

Scientists can measure those attributes, among others, in fossil leaves, so that leaf fossils can be used as proxies for Earth's atmospheric carbon dioxide history.

The sites producing the leaves for the SMU study were discovered separately in years past, but major fossil collections were produced through field work coordinated by the SMU research team and their co-authors, who have been collaborating on this project for several years.

The work has had funding from the National Science Foundation, The National Geographic Committee for Research and Exploration, the SMU Ford Fellowship Program, SMU Research Council, the Institute for the Study of Earth and Man, and the Dallas Paleontological Society Frank Crane Scholarship.

The fossils are housed permanently in the collections at the National Museum of Ethiopia in Addis Ababa. Institutional and governmental support came from the National Museum of Ethiopia, the Authority for Research and Conservation of Cultural Heritage, and Addis Ababa University.

Previous studies firmly established a temperature difference

One of the sites dates to the late Oligocene Epoch, and the other to the early Miocene.

Previous studies that measured ocean temperatures from around the world for the two intervals have firmly established a temperature difference on Earth between the two times, with one much warmer than the other. So the SMU study sought to measure the levels of carbon dioxide for the two time periods.

For the SMU analyses, fossil leaves of a single species were collected from the 27 million-year-old late Oligocene site. The leaves had been deposited during prehistoric times in the area of Chilga in northwest Ethiopia most likely at a river bank. The Earth's climate during the late Oligocene may have been somewhat warmer than today, although glaciers were forming on Antarctica. The SMU study found carbon dioxide levels, on average, around 390 parts per million, about what it is on Earth today.

Fossil leaves of the 22 million-year-old species from the early Miocene were collected from ancient lake deposits, now a rock called shale, from the modern-day Mush Valley in central Ethiopia. The early Miocene climate at that time was warmer than the late Oligocene and likewise the SMU study found higher carbon dioxide levels. Atmospheric carbon dioxide was about 870 parts per million, double what it is on Earth today.

Variations in the concentration of atmospheric carbon dioxide affect carbon fixation during photosynthesis and can be measured on a preserved fossil leaf like this one from Ethiopia. Credit: SMU

The SMU study confirmed a relationship between carbon dioxide and temperature during the late Oligocene and early Miocene.

Paleoclimate data can help predict our planet's future climate

While carbon dioxide isn't the only factor affecting Earth's climate or global mean temperature, it is widely considered by scientists among the most significant. Much is known about climate change and global warming, but questions still remain.

"One of those is 'What's the sensitivity of the Earth's temperature to carbon dioxide concentration? Is it very sensitive? Is it not so sensitive?' Estimating temperature and carbon dioxide concentrations for times in the past can help find the answer to that question," Jacobs said. "There's a lot of work on paleoclimate in general, but not as much on the relationship between carbon dioxide and temperature."

The finding is an important one.

"The amount of temperature change during this interval is approximately within the range of the temperature change that is estimated from climate models for our next century given a doubling of carbon dioxide concentration since the industrial revolution," Jacobs said.

With the new model reaffirming the prehistoric relationship, scientists can look now at related questions, said climate change scientist Lauren Michel, who worked on the study as a post-doctoral researcher at SMU.

"Answering questions about the rate of change and which factors changed first, for example, will ultimately give a clearer picture of the Earth's climate change patterns," Michel said. "I think it is valuable to understand the relationship of greenhouse gases and climate factors represented in the rock record so we can have a better idea of what we can expect in the future and how we can prepare for that."

SMU study confirms relationship that previous methods overlooked

Previous studies found little to no correlation between temperature and carbon dioxide for the late Oligocene and early Miocene. That has puzzled paleoclimate researchers for at least a decade.

"We have a good test-case scenario with these well-preserved plants from both time slices, where we know one time slice, with higher levels of carbon dioxide, was a warmer climate globally than the other," Tesfamichael said.

"It's been a puzzle as to why the previous methods found no relationship, or an inverse correlation," he said. "We think it's for lack of the well-dated proxy—such as our fossil leaves from two precise times in the same region—which deliver a reliable answer. Or, perhaps the models themselves needed improvement."

Previous studies used methodologies that differed from the SMU study, although all methods (proxies) incorporate some aspects of what is known about living organisms and how they interact with atmospheric carbon dioxide.

Some studies rely on biochemical modeling of the relationship between single-celled marine fossils and atmospheric dioxide, and others rely on the relationship between stomata and concentration observed in the living relatives of particular fossil plant species.

"Each method has its assumptions," said Tesfamichael. "We will see if our results hold up with further studies of this time interval using the same methodology we used."

Explore further: Carbon dioxide levels lower than thought during super greenhouse period

More information: Tekie Tesfamichael et al, Settling the issue of "decoupling" between atmospheric carbon dioxide and global temperature: [CO2]atm reconstructions across the warming Paleogene-Neogene divide, Geology (2017). DOI: 10.1130/G39048.1

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Chris_Reeve
1.8 / 5 (11) Nov 14, 2017
Article: "While carbon dioxide isn't the only factor affecting Earth's climate or global mean temperature, it is widely considered by scientists among the most significant."

Their whole argument would seem to really just be a restatement of the original hypothesis. And to get to their conclusion, people who are not averse to applying the principles of science to the domain of climate will have to put some effort into ignoring the fact that correlation does not imply causation.
Sonhouse
3.6 / 5 (5) Nov 14, 2017
Well it's nice they told us Carbon dioxide is known as Carbon dioxide! Really wasn't sure:)
Steven_Scott
5 / 5 (4) Nov 14, 2017
Their whole argument would seem to really just be a restatement of the original hypothesis. And to get to their conclusion, people who are not averse to applying the principles of science to the domain of climate will have to put some effort into ignoring the fact that correlation does not imply causation.


So are you saying you find their findings conclusive?
humy
4 / 5 (4) Nov 14, 2017
Article: " Carbon dioxide, called carbon dioxide, ..."
Err, not exactly informative.
humy
4.4 / 5 (7) Nov 14, 2017
Article: "While carbon dioxide isn't the only factor affecting Earth's climate or global mean temperature, it is widely considered by scientists among the most significant."

Their whole argument would seem to really just be a restatement of the original hypothesis.

clearly they have more than mere "argument" because they have new EVIDENCE.

And to get to their conclusion, people who are not averse to applying the principles of science to the domain of climate will have to put some effort into ignoring the fact that correlation does not imply causation.

have you got any evidence that they are ignoring that correlation doesn't imply causation in this particular case?
Paulw789
1 / 5 (5) Nov 14, 2017
It would have been "a real study" if he would have dated his samples.

Read the paper. What we have is randomized "something".

dustywells
1.6 / 5 (7) Nov 14, 2017
The new analyses confirm research about modern climate—that global temperatures rise and fall with increases and decreases in carbon dioxide in our atmosphere
I can see confirmation "that global temperatures rise and fall."

I can see confirmation that there are "increases and decreases in carbon dioxide in our atmosphere."

I do not see confirmation that they are in lockstep.
TrollBane
4.5 / 5 (2) Nov 14, 2017
"Carbon dioxide, called carbon dioxide, is a gas" Needless repetition, called needless repetition, is a gaffe...
Da Schneib
4 / 5 (4) Nov 15, 2017
This is actually pretty important since it establishes a clear link in past climates between temperature and atmospheric CO₂ (also known as carbon dioxide) concentration.
Chris_Reeve
1 / 5 (2) Nov 15, 2017
@DaSchnieb, each of these researchers go into these papers knowing the conclusions that they want to present. This is not real science.
Captain Stumpy
3.7 / 5 (3) Nov 15, 2017
@DaSchnieb, each of these researchers go into these papers knowing the conclusions that they want to present. This is not real science.
then it should be easily refuted by your presentations of evidence, right?

i mean: you're making a statement
that is all... just a statement

you don't know what the evidence they have says or even what it is
you don't know what correlations were presented, nor how it ties to anything
you have absolutely no scientific papers, publications nor do you have any experience using the scientific method

yet you make a definitive statement claiming it's "not real science"

perhaps the problem isn't the science you see, but rather how you see it?

because it's a threat to your beliefs, you reject it without even understanding it

that is religion, plain and simple

otherwise you would be presenting refuting studies that show the above to be wrong (which is how science works)
Chris_Reeve
1 / 5 (2) Nov 15, 2017
Article: "Scientists know that variations in the concentration of atmospheric carbon dioxide affect carbon fixation in leaves during photosynthesis. This causes leaves to develop anatomical and physiological changes such as the frequency and size of stomata—the pores on the surface of a leaf through which carbon passes. Scientists can measure those attributes, among others, in fossil leaves, so that leaf fossils can be used as proxies for Earth's atmospheric carbon dioxide history."

Nonsense.

https://en.wikipe..._minimum

"Liebig's law of the minimum, often simply called Liebig's law or the law of the minimum, is a principle developed in agricultural science by Carl Sprengel (1828) and later popularized by Justus von Liebig. It states that growth is dictated not by total resources available, but by the scarcest resource (limiting factor)."
snoosebaum
3 / 5 (2) Nov 15, 2017
when some use stomata data they r applauded when othesr use stomata data they r derided

https://wattsupwi...stomata/

Captain Stumpy
3 / 5 (2) Nov 15, 2017
@idiot illiterate eu pseudoscience cult moron chris/hannes
Nonsense
1- your argument isn't relevant as it's only tangentially related

2- the keywords in your first paragraph
... variations in the concentration of atmospheric carbon dioxide affect carbon fixation in leaves...
3- arguing that "variations in atmospheric CO₂ don't affect carbon fixation in leaves" because "growth is dictated by the scarcest resource" is idiotic because you're ignoring the fact that carbon fixation is well known in plants

how do i know that?

4- read up on 14C

captain obvious says: idiot troll is an idiot
Chris_Reeve
1 / 5 (2) Nov 15, 2017
Re: "arguing that "variations in atmospheric CO₂ don't affect carbon fixation in leaves" because "growth is dictated by the scarcest resource" is idiotic because you're ignoring the fact that carbon fixation is well known in plants"

Wikipedia:

"Carbon fixation or сarbon assimilation is the conversion process of inorganic carbon (carbon dioxide) to organic compounds by living organisms. The most prominent example is photosynthesis ..."

Again, the article states:

"This causes leaves to develop anatomical and physiological changes such as the frequency and size of stomata—the pores on the surface of a leaf through which carbon passes."

What is being alleged is that co2 is the only or dominant factor that contributes to frequency and size of stomata.

We are left with the very false premise that other factors like availability of water and nutrients do not also influence the frequency and size of stomata.

That's nonsense. Plant stomata are not simply co2 meters.
Captain Stumpy
1 / 5 (1) Nov 15, 2017
@idiot illiterate eu pseudoscience cult moron chris/hannes
That's nonsense
sigh:
1- measurement
Recent variations in the concentration of atmospheric carbon dioxide ([CO2]atm) have been shown to affect carbon fixation during photosynthesis and are correlated with anatomical and physiological changes observed in leaves of woody dicots. These include changes in stomatal frequency and size and in δ13C values.
please note the specifics before you regurgitate any further idiocy

2- tests
This study tests the link
3- link
...show a statistically significant...
4- cause
[CO2]atm rise from ∼390 ppm in the late Oligocene to ∼870 ppm in the early Miocene
5- conclusion
These values demonstrate a positive correlation between [CO2]atm and global average temperature, contrary to some previous studies for this time interval.
what do you present?

your "interpretation" of a wiki article based upon faulty knowledge

i repeat: idiot troll is an idiot
Captain Stumpy
1 / 5 (1) Nov 15, 2017
@idiot illiterate eu pseudoscience cult moron chris/hannes cont'd
What is being alleged is that co2 is the only or dominant factor that contributes to frequency and size of stomata
no
and again, because you missed it and don't understand what it means - i will eliminate all the hard stuff and boil it down to something more manageable for your monosyllabic vocabulary:
Recent variations ... have been shown...and are correlated with anatomical and physiological changes observed
this aint about guessing at this point
more:
These attributes can be measured
big important point there: measurement... not guessing based upon personal interpretation of wiki, but measurement... ok so far?
to continue
This study tests...The results of this study show... These values demonstrate ...
i concentrate on these for a purpose

if you can debunk the study based upon your argument i suggest publishing today

that is how science works

get it yet?

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