Is it possible that increased CO2 levels during the larger dinosaurs era is a major factor in why dinosaurs grew so big during this period?

And extrapolating this question, is it possible that the increased CO2 during the industrial revolution has contributed to each generation of man growing bigger?

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    $\begingroup$ what would be the mechanism for CO2 (carbon dioxide) levels making dinosaurs bigger? I'm missing some detail to your question. Yes, higher O2 (oxygen) levels are linked to larger animal sizes. But I've never heard of a link to CO2. $\endgroup$
    – Erik
    Commented Nov 11, 2021 at 7:00
  • $\begingroup$ Regarding the second question, what has enabled humans to grow taller is improved nutrition and health, particularly in the first two years of ones life. For example, North Koreans are measurably shorter than are South Koreans, mostly because of extreme poverty in North Korea vs lack thereof in South Korea. $\endgroup$ Commented Nov 12, 2021 at 0:05
  • $\begingroup$ Why Dinosaurs Were So Big discusses four theories and says it is still debated. $\endgroup$ Commented Nov 23, 2021 at 19:18
  • $\begingroup$ Are we sure all dinosaurs are big, as distinct from the ones that make the most headlines? I see some small ones flying around all the time 🐦🦅. $\endgroup$ Commented Dec 24, 2021 at 23:51
  • $\begingroup$ Dinosaurs were around for a long time, oxygen and CO2 levels were both higher and lower than today during their reign. $\endgroup$
    – John
    Commented Dec 25, 2021 at 14:32

3 Answers 3


CO2 is not a factor.

Nutrition is the leading factor for height in human, genetics being the second, you can even correlate local nutrition with average height across time and location for human populations based on nutrition. We even know what receptors are responsible. Nutrition development and the industrial revolution went hand and hand in a few countries, so you can see correlation in those populations but not others.

As for dinosaurs CO2 levels were both higher and lower during the time of large dinosaurs, so there is no reason to believe it is a factor. There are several things contributing to the large size of dinosaurs, most of them physiological. Keep in mind the largest living animal in history is alive today and it habitually holds its breath.


  1. https://www.cambridge.org/core/journals/journal-of-biosocial-science/article/abs/determinants-of-variation-in-adult-body-height/8C3908480AD1B24036A01CE052DE3E03

  2. https://www.nature.com/articles/s41586-021-04088-9.epdf?sharing_token=NmzYDrN3x9C_d6nbFjJH9tRgN0jAjWel9jnR3ZoTv0OCY5eYLa4RUrBjyz-_gxxQ2SzjZ3VMtCKTslN6fKy3owJQ4T4TFYV00ZObOwRID1Et-Om3DIoggbt-AxO3SpIc7McKjG2Kz0mfiL6GCDz7ZN4vjKyNd7AKUfJ64DIi7QczPvp7kDUpRzc3JQQaIAwHsTG310UEH-3pFOdbtUnQ0g%3D%3D&tracking_referrer=www.bbc.com

  • $\begingroup$ There is the thought that holding its breath could indicate some connection to CO2, but generally on the same page as your answer. $\endgroup$ Commented Dec 28, 2021 at 13:46

The reason why humans are growing bigger (excluding any fat jokes) is because bigger humans must eat better, thus are more capable of surviving, and are also much better fighters (better strength/reach). This led to size being considered a favorable trait, leading humans to select larger mates and thus evolve to be larger. Once we started dominating the environment, we all grew larger, but the same instinct persists even today (just ask any guy under 6 feet).

As for the dinosaurs, there was much more oxygen and CO2 in the atmosphere, so plants had more soil to grow in, the earth was hotter so more precipitation occurred, causing massive rainforests, and most importantly there was lots of O2/CO2 to breathe (plants breathe CO2, which gives them the majority of their mass).

Over millions of years this C/O was sequestered underground, and things evolved to be smaller to compete as the earth starved of life-giving Oxygen and Carbon. Now we are putting it back in circulation, reversing this trend. However, this reversal causes changes, and as change is scary it is by default bad.

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    $\begingroup$ O2 and CO2 were both higher and lower than today during the reign of dinosaurs, remember t-rex is closer to you in time than early dinosaurs. $\endgroup$
    – John
    Commented Dec 25, 2021 at 14:34

Climate made the dinosaurs big. Studies of air bubbles trapped in various samples of amber show that the atmosphere of the Cretaceous may have had up to 35 per cent oxygen, compared to only about 21% today. Dinosaurs first appeared during the Triassic when there was lower oxygen so early dinosaurs were small; therefore developed highly efficiency breathing that allowed them to survive. All the while many species became extinct. The Triassic-Jurassic extinction event killed more than half the species, including several mammals and mammal-like reptiles (Synapsids) but allowed new dinosaurs of filling niche. CO2 levels were in the 1000-2000 ppm ratio so it fed a Huge ecosystem of vegetation. CLimate was relatively warm, so much so metabolism was devoted to growth than temperature moderation.

  • $\begingroup$ Dinosaur gigantism has not ben fully understood as yet and agree "Darwin evolution is the key" and i thought increased Co2 levels during this period might be a driving factor for gigantism. that idea also got me thinking that each generation of mankind has also got bigger statistically. yes I agree better nutrition etc but i found it interesting that during the industrial revolution Co2 levels have also increased - making me think about Co2 somehow being a contributing factor to size growth in animals. Not being a scientist, I was looking for a link between Co2 and growth in animals $\endgroup$
    – rhett
    Commented Nov 12, 2021 at 14:49

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