Really, really OLD climate change…

Rebecca Anderson


February 2, 2010

ace students image

Check it out — here’s a question I’ve gotten from a lot of people before:  Wasn’t it a lot hotter back when the dinosaurs were around?

And what that can often lead someone to ask next:  Doesn’t that mean climate change today is no big deal?!

Here’s the answer: YES, it was a lot hotter back when dinosaurs were around.  Here’s their world:

And here’s what CO2 and temperature looked like:

Grey line = CO2
Blue line = temperature
Time goes forward left to right (today is at far right)

The orange section (the Mesozoic) is the Dinosaur Age.  Temps were around 9-18ºF warmer than today and CO2 was between 1200-2000 ppm! (That’s about 3-5 times today’s CO2 level of 389 ppm.)

But… does it mean that climate change today is “no big deal?”

If you go even further back in time, 500-600 million years ago, CO2 was even higher – maybe even as high as 7000 ppm!  (But keep an eye on the gray area around that line.  That’s the uncertainty – could have been more like 3000 ppm.)

And here’s what the globe itself looked like back then:

Pretty different, huh? Doesn’t look much like our world today.  Which, I think, is the real point!

The world was so different back then, that doesn’t make much sense to compare it to today. Strange continents like Gondwana, humongous dinosaurs, and a hot climate to match.

Back then, dinosaurs and their world were accustomed to the climate they had.  Just like we people and the world around us are accustomed to the climate we have today.  They’re just so completely different, that it’s like comparing apples to oranges to compare these two worlds!

The one thing the climate from the dinosaurs can tell us, though, is that Earth, with or without climate change, is going to be just fine.  It can deal with all sorts of changes.

The real question is whether we can…

To dork out and find out how we know what CO2 and temperature were like way back then, read below!

How can people ever know this stuff, if it happened SO long ago??

I have to say, it is pretty amazing that we have figured out how to look back in time and imagine what the world was like back then.  But “imagine” or better yet, “estimate” is the key – it’s really hard to get precise numbers on what temperature or CO2 was hundreds of millions of years ago.  (Maybe it was 7000 ppm…?  Or maybe it was closer to 2000 ppm…)

That being said, here’s how scientists come up with these numbers:


This is done with models that include the whole big carbon cycle and estimate how much carbon was in rocks, plants, ocean, soil and atmosphere and the fluxes between them.  This is based on things like the position of the continents, what mountains were being built and eroded, how many plants were on land and then compared to today’s numbers.  Lots of wiggle room here!


General climate can be recreated by mapping out ancient deposits such as coal, palm trees, alligator fossils (All found in a warm and wet climate.) or desert sands (dry), or deposits from a glacier (cold).  These plant and animals fossils and the type of rocks all give information on what the climate was like when they were formed.  Here’s a cool website that gives maps of these deposits (as well as positions of the continents) all through geologic time.

More exact information on temperature can come from leaf fossils – particularly the ratio between leaves with smooth edges and those with “toothed” edges.  It turns out that the ratio of leaves with smooth vs. toothed edges gives a really good estimation of temperature.  This can be matched with real temperatures today and then projected back to come up with temperatures in the past.

It turns out that’s it’s not well understood exactly why leaf edges and temperature are so well-correlated.  The best explanation I came across is that more teeth are better in colder climates because they allow for more photosynthesis and transpiration early in the growing season.  Something about having more area along the margins for these reactions to take place… Interesting that there’s a whole science based on using this correlation to predict past temperatures, but no one’s really sure why it works so well.

For more info on this, read here.

Reb Anderson

Rebecca Anderson

Director of Education

Rebecca is ACE’s Director of Education. She came to ACE in its inception in 2008. Rebecca develops ACE's science content, manages ACE’s online climate education resource, Our Climate Our Future, and ACE's teacher network and works with schools in the Reno-Tahoe area. Prior to ACE, she did paleoclimate research in the Arctic and Antarctica.

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