Skip to main content

When crocodiles roamed the poles

By Mark Pagani, Special to CNN
updated 1:20 PM EDT, Tue June 25, 2013
CNN's Frederick Pleitgen traveled to Greenland with a team of climate scientists who are gathering up-to-date data on the island's vast ice sheet to guage how much and how fast it is melting. As one scientist on the mission says: "This is where the rubber meets the road when it comes to studying climate change." CNN's Frederick Pleitgen traveled to Greenland with a team of climate scientists who are gathering up-to-date data on the island's vast ice sheet to guage how much and how fast it is melting. As one scientist on the mission says: "This is where the rubber meets the road when it comes to studying climate change."
HIDE CAPTION
Greenland: Secrets in the Ice
<<
<
1
2
3
4
5
6
7
8
9
10
11
>
>>
STORY HIGHLIGHTS
  • Mark Pagani: CO2 level in atmosphere portends major changes
  • He says research on the past shows the dangers of high levels of greenhouse gases
  • Today's CO2 levels comparable to time when Greenland had little ice, sea was 65 feet higher
  • Pagani: With more CO2, we hark back to when crocodiles and sub-tropical plants inhabited the poles

Editor's note: Mark Pagani is a professor in the Department of Geology and Geophysics at Yale and director of the Yale Climate and Energy Institute.

(CNN) -- Most of us can appreciate that the world is an ancient place and that a lot has changed in the almost 4.6 billion years since it took its shape.

It's not easy to have a feel for the amount of time that has passed, but grappling with deep time helps you understand why an atmospheric carbon dioxide concentration (CO2) of 400 parts per million (ppm) is meaningful.

Deep time is geologic time and the scale needed to fathom the evolution of life, mountains, oceans, and Earth's climate.

Climate, one must note, is not weather. Weather is experienced day to day. Climate occurs on longer scales: the tropics are hot and wet; Antarctica is freezing and miserable.

If you wanted to consider the climate of the whole planet you would need to consider its temperature. Without greenhouse gases the world would be a much colder (~30˚C or 65˚F colder) and lonelier place.

Skeptical environmentalist & a scientist
Glaciers melting around the world
Global warming brings on more pollen

All of us have felt the greenhouse effect because water vapor is a greenhouse gas and when summer humidity is high you just can't get any relief. Even at night when the sun is gone, water vapor keeps radiating the heat. Dry desert nights are just the opposite, with temperatures falling fast when the lights go out.

CO2 works the same way as water vapor. More CO2 radiates more heat, increasing the average temperature and turning more surface water into water vapor, which radiates more heat. This is an example of a positive feedback and positive feedbacks push temperatures higher than CO2 alone.

Global climate models tell us that doubling CO2 will lead to a global temperature increase between 2 and 4.5˚C (that's 3.6 to 8˚F), reflecting the climate sensitivity to CO2.

Since 400 ppm marks a 43% man-made CO2 rise (from 280 to 400 ppm in ~200 years), we should soon expect 1˚C (1.8˚F) of warming if low-end estimates of climate sensitivity are correct.

Well, a 1˚C (1.8˚F) global temperature increase is close to what we've already measured, but full warming is not expressed overnight or even over decades because the world is mostly a cold ocean that helps ameliorate immediate warming by taking up heat.

Also, man-made atmospheric particles could be masking up to 0.5˚C (0.9˚F) of the potential temperature rise. With this in mind, we expect temperatures to further increase even if CO2 stopped rising, and so it's not alarming to assume that climate sensitivity might be higher than the belief of an optimist.

So, how much CO2 is too much? This is where deep time helps frame our expectations of things to come. First, as far as we know, the rate of our CO2 rise is unprecedented in Earth history.

That's saying something, isn't it? During the well-known glacial-interglacial cycles that occurred in the last one million years, CO2 fell to a cold 180 ppm and back up to 280 ppm.

Those changes took thousands to tens-of-thousand of years, so, 400 ppm not only breaks that record, but it breaks it in record time. When climate scientists say that they are worried about 2 to 5˚C (3.6 -- 9˚F) of global warming, keep in mind that global temperature was, at most, 4 to 5˚C (7.2 -- 9˚F) colder during the last ice age when miles of ice piled up on land and pushed enough dirt to make Long Island.

Small numbers, like 4˚C (7.2˚F) of cooling can mean big things, but that's not where we're headed any more. Now we're headed deeper into the past. At best, CO2 levels are similar to 4 million years ago when global temperatures were 3 to 4˚C (5.4 -- 7.2˚F) higher, and there was little-to-no ice on Greenland, and sea levels were at least ~~20 m (65 feet) higher.

Even if we were to resolve to live in the warmth of the relatively recent past, the nagging problem is that atmospheric CO2 levels will continue to rise and stay around for a very, very long time without intentional intervention and/or a surprising technological innovation. CO2 is increasing at about 3 ppm per year and we will be arriving at a minimum CO2 concentration of 700 ppm by year 2100 if nothing is done.

In terms of our history, that places us somewhere beyond 35 million years ago when there was no permanent ice on the poles and sea level was over 200 feet higher than today. Add more CO2 to the mix and we step back towards peak temperatures 50 million years ago when CO2 is estimated to have been about 1000 ppm and sub-tropical plants and crocodiles inhabited the poles.

There's lots of uncertainty when trying to reconstruct ancient climates and the factors that produced them, but having some sense of the past informs us in the same way as knowing the history of our grandparents and the potential inheritance of future ailments.

Deep time tells us that we are traveling forward to a world that is an extraordinary warm and different place, something Earth scientists refer to as a greenhouse world. Hopefully we will resist the urge to take the trip, but if we don't, I know a few people who would be happy to study how it all went down.

Follow us on Twitter @CNNOpinion.

Join us on Facebook/CNNOpinion.

The opinions expressed in this commentary are solely those of Mark Pagani.

ADVERTISEMENT
Part of complete coverage on
updated 12:41 PM EDT, Wed April 23, 2014
Robert Hickey says most new housing development is high-end, catering to high-earners.
updated 9:17 AM EDT, Wed April 23, 2014
Alexander Motyl says as Russian President Putin snarled at Ukraine, his foreign minister was signing a conciliatory accord with the West. Whatever the game, the accord is a major stand down by Russia
updated 8:29 AM EDT, Wed April 23, 2014
Les Abend says at every turn, the stowaway teen defied the odds of discovery and survival. What pilot would have thought to look for a person in the wheel well?
updated 6:47 PM EDT, Tue April 22, 2014
Q & A with artist Rachel Sussman on her new book of photographs, "The Oldest Living Things in the World."
updated 3:58 PM EDT, Tue April 22, 2014
Martin Blaser says the overuse of antibiotics threatens to deplete our bodies of "good" microbes, leaving us vulnerable to an unstoppable plague--an "antibiotic winter"
updated 1:37 PM EDT, Tue April 22, 2014
John Sutter asks: Is it possible to eat meat in modern-day America and consider yourself an environmentalist without being a hypocrite?
updated 11:38 AM EDT, Tue April 22, 2014
Sally Kohn notes that Meb Keflezighi rightly was called an American after he won the Boston Marathon, but his status in the U.S. once was questioned
updated 8:56 AM EDT, Tue April 22, 2014
Denis Hayes and Scott Denman say on this Earth Day, the dawn of the Solar Age is already upon us and the Atomic Age of nuclear power is in decline
updated 4:36 PM EDT, Mon April 21, 2014
Retired Coast Guard officer James Loy says a ship captain bears huge responsibility.
updated 1:08 PM EDT, Mon April 21, 2014
Peter Bergen says the latest strikes are part of an aggressive U.S. effort to target militants, including a bomb maker
updated 9:45 AM EDT, Mon April 21, 2014
Cynthia Lummis and Peter Welch say 16 agencies carry out national intelligence, and their budgets are top secret. We need to know how they are spending our money.
updated 8:35 AM EDT, Mon April 21, 2014
Julian Zelizer says President Obama knows more than anyone that he has much at stake in the midterm elections.
updated 8:55 AM EDT, Tue April 22, 2014
Eric Sanderson says if you really want to strike a blow for the environment--and your health--this Earth Day, work to get cars out of cities and create transportation alternatives
updated 10:08 AM EDT, Mon April 21, 2014
Bruce Barcott looks at the dramatic differences in marijuana laws in Colorado and Louisiana
updated 4:47 PM EDT, Fri April 18, 2014
Jim Bell says NASA's latest discovery supports the notion that habitable worlds are probably common in the galaxy.
updated 2:17 PM EDT, Fri April 18, 2014
Jay Parini says even the Gospels skip the actual Resurrection and are sketchy on the appearances that followed.
updated 1:52 PM EDT, Fri April 18, 2014
Graham Allison says if an unchecked and emboldened Russia foments conflict in a nation like Latvia, a NATO member, the West would have to defend it.
updated 9:11 AM EDT, Fri April 18, 2014
John Sutter: Bad news, guys -- the pangolin we adopted is missing.
updated 2:25 PM EDT, Mon April 21, 2014
Ben Wildavsky says we need a better way to determine whether colleges are turning out graduates with superior education and abilities.
updated 6:26 AM EDT, Fri April 18, 2014
Charles Maclin, program manager working on the search and recovery of Malaysia Flight 370, explains how it works.
updated 8:50 AM EDT, Fri April 18, 2014
Jill Koyama says Michael Bloomberg is right to tackle gun violence, but we need to go beyond piecemeal state legislation.
updated 2:45 PM EDT, Thu April 17, 2014
Michael Bloomberg and Shannon Watts say Americans are ready for sensible gun laws, but politicians are cowed by the NRA. Everytown for Gun Safety will prove the NRA is not that powerful.
ADVERTISEMENT
ADVERTISEMENT
ADVERTISEMENT
ADVERTISEMENT