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Climate Change Future Suggested by Looking Back 4 Million Years [Video]

The views expressed are those of the author and are not necessarily those of Scientific American.


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The last time the Earth enjoyed greenhouse gas levels like those of today was roughly 4 million years ago, during an era known as the Pliocene. The extra heat of average temperatures as much as 4 degrees Celsius warmer turned the tropical oceans into a nice warm pool of bathwater, as noted by new research published in Nature on April 4.

By analyzing the ratio of magnesium and calcium in the shells of microscopic animals found in long cores of mud from the deep ocean, the researchers confirmed this massive oceanic warm pool. At about 28 degrees C, the surface sea temperatures were not much warmer than today’s tropical oceans, but these warm waters covered much more of the global ocean surface.

Although such warm water might sound nice, such warm pools of water have profound weather effects; think of El Nino events in the present and the torrential rains this climate pattern creates in some areas. And a Pliocene-like reduction in temperature differences between polar and mid-latitude regions would have similarly profound effects on everything from the number of tropical cyclones in the Pacific Ocean to which areas are covered by desert in Africa, Australia and North America.

The warm water conditions of the Pliocene held steady for more than one million years. In fact, scientists do not understand completely what caused these conditions to change, though a decrease in atmospheric greenhouse gas concentrations of roughly 100 parts-per-million, to around 300 ppm probably helped.

In the last few hundred years, that’s about how much humanity has raised greenhouse gas concentrations through the burning of fossil fuels, the cutting down of forests and other activities. Today’s concentration is about 394 ppm.

Although we cannot be sure that a similarly sized decrease in greenhouse gas concentrations ushered in the present era of ice ages singlehandedly, we can be sure that greenhouse gases change climate. And, unless we want to go back to the Pliocene when our distant ancestors split from chimpanzees, we might want to temper climate change by emitting less CO2, methane and other greenhouse gases.

David Biello About the Author: David Biello is the associate editor for environment and energy at Scientific American. Follow on Twitter @dbiello.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. zstansfi 2:29 pm 04/3/2013

    “Although we cannot be sure that a similarly sized decrease in greenhouse gas concentrations ushered in the present era of ice ages singlehandedly, we can be sure that greenhouse gases change climate… unless we want to go back to the Pliocene… we might want to temper climate change by emitting less CO2, methane and other greenhouse gases.”

    If greenhouse gas levels are as high now as they were in the Pliocene, and temperatures are currently much lower, then we cannot infer a direct relationship between Pliocene greenhouse gas levels and Pliocene temperatures. So the conclusion of this piece makes little sense: just because green house gases affect climate doesn’t imply that we are headed back to the Pliocene.

    Playing fast and loose with your language here SciAm

    Link to this
  2. 2. Trafalgar 3:18 pm 04/3/2013

    zstansfi:

    The oceans are not done heating up. :V
    Remember that we’re releasing this CO2 extremely rapidly, compared to how slowly it was released in all the historical records prior to the human industrial age.

    Link to this
  3. 3. gizmowiz 3:32 pm 04/3/2013

    I hope for severe global warming. That’s the only way to get a more tropical climate in Colorado. I’m all for it!

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  4. 4. tsunami78 3:49 pm 04/3/2013

    @zstansfi – You cannot compare the time scales of modern temperatures to Pliocene temperature yet. We are measuring temperatures in decades, the Pliocene period spanned over 1 million years. Give it a few millennium before you decide your .00001% sample set is applicable. Even then you’ll still be dealing with data sets orders of magnitude smaller, and it will take many more decades or even centuries before we see the full effect of the greenhouse gasses emitted thus far.

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  5. 5. sault 4:18 pm 04/3/2013

    giz, Colorado is more likely to turn into a dust bowl than have a “tropical” climate. Just look a few hundred miles to the south to see generally what the future holds in a warming climate.

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  6. 6. ndoris 5:33 pm 04/3/2013

    hah, I don’t think looking at geologic timescales really brings home how earth-shatteringly catastrophic global warming will be. I mean we are almost to 400 ppm! Who cares if those levels have been well over 1000ppm over the last 600 million years? The truth of the matter is that CO2 levels are nearly as low as they have ever been in earth’s history, and this low CO2 state is not the norm.

    Also, you really can’t say the speed of this CO2 increase is unprecedented in Earth’s history. We don’t have the resolution to really tell how quickly CO2 levels changed (at least not at human timescale resolution) through the vast majority of earth’s history.

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  7. 7. Frishy 10:50 pm 04/3/2013

    If we “solved” human energy demands versus greenhouse gas pollution we’d still have an overpopulation problem.

    And, the mass extinction event we’re facilitating has huge potential for totally interrupting life as we know it on planet Earth.

    Consider this only:
    We now number 7,000,000,000 and more.

    We’ll be that number on the planet, even given wonderful “demographic transitions” FOR THE NEXT 100+ YEARS.

    Name one trajectory of human activity that is sustainable in an ecological sense?

    The insects will be running scared.

    In some people’s minds, it is already immoral to have children.

    Not having children is a great choice.
    www vhemt.org

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  8. 8. reverseentropy 11:12 pm 04/3/2013

    zstansfi: the only mistake of SciAm here is one often made by anyone with a knowledge of a particular subject area: they take it for granted that certain things are not common sense to the laymen. Climate forcings, or impetuses that change the climate, such as the manmade one we are imposing now by significantly increasing greenhouse gases at a rapid rate, may be much faster than the actual response time. But all systems have a response time that generally take millennia and it is that which ends up recorded in the time record. We have only experiencing an ever increasing ghg level for the past 100 years, it’s not enough time for the system to respond. What does that mean? It means that the high temperature level of the pliocine is the one that occurred after the Earth fully responded to the forcing imposed by similar ghg levels as today. In other words, it’s what Earth will experience if we just wait long enough, ie. in our children’s(for me, I’m extremely young)/grandchildren’s lifetimes.

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  9. 9. Carlyle 3:58 am 04/4/2013

    An oft repeated fallacy is that if you reduce the temperature difference between the polar regions & equatorial regions, you will get more & more severe storms. in fact the exact opposite is the case. The greater the temperature difference the greater the power generated, regardless of the type of heat engine, be it the climate or a jet engine. It is called the Carnot cycle.

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  10. 10. MRC06405 9:06 am 04/5/2013

    I found the video extremely muddled. Lets look at the basics.

    We have increased the CO2 concentration the last 150 by an amount that took many thousands of years in geologic history. This is a real shock to the planet.

    Simple physics tells us the CO2 concentrations we have created produce significant changes to the heat balance of the world, and has in the past been a driver for climate change.

    We have subjected the worlds climate to significant and unprecedented shock. We can prepare for significant unprecedented impacts or we can stick our heads in the sand. Which path we will follow is a political decision

    Climate change and what to do about it is an issue the ignorant majority in the Senate and House don’t seem to understand. That is the scariest part.

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  11. 11. jwake05 12:00 pm 04/5/2013

    least we forget that thermodynamics play a part in this as well. Doubling the CO2 concentrations to near 700 ppm amounts to an increase of just 0.2 degC. In addition, you guys at SciAm seem to forget about the North Atlantic Decadel oscillation. Check your history…80 years ago the US was very hot (eg: Dust bowl) and a cat 3 hurricaine hit new York. (so much for unprecedented storms reported by news). In 40 years you’ll be reporting how cold it is and we face the threat of an ice age as reported in the mid 70′s by Time magazine. Cycles guys…cycles

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  12. 12. chrissuard 1:30 am 04/10/2013

    I am sorry to see the disrespectful tone which proponents of a consensus view of science use against those who disagree with their theory. The shrill tone and ad hominem attacks have no place in real science. Stick to your arguments and show us why your conclusions make more sense. A realistic objectivity and thorough analysis of all data will produce a better response than any rush to correct possible dire results at great expense.

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  13. 13. El Dono 9:50 pm 04/10/2013

    We need to realize this is nothing more than conjecture. For example, during an El Nino, the tropical Eastern Pacific gets much warmer. This does not happen by “becoming warmer”. It happens by the warm pool that is usually in the Western Pacific “slumping” back to the Eastern Pacific due to the slacking of the Tropical Easterlies. This wind keeps the warm pool in the west north of Australia and with a surface elevation about 2 feet higher than over the Eastern Pacific. The wind slackens, and the warm water slumps back east. When this occurs the difference in temperature between the air over the Eastern Pacific and over the Polar regions increases. The ocean gets warmer…the Poles remain the same. The increased difference “pulls” the Jet Stream further south and strengthens it. End result…California has very wet, cooler than normal winters. El Nino.
    Global warming, on the other hand, primarily increases the temperatures over the polar regions. This would decrease the temperature difference between the tropical regions and the polar regions. The result would be a weaker Jet Stream that would be further to the north than today. This is almost the opposite of an El Nino.

    And, don’t forget, and increase in CO2 in the atmosphere has a great positive impact on the planetary biosphere.

    I think the current discussion of Global Warming and the human impact on it is a great example of Bad Science. It is also a great diversion away from the more important problems of other far worse emissions into the atmosphere such as sulfur from power plants. We need to get our heads out of the sand and look at all this in a proper scientific manner.

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  14. 14. zstansfi 3:27 pm 07/12/2013

    @ three comments:

    Fair point. If we use the “average Pliocene temperatures” across an entire age, and compare them to the “average temperatures” over a similar length of time (current and future period), then there is still loads of time for our temperatures to catch up to the average.

    Score one for the author.

    Link to this

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