Carbon dioxide did not end the last Ice Age

Sep 27, 2007
Carbon dioxide did not end the last Ice Age
Lowell Stott, professor of earth sciences at the University of Southern California, examines a sediment core. Credit: Dietmar Quistorf

Carbon dioxide did not cause the end of the last ice age, a new study in Science suggests, contrary to past inferences from ice core records.

“There has been this continual reference to the correspondence between CO2 and climate change as reflected in ice core records as justification for the role of CO2 in climate change,” said USC geologist Lowell Stott, lead author of the study, slated for advance online publication Sept. 27 in Science Express.

“You can no longer argue that CO2 alone caused the end of the ice ages.”

Deep-sea temperatures warmed about 1,300 years before the tropical surface ocean and well before the rise in atmospheric CO2, the study found. The finding suggests the rise in greenhouse gas was likely a result of warming and may have accelerated the meltdown – but was not its main cause.

The study does not question the fact that CO2 plays a key role in climate.

“I don’t want anyone to leave thinking that this is evidence that CO2 doesn’t affect climate,” Stott cautioned. “It does, but the important point is that CO2 is not the beginning and end of climate change.”

While an increase in atmospheric CO2 and the end of the ice ages occurred at roughly the same time, scientists have debated whether CO2 caused the warming or was released later by an already warming sea.

The best estimate from other studies of when CO2 began to rise is no earlier than 18,000 years ago. Yet this study shows that the deep sea, which reflects oceanic temperature trends, started warming about 19,000 years ago.

“What this means is that a lot of energy went into the ocean long before the rise in atmospheric CO2,” Stott said.

But where did this energy come from" Evidence pointed southward.

Water’s salinity and temperature are properties that can be used to trace its origin – and the warming deep water appeared to come from the Antarctic Ocean, the scientists wrote.

This water then was transported northward over 1,000 years via well-known deep-sea currents, a conclusion supported by carbon-dating evidence.

In addition, the researchers noted that deep-sea temperature increases coincided with the retreat of Antarctic sea ice, both occurring 19,000 years ago, before the northern hemisphere’s ice retreat began.

Finally, Stott and colleagues found a correlation between melting Antarctic sea ice and increased springtime solar radiation over Antarctica, suggesting this might be the energy source.

As the sun pumped in heat, the warming accelerated because of sea-ice albedo feedbacks, in which retreating ice exposes ocean water that reflects less light and absorbs more heat, much like a dark T-shirt on a hot day.

In addition, the authors’ model showed how changed ocean conditions may have been responsible for the release of CO2 from the ocean into the atmosphere, also accelerating the warming.

The link between the sun and ice age cycles is not new. The theory of Milankovitch cycles states that periodic changes in Earth’s orbit cause increased summertime sun radiation in the northern hemisphere, which controls ice size.

However, this study suggests that the pace-keeper of ice sheet growth and retreat lies in the southern hemisphere’s spring rather than the northern hemisphere’s summer.

The conclusions also underscore the importance of regional climate dynamics, Stott said. “Here is an example of how a regional climate response translated into a global climate change,” he explained.

Stott and colleagues arrived at their results by studying a unique sediment core from the western Pacific composed of fossilized surface-dwelling (planktonic) and bottom-dwelling (benthic) organisms.

These organisms – foraminifera – incorporate different isotopes of oxygen from ocean water into their calcite shells, depending on the temperature. By measuring the change in these isotopes in shells of different ages, it is possible to reconstruct how the deep and surface ocean temperatures changed through time.

If CO2 caused the warming, one would expect surface temperatures to increase before deep-sea temperatures, since the heat slowly would spread from top to bottom. Instead, carbon-dating showed that the water used by the bottom-dwelling organisms began warming about 1,300 years before the water used by surface-dwelling ones, suggesting that the warming spread bottom-up instead.

“The climate dynamic is much more complex than simply saying that CO2 rises and the temperature warms,” Stott said. The complexities “have to be understood in order to appreciate how the climate system has changed in the past and how it will change in the future.”

Source: University of Southern California

Explore further: Africa, from a CATS point of view

add to favorites email to friend print save as pdf

Related Stories

Mars is the next step for humanity – we must take it

Feb 09, 2015

Elon Musk has built a US$12 billion company in an endeavour to pave the way to Mars for humanity. He insists that Mars is a "long-term insurance policy" for "the light of consciousness" in the face of cli ...

Seafloor volcano pulses may alter climate

Feb 05, 2015

Vast ranges of volcanoes hidden under the oceans are presumed by scientists to be the gentle giants of the planet, oozing lava at slow, steady rates along mid-ocean ridges. But a new study shows that they ...

Warming leads to more run-ins with polar bears

Dec 19, 2014

Word spread quickly: a polar bear, then two, were spotted near this remote Inuit village on the shores of Hudson Bay, about 1,800 kilometers (1,120 miles) north of Montreal.

Recommended for you

Antarctica's retreating ice may re-shape Earth

5 hours ago

(AP)—From the ground in this extreme northern part of Antarctica, spectacularly white and blinding ice seems to extend forever. What can't be seen is the battle raging underfoot to re-shape Earth.

The sun has more impact on the climate in cool periods

6 hours ago

The activity of the Sun is an important factor in the complex interaction that controls our climate. New research now shows that the impact of the Sun is not constant over time, but has greater significance ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

jyro
1 / 5 (1) Jan 20, 2008
"warming spread bottom-up instead."
volcanic activity has just been found under antiartica in another article. http://www.physor...297.html
DGBEACH
1 / 5 (1) Jan 24, 2008
Bingo! And I'm quite certain that they'll find alot more.
Ragtime
1 / 5 (1) Jan 30, 2008
It's highly improbable, the Antarctica glaciers are melting just due volcanic activity, because A) the ice melts around whole continent (http://www.eureka...web.jpg) B) most of other glaciers (including those in Tibet and others) are melting too...

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.