Carbon dioxide has played a major part in dictating climate over the last 2.7 million years in the tropics and polar regions.
[social_buttons]New research has established that the climate in the tropics has changed in lockstep with spread and retreat of ice sheets in the Northern Hemisphere over the last 2.7 million years. These findings apart to certify the linkage between the recent Ice Ages and changes in tropical oceans, and go further to conclude that carbon dioxide has played the leading role in these changes.
“We think we have the simplest explanation for the link between the Ice Ages and the tropics over that time and the apparent role of carbon dioxide in the intensification of Ice Ages and corresponding changes in the tropics,” said Timothy Herbert of Brown University and the lead author of the paper in Science. Herbert added, “but we don’t know why. The answer lies in the ocean, we’re pretty sure.”
The research team led by Brown University took cores from the ocean floor in four locations in the topical oceans: the Arabian Sea, the South China Sea, the eastern Pacific and the equatorial Atlantic Ocean. The sedimentary cores showed that climate patterns in the tropics mirrored the Ice Age cycles that have taken place over the last 2.7 million years, and confirmed that carbon dioxide played a significant role in determining global climate patterns.
The How, the What and the Why
The researchers looked at the remains of marine organisms that lived in the topical oceans and were able to extract the surface temperature for the oceans for the last 3.5 million years, well before the beginning of the Ice Ages. Tropical oceans make up approximately half the world’s oceans and themselves play a large role in orchestrating the amount of water that makes it into the atmosphere and thus rainfall patterns for the world over.
Geologists found that approximately 2.7 million years ago the tropical ocean surface temperatures dropped by 1 to 3 degrees C (1.8 to 5.4 F) during each corresponding Ice Age. On top of this the tropical cycles also changed when the Ice Age cycles changed from occurring every 41,000 years to every 100,000 years.
“The tropics are reproducing this pattern both in the cooling that accompanies the glaciation in the Northern Hemisphere and the timing of those changes,” Herbert said. “The biggest surprise to us was how similar the patterns looked all across the tropics since about 2.7 million years ago. We didn’t expect such similarity.”
The History of Carbon Dioxide
Carbon dioxide levels for the past 800,000 years have been in the hands of climate scientists for awhile now, thanks to ice cores taken from Antarctica. This period of time span a total of seven Ice Ages and show that carbon dioxide levels fell by 30% during each Ice Age, and that the large majority of the carbon dioxide was absorbed by high latitude oceans such as the North Atlantic and the Southern Ocean.
The new findings suggest that this pattern began 2.7 million years ago and that the amount of carbon dioxide absorbed by the oceans has grown with each successive Ice Age. This comes in step with the fact that Ice Ages have gotten progressively colder over this time, leading to larger ice sheets.
However why carbon dioxide has played such a major role and why it appears to intensify the Ice Ages is entirely unknown to the researchers, nor do they understand why the Ice Age cycles shifted from a 41,000 year cycle to a 100,000 year cycle.
“This research certainly supports the idea of global sensitivity of climate to carbon dioxide as the first order of control on global temperature patterns,” said Candace Major of the National Science Foundation . “It also points to a strong sensitivity of global temperature to the levels of greenhouse gases on very long timescales, and shows that resulting climatic impacts are felt from the tropics to the poles.”
Source: National Science Foundation
Image Source: Ittiz