New facets of the global climate that may help explain how the ice ages took place and what will happen as Earth continues to warm have been uncovered by researchers.
In a pair of new studies, researchers reconstructed sea surface temperatures in the distant past to study how they have changed over time. Both studies point to links between the seemingly un-connected near-polar regions and equatorial waters.
In one study, researchers used ancient marine sediments to measure ocean temperatures at four widely separated points along the equator at times as far back as 3.5 million years ago. Since then, Earth has gone through 45 ice ages.
"What we found is that every time there was a global cooling at the high latitudes [during] an ice age, each of our tropical sites would cool significantly" and by about the same amount, said study researcher Timothy Herbert of Brown University.
For that to be the case, Herbert said, something must have connected the high and low latitudes. He and his colleagues argue that the link was likely carbon dioxide in the atmosphere. In the past few ice ages, carbon dioxide levels have fallen, which could have driven a cooling over the entire planet.
In the second study, a group of European researchers measured the temperatures of north Atlantic and south Pacific waters close to the poles back to 3.6 million years ago, when Earth was going through a warm phase. They found that the cooling of these areas caused by an expansion of cold water away from the poles was associated with the emergence of a region of shallow cold water called the Pacific equatorial cold tongue.
They wrote that as the globe warms at high latitudes, the cold tongue might disappear, leading to conditions similar to a permanent El Nino event. During an El Nino event, the cold water that usually wells up off the west coast of South America recedes and is replaced with warm water, resulting in changes to weather patterns elsewhere around the globe.
Both findings could actually be pointing to the oceans as the link between poles and equator, said S. George Philander of Princeton University, who wrote a commentary on the two studies, which appear in Science. Tropical land and ocean temperatures differed significantly from each other during the ice ages, indicating that something else besides atmospheric carbon dioxide was playing a role, he said.
Teasing apart the contributions of ocean and atmosphere to the ice ages is important, Philander said. "If we can figure out how much CO2 is responsible it will help a lot in understanding future global warming."