Ancient Ice Could Help Explain Why Earth's Climate Is Warmingby
Scientists search for ice core that's 1.5 million years old
Conference in Tasmania discussed future Antarctic missions
It could be a key to unlocking a mystery about the world’s climate: a piece of ice so old it formed when ice ages were more frequent, about a million years ago. It may even give scientists insight into what is happening now, as the planet warms. But first they have to find it.
This won’t be as easy as picking up a hammer and knocking a few chips off a block. First, they need an ice core that allows them to see changes in the atmosphere over time. Cores are 4 to 5 inches (10 to 13 centimeters) in diameter and stretch for almost 2 miles (3 kilometers) when all the pieces are laid end to end, said Ed Brook, a professor of earth, ocean and atmospheric sciences at Oregon State University in Corvallis. And the oldest ones retrieved to date are 800,000 years old.
Scientists need cores even more ancient because ice-age cycles changed about a million years ago. So “we really want ice that is 1.5 million years old,” Brook said by telephone from Tasmania. “One million won’t be quite good enough for our goal.”
The search for older cores became a hot topic on the Australian island last week when more than 200 scientists and drilling experts from 22 countries gathered in Hobart at the second open conference of the International Partnerships in Ice Core Sciences. That’s because the ice holds clues about how Earth’s climate has shifted.
The warming of the planet is demonstrated by the longer intervals between ice ages. Before a million years ago, the cycles occurred about every 40,000 years; since then they’ve lengthened to about 100,000 years.
“Why the cycles switched is a fundamental question,” Brook said.
There are many theories -- there may even be a correlation with the Earth’s orbit -- but no one theory holds sway, he said. Understanding the 40,000-year cycle is easier because it matches the planet’s wobble on its axis.
The world’s oldest ice is in Antarctica, and radar surveys have given researchers a good idea of where to look for it, so they won’t be wandering around willy-nilly guessing at where to drill. Ice sheets on the continent migrate, they have spit up meteorites and there are a few spots where the ice on the surface is 1 million years old, Brook said. But surface ice isn’t good enough because it lacks the context of a solid core.
Among the things researchers will be looking for in the older ice is the level of carbon dioxide in the atmosphere 1.5 million years ago and how it changed over time because the amount tracks to the Earth’s temperature, Brook said. When there’s more, the planet is warmer; when there’s less, it cools.
The level of the gas measured in February at the Mauna Loa research station in Hawaii was 404 parts per million, an increase of 3.76 from a year earlier, according to the U.S. Earth System Research Laboratory.
“We have never seen anything above 300 parts per million in the last 800,000 years,” Brook said. “We have never seen any levels remotely like the modern atmosphere.” The jump has all taken place since the start of the Industrial Revolution in the eighteenth century. Australia led an international team in 2013-2014 in Antarctica’s Aurora Basin North collecting ice cores to help study temperature changes during the past 2,000 years.
While scientists haven’t scheduled a mission to find the ancient ice, they discussed in Tasmania how a search might be conducted, as well as new types of drills being developed in France and the U.S., Brook said. Once the work starts, it could take four or five years to complete, partly because it can be done only during the South Pole summer in December-February. Core pieces also come out in sections about 10 to 13 feet long and it takes a long time to haul them up and then send the drill back down.
“There is a lot of ice to get through,” he said.