Free Newsletters - Space - Defense - Environment - Energy - Solar - Nuclear
..
. Earth Science News .




ICE WORLD
Ice ages only thanks to feedback
by Staff Writers
Zurich, Switzerland (SPX) Aug 09, 2013


During the last ice age northern regions of America, Europe and Asia were covered under thick ice sheets.

Ice ages and warm periods have alternated fairly regularly in the Earth's history: the Earth's climate cools roughly every 100,000 years, with vast areas of North America, Europe and Asia being buried under thick ice sheets.

Eventually, the pendulum swings back: it gets warmer and the ice masses melt. While geologists and climate physicists found solid evidence of this 100,000-year cycle in glacial moraines, marine sediments and arctic ice, until now they were unable to find a plausible explanation for it.

Using computer simulations, a Japanese, Swiss and American team including Heinz Blatter, an emeritus professor of physical climatology at ETH Zurich, has now managed to demonstrate that the ice-age/warm-period interchange depends heavily on the alternating influence of continental ice sheets and climate.

"If an entire continent is covered in a layer of ice that is 2,000 to 3,000 metres thick, the topography is completely different," says Blatter, explaining this feedback effect.

"This and the different albedo of glacial ice compared to ice-free earth lead to considerable changes in the surface temperature and the air circulation in the atmosphere." Moreover, large-scale glaciation also alters the sea level and therefore the ocean currents, which also affects the climate.

Weak effect with a strong impact
As the scientists from Tokyo University, ETH Zurich and Columbia University demonstrated in their paper published in the journal Nature, these feedback effects between the Earth and the climate occur on top of other known mechanisms.

It has long been clear that the climate is greatly influenced by insolation on long-term time scales. Because the Earth's rotation and its orbit around the sun periodically change slightly, the insolation also varies. If you examine this variation in detail, different overlapping cycles of around 20,000, 40,000 and 100,000 years are recognisable (see box).

Given the fact that the 100,000-year insolation cycle is comparatively weak, scientists could not easily explain the prominent 100,000-year-cycle of the ice ages with this information alone. With the aid of the feedback effects, however, this is now possible.

Simulating the ice and climate
The researchers obtained their results from a comprehensive computer model, where they combined an ice-sheet simulation with an existing climate model, which enabled them to calculate the glaciation of the northern hemisphere for the last 400,000 years.

The model not only takes the astronomical parameter values, ground topography and the physical flow properties of glacial ice into account but also especially the climate and feedback effects. "It's the first time that the glaciation of the entire northern hemisphere has been simulated with a climate model that includes all the major aspects," says Blatter.

Using the model, the researchers were also able to explain why ice ages always begin slowly and end relatively quickly. The ice-age ice masses accumulate over tens of thousands of years and recede within the space of a few thousand years. Now we know why: it is not only the surface temperature and precipitation that determine whether an ice sheet grows or shrinks. Due to the aforementioned feedback effects, its fate also depends on its size.

"The larger the ice sheet, the colder the climate has to be to preserve it," says Blatter. In the case of smaller continental ice sheets that are still forming, periods with a warmer climate are less likely to melt them. It is a different story with a large ice sheet that stretches into lower geographic latitudes: a comparatively brief warm spell of a few thousand years can be enough to cause an ice sheet to melt and herald the end of an ice age.

Box: The Milankovitch cycles
The explanation for the cyclical alternation of ice and warm periods stems from Serbian mathematician Milutin Milankovitch (1879-1958), who calculated the changes in the Earth's orbit and the resulting insolation on Earth, thus becoming the first to describe that the cyclical changes in insolation are the result of an overlapping of a whole series of cycles: the tilt of the Earth's axis fluctuates by around two degrees in a 41,000-year cycle.

Moreover, the Earth's axis gyrates in a cycle of 26,000 years, much like a spinning top. Finally, the Earth's elliptical orbit around the sun changes in a cycle of around 100,000 years in two respects: on the one hand, it changes from a weaker elliptical (circular) form into a stronger one. On the other hand, the axis of this ellipsis turns in the plane of the Earth's orbit.

The spinning of the Earth's axis and the elliptical rotation of the axes cause the day on which the Earth is closest to the sun (perihelion) to migrate through the calendar year in a cycle of around 20,000 years: currently, it is at the beginning of January; in around 10,000 years, however, it will be at the beginning of July.

Based on his calculations, in 1941 Milankovitch postulated that insolation in the summer characterises the ice and warm periods at sixty-five degrees north, a theory that was rejected by the science community during his lifetime. From the 1970s, however, it gradually became clearer that it essentially coincides with the climate archives in marine sediments and ice cores.

Nowadays, Milankovitch's theory is widely accepted. "Milankovitch's idea that insolation determines the ice ages was right in principle," says Blatter. "However, science soon recognised that additional feedback effects in the climate system were necessary to explain ice ages. We are now able to name and identify these effects accurately."

.


Related Links
ETH Zurich
Beyond the Ice Age






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





ICE WORLD
New records for sea ice loss, greenhouse gas in 2012
Washington, District Of Columbia (AFP) Aug 06, 2013
The world lost record amounts of Arctic sea ice in 2012 and spewed out all-time high levels of greenhouse gases by burning fossil fuels, international climate scientists said Tuesday. Last year was among the top 10 on record for global land and surface temperature since modern data collection began, said the State of the Climate report issued annually by researchers in Britain and the United ... read more


ICE WORLD
Protesters blast Russia's undocumented immigrants detention camps

Fukushima operator pumps out toxic groundwater

Legacy of 1986 Chernobyl disaster seen in impact on region's forests

Dark tourism brings light to disaster zones

ICE WORLD
Scientists create light/heat regulating window coating

Bubbles are the new lenses for nanoscale light beams

New insights into the polymer mystique for conducting charges

Toxicologist says NAS panel 'misled the world' when adopting radiation exposure guidelines

ICE WORLD
Tajik President Emomali Rahmon sees country's future in hydropower

Baby corals pass the acid test

Study finds novel worm community affecting methane release in ocean

Tahiti: A very hot biodiversity hot spot in the Pacific

ICE WORLD
Chinese tycoon still hopes to sign Icelandic land deal

Ice ages only thanks to feedback

Greenland ice is melting - also from below

Greenpeace challenges Rosneft vessel in Arctic waters

ICE WORLD
Highest winter losses in recent years for honey bees in Scotland

Nepal steps up poultry cull to combat bird flu

Fonterra executive resigns after milk scare

New Zealand PM to make milk scare apology in China

ICE WORLD
Powerful quake jolts major New Zealand cities

More floods expected in Sudan after 53 die

Russian rescued after days lost on Indonesia volcano

Scientists plan to probe 'plumbing' of Mount St. Helens volcano

ICE WORLD
China's Xi vows stepped up health cooperation with Africa: Xinhua

Keita wins by landslide in Mali presidential vote

Leader of 2012 military coup in Mali promoted

DR Congo colonel defects to M23 rebels with 30 men: army

ICE WORLD
Research effort dates oldest known petroglyphs in North America

Study contradicts concept of 'left brain,' 'right-brain' personalities

Neandertals made the first specialized bone tools in Europe

Scientists have found new evidence to show how early humans migrated into Europe




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement