New Theory Puts Intriguing Spin On Milankovitch Cycles - AFP

[hatrack]

EDIT

William Ruddiman, an environmental scientist with the University of Virginia, provides a novel explanation for the rhythms of the ice ages in a paper just published online in the journal Climate of the Past. Ruddiman found that carbon dioxide is a driver of ice sheets only at the relatively small 23,000-year cycle, but not at the much larger ice-volume cycles at 41,000 years and approximately 100,000 years.

In those cases he found that ice sheets instead control atmospheric carbon dioxide and drive feedbacks that amplify ice growth and melting. He says his carbon dioxide feedback hypothesis explains why the strongest cycles of ice response are not in correspondence with those in the orbital cycles.

Ruddiman concludes (as Milankovitch proposed) that ice sheets are initially driven by the Sun, but then the ice takes control of carbon dioxide changes, producing its own positive feedback (the amplifying effect) at the 41,000-year cycle. This enhancement explains the strength of the 41,000-year ice-sheet changes over the first two-thirds of the ice ages. But over time, as polar climate cooled, summer melting weakened. During the last 0.9 million years, ice sheets have continued to grow at the 41,000-year cycle, but some of the new ice remained in place to help build larger ice sheets.

Ice build-up continued until unusually large solar radiation peaks triggered rapid melting at intervals of 85,000 to 115,000 years. Although solar radiation peaks were the initial trigger for these melting episodes, most of the ice was removed by feedbacks in the climate system, and CO2 feedback was the largest of these. "The origin of the ice-age cycles has been a major mystery in studies of past climates, and some scientists felt the answer must be very complex," Ruddiman said. "Yet this hypothesis is quite simple, requiring only the Sun, the carbon dioxide feedback, and a gradual cooling. The prominent role proposed for carbon dioxide is consistent with its likely effect on future climate."

EDIT

http://www.terradaily.com/reports/New_Co2_Data_Inverts_Current_Ice_Age_Theory_999.html

[phantom power]

1. I wonder...

what this model implies about the expected effects of anthropogenic GHG forcing on the new climate regime we are entering?

[xchrom]

2. it has been theorized that an ice age

precipitated by the warming we are triggering could result.

[Odin2005]

3. I've been actually thinking something similar.

My hypothesis is that Milankovich cycles seem to trigger glacialtion when they are in a configuration that creates warmer then average winters and cooler than average summers in the Taiga belt, warmer winters mean more snowfall and cooler summers mean less melting, causing ice to build up. The reflectivity of the ice triggers runaway cooling. Cooler seas have more nutruents then warmer seas, increasing algae growth. The increased algae growth increases the efficiency of how the oceans absorb CO2 from the air, causing CO2 levels to drop.