By Lewis Page, The Register

Macdonald says that glaciers on land at the Equator means solid pack ice at sea in the tropics, too.

“Climate modeling has long predicted that if sea ice were ever to develop within 30 degrees latitude of the equator, the whole ocean would rapidly freeze over,” he says. “So our result implies quite strongly that ice would have been found at all latitudes during the Sturtian glaciation.”

Enlarged here.

Even on Snowball Earth, however, it’s thought that there must have been “refugia” where liquid surface water and at least occasional sunlight remained, as proto-animal life above the bacterial level is believed to have arisen and survived at around the time of the first, Sturtian snowballing. Macdonald considers that the big freeze may actually have stimulated early, primitive life to get its act together and begin the long process which has led to the present-day biosphere.

“The fossil record suggests that all of the major eukaryotic [other than microbial] groups, with the possible exception of animals, existed before the Sturtian glaciation,” says the prof. “The questions that arise from this are: If a snowball Earth existed, how did these eukaryotes survive? Did the Sturtian snowball Earth stimulate evolution and the origin of animals?”

“From an evolutionary perspective,” he adds, “it’s not always a bad thing for life on Earth to face severe stress.”

Macdonald and his colleagues aren’t sure what triggered the Sturtian snowball effect, but note that a lot of lava came to the earth’s surface at around that point, suggesting that the big chill could have been kicked off by volcanic dust darkening the skies.

The Harvard team publish their results this week in hefty boffinry mag Science.

Global warming may be normal at this point in glacial cycle
By Lewis Page, The Register

German and Russian scientists say that it is normal for an interglacial period like the one just ending to finish with one or more brief - in geological terms - spells of warming before the glaciers return.

According to boffins based at the Helmholtz-Zentrum für Umweltforschung (UFZ) and at the Russian Academy of Sciences, in the Earth’s history thus far there have been eras where the glaciers covered much of Europe, lasting about 100,000 years. These are separated by warmer interglacial periods lasting around 10,000 years. We are currently at the end of an interglacial era called the Holocene.

The scientists, looking into the last interglacial period - the Eemian - which ended around 115,000 years ago, say they have found that that it ended with “significant climate fluctuations” before the rule of the glaciers returned.

The scientists got their results by examining ancient lake sediments exposed by modern open-cast mining in Russia and Germany. They believe that the end of the Eemian interglacial epoch saw “possibly at least two” warming events, according to a statement issued by the UFZ.

“The observed instability with the proven occurrence of short warming events during the transition from the last interglacial to the last glacial epoch could be, when viewed carefully, a general, naturally occurring characteristic of such transition phases,” concludes UFZ boffin Dr Tatjana Boettger.

Boettger and her fellow researchers say that the Eemian ice-free period wound up with sudden - in these terms - warming spells and serious changes in vegetation. Then the glaciers surged south, at their high tide 21,000 years ago reaching as far as Berlin.

This Weichselian Glacial era ended around 15,000 years ago, leading to the conditions which have been seen for all of human history with the ice caps confined to the polar regions. The UFZ says that this Holocene era reached its “highest point so far around 6000 years ago” and that we might now expect to see sudden warmings and changes as at the end of the Eemian - followed by a slow descent into another freezing glacial era.

“Detailed studies of these phenomena are important for understanding the current controversial discussed climate trend so that we can assess the human contribution to climate change with more certainty,” comments Dr Frank W Junge of the Sächsischen Akademie der Wissenschaften (Saxon Academy of Sciences, SAW) in Leipzig.

The profs’ paper Instability of climate and vegetation dynamics in Central and Eastern Europe during the final stage of the Last Interglacial (Eemian, Mikulino) and Early Glaciation can be read here (subscriber link).