Hela planeten lär ha åtnjutit ett tropiskt klimat i några hundratals miljoner år, fram till slutet av eocen, 50 miljoner år sen.
Palms once grew in ice-free Arctic
Palms flourished in the Arctic during a brief sweltering period about 50 million years ago, according to a study that hints at gaps in our understanding of modern climate change.
The Arctic "would have looked very similar to the vegetation we now see in Florida," says Dr Appy Sluijs of Utrecht University in the Netherlands who led the international study. Evidence of palms has never been found so far north before. The scientists, sampling sediments on a ridge on the seabed about 500 kilometres from the North Pole and up to 53.5 million years old, found pollen from ancient palms as well as of conifers, oaks, pecans and other trees.
"The presence of palm pollen implies that coldest month mean temperatures over the Arctic land masses were no less than 8°C", the scientists, based in the Netherlands and Germany, write in the journal Nature Geoscience.
That contradicts computer model simulations, also used to predict future temperatures...
http://www.abc.net.au/science/articles/2009/10/26/2724114.htm
Evidence for middle Eocene Arctic sea ice from diatoms and ice-rafted debris
Oceanic sediments from long cores drilled on the Lomonosov ridge, in the central Arctic1, contain ice-rafted debris (IRD) back to the middle Eocene epoch, prompting recent suggestions that ice appeared in the Arctic about 46 million years (Myr) ago
Together with new information on cosmopolitan diatoms and existing IRD records2, our data strongly suggest a two-phase establishment of sea ice: initial episodic formation in marginal shelf areas approx47.5 Myr ago, followed approx0.5 Myr later by the onset of seasonally paced sea-ice formation in offshore areas of the central Arctic.
http://www.nature.com/nature/journal/v460/n7253/abs/nature08163.html
Tropical climate in the Antarctic:
Palm trees thrived on today's icy coasts 52 million years ago
An international research team has discovered an intense warming phase around 52 million years ago in drill cores obtained from the seafloor near Antarctica.
http://phys.org/news/2012quote-08-tropical-climate-antarctic-palm-trees.html
Ancient Antarctica Was As Warm As Today's Florida And California
Today, Antarctica is consistently one of the coldest places on Earth, featuring annual average land temperatures far below zero degrees Fahrenheit. But it wasn't always that way. Fossilized evidence — including the remains of mighty sauropods — show that plants and animals inhabited the region many millions of years ago. The continent remained warm even after the extinction of the dinosaurs, an era known as the Eocene (40-50 million years ago).
http://io9.com/ancient-antarctica-was-as-warm-as-todays-florida-and-ca-1566063244/+georgedvorsky
Övergången från en tropisk planet - utan årstider - till en omedelbar istid med två globala iskalotter, från södra respektive norra pol när till respektive polcircklar - lär ha anlänt samtidigt och mycket hastigt, som en global kataklysm:
http://www.arkeologiforum.se/forum/index.php/topic,2993.msg69820.html#msg69820Abrupt klimatskifte - från tropiskt till högarktiskt:
http://www.arkeologiforum.se/forum/index.php/topic,2993.msg38859.html#msg38859http://www.arkeologiforum.se/forum/index.php/topic,5804.msg56290.html#msg56290
