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The big picture: 65 million years of temperature swings
JoNova ^ | February 18th, 2010 | Joanne

Posted on 02/26/2010 10:45:29 PM PST by Ernest_at_the_Beach


Greenland Temperatures - last 10,000 years

Greenland Temperatures - last 10,000 years. Are we headed for an ice age? (See below for more detail.)

David Lappi is a geologist from Alaska who has sent in a set of beautiful graphs–including an especially prosaic one of the last 10,000 years in Greenland–that he put together himself (and which I’ve copied here at the top).

If you wonder where today’s temperature fits in with the grand scheme of time on Earth since the dinosaurs were wiped out, here’s the history. We start with the whole 65 million years, then zoom in, and zoom in again to the last 12,000 from both ends of the world. What’s obvious is that in terms of homo sapiens history, things are warm now (because we’re not in an ice age). But, in terms of homo sapiens civilization, things are cooler than usual, and appear to be cooling.

Then again, since T-rex & Co. vanished, it’s been one long slide down the thermometer, and our current “record heatwave” is far cooler than normal. The dinosaurs would have scoffed at us: “What? You think this is warm?”

With so much volatility in the graphs, anyone could play “pick a trend” and depending on which dot you start from, you can get any trend you want. — Jo


GUEST POST by David Lappi

65 million years of cooling

The following two graphs (images created by Robert A. Rohde / Global Warming Art) are climate records based on oxygen isotope thermometry of deep-ocean sediment cores from many parts of the world [1]).  On both graphs, colder temperatures are toward the bottom, and warmer temperatures toward the top. Significant temperature events on the first graph show the start and end of Antarctic glaciation 34 and 25 million years ago, and the resumption of glaciation about 13 million years ago. It is obvious from the graph that we are now living in the coldest period of Earth’s history for the last 65 million years. Despite recent rumors of global warming, we are actually in a deep freeze.

65 million years of global temperatures

65 million years of global temperatures Image created by Robert A. Rohde / Global Warming Art

Image created by Robert A. Rohde / Global Warming Art

5 million years of cooling

The last five million years of climate change is shown in the next graph based on work by  Lisiecki and Raymo  in 2005 [2] . It shows our planet has a dynamic temperature history, and over the last three million years, we have had a continuous series of ice ages (now about 90,000 years each) and interglacial warm periods (about 10,000 years each). There are 13 (count ‘em) ice ages on a 100,000 year cycle (from 1.25 million years ago to the present, and 33 ice ages on a 41,000 year cycle (between 2.6 million and 1.25 million years ago). Since Earth is on a multi-million-year cooling trend, we are currently lucky to be living during an interglacial warm period, but we are at the end of our normal 10,000 year warm interglacial period.

65 million years of global temperatures

65 million years of global temperatures

Image created by Robert A. Rohde / Global Warming Art

The last 10 millenia

To detail the more recent prehistoric temperature changes, scientists have drilled a number of ice cores in ancient glacial ice.  Paleotemperature data from ice cores is considered to be our best continuous record of temperatures on the planet for time-spans up to about 420,000 years ago.  Annual layering in undisturbed glacial ice allows us to precisely date the layers, and gives us a very accurate time and temperature sequence. The US government drilled the GISP 2  ice core in central Greenland over a five-year period, and the data is available here.  This data set is useful because it reports temperatures (measured by oxygen isotopes) every 10 to 60 years — a good resolution.  I sometimes see graphs of ice-core temperatures or greenhouse gasses that are based on measurements every 1,000 or 2,000 years: not nearly of close enough together for comparisons that are useful today. I downloaded and graphed these data in Excel myself. The following graphs have a time scale in years Before Present (BP).

The next graph of temperature from the ice core for the last 10,000 years (the current interglacial period) shows that Greenland is now colder than for most of that period (vertical scale in degrees C below zero). We c