The big picture: 65 million years of temperature swings
August 29, 2013
by Joanne Nova
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
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 ). 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.
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  . 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 multimillion-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.