Milankovitch back to 1974

10/07/2010

Climate Change: News and Comments

Milankovitch and the ice ages – welcome back to 1974

Why am I chuckling? After he’d had misgivings about the Milankovitch theory of the comings and goings of the ice sheets, Luboš Motl now says in The Reference Frame:

… the Milankovitch orbital cycles do describe the glaciation cycles in the recent 1 million years very well and nothing else – CO2 or random internal variations – is needed to account for the bulk of the data.”

You can read Motl’s story in full at http://motls.blogspot.com/2010/07/in-defense-of-milankovitch-by-gerard.html#more

— and download from there a 2006 paper that wins Motl over, by Gerard Roe of the University of Washington in Seattle.

The abstract of that paper reads (with my emphasis added):

The Milankovitch hypothesis is widely held to be one of the cornerstones of climate science. Surprisingly, the hypothesis remains not clearly defined despite an extensive body of research on the link between global ice volume and insolation changes arising from variations in the Earth’s orbit. In this paper, a specific hypothesis is formulated. Basic physical arguments are used to show that, rather than focusing on the absolute global ice volume, it is much more informative to consider the time rate of change of global ice volume. This simple and dynamically-logical change in perspective is used to show that the available records support a direct, zero-lag, antiphased relationship between the rate of change of global ice volume and summertime insolation in the northern high latitudes. Furthermore, variations in atmospheric CO2 appear to lag the rate of change of global ice volume. This implies only a secondary role for CO2 – variations in which produce a weaker radiative forcing than the orbitally-induced changes in summertime insolation – in driving changes in global ice volume.

Roe, G. (2006), In defense of Milankovitch, Geophys. Res. Lett., 33, L24703, doi:10.1029/2006GL027

The reason for my chuckles is that the “change in perspective” that Roe adopts was available more than 30 years earlier in the first formal verification of Milankovitch, which I published in Nature in 1974. Using a pocket calculator, I simply assumed that the rate of change in global ice volume per thousand years was proportional to the difference between the summer sunshine at a high-ish northerly latitude and a level of sunshine at which the ice neither advances or retreats.

Read the rest of this entry »

Advertisements

Star positions matter

18/06/2010

Updating The Chilling Stars

Why star positions matter for climate physics

The Making of History’s Greatest Star Map is an excellent account of the European Space Agency’s Hipparcos mission by the project scientist, Michael Perryman. It brings back vivid recollections:

  • of dismay after the launch in 1989, when the satellite failed to go into the right orbit and frantic steps were needed to improvise a survivable orbit and re-configure the observing programme.
  • of satisfaction when operations continued despite unplanned exposure to the Earth’s radiation belts, as well as some nasty solar flares, until the radiation damage became fatal in 1993.
  • of the appetizer in 1994, when early results of the Hipparcos star mapping helped in accurate prediction of the impacts of the fragmented Comet Shoemaker-Levy 9 on the planet Jupiter.
  • of joy on Isola di San Giorgo, Venice, in 1997 when the Hipparcos science team announced their first large-scale results, after a huge computational effort.

Hipparcos in an ESA impression

Astrometry took that great leap forward 30 years after Pierre Lacroute of the Strasbourg Observatory first proposed a space mission to measure the positions of stars, 20 years after Erik Høg of the Copenhagen Observatory refined the concept, and 17 years after ESA earmarked it as something to do. Ground-based astrometry had stalled, because of imprecisions due the turbulence of the atmosphere, and its remaining aficionados had little lobbying power. As a result, Hipparcos remained a distinctly European space project – the first in which there was no competition with the US or Soviet space science programmes.

Applications of the Hipparcos Catalogue of 100,000 plus stars and the Tycho 2 Catalogue with 2.5 million stars (to a lesser but still unprecedented accuracy) have ranged from detecting a bend in the Milky Way Galaxy to checking Einstein’s theory of gravity, General Relativity. But wanting to pursue here the relevance of Hipparcos to climate physics, I’m pleased to see that Michael Perryman points the way.

Michael Perryman. Photo by Richard Perryman

In The Making of History’s Greatest Star Map, pp. 236-243, Perryman notes the role of Hipparcos in refining observations the wobbles of the Earth’s axis, which are involved in the pacing of ice ages (the Milankovitch theory). Then he points to the link between solar activity and climate change, as evidenced by the Little Ice Age, the Medieval Warm Period and other variations. As to the mechanism for the solar connection, Perryman singles out the suggestion that cosmic rays, modulated by solar activity, influence cloud cover.

He continues the story with the Sun’s journey through the Galaxy and the icy intervals on Earth that correspond to exposure to intense cosmic rays when passing through spiral arms. That’s a major topic in The Chilling Stars and, as Perryman says, the Hipparcos data have improved our knowledge of motions in the Galaxy.

It’s reassuring when a professor of astronomy with no scientific or political axe to grind gives serious attention to the cosmic-ray/climate link (the Svensmark hypothesis). Let me reciprocate by reviewing what’s said about the climate-related significance of Hipparcos and its successor Gaia in The Chilling Stars and see if it needs updating or extending.

Read the rest of this entry »


Next ice age

14/05/2010

Climate Change – News and Comments

also Predictions Revisited

Prophet of the Next Ice Age

A hero from the glory days of discovery half a century ago, before the sophistry about man-made global warming invaded climate science, will be speaking at the Fourth International Conference on Climate Change in Chicago, 16-18 May 2010.

Kukla at work in Czechoslovakia, from The Weather Machine (book). Photo by courtesy of G. Kukla.

In the 1960s a respected geologist in his native Czechoslovakia, George Kukla, counted the layers of loess – windblown mineral dust ground by the glaciers and laid down in the region during recent ice ages. They were separated by darker material left over from warm interglacial periods. Kukla found too many layers of loess. Until then, almost everyone thought that there were just four recent glacial ages, with long interglacials between them. An exception was Cesare Emiliani, who in Chicago in 1955 had traced major variations in heavy oxygen in seabed fossils, and counted seven ice ages. Very few experts believed him until Kukla reported at least nine loess layers in the brickyards of Czechoslovakia.

Following the ill-fated bid for democracy in the “Prague Spring” of 1968 Kukla emerged from behind the Iron Curtain and found refuge at Columbia’s Lamont-Doherty Geological Observatory (now called the Earth Observatory) where he still works.

The observatory perches beside the former glacier valley of the Hudson River. And down at water level Alec Nisbett of BBC-TV filmed Kukla for our multinational TV blockbuster called “The Weather Machine”, broadcast in 1974. By then the count of ice ages had increased still further and the reasons for the comings-and-goings of the ice were better understood. And as you can view here (after a patch of narration read grandly by the actor Eric Porter) Kukla issued a warning. http://www.youtube.com/watch?v=v-Vn5AStFWo

Added 16 May: The wonders of WordPress feedback tell me that only 10% of visitors to this story follow the YouTube link, so I’ll put in the transcript.

Narrator: Will a new ice age claim our lands and bury our northern cities? It’s buried Manhattan Island before, when great glaciers half a mile thick filled the valley of New York’s Hudson River. That’s what an ice age is all about. George Kukla is from Czechoslovakia, where he discovered signs that ice ages are far more frequent that most experts have supposed. Today he continues his work near New York City. For him, the next ice age is not at all remote.

George Kukla: Well almost all of us have been pretty sure that there were only four ice ages, separated by relatively long warm intervals. But now we know that there were twenty in the last two million years. And the warm periods are much shorter than we believed originally. They are something around 10,000 years long. and I’m sorry to say that the one we are living in now has just passed its 10,000 year birthday. That of course means that the ice age is due now any time.

In this post I’ll summarize what was going on in the mid-1970s, about ice age science and climate policy, before catching up with what Kukla thinks nowadays about the coming ice age.

Read the rest of this entry »