Amazon rainforest


Predictions Revisited and Climate Change: News and Comments

Will the Amazon rainforest survive?

A flurry of stories about the rainforests confirms that the proper concern about tropical deforestation has been thoroughly confused by improper attempts to invoke man-made global warming. Before turning to thunderstorms felling trees,  let’s start with the big picture of expectations, past and present, for the Amazon rainforest. For more than 30 years, large-scale assessments have been based on satellite imagery, despite the problem that much of the forest is covered with clouds at any one time. Brazil’s own Instituto Nacional de Pesquisas Espaciais, INPE, has played a leading part.

In a forecast that proved wrong even more rapidly than The Population Bomb (see the previous post) an ecologist Philip Fearnside declared in 1982 that the Amazon forest was vanishing at an accelerating rate, with more than 40% to be gone by 1988. I told the tale in my 1991 book about remote sensing, Spaceship Earth, after visiting INPE in São Paulo.

During the 1980s Brazil found itself at war on two fronts. At home, the government tried to moderate the rate of clearances in the Amazonian forest, and police a frontier region as gun-happy as the old Wild West of the USA. Internationally, they had to deal with a rising chorus of criticism about the rate at which the forest was disappearing. In 1982, on the basis of INPE’s figures, predictions by an American scientist P.M. Fearnside amounted to a forecast that 44 per cent of the Amazonian forest would be lost by 1988.

The Brazilians greeted such estimates with frank disbelief. There then followed a contest between calculation and remote sensing to try to establish the true facts. …

In 1989, the World Bank published estimates indicating that 12 per cent of Legal Amazonia was already deforested by 1988. This was based on calculations from the state of affairs in 1980. By this time the Brazilians were growing very angry. Although the figure was far less than the Fearnside estimate, the fact that it came from the World Bank secured it a place in international environmental folklore. The Brazilians appealed again to the umpires in space: the unblinking instruments of the remote-sensing satellites.

At INPE, Roberto Pereira da Cunha decided to make a ‘wall-to-wall’ assessrnent of the deforestation in Legal Amazonia. As he remarked, ‘No one wants to do the dirty work of gathering the data. It is a very trivial task for scientists.’ Trivial, but not unlaborious. Pereira’s team assembled 234 Landsat scenes and selected for close interpretation 101 images that showed evidence of deforestation. From colour composites of three wavelength bands the scientists outlined the deforested patches, and used a grid to measure their areas. Images for different years established rates of deforestation.

The most important conclusion was that there was no acceleration: deforestation was proceeding at a more or less steady rate. As for the total recent deforestation up till the end of 1988, INPE’S answer was 5 per cent of the area of Legal Amazonia. Meanwhile, Fearnside had changed his forecast. His new figures indicated 7 per cent deforestation of Legal Amazonia by 1989 – a far cry from his 44 per cent figure of just 7 years earlier, and almost in line with INPE’s figure. In 1990 Jim Tucker and Chris Justice of NASA broadly confirmed the Brazilian result by a similar large-scale use of Landsat imagery, but with a different technique, using only a single infra-red channel.

So what do the umpires in space say now, two decades later?

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Milankovitch back to 1974


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

— 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.

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Next ice age


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.

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.

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