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.
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?
Read the rest of this entry »
5 Comments | 2) PREDICTIONS REVISITED, 3a) News and Comments | Tagged: Aldo Lugo, Amazon rainforest, Aziz Ab'Saber of São Paulo University, Barro Colorado Island, biodiversity, Chatham House, Chris Justice, climatic optimum, CO2 fertilization, Daniel Sabatier, David Whitehouse, ice ages, INPE, Institut de Recherche pour le Développement, intermediate disturbance hypothesis, island biogeography, Jean-François Molino, Jeffrey Chambers, Jet Propulsion Lab, Jim Tucker, Joseph Connell, Landsat, Leeds University, Legal Amazonia, logging, Magic Universe, Max Planck Institute for Biogeochemistry, NASA, Nigel Calder, Oliver Philips, paleo-ecology, Paracou, Philip Fearnside, Philip Grime, refuge hypothesis, Roberto Pereira da Cunha, Robinson Negrón-Juárez, Sam Lawson, Sheffield University, Spaceship Earth, squall-line storms, Stephen Hubbell, Tulane University, UC Santa Barbara, World Bank | Permalink
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