Sunday, January 22, 2012

The Limits to Growth - updated 1/22/2012

See comment from John for link to article with graphs.
However, I don't think his arguments against dealing with global warming are valid. He expects economic collapse within a short time, leading to lessening use of fuel, leading to less CO2. I doubt it will be that simple. As he himself points out, economic systems almost always overshoot. And as countries try to deal with the results of such things as shortage of resources, they might use even use fuel faster, because of having to use less efficient processes. And global warming itself will accelerate problems such as food shortages.


The current issue of New Scientist (Jan. 7-13, 2012, page 38) has an article on the book "The Limits of Growth", which was published in 1972.

The book reported the conclusions of group of scientists who used a computer model, World3, to explore possible futures.

http://www.newscientist.com/article/mg21328462.100-boom-and-doom-revisiting-prophecies-of-collapse.html

[...]

The young scientists tried to take a more rigorous approach: using a computer model to explore possible futures. What was shocking was that their simulations, far from showing growth continuing forever, or even levelling out, suggested that it was most likely that boom would be followed by bust: a sharp decline in industrial output, food production and population. In other words, the collapse of global civilisation.

These explosive conclusions were published in 1972 in a slim paperback called The Limits to Growth. It became a bestseller - and provoked a furious backlash that has obscured what it actually said. For instance, it is widely believed that Limits predicted collapse by 2000, yet in fact it made no such claim. So what did it say? And 40 years on, how do its projections compare with reality so far?

[...]

The team compares their work to exploring what happens to a ball thrown upwards. World3 was meant to reveal the general behaviour that results - in the case of a ball, going up and then falling down - not to make precise predictions, such as exactly how high the ball would go, or where and when it would fall. "None of these computer outputs is a prediction," the book warned repeatedly.

[...]

This was unexpected and shocking. Why should the world's economy collapse rather than stabilise? In World3, it happened because of the complex feedbacks between different global subsystems such as industry, health and agriculture. More industrial output meant more money to spend on agriculture and healthcare, but also more pollution, which could damage health and food production.

And most importantly, says Randers, in the real world there are delays before limits are understood, institutions act or remedies take effect. These delayed responses were programmed into World3. The model crashed because its hypothetical people did not respond to the mounting problems before underlying support systems, such as farmland and ecosystems, had been damaged.

Instead, they carried on consuming and polluting past the point the model world could sustain. The result was what economists call a bubble and Limits called overshoot. The impact of these response delays was "the fundamental scientific message" of the study, says Randers. Critics, and even fans of the study, he says, didn't get this point.

The other message missed was that Limits was about how catastrophe could be averted. It did not say that humanity was doomed. In model runs where growth of population and industry were constrained, growth did level out rather than collapse - the stabilised scenario

[...]

The crucial point is that overshoot and collapse usually happened sooner or later in World3 even if very optimistic assumptions were made about, say, oil reserves. "The general behaviour of overshoot and collapse persists, even when large changes to numerous parameters are made," says Graham Turner of the CSIRO Ecosystem Sciences lab in Crace, Australia.

This did not convince those who thought technology could fix every problem. And with so much criticism, the idea took hold that Limits had been disproved. That mantra has been repeated so often that it became the received wisdom, says Ugo Bardi of the University of Florence in Italy, author of a recent book about Limits. "The common perception is that the work was discredited scientifically. I heard it again at a meeting last April," says Homer-Dixon. "It wasn't."

It wasn't just confusion. "Misunderstanding was enhanced by a media campaign very similar to the one that has been recently directed against climate science," says Bardi.

One of the most common myths is that Limits predicted collapse by 2000. Yet as a brief glance at the "standard run" shows, it didn't

[...]

When Matthew Simmons, a leading oil-industry banker, finally read Limits in the 1990s, he was surprised to find none of the false predictions he had heard about. On the contrary, he concluded, population and energy growth largely matched the basic simulation. He felt Limits got so much attention, then lost it, partly because the oil shock of 1973 focused minds on resource shortages that were then largely resolved.

There have been other recent re-appraisals of the book. In 2008, for instance, Turner did a detailed statistical analysis of how real growth compares to the scenarios in Limits. He concluded that reality so far closely matches the standard run of World3.

[...]

We already know the future will be different from the standard run in one respect, says Bar-Yam. Although the actual world population up to 2000 has been similar, in the scenario the rate of population growth increases with time - one of the exponential drivers of collapse. Although Limits took account of the fact that birth rates fall as prosperity rises, in reality they have fallen much faster than was expected when the book was written. "It is reasonable to be concerned about resource limitations in fifty years," Bar-Yam says, "but the population is not even close to growing [the way Limits projected in 1972]."

The book itself may be partly responsible. Bar-Yam thinks some of the efforts in the 1970s to cut population growth were at least partly due to Limits. "If it helped do that, it bought us more time, and it's a very important work in the history of humanity," he says.

Yet World3 still suggests we'll hit the buffers eventually. The original Limits team put out an updated study using World3 in 2005, which included faster-falling birth rates. Except in the stabilising scenario, World3 still collapsed.

Otherwise, the team didn't analyse the correspondence between the real world and their 1972 scenarios in detail - noting only that they generally match. "Does this correspondence with history prove our model was true? No, of course not," they wrote. "But it does indicate that [our] assumptions and conclusions still warrant consideration today."

This remains the case. Forty years on from its publication, it is still not clear whether Limits was right, but it hasn't been proved wrong either. And while the model was too pessimistic about birth and death rates, it was too optimistic about the future impact of pollution. We now know that overshoot - the delayed response to problems that makes the effects so much worse - will eventually be especially catastrophic for climate change, because the full effects of greenhouse gases will not be apparent for centuries.

[...]

We need to apply that knowledge, too. The most important message of Limits was that the longer we ignore the problems caused by growth, the harder they are to overcome. As we pump out more CO2, it is clear this is a lesson we have yet to learn.

..

1 comment:

John said...

You can see graphs of the predictions and other data at: The Limits to Growth - the end of the world as we know it?.

Post a Comment