Don't just do something, stand there! Reflections on the counterintuitive behavior of complex systems, seen through the eyes of System Dynamics, Systems Thinking and simulation.
Model Name: The Energy Transition and the Economy: A System Dynamics Approach
Citation: John D. Sterman, 1981. PhD Dissertation, MIT Sloan School of Management
Source: Replicated by Miguel Vukelic (a heroic effort)
Units balance: Yes
Format: Vensim (Contains data variables and thus requires an advanced version or the free Model Reader)
Model Name: payments, penalties, and environmental ethic
Citation: Dudley, R. 2007. Payments, penalties, payouts, and environmental ethics: a system dynamics examination Sustainability: Science, Practice, & Policy 3(2):24-35. http://ejournal.nbii.org/archives/vol3iss2/0706-013.dudley.html.
Source: Richard G. Dudley
Copyright: Richard G. Dudley (2007)
License: Gnu GPL
Peer reviewed: Yes (probably when submitted for publication?)
Units balance: Yes
Format: Vensim
Target audience: People interested in the concept of payments for environmental services as a means of improving land use and conservation of natural resources.
Questions answered: How might land users’ environmental ethic be influenced by, and influence, payments for environmental services.
Software: Vensim
My dad pointed me to this interesting Paul Romer interview on BBC Global Business. The BBC describes Romer as an optimist in a dismal science. I think of Paul Romer as one of the economists who founded the endogenous growth movement, though he’s probably done lots of other interesting things. I personally find the models typically employed in the endogenous growth literature to be silly, because they retain assumptions like perfect foresight (we all know that hard optimal control math is the essence of a theory of behavior, right?). In spite of their faults, those models are a huge leap over earlier work (exogenous technology) and subsequent probing around the edges has sparked a very productive train of thought.
About 20 minutes in, Romer succumbs to the urge to bash the Club of Rome (economists lose their union card if they don’t do this once in a while). His reasoning is part spurious, and part interesting. The spurious part is is blanket condemnation, that simply everything about it was wrong. That’s hard to accept or refute, because it’s not clear if he means Limits to Growth, or the general tenor of the discussion at the time. If he means Limits, he’s making the usual straw man mistake. To be fair, the interviewer does prime him by (incorrectly) summarizing the Club of Rome argument as “running out of raw materials.” But Romer takes the bait, and adds, “… they were saying the problem is we wouldn’t have enough carbon resources, … the problem is we have way too much carbon resources and are going to burn too much of it and damage the environment….” If you read Limits, this was actually one of the central points – you may not know which limit is binding first, but if you dodge one limit, exponential growth will quickly carry you to the next.
Interestingly, Romer’s solution to sustainability challenges arises from a more micro, evolutionary perspective rather than the macro single-agent perspective in most of the growth literature. He argues against top-down control and for structures (like his charter cities) that promote greater diversity and experimentation, in order to facilitate the discovery of new ways of doing things. He also talks a lot about rules as a moderator for technology – for example, that it’s bad to invent a technology that permit greater harvest of a resource, unless you also invent rules that ensure the harvest remains sustainable. I think he and I and the authors of Limits would actually agree on many real-world policy prescriptions.
However, I think Romer’s bottom-up search for solutions to human problems through evolutionary innovation is important but will, in the end, fail in one important way. Evolutionary pressures within cities, countries, or firms will tend to solve short-term, local problems. However, it’s not clear how they’re going to solve problems larger in scale than those entities, or longer in tenure than the agents running them. Consider resource depletion: if you imagine for a moment that there is some optimal depletion path, a country can consume its resources faster or slower than that. Too fast, and they get-rich-quick but have a crisis later. Too slow, and they’re self-deprived now. But there are other options: a country can consume its resources quickly now, build weapons, and seize the resources of the slow countries. Also, rapid extraction in some regions drives down prices, creating an impression of abundance, and discouraging other regions from managing the resource more cautiously. The result may be a race for the bottom, rather than evolution of creative long term solutions. Consider also climate: even large emitters have little incentive to reduce, if only their own damages matter. To align self-interest with mitigation, there has to be some kind of external incentive, either imposed top-down or emerging from some mix of bottom-up cooperation and coercion.
If you propose to solve long term global problems only through diversity, evolution, and innovation, you are in effect hoping that those measures will unleash a torrent of innovation that will solve the big problems coincidentally, or that we’ll stay perpetually ahead in the race between growth and side-effects. That could happen, but as the Dartmouth clinic used to say about contraception, “hope is not a method.”
I sort of follow a bunch of economics blogs. Naturally they’re all very much preoccupied with the financial crisis. There’s a lot of debate about Keynesian multipliers, whether the stimulus will work, liquidity traps, bursting bubbles, and the like. If you step back, it appears to be a conversation about how to use fiscal and monetary policy to halt a vicious cycle of declining expectations fueled by financial instruments no one really understands – essentially an attempt to keep the perceived economy from dragging down the real economy (as it is clearly now doing). The implicit assumption often seems to be that, if we could only untangle the current mess, the economy would return to its steady state growth path.
What I find interesting is that there’s little mention of what might have been wrong in the real economy to begin with, and its role in the current crisis. Clearly the last decade was a time of disequilibrium, not just in the price of risk, but in the real capital investments and consumption patterns that flowed from it. My working hypothesis is that we were living in a lala land of overconsumption, funded by deficits, sovereign wealth funds, resource drawdown, and failure to invest in our own future. In that case, the question for the real economy is, how much does consumption have to fall to bring things back into balance? My WAG is 15% – which implies a heck of a lot of reallocation of activity in the real economy. What does that look like? Could we see it through the fog of knock-on effects that we’re now experiencing? Is there something we could be doing, on top of fiscal and monetary policy, to ease the transition?
The ongoing bailout/stimulus debate is decidedly Keynesian. Yet Keynes was a halfhearted Keynesian:
US Keynesianism, however, came to mean something different. It was applied to a fiscal revolution, licensing deficit finance to pull the economy out of depression. From the US budget of 1938, this challenged the idea of always balancing the budget, by stressing the need to boost effective demand by stimulating consumption.
None of this was close to what Keynes had said in his General Theory. His emphasis was on investment as the motor of the economy; but influential US Keynesians airily dismissed this as a peculiarity of Keynes. Likewise, his efforts to separate capital projects from ordinary budgets, balanced if possible, found few echoes in Washington, despite frequent mention of his name.
Should this surprise us? It does not appear to have disconcerted Keynes. ‘Practical men were often the slaves of some defunct economist,’ he wrote. By the end of the second world war, Lord Keynes of Tilton was no mere academic scribbler but a policymaker, in a debate dominated by second-hand versions of ideas he had put into circulation in a previous life. He was enough of a pragmatist, and opportunist, not to quibble. After dining with a group of Keynesian economists in Washington, in 1944, Keynes commented: ‘I was the only non-Keynesian there.’
This got me wondering about the theoretical underpinnings of the stimulus prescription. Economists are talking in the language of the IS/LM model, marginal propensity to consume, multipliers for taxes vs. spending, and so forth. But these are all equilibrium shorthand for dynamic concepts. Surely the talk is founded on dynamic models that close loops between money, expectations and the real economy, and contain an operational representation of money creation and lending?
The trouble is, after a bit of sniffing around, I’m not seeing those models. On the jacket of Dynamic Macroeconomics, James Tobin wrote in 1997:
“Macrodynamics is a venerable and important tradition, which fifty or sixty years ago engaged the best minds of the economics profession: among them Frisch, Tinbergan, Harrod, Hicks, Samuelson, Goodwin. Recently it has been in danger of being swallowed up by rational expectations, moving equilibrium, and dynamic optimization. We can be grateful to the authors of this book for keeping alive the older tradition, while modernizing it in the light of recent developments in techniques of dynamic modeling.”
’”James Tobin, Sterling Professor of Economics Emeritus, Yale University
Is dynamic macroeconomics still moribund, supplanted by CGE models (irrelevant to the problem at hand) and black box econometric methods? Someone please point me to the stochastic behavioral disequilibrium nonlinear dynamic macroeconomics literature I’ve missed, so I can sleep tonight knowing that policy is informed by something more than comparative statics.
In the meantime, the most relevant models I’m aware of are in system dynamics, not economics. An interesting option (which you can read and run) is Nathan Forrester’s thesis, A Dynamic Synthesis of Basic Macroeconomic Theory (1982).
Forrester’s model combines Samuelson’s multiplier accelerator, Metzler’s inventory-adjustment model, Hicks’ IS/LM, and the aggregate-supply/aggregate-demand model into a 10th order continuous dynamic model. The model generates an endogenous business cycle (4-year period) as well as a longer (24-year) cycle. The business cycle arises from inventory and employment adjustment, while the long cycle involves multiplier-accelerator and capital stock adjustment mechanisms, involving final demand. Forrester used the model to test a variety of countercyclic economic policies, commonly recommended as antidotes for business cycle swings:
Results of the policy tests explain the apparent discrepancy between policy conclusions based on static and dynamic models. The static results are confirmed by the fact that countercyclic demand-management policies do stabilize the demand-driven [long] cycle. The dynamic results are confirmed by the fact that the same countercyclic policies destabilize the business cycle. (pg. 9)
It’s not clear to me what exactly this kind of counterintuitive behavior might imply for our current situation, but it seems like a bad time to inadvertently destabilize the business cycle through misapplication of simpler models.
It’s unclear to what extent the model applies to our current situation, because it doesn’t include budget constraints for agents, and thus doesn’t include explicit money and debt stocks. While there are reasonable justifications for omitting those features for “normal” conditions, I suspect that since the origin of our current troubles is a debt binge, those justifications don’t apply where we are now in the economy’s state space. If so, then the equilibrium conclusions of the IS/LM model and other simple constructs are even more likely to be wrong.
I presume that the feedback structure needed to get your arms around the problem properly is in Jay Forrester’s System Dynamics National Model, but unfortunately it’s not available for experimentation.
John Sterman’s model of The Energy Transition and the Economy (1981) does have money stocks and debt for households and other sectors. It doesn’t have an operational representation of bank reserves, and it monetizes the deficit, but if one were to repurpose the model a bit (by eliminating the depletion issue, among other things) it might provide an interesting compromise between the two Forrester models above.
I still have a hard time believing that macroeconomics hasn’t trodden some of this fertile ground since the 80s, so I hope someone can comment with a more informed perspective. However, until someone disabuses me of the notion, I have the gnawing suspicion that the models are broken and we’re flying blind. Sure hope there aren’t any mountains in this fog.
More good stuff from my blog reader:
Real Time Economics – Secondary Sources: Rebutting Myths, King on Stability, Green Econ & Secondary Sources: Rates, Innovation, Recession, Suprime Lending
Greg Mankiw – More Commentary on the Financial Mess
Economist’s View – links for 2008-10-23 &Â links for 2008-10-22
Marginal Revolution – Four myths of the credit crisis, again
Econbrowser – More Unhappy Numbers
MetaRoundup:
Several of the economics blogs I read have had useful roundups of bailout commentary. A few I find found useful:
Do we need to act now? on Economist’s View
9/26 Links on Economist’s View
NYT Economix’ analyst roundup
Greg Mankiw’s roundup of commentary
Update 9/29:
Real Time Economics’ Secondary Sources
Update 10/1:Â
Greg Mankiw with more commentary
Alternative Plans:
Economists Against the Paulson Plan
Brad de Long on Krugman on the Dodd plan
WSJ Real Time Economics’ Text of Lawmakers’ Agreement on Principles
Thomas Palley on Saving the Financial System
Marginal Revolution on the Republican plan to rescue mortgages instead of buying mortgage assets
Marginal Revolution with a Modest Proposal (finding and isolating toxic assets)
Update 9/27:
Marginal Revolution with substitute bridges
Greg Mankiw with a letter from Robert Shimer with a nice analysis, including problems with Paulson, the lemons problem, and the Diamond, Kaplan, Kashyap, Rajan & Thaler fix
Update 9/28:
Real Time Economics on securitization
Brad deLong on nationalization (the Swedish model)
Update 9/29:
The Big Picture with Stop Targeting Asset Prices
Marginal Revolution asks, is the Sweden plan better?
I just ran across a May 2008 GAO report, detailing the findings of a panel of economists convened to consider US climate policy. The panel used a modified Delphi method, which can be good or evil. The eighteen panelists are fairly neoclassical, with the exception of Richard Howarth, who speaks the language but doesn’t drink the Kool-aid.
First, it’s interesting what the panelists agree on. All of the panelists supported establishing a price on greenhouse gas emissions, and a majority were fairly certain that there would be a net benefit from doing so. A majority also favored immediate action, regardless of the participation of other countries. The favored immediate action is rather fainthearted, though. One-third favored an initial price range under $10/tonCO2, and only three favored exceeding $20/tonCO. One panelist specified a safety valve price at 55 cents. Maybe the low prices are intended to rise rapidly (or at the interest rate, per Hotelling); otherwise I have a hard time seeing why one would bother with the whole endeavor. It’s quite interesting that panelists generally accept unilateral action, which by itself wouldn’t solve the climate problem. Clearly they are counting on setting an example, with imitation bringing more emissions under control, and perhaps also on first-mover advantages in innovation.