Global warming and structure versus behaviour

This forum contains all archives from the SD Mailing list (go to http://www.systemdynamics.org/forum/ for more information). This is here as a read-only resource, please post any SD related questions to the SD Discussion forum.
Locked
Erling Moxnes
Junior Member
Posts: 3
Joined: Fri Mar 29, 2002 3:39 am

Global warming and structure versus behaviour

Post by Erling Moxnes »

Thanks to Coyle (SD4377) for an opportunity to make, what I think is a
very important point about global warming in light of the philosophy of
system dynamics.

Coyle utters scepticism about global warming ("if that exists except in
the minds of the global warming industry"). He refers to a 20000 year
long time-series to make the point that the recent temperature increase
cannot be seen as anything but a natural variation in world
temperatures. By itself that comment is correct and it is a point often
missed by those who use the recent temperature increases as a proof of
manmade global climate change.

However, as system dynamicists, our first priority should be to look at
the structure of the system. For more than hundred years it has been
known that carbon dioxide works as the glass of a greenhouse, trapping
heat. This is a well established fact. The burden of proof lies on all
those that claim that this is wrong or that other natural mechanisms
(feedback loops) will take over the control of the climate and keep the
temperature at the current level. As far as I know, there is far more
uncertainty about the working of such mechanisms than about the heat
effect of greenhouse gases.

In statistical language, think of the problem in light of Bayesian
decision making. Our prior knowledge suggest global climate change.
Uncertain measurements of temperatures, over long intervals, imply a
likelihood function with a wide spread. Thus, we need more data about
temperature changes before the data start to dominate the prior give by
the physics of greenhouse gases.

In more practical language, think about the following example. You enter
a cold cottage and light a fire in the woodstove. After a few minutes
you measure the change in room temperature, and you notice no
difference. Should you use your time-series data to conclude that the
woodstove does not work? No! Both your experiential knowledge and if you
want, established laws of physics, suggest that if you wait, you will
see that the temperature increases. While waiting for a delayed effect
(the stock to fill up), the time-series data are of little help.

Still we see that both those that believe and those that do not believe
in global warming use time-series to make their points. The discussions
are at times very heated. To rephrase Shakespeares "Much ado about
nothing", one could say: "Much ado about the wrong thing".

The above is a point we stress in our system dynamics education in
Bergen, because it is so natural, even for those with a system dynamics
background, to accept limiting boundaries for discussions about dynamic
issues. Not only must we train ourselves to understand that structure
leads to behaviour, we must also repeatedly remind ourselves that one
cannot discuss one in isolation from the other.

My best regards,

Erling Moxnes
From: Erling Moxnes <
erling.moxnes@ifi.uib.no>
John Sterman
Senior Member
Posts: 117
Joined: Fri Mar 29, 2002 3:39 am

Global warming and structure versus behaviour

Post by John Sterman »

My friend Geoff Coyle is right that we need longer time horizons than
those of politicians or business leaders if we are to deal
appropriately with challenges such as global warming. However, with
all due respect, it is wrong to suggest that anthropogenically
induced global warming is questionable simply because there has been
variation in global mean temperatures over the past 20,000 years.
Geoff knows better than most that it is not proper scientific
procedure to make a judgment about the causes of behavior in a
complex dynamical system by eyeballing a single time series and
subjectively pronouncing that there is or isnt a particular pattern
there.

The issues involved in understanding global warming and the human
contribution to climate change are too vast to go into here. I
suggest those interested in climate change start by reading the most
recent report of the Intergovernmental Panel on Climate Change
(IPCC). The IPCC consists of the best scientists from around the
world working on climate change and is extremely careful not to
overreach the data. Their most recent report, published in 2001, is
available both in print and on the web. There is a nontechnical
"summary for policymakers" and also a technical summary of the
scientific evidence, both available at the IPCC site, <www.ipcc.ch>,
or in J. Houghton, et al., Climate Change 2001: The Scientific Basis
(Cambridge Univ. Press, Cambridge, UK, 2001).

The IPCC documents both that global mean temperatures have varied
over geological time, and that there has been a significant warming
trend since the beginning of the industrial revolution. They
attribute much of this warming to the increase, largely caused by
human activity, in greenhouse gases (GHGs) such as CO2, N2O, CH4, and
others. CO2 is the most important of these in terms of its impact on
net radiative forcing. The IPCC report notes that

"The present CO2 concentration has not been exceeded in the last
420,000 years and likely not during the past 20 million years. The
current rate of increase is unprecedented during at least the past
20,000 years." (IPCC 2001, 7)

Current GHG concentrations contribute about 2.4 watts per square
meter of net radiative forcing at the earths surface, that is,
incoming solar radiation exceeds outgoing radiation by 2.4 w/m2.
Consequently, mean global surface temperatures are rising. Mean
temperatures rose in the 20th century by 0.6 ± 0.2 °C. The warming
has been accompanied by glacier retreat and a decline in winter snow
cover, a 40% decline in summer sea-ice thickness in the arctic, an
increase in average precipitation and in extreme weather events, and
a rise of 0.1 - 0.2 meters in sea level, among other effects (IPCC
2001).

Debate continues about the dynamics of the global climate system and
the consequences of warming. The public discussion has been
polarized by well-financed campaigns to discount the science.
Nevertheless, after considering a wide range of evidence, models, and
other possible sources of variation in climate, the IPCC concluded
that

"most of the warming observed over the last 50 years is attributable
to human activities" (IPCC 2001, 10).

In particular, the IPCC concludes that it is not possible to explain
the warming since the industrial revolution solely on the basis of
natural processes, including terrestrial/geological processes and
variations in insolation due to orbital forcing.

Nothing in the scientific literature published since the IPCCs 2001
report has altered this conclusion.

Those interested in the economic consequences of warming should take
a look at Tom Fiddamans excellent work on, e.g. his paper in the
System Dynamics Review, volume 18(2).

Research shows that peoples mental models of climate change are
grossly inadequate -- we often look for correlations among variables
such as CO2 emissions, atmospheric concentrations, and global mean
temperature to make judgments about the causes and consequences of
climate change instead of recognizing the basic stock-flow
structures, much less the many feedbacks, both positive and negative,
among them (see Sterman, J. D. and L. Booth Sweeney (2002). "Cloudy
Skies: Assessing Public Understanding of Global Warming." System
Dynamics Review 18(2): 207-240). Readers of this list should be
particularly careful to avoid such traps in their own thinking.

John Sterman
From: John Sterman <jsterman@mit.edu>
Tom Fiddaman
Senior Member
Posts: 55
Joined: Fri Mar 29, 2002 3:39 am

Global warming and structure versus behaviour

Post by Tom Fiddaman »

I dont have the book cited by Geoff Coyle, but Ive put corresponding data
from the Vostok ice core and other sources on a web page:
http://www.sd3.info/CO2temp.html
I included other time scales (420,000 years, ~200 years) so you can draw
your own conclusions. I have to agree with Sterman & Moxnes that the
physics takes precedence over eyeballing time series. Its extremely
tempting, for example, to see a smoking gun in the correlation of
temperature and CO2 on the 420kyear timescale, but if this were actually
representative of simple causality, the sensitivity of climate to CO2 would
be greater than models predict. The answer, of course, is that other
factors are involved too - like ice cover, orbital changes, and ocean
circulation.

The global warming industry - if that exists except in the minds of spin
doctors - is much smaller than the fossil industry that has spent
significant effort in the last two decades trying to discredit climate
science. Regrettably that effort seems to have gone largely into vocal
cranks, rather than exploration of credible alternate hypotheses (of which
there are several). See http://www.sd3.info/climatebookmarks.html#Critics

Tom

****************************************************
Thomas Fiddaman, Ph.D.
Ventana Systems http://www.vensim.com
8105 SE Nelson Road Tel (253) 851-0124
Olalla, WA 98359 Fax (253) 851-0125
Tom@Vensim.com http://www.sd3.info
****************************************************
Locked