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July 26, 2006

Global warming-2: Understanding the problem

Understanding global climate concerns is not easy because it is a complex issue which involves many factors and theories, is based on data that span millennia and is not easy to extract, involves sophisticated theories and computer modeling, and requires long chains of inferential reasoning to arrive at conclusions. Compared to it, evolution, that other anathema of Bush and his anti-science Christian base, is a model of clarity.

At least with evolution, the progression shows a clear pattern, with life evolving from simple single cell organisms to the wide array of complex multi-cell systems we see today. If we started discovering anomalous organisms that seem to violate that temporal ordering, that would require a major restructuring of evolutionary theory.

With global warming, on the other hand, there isn't such a steady progression. It is not as if global warming implies that the temperature at each and every location on the Earth rises steadily with time. If it did, then people might be more easily convinced. But that is not how it works. Instead, the relevant data always deal with averages that are calculated (1) over very long time scales (involving tens and hundreds and thousands and even millions of years) and (2) over the whole planet or at least large areas of it.

It is quite possible to have wide fluctuations over shorter time periods and in localized areas that go counter to the long-term trend. Unfortunately, this means that there are plenty of opportunities for those who either do not understand that only averages are relevant, or who are deliberately trying to mislead others, to seize upon these fluctuations to argue that global warming is either not occurring or is not a serious problem. I can surely predict that if, for example, the next winter is colder than average in Cleveland, there will be many snickering comments to the effect that this 'proves' that global warming is a myth. Similarly, the current heat wave in France and California cannot, by themselves, be used, to argue in favor of global warming either. Scientists' conclusions will be unaffected since they know that data from a single year or location has only a tiny effect on averages.

These are the questions that need to be considered when we evaluate whether global warming is serious or not.

1. Is warming occurring? In other words, are average temperatures rising with time?

2. If so, is it part of normal cyclical warming/cooling trends that have occurred over geologic time or is the current warming going outside those traditional limits?

3. Are the consequences of global warming such that we can perhaps live with them (slightly milder winters and warmer summers) or are they going to be catastrophic (causing massive flooding of coastal areas due to rising ocean levels, severe droughts, blistering heat waves, total melting of the polar regions, widespread environmental and ecological damage)?

4. How reliable are the theories and computer models that are being used study this question?

5. What are the causes of global warming? Is human activity responsible and can the process be reversed?

My own ideas on this issue have changed over time. I started out by being somewhat neutral on this issue, not sure whether warming was occurring or not. Like most people, I didn't really understand questions about climate and tended to make the mistake of equating climate with weather. My understanding of weather was strongly influenced by the one feature about weather that we all grow up with, and that is its variability and unpredictability. This tends to create a strongly ingrained belief that we cannot really predict weather and I am sure this spills over into thinking that climate is also highly variable and so should not worry too much about warming since it might just as easily reverse itself.

But the key difference between weather and climate is that while weather systems are chaotic, climate change is not, at least as far as I am aware. In everyday language, chaos means just mess and disorder and confusion. But chaos, in science, is a technical term with a precise meaning. A chaotic system is one that progresses according to particular kinds of mathematical equations, usually coupled non-linear ones, such that the end state of the system is highly sensitive to initial conditions.

With non-chaotic systems, like a thrown ball, a small change in the initial conditions results in small changes in the final state. If I throw the ball slightly faster or at a slightly different angle, the end point of its trajectory will be only slightly different as well. This is what enables us to have expert athletes in any sport involving thrown or struck balls, because based on previous attempts, the professionals know how to make slight adjustments to hit a desired target. The reason that they can do so is because the ball's trajectory obeys non-chaotic dynamical equations.

But with a chaotic system, that is no longer true. A change in the initial conditions, however small, can result in the end state being wildly different, with the divergence increasing with time. But in order to predict the future of any system, we need to specify the current conditions. Since we can never know the initial conditions with perfect accuracy, this means that reliable long-term predictions are impossible. An analogy of a chaotic system might be river rapids. If you place a leaf at one point in the rapids, it might end up at some point further down the river. But making even a tiny change in your initial position will result in you ending up in a completely different place, even if the river flow itself is unchanged.

For example, suppose the mathematical quantity pi enters into a calculation. We know that the value of pi=3.1415927. . . , a sequence that goes on forever. But in performing actual calculations we cannot punch in an infinite sequence of digits into our computers and need to truncate the sequence. Usually for most problems (which are non-chaotic) we can treat pi as being equal to 3.14 or 22/7 or even just 3 and get fairly good results. We can adjust the precision of this input depending on the required precision of the output. But if pi was a particular part of a chaotic system of equations, then using 3.1415927 or rounding up to 3.141593 would give wildly different results. This is why this kind of chaos is better described as "extreme sensitivity to initial conditions."

Weather is thought to obey a chaotic system of equations. This is why, despite "Doppler radar" and other innovations that can give quite accurate measures of the state of weather-related parameters at any given time, weather forecasts become notoriously unreliable after three or four days, or even fewer. There is a reason that your local TV newscasts do not go beyond five-day weather forecasts. They are at the limits of predictability and already pushing their luck.

But the equations that drive climate calculations are not believed to be chaotic. Hence, given a model, one can hope to make reasonable predictions about global temperatures in the next century with some confidence in their reliability, even though one does not know if it is going to rain next week.

(In the terminology of chaos theory, sometimes climate is referred to as a "strange attractor" of the weather system, or a "boundary value problem," whereas weather is an "initial value problem." Basically, weather and climate are thought to evolve according to different kinds of mathematics.)

It is important to realize that the predictability of the results is possible only once a particular model of climate change has been chosen. One could get different results by choosing a different model altogether, although the range of possible models is strongly limited because they have to conform to the fundamental laws of science and be compatible with what we know about the behavior of related systems. The difference with weather is that with weather one can very different results while using the same model, simply because of our inability to specify exactly the initial values of the problem.

Next: The emerging scientific consensus over global warming.

Trackbacks

Trackback URL for this entry is: http://blog.case.edu/singham/mt-tb.cgi/8997 Global warming-7: The current status of the scientific consensus
Excerpt: So what is the scientific consensus about the answers to the key questions concerning global warming? The British magazine New...
Weblog: Mano Singham's Web Journal
Tracked: August 2, 2006 07:19 AM

Comments

I could look this up, but I think I'll ask instead: What is the difference between climate and weather? Or, more precisely, I understand what weather is, but I'm not sure what "climate" means.

Posted by Shruti on July 26, 2006 09:31 AM

wikipedia gives us the IPCC definition of climate:

Climate in a narrow sense is usually defined as the “average weather”, or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. The classical period is 30 years, as defined by the World Meteorological Organization (WMO). These quantities are most often surface variables such as temperature, precipitation, and wind. Climate in a wider sense is the state, including a statistical description, of the climate system.

Which, thanks for bringing this up: I think I've understood that climate & weather were different, but never actually stopped and thought about what the difference actually was.

Posted by V on July 26, 2006 10:02 AM

I believe question #3 to be the most important and is where most global warming resources should be focused.

I believe the effects will be a function of how willingly we change. Human beings are at the top of the food chain because of our ability to adapt. Unfortunately, we have resently become lazy and rely ever more heavily on technology, technology won't be enough.

Will sea levels rise? Yes, and perhaps dramatically. What should we do? Build ever increasingly strong walls to protect cities that are below sea level? NO !!!! MOVE TO HIGHER GROUND!!

Will we experience more sever droughts? Will the deserts expand? Probably yes to both. We can't rely on technology alone to protect us. We need to be willing to accept significant change in our lives. The farmers may need to move from Iowa to Canada or Argentina or somewhere else where the climate will be condusive to growing crops.

These are only a couple of the issues we will likely face, and most likely the smallest. Point being, if we exect to survive this warm period in our Earth's life, be better be willing to change!

Posted by doug on July 26, 2006 12:35 PM

V, why link to an entry in wikipedia, which may or may not have been altered, when the link to the original source is available?

Posted by Brian Gray on July 26, 2006 01:17 PM

Doug -
Your questions lie along the lines of "Why do people live on the sides of volcanos or floodplains?" - it's easy to ask that they not, but with our increasing global population there are simply fewer places for people to live, and as the deserts increase (desertification is a phenomena well known to environmental scientists and deserts have been slowly increasing in size world-wide for decades now, usually due to man kind's efforts to farm or develop edge-lands) there will continue to be less arable land for fewer and fewer people. Why do people live on floodplains? Because they can. The poor especially are in a sense "tied to the land" - they subsist because of their support networks, the people they know, and what tenuous support they have is lost if they move. So for many people, living in a floodplain or other area of potential natural desaster is simply a case of measuring the odds and choosing the most potentially beneficial.

I agree, we as humans need to change our ways, we need to stop having yards... we need to live more communaly, more urbanly, if we are to support our population and maintain our arable land for farming. Last summer I was sickened on a trip to Indiana to hear a developer brag about how soon there would be no corn fields in his state, as they were slowly converting farmland into tracts of luxury homes. Suburbs with no infrastructure, no economy, no use at all. Do we really need more luxury homes? If we allow capatilism to be our only guide, yes, I suppose so, but how shortsighted it seems, to sell off what makes our country wealthy in the first place.

Sorry for the digression. I guess I'm just saying ... we should look to ourselves to change humanity, because we all know how hard it is to change another.

Posted by marie on July 26, 2006 04:54 PM

Marie,

I agree. Mano asked if the effects of global warming would be catastrophic. My response is yes, unless we adapt (and i don't mean reducing CO2 emmissions - see previous days's post) by doing some of the things you mention.

The next serious hurricane to hit N.O. will be catastrophic because we are not adapting. We are trying to prevent the inevitable from happening. We are not strong enough to beat mother nature.

Posted by doug on July 27, 2006 12:47 PM

Doug,

The citation you provided yestarday is not only 10 years old, but doesn't really support your position. Namely, it neither supports nor dismisses the idea that CURRENT global warming is man made.

If we can learn anything from medicine, prevention is always a "cheaper" avenue than reactive medicine.

Posted by on July 27, 2006 04:21 PM

brian: laziness, mostly. It's quicker to type "ctrl-L,ctrl-C" than it is to right-click and copy.

You're right though, that using the original link is more desirable.

Posted by V on July 28, 2006 11:08 AM

Another interesting read, certainly opens your eyes on certain subjects

i hope my site can produce the same sort of info in the future - Global Warming

Posted by bob smith on August 29, 2007 09:23 AM

I agree to Mano singham and in addition to it, i recommend to all the computer user to make their pc an laptop green and use minimum energy. one can also dispose pc once it is not in use. this will help in reducing global warming.

Posted by Computer Support on November 13, 2008 06:57 AM