Some Comments On Global Modelling And The Ipcc Options

[Doly Garcia]

There are some global models underpinning the IPCC emissions scenarios. Some information about them can be found here:

http://www.ipcc.ch/pdf/special-reports/spm/sres-en.pdf

I have concerns about all of them. My main concerns are the following:

1) Population seems to be derived from the UN projections in all of the models and scenarios. The UN projections, as far as I know, don't consider the possible effects of climate change in any way. However, it's obvious that future population figures will depend strongly on the availability of food, and the availability of food is likely to depend on climate change, as climate change is expected to have an effect on crops.

2) Economic growth seems to be used as an input in several of the models, as if some trends were estimated for economic growth and used as an input to calculate other variables. But it's much more realistic to represent in a model the reverse causality (more energy leads to more economic growth) or a feedback loop between energy usage and economic growth. Also, I can see nothing to indicate that GDP is calculated as a sum of the three traditional sectors (agriculture, industry and services), so I'm not sure how it's calculated. At one point the report says that all scenarios assume more affluent worlds, is this just taken a priori as an assumption?

3) Several models don't seem to contain any kind of land model, and those that do, don't seem to have good feedbacks into other parts of the model. It's fair to assume that if a region had problems to feed their population, they would divert more resources into food production.

4) None of the models seem to give any consideration to the idea that the quality of the remainder of fossil fuels and nuclear fuels gets lower over time, as the higher quality grade are exploited first. This has implications for the supply of energy and the resources devoted to obtain energy.

5) It's unclear if the models allow for the possibility of energy demand not being met by supply, due to depletion.

Some of these concerns may not be valid for some of the models, but I don't get the impression that any of the models is satisfactory in respect of the 5 points. I would love to have further clarification on whether the concerns are valid or not.

I have a model based on the original World3 ("Limits to growth") model here, anybody interested can read the details here:

http://europe.theoildrum.com/node/5145

Some further study on the energy issues can be found here:

http://europe.theoildrum.com/node/5688

[Bert McInnis]

There are some global models underpinning the IPCC emissions scenarios. Some information about them can be found here:

http://www.ipcc.ch/pdf/special-reports/spm/sres-en.pdf

I have concerns about all of them. My main concerns are the following:

1) Population seems to be derived from the UN projections in all of the models and scenarios. The UN projections, as far as I know, don't consider the possible effects of climate change in any way. However, it's obvious that future population figures will depend strongly on the availability of food, and the availability of food is likely to depend on climate change, as climate change is expected to have an effect on crops.

These UN projections most likely come from cohort population models where the outcomes are determined by exogenous projections of fertility, mortality and migration. Models of this type are accounting identity tautologies. That is both their strength and weakness. They fit into the model use class we refer to as the subjective stance and are thus used from the point of view of design rather than prediction. From the point of view of model construction the issues of model design are level of aggregation (country, region, global) and the degree of stickiness to be associated with migrating populations (when they move how does their fertility and mortality morph into the geographic area they move into). Models of the type you hint at above we would class as models to be used in the objective stance and are thus used from the point of view of prediction. In these models the mechanisms for making the fertility, mortality and migration endogenous are voluminous and not easily validated. We think that models of the subjective stance are most appropriate for strategic long term policy direction analysis and models of the objective stance are most appropriate for short term policy guidance analysis. We would caution against models that are designed to strongly couple models of the objective stance with those of the subjective stance. So to take your example of a population model we would suggest a cohort model whose inputs of fertility, mortality and migration are exogenous and a behavioral model that would determine fertility,mortality and migration from other variables which are themselves conditioned by population. This leads to a tension between the parameters that flow from the long term policy objectives and those that are determined by the behavioral model. The resolution of that tension is the proper domain of general policy analysis. Now there are probably as many behavioral models as there are analysts while the cohort model is much more constrained. As a side note I think your statement "population figures will depend strongly on the availability of food" may not be correct. Given that food is very low on the Maslow scale of needs I think that population will be very elastic with respect to food availability.

2) Economic growth seems to be used as an input in several of the models, as if some trends were estimated for economic growth and used as an input to calculate other variables. But it's much more realistic to represent in a model the reverse causality (more energy leads to more economic growth) or a feedback loop between energy usage and economic growth. Also, I can see nothing to indicate that GDP is calculated as a sum of the three traditional sectors (agriculture, industry and services), so I'm not sure how it's calculated. At one point the report says that all scenarios assume more affluent worlds, is this just taken a priori as an assumption?

3) Several models don't seem to contain any kind of land model, and those that do, don't seem to have good feedbacks into other parts of the model. It's fair to assume that if a region had problems to feed their population, they would divert more resources into food production.

4) None of the models seem to give any consideration to the idea that the quality of the remainder of fossil fuels and nuclear fuels gets lower over time, as the higher quality grade are exploited first. This has implications for the supply of energy and the resources devoted to obtain energy.

5) It's unclear if the models allow for the possibility of energy demand not being met by supply, due to depletion.

Some of these concerns may not be valid for some of the models, but I don't get the impression that any of the models is satisfactory in respect of the 5 points. I would love to have further clarification on whether the concerns are valid or not.

I have a model based on the original World3 ("Limits to growth") model here, anybody interested can read the details here:

http://europe.theoildrum.com/node/5145

Some further study on the energy issues can be found here:

http://europe.theoildrum.com/node/5688

[Bert McInnis]

There are some global models underpinning the IPCC emissions scenarios. Some information about them can be found here:

http://www.ipcc.ch/pdf/special-reports/spm/sres-en.pdf

I have concerns about all of them. My main concerns are the following:

1) Population seems to be derived from the UN projections in all of the models and scenarios. The UN projections, as far as I know, don't consider the possible effects of climate change in any way. However, it's obvious that future population figures will depend strongly on the availability of food, and the availability of food is likely to depend on climate change, as climate change is expected to have an effect on crops.

2) Economic growth seems to be used as an input in several of the models, as if some trends were estimated for economic growth and used as an input to calculate other variables. But it's much more realistic to represent in a model the reverse causality (more energy leads to more economic growth) or a feedback loop between energy usage and economic growth. Also, I can see nothing to indicate that GDP is calculated as a sum of the three traditional sectors (agriculture, industry and services), so I'm not sure how it's calculated. At one point the report says that all scenarios assume more affluent worlds, is this just taken a priori as an assumption?

Yes economic growth defined as increasing GDP is often used as a driver for the underlying activities of an economy. This however is like trying to lead the donkey with its tail. GDP itself is an index of economic activity determined by a bottom up calculation. The economic activity that is the basis of GDP is measured by a system of national accounts which is assumed to be an appropriate measure of this detailed economic activity. In this day and age with the ubiquitous access to compute power it would be more appropriate to simulate (model) the physical actions underlying this economic activity directly and then one would calculate GDP as one of many possible indexes to be used to flesh out the meaning of some model trajectory. We have done this with the Australian Stocks and Flow Framework

Your comment " much more realistic to represent in a model the reverse causality" implies that if a model that says A is a function of B it also means that A is caused by B. I think that is a false identification. It should be taken to mean that A and B are to be thought of as coordinated or correlated. Causality should be left in the mind of the user of the model.

3) Several models don't seem to contain any kind of land model, and those that do, don't seem to have good feedbacks into other parts of the model. It's fair to assume that if a region had problems to feed their population, they would divert more resources into food production.

4) None of the models seem to give any consideration to the idea that the quality of the remainder of fossil fuels and nuclear fuels gets lower over time, as the higher quality grade are exploited first. This has implications for the supply of energy and the resources devoted to obtain energy.

5) It's unclear if the models allow for the possibility of energy demand not being met by supply, due to depletion.

Some of these concerns may not be valid for some of the models, but I don't get the impression that any of the models is satisfactory in respect of the 5 points. I would love to have further clarification on whether the concerns are valid or not.

I have a model based on the original World3 ("Limits to growth") model here, anybody interested can read the details here:

http://europe.theoildrum.com/node/5145

Some further study on the energy issues can be found here:

http://europe.theoildrum.com/node/5688

[Bert McInnis]

There are some global models underpinning the IPCC emissions scenarios. Some information about them can be found here:

http://www.ipcc.ch/pdf/special-reports/spm/sres-en.pdf

I have concerns about all of them. My main concerns are the following:

1) Population seems to be derived from the UN projections in all of the models and scenarios. The UN projections, as far as I know, don't consider the possible effects of climate change in any way. However, it's obvious that future population figures will depend strongly on the availability of food, and the availability of food is likely to depend on climate change, as climate change is expected to have an effect on crops.

2) Economic growth seems to be used as an input in several of the models, as if some trends were estimated for economic growth and used as an input to calculate other variables. But it's much more realistic to represent in a model the reverse causality (more energy leads to more economic growth) or a feedback loop between energy usage and economic growth. Also, I can see nothing to indicate that GDP is calculated as a sum of the three traditional sectors (agriculture, industry and services), so I'm not sure how it's calculated. At one point the report says that all scenarios assume more affluent worlds, is this just taken a priori as an assumption?

3) Several models don't seem to contain any kind of land model, and those that do, don't seem to have good feedbacks into other parts of the model. It's fair to assume that if a region had problems to feed their population, they would divert more resources into food production.

Yes the limited land resource needs to be represented. That is done in the whatIf GSS.

4) None of the models seem to give any consideration to the idea that the quality of the remainder of fossil fuels and nuclear fuels gets lower over time, as the higher quality grade are exploited first. This has implications for the supply of energy and the resources devoted to obtain energy.

5) It's unclear if the models allow for the possibility of energy demand not being met by supply, due to depletion.

Some of these concerns may not be valid for some of the models, but I don't get the impression that any of the models is satisfactory in respect of the 5 points. I would love to have further clarification on whether the concerns are valid or not.

I have a model based on the original World3 ("Limits to growth") model here, anybody interested can read the details here:

http://europe.theoildrum.com/node/5145

Some further study on the energy issues can be found here:

http://europe.theoildrum.com/node/5688

[Bert McInnis]

There are some global models underpinning the IPCC emissions scenarios. Some information about them can be found here:

http://www.ipcc.ch/pdf/special-reports/spm/sres-en.pdf

I have concerns about all of them. My main concerns are the following:

1) Population seems to be derived from the UN projections in all of the models and scenarios. The UN projections, as far as I know, don't consider the possible effects of climate change in any way. However, it's obvious that future population figures will depend strongly on the availability of food, and the availability of food is likely to depend on climate change, as climate change is expected to have an effect on crops.

2) Economic growth seems to be used as an input in several of the models, as if some trends were estimated for economic growth and used as an input to calculate other variables. But it's much more realistic to represent in a model the reverse causality (more energy leads to more economic growth) or a feedback loop between energy usage and economic growth. Also, I can see nothing to indicate that GDP is calculated as a sum of the three traditional sectors (agriculture, industry and services), so I'm not sure how it's calculated. At one point the report says that all scenarios assume more affluent worlds, is this just taken a priori as an assumption?

3) Several models don't seem to contain any kind of land model, and those that do, don't seem to have good feedbacks into other parts of the model. It's fair to assume that if a region had problems to feed their population, they would divert more resources into food production.

4) None of the models seem to give any consideration to the idea that the quality of the remainder of fossil fuels and nuclear fuels gets lower over time, as the higher quality grade are exploited first. This has implications for the supply of energy and the resources devoted to obtain energy.

This is also done in the whatIf GSS. Fossil fuels have increasing unit costs for discovery and the metal mine has production unit costs that increase with cumulative production.

5) It's unclear if the models allow for the possibility of energy demand not being met by supply, due to depletion.

Energy demand and supply are not equilibrated in the whatIf GSS. In fact this is one of the three main tensions designed into the whatIf GSS, the other two being crops and wood.

Some of these concerns may not be valid for some of the models, but I don't get the impression that any of the models is satisfactory in respect of the 5 points. I would love to have further clarification on whether the concerns are valid or not.

I have a model based on the original World3 ("Limits to growth") model here, anybody interested can read the details here:

http://europe.theoildrum.com/node/5145

Some further study on the energy issues can be found here:

http://europe.theoildrum.com/node/5688