The inspiration for this tool is a chapter by Jørgen Nørgård in a recent book "Rethinking Climate and the Energy Policies".


The equation I=P*A*T which combines population (P), affluence (A) and technological eco-intensity factor (T), has  been known since  Ehrlich and Holdren presented it in 1971. This equation aims to show that reducing climate change by means of only reducing T may be incredibly difficult if no measures are taken in the other two factors, i.e. P and A.


In our version we have extrated diet (D) as a seperate impact and therefore the equation I=PAT(D). The ecological impact is represented by CO2 emissions and the global concentration level is translated into mean global temperature increase until 2100. The impacts are tracked on 16 different regions of the world and equality within population growth and affluence can therefore be investigated.


The ecological footprint is also tracked based on data from  www.footprintnetwork.org and illustrates how much area is needed to maintain a sustainable production of food and energy to  cover the global demand. The result is how many earths are needed with a given level of consumption.




We would like to thank the GLOBAL FOOTPRINT NETWORK for providing us with data that made the estimation of the footprint possible.

“© Global Footprint Network 2016.  National Footprint Accounts, 2016 Edition.  Licensed and provided solely for informational  purposes.  Contact Global Footprint Network at www.footprintnetwork.org to obtain more information.”


Input scenarios included in the IPAT(D) model

The IPAT(D) model includes a database with the scenarios listed below for population, affluence, technological development, GHG emissions and diet. All combinations of these parameters can be tested in the model.


Population and Affluence Scenarios

The population and affluence scenarios are based on the Shared Socio-economic Pathways (SSPs) data (Moss et al 2010, Kriegler et al 2012, O’Neill et al 2014) illustrating possible pathways for change in population and economic development.

Each SSP consists of quantitative projections of GDP, Population and Urbanisation along with resource and technology constraints consistent with the underlying qualitative narrative.  SSP1 “Sustainability – taking the green road” is a scenario in which the world shifts gradually, but pervasively towards a more sustainable path, with a focus on inclusive development within environmental limits. SSP2, “Middle of the Road” is a world in which social, economic and technological trends do not significantly change from historical rates of change. SSP3, “Regional Rivalry – A Rocky Road” is characterised by resurgent nationalism, competitiveness, fragmentation and little cooperation on environmental policy with a focus on energy and food security within nation development goals. SSP4, “Inequality – A Road Divided”, is a scenario in which there is increasingly inequality in economic opportunity and political power, leading to social stratification across the world and within countries. Social cohesion degrades and conflict becomes common. SSP5, “Fossil-fuelled Development – Taking the Highway”, relies heavily on the open market and innovation to drive rapid technological change and development of human capital towards sustainable development.


Population scenarios


Low fertility in current low and medium income countries, medium fertility in current rich OECD countries


Medium fertility in all countries


High fertility in current low and medium income countries, low fertility in current rich OECD countries


High fertility in current low income countries, low fertility in current medium income and rich countries and medium fertility in rich OECD countries


Low fertility in current low and medium income countries, high fertility in current rich OECD countries

Low fertility

Low fertility, immediately fall to < 1.5 birth per woman in all countries

No change

No change in population from 2015 and forward

Affluence scenarios


High growth in current low and medium income countries, medium growth in current high income countries


Medium uneven economic growth in all countries


Low economic growth in all countries


Low economic growth in current low income countries, medium growth in other


High economic growth in all countries

No change in affluence

No change from 2015, constant in each region on the level of 2015

Economic crisis

Crisis until 2050, stronger in high income countries, and then slow recovery


All regions reach by 2100 the level of USA in 2015

Catching up

Continuing historic growth rates until 2050, after 2050 the current low income countries catch up with current high income countries

Shifting power                  

Low economic growth in current high income countries and high growth in current low income countries


Diet scenarios

Dietary impacts can be altered for each region in the model, but for simplicity sake, only three alternatives are used in this model. The diets from different countries and regions are based on FAOSTAT (2017) and change in environmental impact from Ranganathan J et al (2016).  


Diet scenarios

IND Diet

India’s diet in all countries, transition over 20 years

USA Diet

USA or EU diet in all countries, transition over 20 years

No Change

No change from today


Technology scenarios and associated GHG share

Three scenarios are chosen from a large number of technology scenarios from TIAM-World driven by the different SSP scenarios, to represent the potential technological development. The TIMES Integrated Assessment Model (TIAM) is a multi-regional and inter-temporal partial equilibrium model of the entire energy/emission system of the world, based on the TIMES paradigm (Loulou and Labriet 2008; Loulou 2008). Several variants of the model exist that differ with regard to, e.g. regional aggregation, sectoral details, etc. TIAM-World is the model variant used in the IPAT(D) model.

From each scenario in TIAM-World, CO2 emissions per GDP has been calculated by year and region, and is used in the IPAT(D) model to scale the GHG emissions with change of regional GDP, which is further scaled with the change in regional population.


Technology scenarios

Business As Usual

No policies or targets implemented, competitive markets secure global cost minimized solution

Strong Technology  Development

90% non-fossil power, 50% non-fossil primary energy in 2050. More than 90% non-fossil primary energy in 2100

Radical Technology Development

100% non-fossil power, 85% non-fossil primary energy in 2050. 95% non-fossil primary energy in 2100



Ehrlich P and Holdren J (1971) Impact of population growth, Science (New Science), 171(3977), 1212-1217

FAOSTAT (2017) Food and Agriculture Organization of the United Nations data. Available athttp://www.fao.org/faostat/en/#data

Jespersen and Chick (2016) John Maynard Keynes (1883-1946). I. G. Faccarello & HD Kurz (red), Handbook on the History of Economic Analysis: Great Economists since Petty and Boisguilbert. vol. 1, Edward Elgar Publishing, Incorporated, Cheltenham, UK, s. 468-483.

Kanors-EMR (2017) TIAM-WORLD. Available athttp://www.kanors-emr.org/models/tiam-w

Kriegler E et al (2012) The need for and use of socio-economic scenarios for climate change analysis: A new approach based on shared socio-economic pathways. Global Environmental Change 22, 807–822.

Loulou R, Labriet M (2008) ETSAP-TIAM: the TIMES integrated assessment model Part I: Model structure. Computational Management Science, 5, issue 1, p. 7-40, https://EconPapers.repec.org/RePEc:spr:comgts:v:5:y:2008:i:1:p:7-40

Loulou  R (2008) ETSAP-TIAM: the TIMES integrated assessment model Part II: Mathematical formulation. Computational Management Science, Special issue Managing Energy and the Environment, 5(1-2), 41-66

Moss RH et al (2010) The next generation of scenarios for climate change research and assessment. Nature 463, 747–756NASA (2017) Data. Available at: http://climate.nasa.gov/vital-signs/global-temperature/

O’Neill BC et al (2014) A new scenario framework for climate change research: the concept of shared socioeconomic pathways. Climatic Change 122, 387–400

Ranganathan J et al (2016) Shifting diets for a sustainable food future. Available at: http://www.wri.org/sites/default/files/Shifting_Diets_for_a_Sustainable_Food_Future_1.pdf

Rees W and  Wackernagel M  (1996) Our Ecological Footprint: Reducing Human Impact on the Earth”, New Society Publishers, Gabriola Island, BC

Shrinkthatfootprint (2017) Life Cycle Assessment Data. Available athttp://shrinkthatfootprint.com/food-carbon-footprint-diet

Wackernagel M et al (2014) Ecological footprint accounts, Handbook of Sustainable Development (second revised edition), Edward Elgar Publishing, Cheltenham, Glos, UK.


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