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We have begun to see the factors that control CO2 emission: population, GDP, energy use per dollar GDP, and carbon release per Watt of energy. CO2 emission can be estimated by multiplying these factors together; check it out for yourself that the units cancel correctly. Constructing CO2 emission from these pieces is called the Kaya identity; it looks like this.

$GDP Watts CO2 emitted

person $ Watts

You can play with the Kaya identity and make your own forecast online at http://understandingtheforecast.org/models/kaya.html, and see results in Fig. 9.12.

Population has been rising at a rate of about 1.3% per year, but this rate of growth is not expected to continue. Rates of population growth tend to decrease with affluence of societies. Population is forecast to level off at some value, but that value could be

9 billion people or it could be 15 billion people. A typical "business-as-usual" forecast puts the leveling-off point at about 11 million people.

The second factor, $GDP/person, has been rising throughout the last century at a rate of about 1.6% per year, rising from US $930 in 1990 to $4800 per person in 2000.

The third factor is the energy intensity: how many Watts of energy it takes to make a dollar GDP. The energy intensity not only reflects efficiency but also the difference between heavy and light industry (Fig. 9.13c). Energy intensity has been dropping by a rate of about 0.55% per year over the past century, but the last few decades have seen a drop by about 1% per year. According to the model on the web site, the slower rate of decrease results in 825 ppm pCO2 in 2100, while 1% per year results in about 700 ppm (Fig. 9.14).

1900 1950 2000 2050 2100

Year

Fig. 9.13 Results from the Kaya identity model (http://understandingtheforecast.org/ Projects/kaya.html). (a) Population, (b) GDP per capita, (c) energy intensity, and (d) carbon efficiency.

1900 1950 2000 2050 2100

Year

Fig. 9.13 Results from the Kaya identity model (http://understandingtheforecast.org/ Projects/kaya.html). (a) Population, (b) GDP per capita, (c) energy intensity, and (d) carbon efficiency.

700 650 600 550 E 500 â 450 400 350 300 250

(c)

25

20

¿2

15

T5 g

10

2

<B

5

1-

0

1950

2000 Year

2050

2100

Fig. 9.14 More results from the Kaya identity model. (a) Carbon emissions, (b) ISAM carbon cycle model pCO2, and (c) carbon-free energy required for CO2 stabilization.

The final factor, the carbon released per energy yield, is not only the result of efficiency of the power plants but also the characteristics of the feedstock energy source. Coal contains intrinsically less energy per carbon than does oil or gas whereas nuclear and hydroelectric energy release no carbon at all. CO2 emission scenarios from the Intergovernmental Panel on Climate Change, or IPCC, ranged from 6 to 26 Gton C emission per year in 2100. We will return to this model in Chapter 10 to see what happens to that CO2 and in Chapter 13 to see what it means in terms of energy.

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Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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