Man s Use of Energy - Units

Transcription

1 Man s Use of Energy - Units Energy figures are quoted in a wide range of units. During the following lectures we will mainly use Joules for smaller energy quantities, TWh for discussions about national energy energy consumption, or the Q for quantities on a world scale (1 Q=10 18 BTU or 1.055x10 21 J ~ J for our purposes). British Thermal Unit x 10 3 J 1 kwh 3.6 x 10 6 J 1 MWh 3.6 x 10 9 J 1 TWh 3.6 x J 1 Q x J Energy equivalent units are also often used. Usually a mass or volume of a fuel is converted to its energy equivalent. Problematic as fuel grades vary and the method of power generation affects the total amount of energy retrieved. E.g. 1 tonne of Uranium equivalent to 8.6x10 14 J if used in a thermal reactor but 8 x J if used in a breeder reactor. Typical energy equivalent units are: Gallon of petrol 1.4 x 10 8 J Barrel of oil 5.8 x 10 9 J tonne of coal 2.6 x J

2 Natural Energy Flows Mean Solar Input 5000 Q/year Reflected radiation (albedo 30%) 1500 Q/y Photosynthesis 1 Q/y Mean tidal power assoc with Earth-Sun-Moon ~ 0.1 Q/y Geothermal outflow from Earth ~ 1 Q/y Atmosphere Earth Solar power assoc. with winds waves and currents 12 Q/y Absorption and reradiation 2350 Q/y Evaporation and precipitation 1300 Q/y

3 Population Projection Ranges Population is one of the fundamental driving forces of future emissions. Three main research groups project global population United Nations (UN, 1998, 1999), World Bank (Bos and Vu, 1994), and IIASA (Lutz et al., 1997). Most of the central population projections lead to a doubling of global population by 2100 (to about 10 billion people compared to 5.3 billion in 1990). In recent years the central population projections for the year 2100 have declined somewhat, but are still in line with a doubling by For example, the latest UN (1998) medium low and medium high projections indicate a range of between 7.2 and 14.6 billion people by 2100, with the medium scenario at 10.4 billion. The IIASA central estimate for 2100 is also 10.4 billion, with a 95% probability that world population would exceed six and be lower than 17 billion (Lutz et al., 1997).

4 Population Projection Ranges

5 Gross World Product Economic development and growth are fundamental prerequisites to achieve an increase in living standards. It is thus not surprising that assumptions about economic development constitute among the most important determinants of emissions levels in the scenarios. However, economic growth prospects are among the most uncertain determinants of future emissions. Increases in gross world product compared correlates closely with energy use The historical gross world product growth rate has been about 4% per year since 1950; in the scenarios the average annual growth rates to 2100 range from 3.2% per year to 1.1% per year, with the median value at 2.3% per year.

6 Extrapolation of World Energy Consumption What of the future? Let s try to put limits on what will happen to 1970 was a Golden Age when economic growth was at a maximum. Much of the investment that made this growth possible was in power stations so we can assume that the rate of increase of energy production was also at its maximum (also ~4%/yr) Assume that this will continue for the next 100 years. Energy consumption per year, E n, at n years after 1970 is E n =E 0 (1+R) n, where E 0 is the energy consumption in 1970 and R is the rate of growth per year: E n =E 0 (1.04) n So using this projection an energy use of 30 Q/year is exceeded by 2098 This is 1 % of the net solar input of 3000 Q/year. The extra energy will be lost eventually by re-radiation E/E 0 =(T/T 0 ) 4 as E=1.01E 0 T-T 0 ~1 K If we could stand a 1 K rise rise in global T we couldn t cope with much more. This is not due to emissions but direct heating from energy conversion. We have put limits on energy use by saying that energy use WILL NOT get above the rising line but CANNOT get above the horizontal line given by 30 Q/year

7 Extrapolation of World Energy Consumption 30 Energy Use (Q/year) Year Energy Use (Q/year) Year

8 Extrapolation of World Energy Consumption The Reference Projection we have just made puts bounds on the future energy use Now consider world population growth and estimate the desired standard of living to derive an estimate of future energy consumption. This will serve to highlight whether we have a resource problem, and if so, how acute it is. Lets make a series of initial assumptions about where we want our future energy consumption curve to lie. 1. The actual course of events will lie everywhere below the reference projection, but will steadily increase to an asymptotically constant level. 2. This level should be enough to allow the total world population a comfortable standard of living, if possible not lower than that which we now enjoy. 3. Since, as we ll see there is a resource problem this level should be as low as possible.

9 Trends in World Population Clearly we cannot meet both points 1 and 2 unless the world population stabilises. This has almost occurred in richer countries. However, the mass of population is in poorer countries and here the age structure is, apart from catastrophes, such that it is inevitable that the population will rise considerably over the next few decades. To gauge world energy use we need to look at world population trends. Historically, populations were typically in balance, or slowly increasing, with both birth and death rates high. 200 years ago, the death rate began to fall in European countries, but the birth rate remained higher for some time longer before following the death rate downwards. Both have now stabilised at a much lower level. The passage through this demographic transition took about 150 years to complete. The graphs show both past trends and future projections for different regions of the world. The birth rate falls due to improved economic circumstances and social change

10 Trends in World Population The model divides the history of population growth into four stages, characterized primarily by changing patterns of birth and death rates. Stage 1, the situation that has characterized the world throughout most of history, is marked by high death and birth rates. Population levels fluctuate somewhat but there is no steady growth. In Stage 2, which began in the West around 1800, birth rates remain steady but mortality rates begin to decline because of improvements that reduce the toll of infectious diseases--the big killer in countries with high death rates. Population begins to grow. In Stage 3, a continuing decrease in death rates is accompanied by a decline in birth rates. Falling childhood mortality means that the number of births needed to reach a desired family size drops. In response, fertility rates decline, but the population continues to grow because the number of births in a society is based not only on the number of children each woman bears but also on the number of women of childbearing age. With a disproportionate share of people in the childbearing years, population grows even after fertility rates decline. In Stage 4, the situation in the developed world today, there is a rough parity between births and deaths. Correspondingly, the population grows very slowly--if at all. Once a Stage 4 equilibrium of low birth and death rates is reached, immigration becomes the driving force for additional population growth.

11 Trends in World Population

12 Trends in World Population Progress Toward Population Stabilization by Region, Source: United Nations (U.N.) Population Division, World Population Prospects, (The 1996 Revision), on diskette (U.N., New York, 1996). Note: Progress toward stabilization is measured by dividing a region's crude birth rate by its death rate. A ratio of 1 indicates a stable population. Values are based on 5-year rates.

13 Extrapolation of Energy Use Lets now consider assumption (2) our desired standard of living In 1980 the world energy use was 0.28 Q/year for 4 billion people this is equivalent to 0.07 Q/year/billion. However, in the USA the figure was about 0.07 Q/year for 0.2 billion people this is equivalent to 0.35 Q/year/billion Let us assume that a desirable world standard of living is that currently enjoyed by Americans at the moment Then suppose that with the projected world population from the IPCC the energy consumption will be: High Variant Medium Variant Low Variant billion people Q/year in 2100 A worrying thought, however, less than the 30 Q/year maximum. Let s be pessimistic for now and say energy use will reach 5 Q/year.

14 Timescales for Change birth rate decline assoc. economic growth, death rate driven by human health (rapid) Econ. Growth closely linked to inc. in energy supply, essentially the faster a nation inc its use of energy the faster its econ. Grows and earlier birth rate falls. Lowering birth rate sooner reduces the demographic transition time and so reduces final population of the nation. In the long term this also reduces its final energy burden. So far we have ignored the limits imposed by economics on the rates of change. To meet this increase in energy demand may require substantial changes in the way our system functions. We may need to change our economy to preserve our energy supply. (This is already happening due to CO 2 emissions limitations post Kyoto) These changes cannot be made overnight and are subject to economic constraints. We need rough estimates of the timescales involved.

15 Timescales for Change 2 Our standard of living is greater than we would have if we were each self sufficient. This is the result of previously invested capital. Our national income is essentially the return on that capital investment, at say a rate of 10% per year. We must reinvest some of this income to replace our capital. If we reinvest 10% of our income to form new capital then we replace it at 1% per year So get complete renewal of capital base every 100 years, more detailed estimates give about a 60 year renewal time. So we have just about enough time to replace our existing utilities. The same thing applies to developing countries raising income to our level. Once again it is a resource consideration that may force us to make such changes.

16 Summary We have so far assumed that there is a limit to the rate at which we can increase energy supply that we CANNOT exceed and there is a maximum energy usage of 30 Q/year that we MUST not exceed. These considerations are based on current increases in use and a limit to the atmospheric warming we are prepared to accept. CO2 and climate change is providing a greater brake on the system presently. World population projected to be between 8 and 16 billion by Implying an energy supply of between 3 and 5 Q/year. With no further population or std of living change this level of energy use remains fixed. We want the energy supply to grow as fast as possible to max econ growth in the developing world and allow it to pass through a demographic transition quickly. Timescales for this change are envisaged as being longer, though only slightly, than those required for extensive reinvestment in infrastructure. We have assumed that the transition will be smooth, this is by no means guaranteed. In addition, we assumed that the world s desired standard of living is that which the US now enjoys. This will not lead to equality unless countries close to this standard do not further increase their energy consumption. Other countries coming from behind while we remain static may be hard to accept, an implicit assumption in our scenario.