Greenhouse Effect

Without the protection of Earth's atmosphere, the global mean ambient temperature would be as low as -18°C. Particular gases in the atmosphere such as carbon dioxide (CO2), water vapour and methane capture parts of the incoming solar radiation, acting like a greenhouse. These gases have natural as well as anthropogenic, or human-induced, sources. Figure 1.6 illustrates the anthropogenic greenhouse effect.

Human Induced Greenhouse Effect
Figure 1.6 Origin of the Anthropogenic (Human-induced) Greenhouse Effect

The existing natural greenhouse effect makes life on Earth possible. Without the natural greenhouse effect, Earth would emit most of its heat radiation into space. Incident sunlight heats the Earth's surface, and the mean global ambient temperature is roughly +15°C due to the retention of this heating energy.

Over millions of years, nature has created a balance in the concentration of atmospheric gases. This has made life as we know it today possible. Several natural temperature variations have occurred over the preceding millennia, as evidenced by different ice ages.

Additional greenhouse gases are emitted to the atmosphere as a result of energy consumption and other human-induced influences. These gases cause the anthropogenic greenhouse effect. Table 1.7 summarizes the characteristics of the most important greenhouse gases.

Anthropogenic carbon dioxide (CO2) results from burning fossil fuels and biomass. It contributes 61 per cent to the greenhouse effect and is the most relevant greenhouse gas. Biomass is carbon dioxide neutral if it is used at the same rate as it is grown again. On the other hand, fire clearing in the rain forest produces vast amounts of CO2 that has been bound by these plants over decades or centuries and thus can be considered a contributor to the greenhouse effect. However, the burning of fossil fuels emits the largest amount of anthropogenic carbon dioxide. The share of fossil fuel-related carbon dioxide emissions is currently 75 per cent, and is increasing. The carbon dioxide concentration in the outer atmosphere has already risen from 280

Table 1.7 Characteristics of Greenhouse Gases in the Atmosphere in 1998

Greenhouse gas

CO2

ch4

n2o

O3

CFC-11

HFC-23

Concentration in

ppm

365

1.745

0.314

0.03

0.000268

0.000014

Atmospheric lifetime

in years

5-200

12

114

0.1

45

260

Rate of

concentration

change in %/year

0.4

0.4

0.25

0.5

-0.5

3.9

Specific global

warming potential

1

32

150

2000

14,000

10,000

Global warming

share in %

61

15

4

<9

11 (all fluorocarbons)

Source: IPCC, 2001

Source: IPCC, 2001

ppmv (parts per million by volume) in 1850 to 372 ppmv in 2002 (Biasing and Jones, 2003). If there is no change in energy policy, this development will accelerate in the coming decades. Today's carbon dioxide concentration in the atmosphere is already higher than at any other time during the past 250,000 years.

Anthropogenic methane (CH4) sources are coal mining, production of natural gas, waste disposal and agriculture such as cattle farming or cultivation of rice. The production and use of fossil fuels causes the majority of methane emissions. Although the concentration of methane in the atmosphere is less than 1 per cent of the carbon dioxide concentration, methane has a high climate change potential (15 per cent contribution to the greenhouse effect), i.e. the global warming potential of methane is much higher than that of carbon dioxide. Therefore, much smaller emission quantities are critical. In 1998 the average tropospheric concentration of 1.745 ppmv of methane had already more than doubled compared to the pre-industrial concentration of 0.7 ppmv.

Chlorofluorocarbons (CFCs) have been used in large quantities as refrigerants or propellants in spray cans. CFCs fell into disrepute mainly due to their destructive influence on the ozone layer in the stratosphere at a height of 10-50 km. International agreements to reduce CFC production in a step-by-step process initially slowed down the increase and finally decreased the concentration in recent years. However, the greenhouse potential of CFCs (11 per cent contribution to the greenhouse effect) was no significant argument in the CFC reduction discussions. Some substitutes for CFCs such as HFC-23 or R134a have significantly lower ozone-destroying potential but nearly the same greenhouse potential.

Fire clearance of tropical rain forests and the use of nitrogenous fertilizers are sources of anthropogenic nitrous oxide (N2O). In 2001 the atmospheric N2O concentration of 0.317 ppmv was only 16 per cent above the pre-

industrial value; however, nitrous oxide also has a critical influence on climate change since it has a relatively long atmospheric residual time.

Motorized road traffic using fossil fuels also causes pollutants responsible for the formation of ground level ozone (O3). Human-induced stratospheric water vapour (H2O) also influences the greenhouse effect. However, the extent of the impact of these gases and other gases is difficult to estimate.

The contribution of different sources to the anthropogenic greenhouse effect can be summarized as:

use of fossil fuels 50 per cent chemical industry (CFCs, halons) 20 per cent destruction of tropical rain forests

(fire clearance, rotting) 15 per cent agriculture 15 per cent

These contributions vary regionally. In developing countries, the burning of rain forests and agriculture have the highest climatic influence, while in industrial countries, the use of fossil fuels dominates. As indicated in Figure 1.7, the energy demand and resulting carbon dioxide emissions also vary enormously.

Per capita, the UK emits about 9 times more carbon dioxide than does India; for Germany it is 11 times more and for the US, 20 times more. If the people of all countries caused the same amount of anthropogenic carbon dioxide as those in the US, global carbon dioxide emissions would increase five times and the anthropogenic greenhouse effect would double. The per capita CO2 emissions of road traffic alone in Germany are twice as high as the total per capita emissions in India. In the US the picture is even worse.

The reasons for climate change are controversial. Even today, studies are published questioning the anthropogenic greenhouse effect. In fact, part of the global temperature increase of 0.6°C during the past 100 years is linked to natural fluctuations. However, the majority comes from anthropogenic emissions. In most cases it is obvious that the authors who refute the existence of anthropogenic climate change are associated with lobby groups that would be disadvantaged if a radical change of energy policy were to take place.

There are several undeniable facts substantiating a creeping climate change. In 2001, the following events were seen as indications for the increasing greenhouse effect (IPCC, 2001):

• Worldwide, 1998 was the warmest year since temperature measurements began in 1861

• The 1990s were the warmest decade since records began

• Global snow cover and the extent of ice caps has decreased by 10 per cent since the late 1960s

• Non-polar glaciers are undergoing widespread retreat

• Global mean sea level rose by 0.1-0.2 m during the 20th century

• During the 20th century, precipitation increased by 0.5-1 per cent per decade

USA Australia Canada Germany United Kingdom Japan Former USSR Switzerland China Latin America Asia India Africa Bangladesh World (mean)

Annual per capita CO2 emissions from fuel combustion (t CO2)

Annual per capita CO2 emissions from fuel combustion (t CO2)

Source: IEA, 2003a

Figure 1.7 Annual per capita Carbon Dioxide Emissions from Fuel Combustion for Different Countries in 2001

• Heavy precipitation events increased at mid latitudes and far northern latitudes

• The frequency and intensity of droughts in Asia and Africa increased in recent decades.

A detailed prediction of the consequences of the anthropogenic greenhouse effect is not possible. Climatic models can only give an estimate of what will happen should the emission of greenhouse gases continue unchecked.

If we do not reduce anthropogenic greenhouse gas emissions, the carbon dioxide concentration in the atmosphere will more than double by the end of this century with respect to pre-industrial values. As a result, the mean global temperature will rise more than 2°C. The currently predicted range is from + 1.4°C to +5.8°C. Such a temperature rise is similar to that between the ice age of 18,000 years ago and today's warm period. However, the transition from the last ice age to the current warm period took over 5000 years, but we are discussing a temperature change that will happen over 100 years.

A temperature rise of +2°C or more than +0.1°C per decade is already a very critical value, which will cause catastrophic consequences for food production and ecosystems. Global warming will have a drastic influence on global forest viability and agriculture. Globally, the lack of food in some regions will get significantly worse due to a predicted widespread decrease in agricultural production. The result could be famines and mass migrations. Furthermore, global warming will increase storm intensities with disastrous effects in tropical regions as well as in mid-range latitudes. Global sea level will rise between 0.1 and 0.9 metres in this century. The long-term sea-level rise could be as high as several metres, with severe influences on low-lying regions. Recent flood disasters give us an indication of what is to come. For example, about 139,000 people died from floods in Bangladesh in 1991. Many low-lying regions and islands will disappear from the map.

It is a sad fact that these consequences cannot be avoided completely. The limiting of global warming to +2°C is possible only if enormous efforts are undertaken immediately. By the year 2100, the various greenhouse gas levels must be reduced drastically compared with 1990 levels. This could be achieved in the following way:

• decrease global carbon dioxide emissions by 70 per cent

• reduce global N2O and CH4 emissions by 50 per cent and 5 per cent, respectively

• completely ban the use of all CFCs, halons and HFC-22.

Furthermore, demographers predict an increase of the world population to 15 billion (IPCC, 2000) (see also Table 1.16), more than twice the current population. Consequently, to achieve a 70 per cent reduction in global carbon dioxide emissions, the per capita carbon dioxide emissions in 2100 will have to be reduced to 15 per cent of the emissions for 1990.

The industrial countries cause the largest amount of emissions. The developing countries are currently lagging behind, but if they catch up, the industrial countries will have to achieve the following higher emission reductions for effective climate protection:

• 25 per cent reduction of CO2 emissions by 2005 compared with 1990

• 50 per cent reduction of CO2 emissions by 2020 compared with 1990

• 80 per cent reduction of CO2 emissions by 2050 compared with 1990

• 90 per cent reduction of CO2 emissions by 2100 compared with 1990.

This would mean a virtually complete withdrawal from the use of fossil fuels in this century. Technically and economically this is possible; however, in the face of a half-hearted climate policy, every possible effort has to be made.

It is not impossible to adhere to these climate reduction targets while still increasing global prosperity. However, everybody has to recognize the necessity of strong reductions and the consequences of failure. Sufficient possibilities to cover our energy demand without fossil energy sources exist today: the power industry could be based entirely on renewable energies. Thus, the question of whether our energy supply could be managed without fossil fuels is easy to answer. The question yet to be answered is: when will society be ready to establish a sustainable energy supply without fossil fuels and face up to its responsibilities to future generations?

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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