Essay on Global Warming and Greenhouse Effect

Essay on Global Warming and Greenhouse Effect!

The Earth receives shortwave radiation from the sun (including the visible part of the spectrum), one- third of which is reflected while the rest is absorbed by the atmosphere, ocean, ice, land, and biota. The energy absorbed from solar radiation is balanced, in the long term, by outgoing radiation from the Earth and atmosphere. Terrestrial radiation is emitted in the form of long wave infrared energy.

The balance between energy absorbed and emitted as long wave infrared radiation can change due to a number of factors:

Changes in the sun’s energy output, slow variations in the Earth’s orbit and the greenhouse effect. The greenhouse effect is one of the most important factors and is one which humankind has the capacity to change.

Shortwave radiation can pass easily through the atmosphere, whereas long wave terrestrial radiation emitted by the warm surface of the Earth is partially absorbed by a number of trace gases in the atmosphere. These trace gases are called greenhouse gases (GHG). The main natural GHGs are carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), water vapour (H₂O) and ozone (O₃) in the troposphere and stratosphere. Further human activities in recent decades add new halocarbons (HFCs) as GHG.

The warming effect on the earth’s surface by certain gases in the atmosphere was first recognized in 1827 by Jean-Baptiste Fourier, the famous French mathematician. Around 1860, the British scientist John Tyndall measured the absorption of infrared radiation by CO₂ and water vapour, and he suggested that the cause of the ice ages may be due to a decrease of atmospheric concentrations of CO₂.

In 1896, the Swedish scientist Svante Arrhenius estimated that doubling the concentration of CO₂ in the atmosphere may lead to an increase of the earth’s surface temperature by 5-6°C. Thus the greenhouse effect arises because the atmosphere is largely transparent to incoming solar radiation, while being quite heavily absorbing to outgoing thermal radiation from the planetary surface and the atmosphere.

Since the beginning of the earth’s origin, the effect exists as a natural process. 

Twentieth century the effect is enhanced by man’s activities that are liable to destabilize the natural balance. Different trace gases in the atmosphere contribute to the greenhouse effect, but among them the major gases are carbon dioxide (CO₂), chlorofluorocarbons (CFCs), methane (CH₄) oxides of nitrogen (NO_x), water vapour (H₂O) and per-fluorocarbon (CF₄) and other trace gases.

The important greenhouse gases and their anthropogenic sources are given in Table 16.1.

The relative effect of different gases on the greenhouse effects has been calculated by a number of authors.

Since pre-industrial period (1750-1800) to present day (2011), IPCC scientific committee assessed the changes of major greenhouse gases affected by man’s activities (Table 16.2) and opined that if current trend continues, an average global warming over the 21st century will be at 0.3°C per decade, with associated major changes in regional climate patterns and sea level rises averaging about 6 cm per decade.

From time to time, it was attempted to assess the emission of greenhouse gases by different countries, some figures were given in Figs. 16.1 & 16.2. There are debate about the percentage responsibility of different countries on emission of GHGs.

The summarised details are given in Fig. 16.3. Historically, it is true that developing countries have contributed relatively little to the risk of global warming, being responsible for only about 15% of world greenhouse gas emissions between 1870 to 1986, although some 75% of the world population lives in the Third World, the developing countries.

The chemical composition of troposphere and the stratosphere is an important factor determining the mean temperature of the planet’s surface and, thus, its climate.

The amount of heat trapped depends mostly on the concentrations of various heat trapping gases—known as greenhouse gases—in the troposphere. The principal greenhouse gases are carbon dioxide contributing the major share along with other trace gases as stated earlier.

Until recently, most greenhouse gases were emitted and removed from the troposphere by the Earth’s major biogeochemical cycles, without disruptive interferences from human activities.

However, since the Industrial Revolution (1760) and especially since 1950, we have been putting enormous quantities of greenhouse gases into the atmosphere, primarily from the fuel burning (57%), the use of CFCs (17%), agriculture (15%) and deforestation (8%). There is growing concern that these gases can amplify the natural greenhouse effect and turn up the planets thermostat fairly rapidly.

Greenhouse Gases and Global Climate Changes:

The changes in CO₂ level—as measured at Mauna Loa observatory in Hawai—ranges from 315 ppm in 1958 to 380 ppm in 2006 with a narrow seasonal oscillation every year.

There are two most important human activities that lead to gradual rise of CO₂ level in the atmosphere, viz., over increasing burning of fossil fuel and loss of CO₂ sink i.e., the gradual rise of destruction of forest cover, coal and oil consumption increased many fold over the years as chief energy sources (Fig. 16.4).

The rise of CO₂ level have immediate effect on the rise of global temperature. There are clear examples that rise of CO₂ level in atmosphere have positive correlation with rise of temperature on earth surface in pre-historic period or even in post-industrialisation phase (Fig. 16.5).

Over the years other GHGs like NO_x, CH₄ and CFCs were also added to the atmosphere in alarming rate. As per NASA report, CFCs rise is about 5% per year, while CH₄ rise about 1 % per year.

On the whole if the above rise of GHGs takes place in the current rate the overall rise of each pollutant gases that contribute the greenhouse effect will be somewhat in fairly higher side with doubling point sometime in 2030 (Figs. 16.6 & 16.7). Thus the corresponding temperature changes from 1850 to 2050 at the magnitude of 0.25°C to 3.5°C (Fig. 16.8). Thus it is very urgent to restrict the current rate of GHGs emission.

Though the GHGs effect on climate is slow and imperceptible immediately but its impact on climate change in the long run become alarming and irreversible. A summarised idea of changes in atmospheric trace gases and its relevance to global climate change is given in Table 16.3.

In spite of repeated global effects for abating the emission of greenhouse gases, yet there is cumulative rise of greenhouse gases over the years. Ramanathan (1976) presented a model for growth in some green­house gases, 1980-2030 (Table 16.3).

Global Warming Potential:

Global warming potential (GWP) is an index that attempts to quantify the climate impact of the same emission of a given greenhouse gas relative to that of a reference gas (usually CO₂), by taking into account the different heat trapping abilities on a molecule by molecule basis and the different rates of removal of the two gases.

This is a calculation of possible warming effect on the lower atmosphere of each of the greenhouse gases relative to CO₂.

The details of warming potential are:

However, this computation is subject to change with time as our knowledge continuously improves.

Possible Impact of Global Warming:

The rise of greenhouse gases and consequent global warming phenomenon have a number of effects on earth climate, ecosystems and biospheric processes.

The major events are:

(a) Sea Level Change:

One major consequence of global warming arising out of greenhouse effect is the sea level rise. Four major changes take place prior to sea level rise as consequence of global warming.

They are:

Thermal expansion, mountain glacier melting, Greenland ice sheet melting and Antarctic ice sheet melting. Tables 16.4, 16.5 & 16.6 provide an estimate of sea level changes in the past 100 years, between 1990-2030 and future trend if CO₂ emission rate continued as usual or not modified suitably.

In spite of uncertainties about the degree of rise in sea level, any rise would pose a direct threat to low-lying coastal zones and islands and tropical coastal wetlands, where the mangrove ecosystems are under threat. Where rising sea level is combined with tectoxic subsidence and/ or human actions that may exacerbate the problem, the situation is potentially very serious.

Table 16.7, indicates the synthesised results in sea level by the year 2100 based on the high estimate of global warming under the 1900 business-as-usual scenario. This may be regarded as extreme but down-scaling still implies substantial problems for countries such as Bangladesh and-China, particularly where economic growth in terms of GNP remains at a low level.

There are also reports of:

1. Rise in Arctic & Atlantic sea water levels due to melt water lakes (as the one on the surface of the Petermann Glacier in Greenland in 2009).

2. Continuously lowering salinity level in the ‘Brackish-water ecosystem’ in the Baltic sea.

(b) Crop Yield:

But with respect to crop yield it is expected to rise to 60-80% in some areas because of rise of CO₂ level. However, other factors could offset these effects. There is also a prediction of regional climate changes along the ecosystem.

Overall, the climate change is likely to be beneficial, due to the dominance of C₃ crops such as barley, wheat, rice and soybeans. The C₃, annual crops show yield increases of up to 30% at doubled (700 ppm) CO₂ concentrations under controlled experimental conditions (Table 16.8).

This productivity could be further enhanced, since fourteen out of eighteen of the world’s worst weeds are C₄ plants and would not directly benefit from the CO₂ fertilization effect. Potentially limiting factors include changes in insect life cycles and an increase in the survival, growth and spread of pathogens.

(c) Water Balance:

Although changes in sea-level have received much publicity, problems of water availability are likely to be more serious and perhaps more expensive to solve. In future, warmer world will have water crisis in some parts while in other region it will be wetter than today.

There is uncertainty regarding regional forecasts of future precipitation as warming of the globe makes it difficult to predict. So also pattern of agricultural changes, or effects on ecosystems at large are fairly unpredictable.

(d) Human Health:

In recent years, there were newer reports of major tropical disease spread with changing climate. More people will likely be affected on the globe by tropical diseases, in coming decades as globe will become warmer in future. The detailed prediction is given in Table 16.9.

On the whole, a generalized scheme for global environmental threat that arises out of green­house gas emission is depicted in Fig. 16.10.

Climate Change:

Climate can change naturally for a variety of reasons. Some of the driving factors of climate change operate at time scales of hundreds of million years, whereas others fluctuate over a time period of only a few years.

The major driving factors of climate changes are:

1. Changes in the composition of the earth’s atmosphere (specially atmospheric CO₂ level);

2. Changes in topography, land-sea geography and bathymetry of ocean;

3. Changes in solar luminosity;

4. Changes in earth’s orbit;

5. Changes in earth’s volcanic activity;

6. Changes in internal variability of atmosphere—ocean system.

In addition human induced causes also accelerates the climate changes viz., increased concentrations of well-mixed GHGs; changes in the O₃ concentration, increasing concentration aerosol and changes in the land surface. However, the key component of climate changes is the heat trapping due to increase in CO₂ and other GHGs, which could easily reach 6-6 ωm² by the end of the 21st century.

This is much larger than the perturbation that can be reasonably expected due to natural fluctuation over a time span as short as 100 years. Furthermore the aerosol cooling effect is much lesser than GHGs heating effect. Thus major driving force of climate change of 21st century will be enhancement of GHGs. The climate change hazards are given in Table 16.10.

Greenhouse Effect—Policy Response:

1. The prospect of future environmental security being compromised by global warming are now so real as to make adoption of a precautionary response imperative—in other words, policy should focus on buying insurance and policy-makers should be clearly aware that waiting in perpetuity for better scientific data entails the real risk of waiting until it is too late.

2. The main routes to surviving the greenhouse threat are energy efficiency, renewable forms of energy production of all CFCs and related gases, less greenhouse gas-intensive agriculture, stopping deforestation and reforestation.

3. The world community should strive to achieve a low energy future of the kind spelt out by the end-use global energy project, with a world energy conservation of not much more than around 12 terawatts (TW) by 2025, but spread through the world more equitably than the 10 TW consumed today, so the developing countries can enjoy standards of living akin to those enjoyed in the industrialised countries.

4. This pattern of consumption should be achieved by massive investment in energy efficiency in the industrialised countries and large-scale transfer or up to date energy efficiency and non-CFC dependent technologies from the industrialised countries to the developing countries, to enable them to leap-frog the kind of energy-intensive, polluting routes which the developed countries took during industrialisation.

5. Given suitable investment of funding and resources, the goal should be for the world’s entire energy requirement to be produced by renewable forms of energy production as soon as possible in the 21st century.

6. Expansion of the nuclear power industry, or replacement of existing nuclear power stations when they come to the ends of their operating lifetimes, would involve diversity funds from cost-effective energy-solutions to the greenhouse crisis—especially when viewed in concert with safety waste disposal- decommissioning and nuclear weapons proliferation problems should have no role to play in the international policy response.

7. The detailed mix of policy prescriptions and their quantification should be subject to scientific research results during the 21st century, but essential first steps are:

(a) Implementation of immediate cuts in carbon dioxide emissions and the drawing-up of integrated strategies aimed at the phase-out of fossil fuels as early as possible in the 21st century;

(b) No effort be spared to arrest deforestation and halt the production or use of CFCs and related compounds, such as HFCs.

8. The large sums needed to fund these and other anti-greenhouse strategies, plus the expanded scientific research effort which is essential in the 21st century to narrow down the remaining scientific uncertainties, can come from diverting the greater part of the $ 1,000 billion spent for armaments annually by the world community, as benefits the changing concepts of global security which the late 1980s have heralded.

9. GHG control strategic options needs to be implemented specially with respect to controlling CO₂ emissions.

Emission reduction of CO₂ can be accomplished by a combination of several of the following approaches:

(a) End use efficiency improvements and conservation of energy.

(b) Energy supply side efficiency improvement;

(c) Capture and sequestration of CO₂ in subterranean reservoir or in the deep ocean;

(d) Utilisation of CO₂ for enhanced oil and natural gas recovery and for enhanced biomass production (photosynthesis);

(e) Shift to non-fossil energy sources.

The capture of CO₂ is only worthwhile in large power plants specially in coal fired power plants, where 1000 MG coal thermal power plant emits between 6 to 8 Mty^-1 CO₂.

The following CO₂ capture techniques can be adopted viz., Air separation CO₂ recycling, solvent absorption and membrane gas separation. After capture, the CO₂ needs to sequestered in a reservoir for an indefinite period, so it will not re-emerge into the atmosphere.

The following reservoirs are so far identified viz., deep aquifers, deep ocean and depleted oil and gas reservoirs. A number of such locations are identified in USA, Europe, Asia, Australia and Oceania. There are other ways of CO₂ utilisation viz., production of urea from CO₂, production of methanol from CO₂ and most important one is the biomass yield from CO₂ through enhanced photosynthesis.

Further, it goes without saying that the CO₂ caused climate change as induced by global- warming can be ameliorated by shifting to non-fossil energy source. A combination of approaches needs to be implemented. It is well-known that estimated higher share of GHGs producing countries are mostly developed world with about only 15% of the global population (Table 16.11).

So the developed world should come forward to combat the problems in more meaningful manner. The UN-environment and development conference held in Brazil in 1992 was disappointing for those who hoped for early action to reduce our use of fossil fuels. As such, the GHGs gas emission increase over the years in unabated manner.

The Kyoto Conference (1997) on climate change indicated the fact that countries which did not sign the earlier treaties emit enormous amount of GHGs, particularly CO₂.

Thus there is a great need for GHGs emission sources by changing the energy generation pattern, as well as motivating people round the world for prevention of accelerated man-made climate changes (Table 16.12). Subsequently, sink area must be enhanced by increasing forested area, particularly in industrialised nations.

Climate Chance and Clean Development Mechanisms:

Climate change emerged on the political agenda in the mid 1980s with the increasing scientific evidence of human interference in the global climate system and with growing public concern about the environment. The UN general assembly formulate an international treaty on global climate protection which resulted in completion of the United Nations Frameworks Convention on Climate Change (UNFCCC) in May 1992.

The legally binding Kyoto Protocol enforced since 1997 (Box 16.3). The Clean Development Mechanism (CDM) is an arrangement under the Kyoto Protocol allowing industrialised countries with a greenhouse gas reduction commitment to invest in projects that reduce emissions in developing countries as an alternative to more expensive emission reductions in their own countries.

Clean Development Mechanism (CDM) was instituted in 2001 under the Kyoto Protocol (Article 12). It is designed as an element of the sustainable development strategy allowing industrialised countries invest in clean projects in developing countries also to gain emission credits.

These credits are given in the form of Certified Emission Reductions (CERs), which, like all the other Kyoto accounting units, are expressed in tons of CO₂ equivalent. CERs are “certificates” just like a stock, given by the Executive Board in 15 different sectorial projects to be implemented in developing countries.

This is often called carbon trading. As on 2008 India contribute maximum CDM project (i.e. over 400 projects) in energy, transport, waste management and afforestation sectors.

Thus approaches to dealing with climate change involve technological change coupled with political will and economic realities. A major step towards slowing global warming would be to increase the efficiency of energy utilization.

More efficient use of fuels conserves the shrinking supplies of energy resources. It makes sense to increase energy efficiency, thus reducing CO₂ production, even if global warming is not a concern.

Another approach to the problem is to increase the amount of CO₂ removed from the atmosphere. If enough biomes is present the excess CO₂ can be used by vegetation during photosynthesis, thereby reducing the impact of CO₂ released by fossil fuel burning. Many countries have already undertaken the job of massive tree plantation of help for removal of CO₂ from the atmosphere under CDM projects.

Ocean-Atmosphere Interactions:

The ocean form the surface boundary conditions for 70 per cent of the atmosphere. This leads to a number of ocean and atmosphere interactions. One of the most well-known is the EL-Nino Southern Oscillation (ENSO). It is an inter annual change resulting from internal interaction within the Earth’s ocean-atmosphere system. It is not the result of external forcing.

The ENSO is an extremely important phenomenon which may have a global significance for the climate system. For many centuries Peruvian fishermen had noted that the ocean waters in which they fished occasionally experienced unusually high temperatures. The fish and birds disappeared and the usually dry desert land became fertile as rains fell.

These years were called the ‘years of abundance’. It did not occur regularly and consecutive events could be anything from 2 to 11 years apart. The warmer temperatures started around Christmas time and the Peruvian called the phenomenon El Nino, a Spanish word meaning Little Body or Christ child. The details of EL Nino climate events are given in box 16.7.

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