Effects of Increasing Greenhouse Gases

Effects of Increasing Greenhouse Gases

The increasing abundance of greenhouse gases in the atmosphere has both positive and negative effects.

Example of positive effect —

1. Carbon dioxide fertilisation effect on plants, etc.

Examples of negative effects —

2. Global warming

3. Ozone Depletion, etc.

1. Carbon dioxide Fertilisation Effect on plants

• The measurements made at Mauna Loa Observatory in the USA have shown that atmospheric carbon dioxide concentration has been rapidly rising since 1959.

• If this rising trend continues, it is expected that the atmospheric carbon dioxide concentration will increase between 540-970 ppm by the end of the 21st century.

• With a doubling of the atmospheric carbon dioxide concentration, the growth of many plants, particularly the C3 species, could increase by about 30% on average in a few years.

• The response of plants to elevated concentrations of carbon dioxide is known as the carbon dioxide fertilisation effect.

However, under natural conditions, the positive effects of carbon dioxide may not be realised because of the negative effects of global warming.

2. Global Warming

Global warming is the phenomenon of a gradual overall increase in the average temperature of the Earth's atmosphere due to the accumulation of certain gases.

• The term 'Global warming' was popularised by British environmentalist Wallace Smith Broecker (1931-2019) in 1970.

• An increase in the level of greenhouse gases has led to considerable heating of Earth, leading to global warming.

• Global warming affects the sea level, weather, and climate, and the distribution and phenology of organisms, food production, and fishery resources in the oceans.

(a) Sea Level Rise

Sea level has been raised by 1 to 2 mm per year during the 20th century.

• It is predicated that by the year 2100, the global mean sea level can increase up to 0.88 m over the 1990 level.

• Global warming causes sea level rise due to the thermal expansion of the ocean as it warms and the melting of glaciers and ice sheets, for example, the melting of hanging glaciers in 2021 in Uttarakhand and 2022 in Chile, etc.

• A rise of even half a meter in sea level would profoundly affect the human population, one-third of which lives within 60 km of a coastline.

• Many of the world's important cities and coastal areas will come under the threat of flooding.

• Several low-lying islands are submerging in water; for example, Tebungianko, a village on the central Pacific island nation of Kiribati, has disappeared in recent years.

• Similarly, Ghoramara, a tiny island in the Sundarban Delta, will soon vanish under the sea.

• Between 1972 and 2010, Ghoramara lost at least half of its land to the sea.

• Two other islands in the Sundarban Delta region have already disappeared, and more are likely to follow.

• The islands of Sundarban are not a single example of submergence due to sea level rise.

• All over the world, countries consisting of small, low-lying islands such as Tuvalu, Kiribati, and the Solomon Islands are facing the effects of the rising sea level.

• Bangladesh and the Maldives could also face severe erosion in the future.

• Inundation of coastal salt marshes and estuaries may deprive many important birds and fish of their breeding ground, forcing their extinction.

Thus, sea level rise is projected to have negative impacts on human settlements, tourism, freshwater supplies, fisheries, exposed infrastructure, agricultural lands, and wetlands.

(b) Severe Weather and Climate

The global mean temperature has increased by about 0.6°C in the 20th century. The average temperature may increase by 1.4°C - 5.8°C by the year 2100 from the 1990 level.

• Temperature changes are expected to be most marked in regions of middle and higher latitudes.

• Warming of the atmosphere will considerably increase its moisture-carrying capacity.

• As the troposphere warms up, the stratosphere will cool down.

This would cause widespread changes in precipitation patterns due to changed patterns of air-mass movement.

Expected precipitation changes:

• Increase at higher latitudes in both summer and winter.

• Increase in southern and eastern Asia in summer.

• Decrease in winter precipitation at lower latitudes.

Besides, the frequency of extreme events (e.g., droughts, floods, etc.) is expected to increase substantially. Climate change will increase threats to human health, particularly in tropical (warm) countries, due to changes in the ranges of disease vectors, water-borne pathogens, etc.

(c) Change in the distribution pattern of organisms (flora and fauna)

Global warming is likely to shift the temperature ranges and, therefore, would affect the altitudinal and latitudinal distribution patterns of organisms.

• With increasing global warming, many species are expected to shift slowly poleward, or toward high elevations in mountain areas.

  • For example, with a global temperature rise by 2°C to 5°C during the 21st century, the temperate region vegetation may extend 250-600 km poleward.

• Since trees are sensitive to temperature stress, a rapid temperature rise may cause large-scale death of trees and their replacement by scrub vegetation.

Many species may not be able to migrate fast enough to track temperature changes and may disappear.

(d) Decline in Food Production

Increased temperature will cause the eruption of plant diseases and pests, explosive growth of weeds, and increased basal rate of respiration of plants.

• A combination of all these factors will decrease crop production.

• Small temperature increases may slightly enhance crop productivity in temperate regions, but larger temperature changes will reduce crop productivity there.

• In all tropical regions, even a small temperature rise will have a detrimental effect on crop productivity.

• Rice yield alone, in South-East Asia, will reduce by 5% for each 1°C increase in temperature.

• Despite the beneficial carbon dioxide fertilisation effect, the overall world crop productivity will, in all probability, decline considerably due to projected global warming.

• This will have alarming consequences on the world food supply.

Approaches to Deal with Global Warming

Some of the strategies that could reduce global warming are—

(i) Reducing greenhouse gas emissions by limiting the use of fossil fuels, and by developing alternative renewable sources of energy (e.g., solar energy, wind energy, etc.)

(ii) Increasing the vegetation cover, particularly the forests, for photosynthetic utilisation of carbon dioxide.

(iii) Minimizing the use of nitrogen fertilisers in agriculture for reducing nitrous oxide emissions.

(iv) Developing substitutes for chlorofluorocarbons.

Apart from the above mitigation strategies, adaptations to address localised impacts of climate change will be necessary.

3. Ozone Depletion

Ozone layer

In the stratosphere of the atmosphere, ultraviolet (UV) radiation from the sun causes the photodissociation of ozone (O₃) into O₂ and O. But O₂ and O quickly recombine to form ozone (O₃) again. Thus, ozone is an unstable gas.

• The dynamism of ozone dissipates the energy of ultraviolet (UV) rays as heat.

• An equilibrium is established between the generation and destruction of ozone (O₃), leading to a steady state concentration of the ozone layer in the atmosphere between 20 to 26 km above the sea level.

• The thickness of the vertical column of stratospheric ozone (O₃) layer, condensed to standard temperature and pressure, averages 0.29 cm above the equator and may exceed 0.40 cm above the poles at the end of the winter season.

• This layer acts as the ozone shield protecting the Earth's biota (the flora and fauna of a region) from the harmful effects of strong ultraviolet radiation.

• Absorption of ultraviolet radiation by the ozone layer increases exponentially with its thickness.

• Therefore, the maximum amount of ultraviolet passes through the atmosphere and reaches the earth's surface in the tropics, i.e., near the equator, and this amount decreases towards the poles.

The concentration of O₃ in the stratosphere changes with seasons, the concentration being highest during the period February-April (spring season) and lowest during July-October (rainy season).

Ozone Hole

There is a thin layer of ozone that circles the Earth at a height of 15-50 km above sea level.

• Its protective presence shields the life of the organism by absorbing the high-energy ultraviolet radiation of the Sun.

• During the period 1956 to 1970, the springtime ozone layer thickness above Antarctica varied from 280 to 325 Dobson Units (1DU = 1 ppb).

• The thickness was sharply reduced to 225 DU in 1979 and to 136 DU in 1985. Later, the ozone layer thickness continued to decline to 94 DU in 1994.

• The decline in spring-time ozone layer thickness is termed the Ozone Hole.

• The ozone hole was first discovered in 1985 over Antarctica. The existence of the ozone hole was also confirmed above the Arctic in 1990.

Causes of Ozone Depletion

The chlorofluorocarbons (CFCs, Chemical composition—CCl₂F₂, Chemical name—Freon), methane (CH₄), and nitrous oxide (N₂O) escape into the stratosphere and destroy ozone (O₃) there.

• Of the many chemicals blamed for causing the ozone hole, the chlorofluorocarbons, widely used by the refrigeration industry, have been held primarily responsible.

• Most damaging is the effect of CFCs, which produce active chlorine (Cl and ClO radicals) in the presence of ultraviolet radiation. These radicals catalytically destroy ozone, converting it into oxygen.

• Methane (CH₄) and nitrous oxide (N₂O) also cause ozone destruction through a complicated series of reactions.

For making these discoveries related to ozone destruction, Sherwood Rowland and Mario Molina, along with Paul Crutzen, were honoured with the Nobel Prize for Chemistry in 1995.

Effect of Ozone Depletion

The thinning of the ozone layer results in an increase in UV-B radiation reaching the surface.

• A 5% loss of ozone results in a 10% increase in UV-B radiation.

• There are three basic types of UV rays: UV-A, UV-B, and UV-C, of which UV-A and UV-B rays reach the earth's surface, but UV-C rays are blocked by the ozone layer of the atmosphere.

• 5% of UV-A (wavelength 315-400 nm) and 95% of UV-B (wavelength 280-315 nm) are absorbed by the ozone layer, and the rest percentages of UV-A and UV-B reach the surface, whereas 100% of UV-C (wavelength 100-280 nm) is absorbed by the ozone layer.

• UV-C radiation of wavelength shorter than UV-B is almost completely absorbed by Earth's atmosphere, given that the ozone layer is intact.

• But UV-B (Ultraviolet of type B) rays are the middle energy between tanning rays (UV-A) and the intense germicidal rays (UV-C), and are highly injurious to living organisms.

• UV-B damages DNA, and mutations may occur. It causes aging of skin, damage to skin cells, and various types of skin cancers (including melanoma).

• In the human eye, the cornea absorbs UV-B radiation, and a high dose of UV-B causes inflammation of the cornea, called snow-blindness, cataract, etc. Such exposure may permanently damage the cornea.

• UV-B also diminishes the functions of the immune system.

• Elevated levels of UV-B radiation affect photosynthesis, as well as damage nucleic acids in living organisms.

UV-B radiation inhibits photosynthesis in most phytoplankton (Plankton plants) as it penetrates through the clear open ocean waters. This, in turn, can affect the whole food chain of organisms that depend on phytoplankton.

International Initiative for Mitigating Climate Change

Recognising the deleterious effects of ozone depletion, an international treaty, known as the Montreal Protocol, was signed at Montreal (Canada) in 1987 (effective in 1989) to control the emission of ozone-depleting substances.

Subsequently, many more efforts have been made and protocols have laid down definite roadmaps, separately for developed and developing countries, for reducing the emission of CFCs and other ozone-depleting chemicals.

Such efforts are—

• Earth Summit (1992) held at Rio de Janeiro, Brazil, United Nations Conference on Environment and Development (UNCED)

• Kyoto Protocol (1997) was held at Kyoto, Japan.

• Cancun Agreement (2010), held at Cancun, Mexico, United Nations Climate Change Conference.

• Paris Agreement (2015), held at Paris, France.

Final Thoughts

The effects of increasing greenhouse gases are already visible in our changing climate, rising sea levels, and shifting ecosystems. While carbon dioxide fertilisation may offer short-term benefits for some plants, the negative impacts of global warming and ozone depletion far outweigh these gains.

From extreme weather events to declining food production and loss of biodiversity, the challenges are urgent and far-reaching. The solutions are within our reach — reducing emissions, embracing renewable energy, conserving forests, and protecting our ozone layer. Global cooperation and local action are both essential to safeguard our planet’s future.

The choices we make today will decide whether we face a sustainable, thriving Earth or an environment pushed beyond its limits. Acting now is not optional — it’s a necessity.