Global issues and responsible development practices

Humans have always changed their environment, but the scale of change has grown with each stage of development.

Environmental problems from development

• Population growth and urbanisation raise demand for food, water, energy and housing.
• Fossil fuel use causes air pollution and global warming.
• Industrial and municipal waste pollutes land and water; chemical use creates hazardous waste.
• Deforestation, over-grazing and mining cause biodiversity loss and land degradation.
• Consumption and resource depletion exceed the earth's carrying capacity.

Sustainable development

Defined by the Brundtland Commission (1987): "development that meets the needs of the present without compromising the ability of future generations to meet their own needs". It balances three pillars: economic growth, social equity and environmental protection. Practices include renewable energy, cleaner production, 3R of waste, efficient use of resources, environmental impact assessment, and the UN Sustainable Development Goals (2030).

Ozone layer

About 90% of atmospheric ozone lies in the stratosphere (10-50 km, peak near 20-25 km). It absorbs harmful solar ultraviolet radiation (UV-B 280-315 nm and UV-C) and protects life. It is formed and destroyed naturally in the Chapman cycle:

$$\text{O}_2 + h\nu\ (\lambda<242\ \text{nm}) \rightarrow 2\text{O}, \qquad \text{O} + \text{O}_2 + M \rightarrow \text{O}_3 + M$$ $$\text{O}_3 + h\nu \rightarrow \text{O}_2 + \text{O}, \qquad \text{O} + \text{O}_3 \rightarrow 2\text{O}_2$$

Ozone concentration is measured in Dobson Units (DU); normal is about 300 DU, and the "hole" is a region below 220 DU.

Depletion by CFCs

CFCs (e.g. CFC-11 $\text{CCl}_3\text{F}$, CFC-12 $\text{CCl}_2\text{F}_2$) are stable and inert in the lower atmosphere, so they reach the stratosphere, where UV breaks them down and releases chlorine atoms:

$$\text{CCl}_2\text{F}_2 + h\nu \rightarrow \text{CClF}_2 + \text{Cl}$$

Catalytic cycle:

$$\text{Cl} + \text{O}_3 \rightarrow \text{ClO} + \text{O}_2$$ $$\text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_2$$ $$\text{Net: O}_3 + \text{O} \rightarrow 2\text{O}_2$$

The chlorine atom is regenerated, so one Cl atom can destroy about $10^5$ ozone molecules before it is removed. Bromine (halons) and nitrogen oxides also destroy ozone.

Antarctic ozone hole

In the polar winter, very cold air forms polar stratospheric clouds. On their surface, inactive chlorine ($\text{HCl}$, $\text{ClONO}_2$) is converted into reactive $\text{Cl}_2$. When sunlight returns in spring (September-October), $\text{Cl}_2$ splits to Cl atoms that rapidly destroy ozone, in cycles such as $\text{ClO}$ dimer, giving the ozone hole. The isolated polar vortex prevents replacement of ozone.

Effects

• Humans: skin cancer, sunburn, cataract, weakened immunity.
• Plants: reduced growth and crop yield.
• Aquatic life: damage to phytoplankton at the base of the food chain.
• Materials: faster degradation of plastics and paints.
• Increased ground-level smog and climate change.

Vienna Convention and Montreal Protocol

The Vienna Convention (1985) set up international cooperation to protect the ozone layer. The Montreal Protocol on Substances that Deplete the Ozone Layer (1987) is the treaty with binding limits on production and consumption of ozone depleting substances (ODS). It has been amended several times (London 1990, Copenhagen 1992, Montreal 1997, Beijing 1999) and is regarded as the most successful environmental agreement.

Key features:

• Controlled substances: CFCs, halons, carbon tetrachloride, methyl chloroform (fast phase-out), HCFCs (transitional substitutes), methyl bromide, HBFCs.
• Phase-out schedule: developed countries phased out CFCs by 1996; developing countries (Article 5 parties) by 2010, with a grace period.
• HCFCs: freeze in 2013 for developing countries, with reductions leading to complete phase-out around 2030, and 2040 for servicing. HFCs substitute them but are greenhouse gases, so the Kigali Amendment (2016) phases down HFCs.
• Trade restrictions with non-parties, and the reporting of data.
• Multilateral Fund gives financial and technical help to developing countries; the principle of "common but differentiated responsibilities".

Control of ODS in Nepal

• Nepal became a party to the Vienna Convention and Montreal Protocol in 1994 and is an Article 5 country.
• The Ozone Depleting Substances Consumption (Control) Rules, 2001 (2058 BS) under the Environment Protection Act regulate import, export, sale and use of ODS, with licensing and quotas. Imports of CFC-based equipment are restricted.
• A National Ozone Unit (in the Ministry responsible for environment) coordinates implementation; the Customs Department checks imports.
• Nepal prepared the HCFC Phase-out Management Plan (HPMP), trained refrigeration technicians and customs officers, promoted recovery and recycling of refrigerants and replacement with non-ODS refrigerants (hydrocarbons, HFCs).
• Nepal reported the phase-out of CFC consumption in line with the 2010 target (as per the Ozone Unit reports).

(a) Greenhouse effect

Short-wave solar radiation passes through the atmosphere and warms the earth. The earth re-emits long-wave infrared radiation, and greenhouse gases (GHGs) absorb part of it and send it back, keeping the earth about 33 $^\circ$C warmer (average 15 $^\circ$C instead of $-18\ ^\circ$C). This natural effect is essential for life; the problem is the enhanced greenhouse effect due to rising GHG levels.

   Sun --short-wave--> |  atmosphere (CO2, CH4, N2O, H2O)
                       |   ^   absorbs and re-radiates
   Earth --long-wave IR---+----> part escapes to space

Main GHGs and causes of increase:

Atmospheric $\text{CO}_2$ has risen from about 280 ppm before industrialisation to above 420 ppm today because of fossil fuels and deforestation.

Effects of global warming: rise in global temperature, melting of glaciers (serious for Himalayan glaciers and rivers) and polar ice, sea-level rise, more floods, droughts and extreme weather, glacial lake outburst floods (GLOF), threat to food production, spread of vector-borne diseases, loss of biodiversity, ocean acidification.

(b) Numerical

Reaction: $\text{C} + \text{O}_2 \rightarrow \text{CO}_2$, mass ratio $44/12$.

Carbon in coal $= 0.75\times1\ \text{t} = 0.75$ t.

$$m_{\text{CO}_2} = 0.75\times\frac{44}{12} = 2.75\ \text{t}$$

Methane CO$_2$-equivalent:

$$\text{CO}_2\text{e} = 100\ \text{t}\times28 = 2800\ \text{t CO}_2\text{e}$$

Answer: 1 t of coal gives 2.75 t of CO$_2$; 100 t of methane is equal to 2800 t CO$_2$e.