Physical Geography & Environment

Climate change and greenhouse gas mitigation

Climate change mitigation means reducing greenhouse gas emissions or enhancing their removal from the atmosphere. The main greenhouse gases in the Kyoto Protocol and later climate agreements are carbon dioxide, methane, nitrous oxide, and the fluorinated gases (hydrofluorocarbons, perfluorocarbons and sulphur hexafluoride). Sulphur dioxide is not in this group. It is an air pollutant that forms sulphate aerosols, which tend to cool rather than warm the surface.

The principle of common but differentiated responsibilities and respective capabilities (CBDR-RC), part of the UNFCCC, holds that all states share the duty to fight climate change, but developed countries bear a larger share of emission cuts because of their historical emissions and greater financial and technical capacity. The principle concerns emission reduction, not vaccines, financial quotas, or peacekeeping.

The Intergovernmental Panel on Climate Change (IPCC) is the international scientific body that assesses the science of climate change, its impacts and mitigation options. It was set up in 1988 jointly by the World Meteorological Organization and the United Nations Environment Programme, not by the WMO alone.

India's Paris Agreement commitments are framed as emissions intensity of GDP, non-fossil power capacity, and net-zero emissions. The 2015 target of a 33 to 35 per cent cut in emissions intensity by 2030 (from the 2005 level) was raised to 45 per cent in the updated Nationally Determined Contribution of 2022. The target of 500 GW of non-fossil fuel capacity and the net-zero target for 2070, both announced at COP26, remain current.

Sovereign Green Bonds are a fiscal tool to finance green infrastructure and reduce the carbon intensity of the economy. Their issue was announced in the Union Budget 2022-23.

The United Nations Carbon Offset Platform is an online marketplace where carbon credits can be bought to compensate for emissions. Companies, organisations and individual citizens are all eligible buyers.

Multilateral environmental conventions

Several multilateral environmental agreements deal with specific environmental problems, and exam questions test which problem each one addresses.

• Basel Convention — controls the transboundary movement and environmentally sound disposal of hazardous wastes. Example: a shipment of hazardous e-waste sent across a border needs prior notification and consent.
• Rotterdam Convention — sets a prior informed consent procedure for certain hazardous chemicals and pesticides in international trade.
• Stockholm Convention — targets persistent organic pollutants (POPs), which persist and accumulate in food chains.
• Minamata Convention — a binding instrument on mercury and its compounds.
• Ramsar Convention — adopted at Ramsar, Iran, in 1971; it gives the framework for national action and international cooperation for the conservation and wise use of wetlands.

The Basel, Rotterdam and Stockholm conventions together form the framework for managing hazardous chemicals, wastes and pollutants. They are not concerned with prisoners' rights or river conservation, which are governed by other instruments. Matching these conventions with their themes requires memorising the specific subject of each: Stockholm with POPs, Minamata with mercury, Basel with hazardous waste movement, and Rotterdam with pesticide and chemical trade. Wetland conservation under the Ramsar Convention is distinct from fish, wildlife or cultural protection, which are covered by other treaties.

Atmospheric pressure systems and lapse rate

On a weather map, a trough is an elongated extension of low pressure projecting from a low-pressure centre, while a ridge is an elongated extension of high pressure projecting from a high-pressure centre. The pairing is therefore low pressure for the trough and high pressure for the ridge.

Lapse rate is the rate at which air temperature falls with increasing altitude. The normal (environmental) lapse rate in the troposphere is about 6.5\,^{\circ}\mathrm{C} per kilometre. Because heat is supplied mainly from the ground, the temperature is highest near the surface and decreases steadily with height. For example, if the surface temperature is 30\,^{\circ}\mathrm{C}, the temperature at 3 km under the normal lapse rate is about 30 - 3 \times 6.5 = 10.5\,^{\circ}\mathrm{C}.

Map projections and great circles

Maps are used mainly to show spatial relationships among places, such as distance, direction and the arrangement of features. Route maps, such as road maps, do show the path from one place to another, so a map is not limited to static spatial patterns.

Projections are classified by the property they preserve. Conformal projections keep angles and the true shapes of small areas, while equal-area projections keep the relative sizes of areas. In the statement used in the exam, the preservation of shape is the defining property of a conformal map.

A great circle is the circle formed on a sphere when a plane passes through the centre of the sphere. Its properties are:

• it divides the Earth into two equal hemispheres;
• its circumference equals that of the Earth;
• it is the largest circle that can be drawn through two given points on the sphere;
• the great-circle route is the shortest path between two points on the surface.

A common error is to call a great-circle route the longest route, but it is in fact the shortest.

Soil types of India

Laterite soil forms under high temperature, heavy seasonal rainfall and alternating wet and dry periods. Intense leaching removes silica and bases, leaving iron and aluminium oxides, which give the soil its red colour. Laterite is typically found on plateaus and hill areas, not in the high Himalayan altitudes. Because nitrogen, potash, lime and humus are leached out, laterite is poor in these nutrients and is not very fertile without manure.

Soil formation processes are named by their dominant conditions:

• Laterization — hot, humid tropics with good drainage.
• Podzolization — cool, humid forest areas with leaching of humus and iron.
• Calcification — semi-arid regions where calcium carbonate accumulates.
• Gleization — waterlogged, anaerobic conditions in which iron is reduced and a grey gleyed horizon forms.

The floating vegetation mats called Phumdis on Loktak Lake in Manipur remain waterlogged, so gleization is the process at work there.

Rock types and classification

Sedimentary rocks are classified as clastic (formed from fragments of older rocks, such as conglomerate and sandstone) or non-clastic (formed by chemical or organic precipitation, such as limestone and rock salt). Conglomerate is a clastic sedimentary rock made of rounded fragments.

Metamorphic rocks form from existing rocks under heat and pressure. Slate is metamorphic, formed from shale, so it must not be described as a sedimentary rock.

Igneous rocks are classified by where they cooled. Plutonic (intrusive) rocks such as granite crystallise slowly at depth. Extrusive rocks such as basalt cool quickly from lava at the surface. A sill is a sheet-like body of intrusive igneous rock and is not a permeable rock type.

Permeability depends on pores, joints and dissolution channels. Limestone is permeable because water percolates through its pores and fractures, while granite and quartzite are dense rocks with very low porosity and are largely impermeable.

Tides and lunar-solar gravitation

Tides result mainly from the gravitational pull of the Moon, with the Sun contributing a smaller effect. When the Sun and the Moon are aligned, at new moon and full moon, their gravitational forces act together. These spring tides have a greater range than average. The high tide rises higher than the average high tide, and the low tide falls lower than the average low tide.

Neap tides occur at the first and third quarter Moon, when the Sun and the Moon are at right angles (quadrature). Here the Sun's gravitational pull partly counteracts the Moon's tide-raising attraction, so the tidal range is smaller. Spring and neap tides alternate roughly every 7.4 days, so two successive neap tides are about 14.8 days apart, not seven days.

Example: if the average high tide is 3 m, a spring high tide might reach 3.5 m, while a neap high tide might reach only 2.7 m.

Biomes and biodiversity hotspots

Biodiversity is greatest where conditions are warm and wet throughout the year, which allows high primary productivity and many ecological niches. Tropical moist forests, such as the Amazon and Southeast Asian rainforests, therefore hold the greatest diversity of plant and animal species. Temperate forests are less rich because of seasonal extremes, while deserts, savannas and Arctic or alpine systems support fewer species because of water shortage or cold.

Temperate grasslands have different regional names:

• Prairies — North America.
• Steppes — Eurasia.
• Pampas — South America.
• Veldt — South Africa.

Memorising these names with their regions is a standard requirement in the biome topic.

Earth's axial tilt and seasons

The Earth's axis is inclined at about 23.5^{\circ} to the plane of its orbit around the Sun. As the Earth revolves, the hemisphere tilted towards the Sun receives more direct insolation and longer days, which gives summer, while the opposite hemisphere has winter. The change in seasons therefore depends on the tilt of the axis, which changes the angle of sunlight and the length of the day.

Rotation of the Earth on its own axis produces day and night, and its speed affects the length of the day, but it does not cause seasonal variation. The seasonal variation in solar energy received at a place is governed by the inclination of the Earth's axis, because the tilt changes the incident angle of sunlight through the year. Pollution and cloudiness are irregular local influences, not the regular cause of seasons.

The Moon revolves around the Earth, not the Sun, and its motion does not produce seasons.

Jet streams and El Niño

Jet streams are fast-moving, narrow bands of high-altitude winds, and in both hemispheres they are westerly winds, not easterly. They are found near the tropopause and influence the movement of weather systems.

El Niño is a periodic warming of surface waters in the eastern and central equatorial Pacific. It develops along the coast of Peru and Ecuador, and the warm water mass is described as a warm ocean current. Its opposite phase, La Niña, brings cooler water to the same region.

Types of plains in India

The plains of India are classified by origin and the materials they contain:

• Bhabar — a narrow belt at the foothills of the Himalaya, made of porous gravels and boulders, through which streams disappear underground.
• Bhangar — the older alluvial upland, containing kankar (calcareous nodules).
• Khadar — the newer alluvium of the floodplains, renewed by fresh silt deposition every year.
• Delta — a low-lying, marshy depositional area at the river mouth.

The correct matching is therefore Bhabar with gravels, Bhangar with kankar, Khadar with silt, and Delta with marsh.