(a) Examine the formation of atmospheric tricellular circulation system. Describe with example its importance in making the Earth…

(a) Atmospheric tricellular circulation

Earth’s atmosphere operates as a tricellular system because differential solar heating, the Coriolis force and pressure-belt formation together produce three meridional cells in each hemisphere. Intense equatorial heating creates low pressure and rising air at the ITCZ; air diverges aloft, descends near 30° latitude to form subtropical highs, and returns as trade winds, constituting the Hadley cell. The Ferrel cell is an indirect cell between 30° and 60°, where surface westerlies carry warm, moist air poleward toward the subpolar low, while upper-level air returns equatorward. The polar cell completes the system, with cold air descending at the pole and blowing as polar easterlies toward the subpolar low. This circulation is not merely a schematic; it redistributes heat, organises precipitation and maintains biodiversity. The ITCZ’s seasonal migration sustains tropical rainforests and monsoonal rainfall; in India, the south-west monsoon, modulated by the Hadley cell and pressure contrasts, supports rice cultivation and groundwater recharge. Westerlies transport moisture to temperate zones and drive the Antarctic Circumpolar Current; polar easterlies help maintain cold, dry polar air masses and influence sea-ice dynamics that regulate Antarctic marine food webs. Thus the tricellular system makes Earth habitable by moderating temperature extremes and stabilising water cycles.

(b) UN Decade on Ecosystem Restoration

The UN Decade on Ecosystem Restoration (2021–2030) is a global initiative to restore degraded ecosystems, enhance biodiversity, and improve livelihoods. It aligns with UNCCD’s land-degradation-neutrality goals and the CBD Kunming-Montreal Global Biodiversity Framework, which calls for restoring at least 30 per cent of degraded ecosystems by 2030 and the 30x30 conservation target; the Decade has also mobilised commitments toward restoring 1 billion hectares. Mechanisms include the Bonn Challenge (India has pledged to restore 26 million hectares of degraded land by 2030), national commitments, flagship initiatives such as Africa's Great Green Wall, and landscape restoration that combines forests, wetlands, soils and agricultural systems. The Decade balances ecological goals with socio-economic needs by making restoration productive. Agroforestry using nitrogen-fixing Sesbania with fast-growing Moringa for fodder and food can restore degraded lands while improving nutrition and soil fertility. Payment for ecosystem services rewards communities for watershed protection, carbon storage and pollination. In India, Joint Forest Management under forest governance frameworks mobilises local communities to restore forests, protect biodiversity and secure non-timber forest produce. Nature-based solutions such as wetland restoration and soil conservation enhance food security by improving water availability, crop resilience and livelihoods.

(c) Himalayan uplift

The statement “The Himalaya is still rising” is tectonically accurate. India converges with Eurasia at about 4–5 cm/yr, of which roughly 2 cm/yr is absorbed across the Himalaya; this convergence causes crustal shortening, underthrusting along the Main Himalayan Thrust, and active faulting along the Main Boundary Thrust. Neo-tectonic processes include MHT activity, duplex formation and continued crustal shortening. GPS measurements show continued northward movement of India and uplift in parts of the range; river incision rates and frequent seismicity, including major Himalayan earthquakes, confirm active deformation. A cross-section sketch would show the Indian plate underthrusting Eurasia, the MHT as a major ramp, duplex formation in the mid-Himalaya, and a foreland fold-thrust belt; a drainage sketch would show terraced river valleys, knickpoints and anomalous captures.

Examples are the Nanga Parbat-Haramosh massif, where steep topography and active faulting indicate rapid uplift, and the Arun-Kosi river captures, where river reorganisation reflects differential uplift and tectonic control. The deformation front has migrated south to the Main Frontal Thrust, where the 1934 Bihar–Nepal and 2015 Gorkha-type ruptures and uplifted Siwalik terraces record ongoing shortening, while the MBT remains active. Erosion also feeds uplift: a 2024 study attributes part of Everest's anomalous height to isostatic rebound after the Arun river captured and eroded an upstream drainage.