Global Warming and the Role and Response of Man in Climatic Change

• Global warming is the rise in the Earth’s average surface temperature since the pre-industrial period (1850–1900), caused mainly by human emissions of greenhouse gases. It is the core of present anthropogenic climate change.
• The IPCC’s Sixth Assessment Report (AR6, 2021–2023) states that it is “unequivocal” that human influence has warmed the atmosphere, ocean and land. The world was ~1.1 °C warmer in 2011–2020 than in 1850–1900.
• 2024 was the warmest year on record (~1.55 °C) and the first calendar year above 1.5 °C; 2025 (~1.43 °C) ranked second or third.
• Man’s role is that of the principal forcing agent; his response is mitigation (cutting the cause) and adaptation (living with the effects).

Role of Man: Anthropogenic Forcing

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The Enhanced Greenhouse Effect

• Greenhouse gases are transparent to incoming short-wave sunlight but absorb outgoing long-wave radiation and re-radiate part of it downward, like the glass of a greenhouse.
  • The natural greenhouse effect keeps the surface at about +15 °C instead of −18 °C, keeping the heat budget of the Earth in a habitable balance.
  • Adding more gases thickens the “blanket”: the planet must warm until outgoing radiation again equals incoming. This is the enhanced greenhouse effect.
• Charles David Keeling began continuous CO2 measurement at Mauna Loa in 1958; the rising Keeling Curve is the iconic record of human influence.

Greenhouse Gases

• CO2 rose by a record 3.5 ppm from 2023 to 2024, to about 152% of its pre-industrial level, the highest in at least 800,000 years. Only about half of emitted CO2 stays in the air; oceans and land plants absorb the rest.
• Methane is short-lived (~12 years) but potent; it is responsible for roughly 0.5 °C of the present warming.
• CFCs both trap heat and destroy stratospheric ozone. They were phased out under the Montreal Protocol (1987); their HFC substitutes are being cut under the Kigali Amendment (2016).
• Water vapour is the largest greenhouse gas, but humans do not control it directly: it acts as a feedback, rising about 7% per °C of warming.

Aerosols and Land Use

• Aerosols from fossil fuels, biomass burning and dust:
  • Sulphate aerosols cool the surface by reflecting sunlight and brightening clouds. This “global dimming” masked part of the warming between the 1950s and 1980s.
  • Black carbon (soot) warms the air and darkens snow; the Atmospheric Brown Cloud over the Indo-Gangetic Plain hastens Himalayan glacier melt and alters monsoon rainfall.
• Land-use change:
  • Deforestation (Amazon, Congo, South-East Asia) releases stored carbon and reduces evapotranspiration.
  • Agriculture emits methane and N2O; urbanisation creates local heat islands.
  • Large-scale irrigation in north-west India cools the land surface locally.

Attribution: Why Present Change Is Man-Made

• AR6 attribution (2010–2019 relative to 1850–1900):
  • Total human-caused warming: ~1.07 °C (likely 0.8–1.3 °C), essentially all the observed 1.09 °C
  • Greenhouse gases: +1.0 to +2.0 °C
  • Aerosols and other human drivers: 0 to −0.8 °C
  • Sun and volcanoes: about 0 °C
  • Internal variability: ±0.2 °C
• Human-induced warming reached ~1.36 °C in 2024 and is rising at ~0.27 °C per decade; the remaining carbon budget for a 50% chance of 1.5 °C was only ~130 billion tonnes of CO2 at the start of 2025, about three years of current emissions.
• Fingerprints that rule out natural causes:
  • The stratosphere is cooling while the troposphere warms. A brighter Sun would warm both.
  • Nights and winters are warming faster than days and summers.
  • The isotopic signature of atmospheric carbon shows a fossil origin.
  • Solar output has been flat or falling since the 1950s.
• Natural factors still explain year-to-year swings (El Niño years such as 1998, 2016, 2023–24), but not the trend.

Impacts of Global Warming

Global Impacts

• Temperature and extremes:
  • Land has warmed nearly twice as much as the ocean (1.59 °C vs 0.88 °C in 2011–2020).
  • Heatwaves, heavy downpours and agricultural droughts have become more frequent and intense.
• Oceans:
  • Over 90% of the extra heat goes into the oceans, whose heat content set new records each year to 2025.
  • Ocean acidification, and mass coral bleaching (the fourth global event, declared in 2024)
• Cryosphere:
  • glaciers retreating worldwide
  • Arctic sea ice at or near record lows
  • Greenland and Antarctic ice sheets losing mass
  • permafrost thawing
• Sea level:
  • rose ~0.20 m between 1901 and 2018, at 3.7 mm per year in 2006–2018 and accelerating, from thermal expansion and melting land ice
  • threatens deltas and small islands (Maldives, Tuvalu, Bangladesh)
• Life and society:
  • Species shifting poleward and upslope
  • Crop-yield losses in the tropics
  • Spread of vector-borne diseases (malaria, dengue) to new latitudes and altitudes
  • Heat-related deaths
  • Climate-driven migration

Why Impacts Differ from Place to Place

• The physical warming is uneven: high latitudes and land warm most, oceans least.
• Exposure and vulnerability differ more: poor, low-lying, farm-dependent societies with little adaptive capacity suffer most.

Impacts on India

• Temperature:
  • India warmed by about 0.7 °C over 1901–2018.
  • 2024 was India’s warmest year since 1901 (+0.65 °C above the 1991–2020 average).
  • May 2024 brought 50.5 °C at Churu and long heatwaves across the north.
• Rainfall:
  • The frequency of very heavy rain days (>150 mm) rose by ~75% over 1950–2015, while droughts became more frequent and widespread.
  • The Indian monsoon is becoming more erratic: long dry spells broken by cloudbursts.
  • Recent disasters: Wayanad landslides (July 2024); Himachal and Punjab floods (2025).
• Cryosphere:
  • Himalayan glaciers lost mass about 65% faster in 2011–2020 than in the previous decade.
  • The South Lhonak GLOF (October 2023) in Sikkim destroyed the Teesta-III dam.
• Sea and coasts:
  • The North Indian Ocean rose ~3.3 mm per year (1993–2017).
  • Severe post-monsoon tropical cyclones over the Arabian Sea have increased.
• Agriculture: the early heat of March 2022 cut wheat yields in Punjab and Haryana.

Response of Man

Mitigation and Adaptation

• Geoengineering (solar radiation management, carbon dioxide removal) is debated as a supplement, not a substitute.

The International Climate Regime

• IPCC (1988): set up by the WMO and UNEP to assess the science; six assessment reports (AR6 completed in 2023).
• UNFCCC (Rio, 1992; in force 1994): goal to stabilise greenhouse gases at a safe level, on the principle of Common But Differentiated Responsibilities and Respective Capabilities (CBDR-RC).
• Kyoto Protocol (1997; in force 2005):
  • binding cuts for developed (Annex I) countries (~5% below 1990 in 2008–2012)
  • Clean Development Mechanism, Joint Implementation, emissions trading
  • weakened when the USA stayed out and large emerging emitters had no targets
• Paris Agreement (COP21, 2015; in force 2016):
  • holds warming well below 2 °C, pursuing 1.5 °C
  • every country submits Nationally Determined Contributions (NDCs), raised every five years
  • a global stocktake
• Later COPs:

• COP31 meets in Antalya, Türkiye, in November 2026, with Australia leading the negotiations.

India’s Response

• National Action Plan on Climate Change (NAPCC, 2008): eight national missions:
  • Solar
  • Enhanced Energy Efficiency
  • Sustainable Habitat
  • Water
  • Sustaining the Himalayan Ecosystem
  • Green India
  • Sustainable Agriculture
  • Strategic Knowledge for Climate Change
  • States add State Action Plans on Climate Change.
• NDC targets:

• Progress: the 50% non-fossil capacity target was reached in mid-2025, five years early; emissions intensity fell about 36% between 2005 and 2020.
• Net zero by 2070, Mission LiFE (2022) for sustainable lifestyles, the International Solar Alliance (2015), the Green Credit Programme (2023) and the MISHTI mangrove programme.
• Equity stance:
  • Per-capita emissions remain less than half the world average.
  • India presses for climate finance, technology transfer and the developed world’s historical responsibility.
• Carbon neutrality (net zero) means balancing remaining emissions with removals. Bhutan, Suriname and Panama are already carbon-negative, absorbing more than they emit.

Evaluation

• Progress: Paris turned climate action universal, and renewables are now the cheapest new power in most countries.
• The gap:
  • Emissions are still near record highs, and national pledges remain well short of a 1.5 °C pathway; the 1.5 °C limit is now likely to be crossed on a multi-decade average around the early 2030s.
  • Finance falls short of developing-country needs.
• Adaptation and loss and damage have therefore moved to the centre of negotiations.