Climate Change & Global Accords

Syllabus Unit: Environment & Ecology

Why it matters

Chapter overview

Climate change moved from an environmental footnote to the organising issue of 21st-century diplomacy over three decades of treaty-building — from the 1992 Rio framework through the binding-but-narrow Kyoto Protocol to the universal, pledge-based Paris Agreement. This topic covers the science of warming, the treaty architecture built to fight it, the annual COP summits where it plays out, and the finance and carbon-market mechanisms meant to fund the transition — all high-frequency current-affairs territory for GS-I.

General Studies Paper I Environment & Ecology 12%–15% weightage

Live Animation1 / 4

1Sunlight (shortwave) reaches Earth's surface

2Surface warms, re-emits infrared (longwave)

3Greenhouse gases absorb & trap infrared

4Heat re-radiated back to surface: net warming

1Greenhouse Effect & Global Warming

The greenhouse effect is what makes Earth habitable at all — the crisis is that human emissions have supercharged a naturally beneficial process.

Learning Objectives

Explain the natural greenhouse effect mechanism: incoming solar radiation, re-emitted infrared, and trapping by greenhouse gases.
Name the three major greenhouse gases (CO2, CH4, N2O) and their primary anthropogenic sources.
Define Global Warming Potential (GWP) and rank CO2, CH4 and N2O by their 100-year GWP.
State the IPCC's finding on how much global temperature has already risen since the pre-industrial era, and the Paris Agreement's 1.5°C target.

Key Terms

Greenhouse EffectThe natural process by which certain atmospheric gases trap outgoing infrared radiation, warming Earth's surface roughly 33°C above what it would be otherwise.

Global Warming Potential (GWP)A measure of how much heat a greenhouse gas traps relative to the same mass of CO2 over a set period (usually 100 years); CO2's GWP is defined as 1.

IPCCIntergovernmental Panel on Climate Change — the UN body whose assessment reports (AR6, 2021) are the authoritative scientific basis for climate negotiations.

1.5°C TargetThe more ambitious Paris Agreement goal of limiting global warming to 1.5°C above pre-industrial levels, beyond which climate impacts are projected to sharply intensify.

The **greenhouse effect** is a natural process: the sun's shortwave radiation passes through the atmosphere and warms the Earth's surface, which re-radiates the energy as longwave infrared. Certain gases absorb and re-emit that infrared instead of letting it escape to space, trapping heat and keeping Earth's average surface temperature around 15°C — about 33°C warmer than it would be with no atmosphere at all.

Three major greenhouse gases

Carbon dioxide (CO2) — from fossil fuel combustion and deforestation; the largest total contributor to warming due to sheer emission volume, GWP = 1 (baseline).
Methane (CH4) — from livestock digestion, rice paddies, landfills and fossil fuel leakage; GWP roughly 28-36 times CO2 over 100 years.
Nitrous oxide (N2O) — from nitrogen-based fertilisers and industrial processes; GWP roughly 265-298 times CO2 over 100 years, the highest of the three.

Common MistakePrelims trap: N2O has by far the highest per-molecule GWP of the three, but CO2 still causes the most total warming because it is emitted in vastly larger quantities and persists in the atmosphere for centuries.

The measured impact

The IPCC's Sixth Assessment Report (AR6, 2021) found global surface temperature has already risen about 1.1°C above pre-industrial levels, driven 'unequivocally' by human activity — the basis for the Paris Agreement's goal of holding warming 'well below 2°C' while pursuing efforts to limit it to 1.5°C.

Solar (shortwave) radiation in → Earth's surface warms → infrared (longwave) radiated out → greenhouse gases absorb & re-emit it → net warming