Climate change

Story hook

On 24 June 1988, in a Senate hearing room in Washington D.C., the AC was deliberately switched off and the windows opened. The room sweltered at 38°C as Dr James Hansen, head of NASA's Goddard Institute, faced the microphones. "Global warming has begun," he said. "It is 99 % certain that the warming trend is not natural variation. The greenhouse effect has been detected, and it is changing our climate now."

It was a punchy line on a day when Washington itself was breaking records. The press carried it as front-page news. Eighteen months later, the UN established the Intergovernmental Panel on Climate Change (IPCC).

Today — 2026 — Hansen looks understated. Atmospheric CO₂ has climbed from ~350 ppm in 1988 to 425 ppm today. 2023 was the hottest year on record at 1.45°C above pre-industrial; 2024 broke that. The 1.5°C Paris threshold is functionally breached on a 12-month rolling basis. The Arctic is warming four times faster than the global average. Greenland is losing 270 GT of ice per year. The Atlantic Meridional Overturning Circulation has slowed 15 % since 1950.

This file is about the physics behind those numbers — what greenhouse gases do, why they do it, and why feedback loops mean the warming we have already locked in may not be the warming we end up with.

Why this matters for UPSC

Climate change is the single most tested topic in Environment & Ecology — 3-4 Prelims questions every year (GHGs, GWP, IPCC, COP outcomes), 1-2 Mains questions every year, and a near-certainty in the interview. GS-III (environmental challenges) + GS-II (international relations)

• Essay (technology/development trade-offs) all draw from this topic.