Discuss the evolution of climate emission scenarios from SRES to RCPs to SSPs and the significance of the 2026 scenario revision for India's climate commitments.

Q. Discuss the evolution of climate emission scenarios from SRES to RCPs to SSPs and the significance of the 2026 scenario revision for India's climate commitments. (15 marks, 250-350 words)

Emission scenarios are not forecasts but structured "what-if" pathways translating socio-economic choices into greenhouse gas concentrations. Their successive revision reflects a maturing science — and the 2026 revision resets the benchmark against which India's climate pledges will be assessed.

From storylines to pathways: the evolution - SRES (2000): four qualitative storyline families — A1, A2, B1, B2 — yielding about 40 scenarios that deliberately assumed no climate policy, used in IPCC AR3 and AR4 [1]. - RCPs (AR5, 2013–14): scenarios redefined by their radiative forcing in 2100 — RCP2.6, RCP4.5, RCP6.0 and the very-high RCP8.5 — generated through Integrated Assessment Models. Physics gained precision; the socio-economic narrative was stripped out [2]. - SSPs (AR6, 2021): five narratives from SSP1 (sustainability) to SSP5 (fossil-fuelled development) were paired with forcing levels (SSP1-1.9 … SSP5-8.5), restoring the "how we get there" dimension; AR6 already flagged SSP5-8.5 as high-end [3]. - 2026 revision: a modelling team published seven new scenarios for AR7, retiring RCP8.5/SSP5-8.5 as implausible given the rapid renewable transition, notably in China; the new ceiling is about 3.5°C. Prof. G. Bala (IISc) was part of the team [4].

Significance for India's climate commitments - Realistic planning baselines: State and national adaptation plans for monsoon variability, heat stress and coastal risk can be costed against a credible high-end rather than an extreme tail [4]. - Scientific voice in negotiations: Indian participation in scenario-building strengthens credibility while arguing equity and differentiated responsibility [4]. - No case for complacency: current policies still point to roughly 2.8°C, far above Paris goals [5] — validating India's push on 50% non-fossil installed capacity and a 45% cut in emissions intensity by 2030, en route to net-zero 2070 [6].

Scenario evolution shows science self-correcting rather than softening. For India, the retirement of the catastrophic tail is an opportunity to shift resources from worst-case alarm to credible mitigation and adaptation delivery — deepening renewable capacity, climate finance and resilient infrastructure, so that a narrower risk band translates into greater ambition, not lesser urgency.

(~330 words)

Sources: 1. IPCC, Special Report on Emissions Scenarios — Summary for Policymakers (2000) — SRES A1/A2/B1/B2 families and no-policy assumption 2. IPCC AR5 WGI, Summary for Policymakers (2013) — RCP2.6–RCP8.5 defined by radiative forcing, built via IAMs 3. IPCC AR6 WGI, Summary for Policymakers (2021) — five SSP narratives and SSPx-y scenario set 4. "Scientists rule out worst-case climate scenario, with caution", The Hindu, 7 June 2026 — retirement of RCP8.5, ~3.5°C new high end, China's renewable transition, Prof. G. Bala (IISc) 5. UNEP, Emissions Gap Report 2025 — current-policies warming projection of about 2.8°C 6. PIB, India's updated Nationally Determined Contribution — ~50% non-fossil installed capacity and 45% emissions-intensity reduction by 2030