GS Paper 1 10 marks · 150w 9 min Easy
What is sea surface temperature rise? How does it affect the formation of tropical cyclones?
Subtopic: Geography · oceanography and tropical cyclones
How to structure your answer
Introduction (define SST rise, ocean heat uptake) → the 26.5°C cyclogenesis threshold and expanded breeding zones → latent-heat fuel and intensification → rapid intensification and the Arabian Sea shift → wetter storms and surge; caveat on other formation conditions → Conclusion
Detailed model answer
210 words · target 150 words · 9 min
Sea Surface Temperature Rise
Sea surface temperature (SST) rise is the sustained warming of the ocean's upper layer, driven by greenhouse warming — the oceans have absorbed over 90% of the excess heat in the climate system. Global SSTs touched record highs in 2023–24, with increasingly frequent marine heatwaves.
Effect on Tropical Cyclone Formation
- Threshold condition: cyclogenesis requires SSTs of about 26.5°C through a layer roughly 50–60 m deep; warmer oceans expand the area and lengthen the season over which this condition is met.
- More fuel: higher SSTs increase evaporation and latent-heat release — the energy engine of a cyclone — producing deeper convection and stronger updrafts.
- Rapid intensification: warm, deep ocean layers let storms jump intensity categories within hours, as with Cyclones Tauktae (2021) and Biparjoy (2023) in the fast-warming Arabian Sea, once a relatively quiet basin.
- Wetter, surgier storms: a warmer atmosphere holds about 7% more moisture per degree Celsius, raising extreme rainfall, while sea-level rise compounds storm surge at landfall.
- Caveat: formation still needs low vertical wind shear, the Coriolis effect and mid-tropospheric moisture — so warming raises the intensity, rainfall and rapid-intensification share of cyclones more clearly than their total number.
Conclusion
SST rise is loading the dice towards fiercer, wetter and faster-intensifying tropical cyclones. Upgraded ocean monitoring, impact-based early warning and resilient coastal planning are the necessary response.
What an examiner expects to see
- SST rise = sustained warming of the ocean's surface layer; oceans have absorbed over 90% of anthropogenic excess heat, with record global SSTs in 2023–24.
- Tropical cyclogenesis needs about 26.5°C SST through a ~50–60 m deep layer — warming widens the breeding zones and lengthens cyclone seasons.
- Warmer surfaces mean more evaporation and latent-heat release, deepening convection and strengthening cyclone updrafts.
- Deep warm layers drive rapid intensification — storms jumping categories within hours — as in the Arabian Sea's Tauktae and Biparjoy.
- Warmer air holds ~7% more moisture per °C, so cyclones dump heavier rain; sea-level rise worsens storm surge.
- Formation also requires low wind shear and Coriolis force, so the clearest signal is fiercer and wetter cyclones rather than simply more of them (IPCC AR6: rising share of Category 4–5 storms).
Concrete cases, schemes and judgments
- Cyclones Tauktae (2021) and Biparjoy (2023) in the fast-warming Arabian Sea
- Hurricane Otis (2023) — record rapid intensification to Category 5 before hitting Acapulco
- Record global SSTs and marine heatwaves of 2023–24
- IPCC AR6 finding of an increasing proportion of intense (Category 4–5) tropical cyclones
Terminology to weave into the answer
sea surface temperaturecyclogenesislatent heatrapid intensificationmarine heatwavestorm surge