What is sea surface temperature rise? How does it affect the formation of tropical cyclones?

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Ghissu Editorial · Accepted Answer

Sea surface temperature rise warms the ocean layer that fuels tropical cyclones, so storms form over wider areas, intensify faster and carry more rain, rather than simply growing more numerous. Arabian Sea cyclones rose 52% in 2001-2019 over 1982-2000, as a Climate Dynamics study (2021) found.

**Introduction**

Sea surface temperature (SST) rise is the long-term warming of the ocean's top layer, as the oceans absorb over 90% of the heat trapped by greenhouse gases. The IPCC (2021) found global SST rose about 0.88°C between 1850-1900 and 2011-2020, with the Indian Ocean warming fastest among tropical oceans.

**Why Warm Seas Power Tropical Cyclones**

SKETCH: flow-cycle | Warm Ocean Cyclone Engine
- Warm sea surface
- More evaporation
- Latent heat released
- Lower central pressure
- Stronger winds

1. **Temperature threshold**: Cyclones need seas warmer than about 26.5°C to roughly 50 m depth, plus Coriolis force, low wind shear and a prior disturbance.
2. **Heat engine**: Evaporation feeds latent heat into the storm, deepening the low and speeding winds that draw up more moisture.
3. **Wider breeding ground**: Warmer seas cross the threshold over larger areas and for longer, lengthening cyclone seasons.

**How Rising SST Is Changing Cyclones**

1. **Rapid intensification**: Amphan (2020) went from cyclonic storm to super cyclonic storm in under two days over a very warm Bay of Bengal.
2. **Arabian Sea shift**: A Climate Dynamics study (2021) found Arabian Sea cyclones rose 52%, and very severe ones 150%, in 2001-2019 over 1982-2000; Biparjoy (2023) lasted about 13 days.
3. **Wetter, more intense storms**: Air holds about 7% more moisture per 1°C, so rain is heavier; the IPCC sees no clear rise in cyclone numbers but a likely higher share of intense ones.

**Conclusion**

Rising SST makes cyclones stronger, wetter and quicker to intensify rather than simply more frequent, which shrinks warning time. Impact-based forecasting and shelters must now be planned for the fiercer storms of a warmer Indian Ocean.

What is sea surface temperature rise? How does it affect the formation of tropical cyclones?

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