Tropical cyclones form when warm tropical oceans supply heat and moisture to a rotating low-pressure system. Global warming can increase their intensity by raising ocean temperatures and atmospheric moisture.
This is HL-only content in Subtopic 2.4, Climate and biomes.
How a Tropical Cyclone Forms
| Condition | Role in formation |
|---|---|
| Warm ocean water | Increases evaporation and supplies thermal energy. |
| Moist, unstable air | Rises and forms clouds and thunderstorms. |
| Low pressure | Draws more warm, moist air towards the centre. |
| Coriolis force | Deflects moving air, creating rotation away from the equator. |
| Low vertical wind shear | Prevents the storm structure from being disrupted. |
Moist air rises, cools and condenses. Condensation releases latent heat, warming nearby air so it rises further. Surface pressure falls, drawing in more air and strengthening winds. This positive feedback loop amplifies the initial disturbance.
A cyclone weakens over land or cooler water because its heat and moisture supply declines.
How Global Warming Affects Intensity
Warmer oceans increase evaporation and heat transfer into cyclones. A warmer atmosphere can hold more water vapour, contributing to heavier rainfall. These conditions can increase maximum wind speeds, rainfall and rapid intensification.
A common misconception is that global warming causes every cyclone or guarantees that all cyclones strengthen. Formation still depends on interacting conditions, and regional patterns vary. Warming instead raises the potential intensity of the strongest storms.
Typhoon Haiyan in the Philippines (2013) illustrates severe effects, including storm surge and major loss of life. This raises environmental justice concerns because highly vulnerable communities may have contributed little to greenhouse gas emissions.
Exam Technique
For an explain question, present the sequence: warm water, evaporation, rising air, condensation, latent heat, lower pressure and stronger winds. Then link warming to increased energy and moisture without claiming it is the sole cause of an individual cyclone.
