Tropical Cyclones & Climate Change (HL) (DP IB Environmental Systems & Societies (ESS))

Tropical Cyclones & Climate Change

What are tropical cyclones?

• Tropical cyclones are large, rapidly rotating storm systems that form over warm tropical oceans

• They have a low-pressure centre (the 'eye') and are characterised by strong winds, heavy rainfall, and thunderstorms

• Once sustained wind speeds exceed 119 km/h, a tropical cyclone is classified as:

  • A hurricane (in the Atlantic and eastern Pacific, including the Gulf of Mexico, Caribbean Sea, and west coast of Mexico)

  • A typhoon (in the South China Sea and western Pacific)

  • Other regions may call them cyclones (Indian Ocean and South Pacific, including the Bay of Bengal and northern Australia)

How tropical cyclones form

• Tropical cyclones form over warm ocean waters (above 26.5 °C)

• The energy for these storms comes from the evaporation of this warm water

  • This fuels the storm as the water vapour in the warm, moist air rises and then condenses into clouds and rain, releasing huge amounts of latent heat energy

  • This release of latent heat warms the surrounding air, causing it to rise further, reducing pressure at the surface

  • The low pressure at the centre pulls in more warm, moist air, which continues the cycle of evaporation, condensation, and heat release

  • This continuous cycle of rising warm air and condensation intensifies the storm, leading to the development of a tropical cyclone

• The Coriolis effect, due to the Earth's rotation, causes the storm to rotate and develop its characteristic spiral structure

Impact of climate change on tropical cyclones

Ocean warming and increased cyclone intensity

• Global warming is causing the oceans to warm, which provides more energy for tropical cyclones

  • Warmer water allows for greater evaporation, leading to stronger and more sustained storm systems

• As sea surface temperatures rise, the intensity of tropical cyclones increases, leading to:

  • Stronger winds that can cause severe damage to infrastructure and ecosystems

  • Heavier rainfall, leading to more flooding in coastal and inland areas

Frequency and duration of tropical cyclones

• Some studies suggest that while the total number of tropical cyclones may not increase, the frequency of the most intense storms (category 4 and 5) has risen

  • For example, the Atlantic hurricane season has seen an increase in major hurricanes in recent decades

• Rising sea levels caused by global warming contribute to higher storm surges, worsening coastal flooding during tropical cyclones

Evidence of climate change impacts

• Typhoon Haiyan (2013):

  • One of the strongest tropical cyclones ever recorded, with wind speeds exceeding 315 km/h

  • Scientists believe the warmer sea temperatures increased its intensity

• Hurricane Harvey (2017):

  • Warmer waters in the Gulf of Mexico caused record rainfall, leading to catastrophic flooding in Texas

• Research indicates a 40% increase in the likelihood of storms reaching category 3 or above since the 1980s