Source: DTE
Subject: Geography
Context: A new study reveals that tropical cyclones passing over marine heatwaves are far more destructive, resulting in 60% more billion-dollar disasters due to rapid intensification.
About Marine heatwaves:
What are Marine Heatwaves?
- A marine heatwave (MHW) is a prolonged period of unusually high ocean temperatures in a specific region. They are defined by their duration (lasting several days to months) and intensity (deviations from average sea surface temperatures, known as temperature anomalies).
- While exact thresholds vary, an anomaly of 1 degree Celsius to 3 degree Celsius above the long-term average for a particular season is typically characterized as a marine heatwave event.
Factors Affecting Marine Heatwaves:
The severity and frequency of MHWs are influenced by several global and local factors:
- Climate Change: Rising greenhouse gas emissions lead the oceans to absorb over 90% of excess heat in the climate system, raising the baseline temperature.
- Ocean Currents: Changes in large-scale currents can move massive pools of warm water into typically cooler regions.
- Atmospheric Pressure: Systems like the North Pacific High influence wind patterns that either cool or allow the ocean surface to heat up.
- Climate Oscillations: Events such as El Niño significantly raise sea surface temperatures across the Pacific, often triggering the largest recorded MHWs.
How They Are Formed?
Marine heatwaves primarily form through a breakdown in the ocean’s natural cooling mechanisms:
- Weakening Winds: Winds normally cool the ocean through evaporation and by mixing the warm upper layer with cooler, deeper waters.
- Stratification: When these winds weaken, the top layer of the ocean becomes thinner and trapped at the surface.
- Solar Heating: This thin surface layer absorbs solar radiation more rapidly. Without the ability to mix with deeper, colder water, the temperature spikes, creating a localized heat dome in the ocean.
Implications:
The consequences of MHWs extend from the deep sea to coastal economies:
- Supercharging Storms: MHWs provide high-octane fuel for tropical cyclones, leading to Rapid Intensification (RI). This boosts wind speeds and rainfall, causing storms to stall longer over land and decay more slowly.
- Economic Loss: MHW-influenced cyclones are 1.6 times more likely to become billion-dollar disasters, as seen with Hurricanes Helene and Milton in 2024.
- Biodiversity Loss: Warmer waters disrupt fish reproduction and migration. While some species (the Winners) expand their range north, others (the Losers, like cold-water salmon) face mass die-offs.
- Harmful Algal Blooms: Unusually warm water serves as a habitat for toxic algae. These blooms can produce toxins like domoic acid, which move up the food chain and force the closure of key commercial fisheries.
- Ecosystem Collapse: MHWs contribute to massive coral bleaching events and the destruction of kelp forests, which are vital carbon sinks and nurseries for marine life.
