2014-2016 Pacific marine heatwave wiped out four million of Alaska’s seabirds

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A new study reveals the largest documented vertebrate die-off linked to warming oceans, showing rapid and intense climate impacts.

About Marine Heat Waves (MHWs)

Definition: A marine heat wave is an extreme weather event. It occurs when the surface temperature of a particular region of the sea rises to 3 or 4 degrees Celsius above the average temperature for at least five days.
- MHWs can last for weeks, months or even years.
Two Main Drivers of MHWs:
- Surface heat flux: Heating from the atmosphere, which tends to occur when an atmospheric high-pressure system sits above a region of water for an extended period.
  - Surface heat flux tend to be shallower and shorter in duration
- Advection: movement of warmer waters into the region by ocean currents. It can be deeper and longer in duration

Ecosystem Disruption: MHWs cause mass mortality of habitat-forming species like kelps and corals, disrupting ecosystem productivity.
Species Impact: Upper-trophic-level species face reduced reproductive success, increased mortality, and mass die-offs.
Shifting Species: Native species migrate to cooler waters, while invasive species like sea urchins and jellyfish thrive.
Toxic Blooms: Higher temperatures and deoxygenation can lead to toxic algal blooms.
Extreme Weather: Marine heatwaves contribute to extreme weather events like tropical storms and hurricanes.

The number of MHWs events has doubled since 1982.
MHWs have increased by up to four-fold in the tropical Indian Ocean, aided by rapid warming in the Indian Ocean and strong El Niños.
The total number of days with marine heatwaves, averaged over the entire globe, has increased by 50% over the last century.