Impact of climate crisis on marine heatwave intensity

Why in the NEWS?

• A marine heat wave in Western Australia in January 2025 causes the deaths of more than 30,000 fish.

Key Points:

• Marine Heatwaves (MHW) are intensifying due to climate change, with sea surface temperatures rising significantly in various regions, such as Western Australia.
• MHW leads to devastating impacts on marine life, including large-scale fish deaths, coral bleaching, and the destruction of kelp forests.
• The frequency and severity of MHWs have increased over the past few decades, with global warming exacerbating these trends.

What will you read next in this topic?

1. What are marine heatwaves (MHW)?
2. Event in Western Australia (January 2025):
3. Increasing intensity of marine heatwaves: 
4. Effects on marine life: 
5. Impacts on the Great Barrier Reef:
6. Global consequences of marine heatwaves:
7. Implications for marine ecosystems:
8. Projections for the future:

What are marine heatwaves (MHW)?

• Definition: A marine heatwave (MHW) is a climate phenomenon in which the sea surface temperature (SST) in a specific region is 3-4°C above the average temperature for at least five consecutive days.
• Duration: MHWs can last for weeks, months or even years. As defined by NOAA (National Oceanic and Atmospheric Administration), these heatwaves can vary in duration depending on environmental conditions.
• Significance: SST during a heatwave can rise to levels that severely impact marine ecosystems, causing disruptions to marine biodiversity, fisheries and coastal habitats.

Event in Western Australia (January 2025):

• Event overview: In January 2025, more than 30,000 fish died due to an ongoing MHW in the coastal waters of Western Australia.
• Climate change impacts: According to an analysis by Climate Central, this event is 100 times more likely to be induced by climate change.
• The MHW began in September 2024 and continues, further increasing the region’s vulnerability to extreme climate events.
• Regional consequences: This MHW is now considered the second most severe in Western Australia’s recorded history, underlining the increasing intensity of such events.

Increasing intensity of marine heatwaves: 

• Long-term trend: Over the past few decades, SSTs have increased by about 0.9°C globally.
• A significant portion of this increase is due to climate change, with oceans absorbing about 90% of the additional heat caused by global warming.
• Increased frequency and severity: From 1982 to 2016, the number of days affected by MHWs doubled, according to a study published in the journal Nature in 2018.
• The International Union for Conservation of Nature (IUCN) reported a 50% increase in MHWs over the last decade, noting that these events now last longer and are more severe.
• Forecasts for the future: MHWs are projected to become more intense as global temperatures increase.
• One study indicated that with 1.5 degrees Celsius of global warming, the number of MHWs will increase 16-times, and with 2 degrees Celsius, they will increase 23-times. 

Effects on marine life: 

• Massive fish kills: MHWs caused by these events cause sudden deaths of marine species in some areas, dramatically impacting local marine populations.
• Destruction of kelp forests: Kelp forests, which thrive in cold waters, provide critical habitats and food sources for many marine species.
• MHWs pose a major threat to these ecosystems, causing their degradation, which in turn affects the wider marine food web.
• Coral Bleaching: One of the most severe consequences of MHW is coral bleaching.
• Increased water temperatures cause corals to expel the symbiotic algae that live within them, causing corals to turn white and become more susceptible to disease.
• This is detrimental to coral reef ecosystems, which support a large number of marine species.

Impacts on the Great Barrier Reef:

• Recent events: In 2024, the Great Barrier Reef experienced a catastrophic level of coral bleaching, triggered by an intense MHW.
• This was the seventh mass bleaching event recorded on the reef.
• Such frequent events of coral bleaching reflect the continued vulnerability of these delicate ecosystems to rising sea temperatures.
• Long-term consequences: The recurring nature of coral bleaching events threatens the long-term viability of the reef. 
• If these MHWs continue, it could lead to a permanent loss of biodiversity in these ecosystems, causing further disruption to marine life and the local economies that depend on them.

Global consequences of marine heatwaves:

• Deteriorating global situation: As the planet warms, the intensity, frequency, and duration of MHWs are expected to worsen globally.
• According to a study in the journal Nature, the number of MHW days is steadily increasing globally.
• With 1.5°C global warming, MHWs could become a ubiquitous phenomenon that could affect a wide range of marine ecosystems.
• Regional variability: While significant impacts are already being observed in areas such as Western Australia, the threat is global.
• Sea heat waves have been observed in both surface and deep ocean layers, at different latitudes, and in all types of marine ecosystems, making them a widespread and growing concern for marine biodiversity.

Implications for marine ecosystems:

• Biodiversity disruption: The combination of fish kills, kelp forest degradation and coral bleaching results in severe disruption of marine biodiversity.
• Marine heatwaves affect the reproductive cycles of marine species, reducing biodiversity and can lead to long-term ecological shifts.
• Economic impacts: Marine industries such as fisheries, tourism and coastal management are also significantly affected by the consequences of MHWs.
• As marine life populations decline and ecosystems deteriorate, the livelihoods of people dependent on these industries are at risk.

Projections for the future:

• Increased vulnerability: As global temperatures rise, marine ecosystems will become more vulnerable to heat stress.
• With higher global SSTs, the likelihood of more frequent and severe MHWs is expected to increase, putting further pressure on marine biodiversity and ecosystems.
• Possibility of ocean changes: Continued warming of the oceans can lead to major changes in ocean currents, making marine life cycles and habitats even more unstable.
• Its effects can be felt throughout the global food chain, from the smallest plankton to the largest marine mammals.