Marine Heatwaves

Marine heatwaves (MHWs) have emerged as a critical environmental issue, particularly evident off the coast of Western Australia. Recently, MHWs contributed to the death of over 30,000 fish. This alarming event marks the increasing frequency and intensity of MHWs, driven primarily by climate change. A recent analysis by Climate Central indicates that these heatwaves are now up to 100 times more likely to occur due to human-induced climate change.

About Marine Heatwaves

• Marine heatwaves are defined as extreme weather events where sea surface temperatures rise 3 to 4 degrees Celsius above average for at least five consecutive days.
• They can last from weeks to years. Recent studies show that MHWs have become more frequent and severe over the past few decades.
• Between 1982 and 2016, the number of MHW days doubled.
• The International Union for Conservation of Nature reported a 50% increase in MHWs over the last decade.

Causes of Intensification

• The primary driver of intensified marine heatwaves is the climate crisis.
• Global temperatures have risen by approximately 1.3 degrees Celsius since pre-industrial times.
• The oceans have absorbed 90% of this excess heat, leading to a 0.9 degrees Celsius increase in global mean sea surface temperatures since 1850.
• The past four decades alone have seen a rise of about 0.6 degrees Celsius.

Impact on Marine Ecosystems

The consequences of MHWs are severe for marine life. The 2010-11 MHWs in Western Australia resulted in fish kills and the destruction of kelp forests. Kelp, which thrives in cooler waters, is vital for marine ecosystems as it provides habitat and food. MHWs also contribute to coral bleaching, which severely impacts coral health and reproductive capabilities. The Great Barrier Reef experienced catastrophic coral bleaching in 2024, marking its seventh mass bleaching event.

Future Projections

The situation is expected to worsen globally. Projections indicate that the frequency of MHWs could increase by a factor of 16 with global warming of 1.5 degrees Celsius and by a factor of 23 with a rise of 2.0 degrees Celsius. This alarming trend poses threat to marine biodiversity and the health of ocean ecosystems.

Current Situation in Western Australia

In Western Australia, MHWs have reached unprecedented levels. In September 2024, temperature anomalies averaged around 1.2 degrees Celsius. By January 2025, these anomalies exceeded 2 degrees Celsius on multiple occasions. The ongoing MHWs are now recorded as the second worst in the region’s history, following the extreme events of 2010-11.

Global Implications

The implications of MHWs extend beyond local ecosystems. They disrupt food chains and impact fisheries, crucial for both local economies and global food security. The increasing severity of MHWs necessitates urgent action to address climate change and its far-reaching effects on marine environments.

Questions for UPSC:

1. Critically analyse the impact of marine heatwaves on marine biodiversity and coastal ecosystems.
2. Estimate the potential effects of climate change on global fisheries and food security.
3. With suitable examples, explain the phenomenon of coral bleaching and its implications for marine life.
4. Point out the relationship between sea surface temperature rise and the frequency of extreme weather events.

Answer Hints:

1. Critically analyse the impact of marine heatwaves on marine biodiversity and coastal ecosystems.

1. MHWs lead to large-scale fish kills, disrupting local fish populations and food webs.
2. Destruction of kelp forests occurs, which are essential for habitat and food for marine species.
3. Coral bleaching from MHWs reduces coral health and reproductive success, threatening reef ecosystems.
4. MHWs can alter species distributions, favoring some species over others, thus impacting biodiversity.
5. Overall ecosystem resilience is diminished, making marine environments more vulnerable to other stressors.

2. Estimate the potential effects of climate change on global fisheries and food security.

1. Climate change-induced MHWs disrupt fish breeding and migration patterns, affecting fish stocks.
2. Decreased fish populations lead to reduced catches, impacting livelihoods dependent on fishing.
3. Changes in marine ecosystems can result in the loss of biodiversity critical for sustainable fisheries.
4. Food security is threatened as fish are a major protein source for billions globally.
5. Increased competition for dwindling resources may lead to conflicts and economic instability.

3. With suitable examples, explain the phenomenon of coral bleaching and its implications for marine life.

1. Coral bleaching occurs when corals expel the symbiotic algae (zooxanthellae) due to stress, such as MHWs.
2. Example – The Great Barrier Reef experienced catastrophic bleaching in 2024, affecting its biodiversity.
3. Bleached corals become more susceptible to diseases, leading to higher mortality rates.
4. Loss of coral reefs impacts species that rely on them for habitat, food, and breeding grounds.
5. Coral bleaching can diminish the protective functions of reefs, increasing coastal vulnerability to storms.

4. Point out the relationship between sea surface temperature rise and the frequency of extreme weather events.

1. Higher sea surface temperatures (SST) increase the energy available for extreme weather phenomena.
2. MHWs have become more frequent due to a rise in global mean SST, linked to climate change.
3. As SST rises, the likelihood of severe weather events, such as hurricanes and storms, also increases.
4. Data shows a correlation between increased SST anomalies and the intensity of marine heatwaves.
5. This relationship marks the broader implications of climate change on weather patterns globally.