UPSC Mains 2019 GS1 Q4: Impact of Global Warming on the Coral Life System

Reef-building coral lives in a narrow temperature range. Even a rise of 1-2°C above the normal summer maximum can trigger stress.

Under heat stress, coral expels the symbiotic algae living in its tissue that give it colour and most of its food. This turns the coral white, a state called bleaching.

A bleached coral is still alive but starving and vulnerable. If warm conditions persist too long, the coral eventually dies rather than recovering.

Global warming has driven repeated mass bleaching events across major reef systems, including Australia’s Great Barrier Reef, in recent decades.

Rising CO2 also makes seawater more acidic, making it harder for coral to build its calcium carbonate skeleton. This adds a second, chemical stress on top of rising temperature.

Rising sea levels can reduce the sunlight reaching coral if it can’t grow upward fast enough to stay near the surface, since coral depends on sunlight for its symbiotic algae.

Coral reefs support roughly a quarter of all marine species despite covering under 1% of the ocean floor. Reef collapse threatens this disproportionate share of marine biodiversity.

Healthy reefs absorb wave energy and protect coastlines from storm damage and erosion. Degraded reefs leave coastal communities more exposed.

Reef fisheries feed many coastal communities, and reef tourism generates significant revenue for reef-adjacent economies. Both decline as reefs degrade.

Explain why coral is heat-sensitive and what bleaching is, then assess impacts through named examples like the Great Barrier Reef, closing with consequences for biodiversity, coastal protection, and livelihoods.