When wildfires rage across landscapes, smoke fills our skies and chokes our lungs. It makes headlines, emergency measures are triggered, and communities rally to respond. We act because we can see it, smell it, and feel it. But beneath the ocean’s surface, another crisis is silently unfolding. What happens when our oceans — the planet’s blue lungs — struggle to breathe? As global leaders and changemakers gather for the U.N. Oceans Conference, we must confront a growing but often overlooked threat: marine hypoxia. When oxygen levels in parts of the ocean drop dangerously low, they create hypoxic “dead zones” where marine life can no longer thrive. Over the past 50 years, dead zones and low-oxygen areas in the open ocean have grown by 4.5 million square kilometers (1.7 million square miles) — an area the size of the European Union — and the volume of areas with no oxygen has more than quadrupled. In coastal zones, there were just 10 recorded dead zones in the 1960s; today, more than 500 coastal sites have reported hypoxia. Humpback whales off the coast of Australia. Image courtesy of Emilie Ledwidge/Ocean Image Bank. Dead zones were almost entirely unknown until the use of fertilizers became widespread. Despite a massive boost in agricultural yields, it sparked a chain reaction reaching the depths of the ocean. When excess nutrients (such as nitrogen and phosphorus) from agriculture, urban runoff and industrial waste wash into rivers and coastal waters, they trigger massive algal blooms that block sunlight and…This article was originally published on Mongabay