Global ocean temperatures have been rising, but the consequences of these increases are not fully clear. A recent paper published in PNAS clarifies one of them by showing that harmful algal blooms have already become more intense.

Some types of algae naturally produce toxins. When these algae grow rapidly, they create a bloom that can kill off other species in the same ecosystem. A number of species (including Alexandrium fundyense and Dinophysis acuminate) produces toxins that accumulate in shellfish. People who eat these shellfish can experience paralytic or diarrhetic shellfish poisoning. So these blooms can hurt aquatic ecosystems, fisheries, and people.

The recent paper in PNAS used data from the National Oceanic and Atmospheric Administration to model sea-surface temperatures and track algal blooms. These models showed that warming in the North Atlantic since 1982 has significantly increased the growth rate of the two most dangerous species of algae. For both of these species, algal blooms have grown to cover a much larger area of the oceans in the last 35 years. Additionally, the length of bloom season has increased by as much as eight weeks over that same time period.