Striking satellite photos taken from space reveal how the earth’s toxic algae blooms dramatically increased as the climate warmed.
In a study published in Nature last week, a team of researchers at the Southern University of Science and Technology in China analyzed over 760,000 satellite images of the earth obtained from NASA’s Aqua satellite from 2003 to 2020.
The researchers found that the total area affected by algae blooms, otherwise known as phytoplankton blooms, has increased by 13.2% in less than two decades and now covers at least 12.1 million square miles of the earth’s oceans.
Phytoplankton blooms are accumulations of microscopic algae that can cause discoloration of water and form characteristic fluorescent swirls on the surface of oceans, rivers, and lakes that, when large enough, can be seen from space.
While the swirling blooms of luminous green, turquoise, and yellow algae in the photos may look beautiful in these satellite images, they actually serve as a chilling warning for the ocean. And although phytoplankton blooms serve as a food source for some sea creatures, they can also cause problems, such as carrying and dispersing toxic material.
Such toxins have been found to accumulate in ocean networks, sometimes leading to oxygen depletion, which can lead to ocean “dead zones” where aquatic life cannot survive. These dead zones wreak chaos on the food chain and fisheries.
According to the study, human activity has played a big role in the growth of phytoplankton in the last seventeen years.
Due to the effects of anthropogenic climate change, ocean temperatures have steadily increased. The researchers found that rising sea temperatures have increased the frequency of algal blooms over the last two decades, as warmer waters extend the length of the blooming season.
“Changes in climate can also affect ocean circulation, altering ocean mixing and the transport of nutrients that drive the growth of marine phytoplankton and bloom formation,” the authors write in the paper.
Nutrient pollution from fertilizers and sewage also causes phytoplankton to grow quickly and can result in red tide.
The images in the study show how coastal phytoplankton blooms have increased by 1.53 million square miles in seventeen years. In 2020, they covered 8.6% of all global ocean areas.
The average annual number of blooms observed was also found to increase by 59.2% between 2003 and 2020 — the equivalent of 2.19% each year.
The researchers hope their findings will help minimize the damage from blooms by forecasting them better and improving policy in terms of preventing nutrients from fertilizer from running off the land.
Image credits: All photos by Lian Feng