World’s oceans losing their greenness through global heating, study finds | Oceans

The world’s oceans are losing their greenery due to global warming, according to a study that suggests our planet’s ability to absorb carbon dioxide could be weakening.

The change in the palette of the seas is caused by a decline in phytoplankton, the tiny marine creatures responsible for almost half of the productivity of the biosphere.

The findings, which also have alarming implications for oxygen levels and food chains, are based on a groundbreaking study of daily chlorophyll concentrations in low- and mid-latitude oceans from 2001 to 2023.

Chlorophyll is a green pigment responsible for photosynthesis, the process by which plants, algae and phytoplankton convert sunlight, water and carbon dioxide into oxygen and glucose. It is one of the foundations of life on Earth.

Using deep learning algorithms, the authors of the new paper compiled data from satellites and monitoring ships to assess the changing hue of the oceans. They found a significant decline in greenery – about 0.35 micrograms per cubic meter each year – over the more than two decades of the study. The trend was twice as high in coastal regions and more than four times higher near river estuaries.

They associate this with a reduction in the ecological functioning of the ocean, finding an annual decrease of 0.088% in carbon sequestration capacity, the equivalent of 32 million tonnes. “The decline in the carbon sequestration capacity of surface phytoplankton has profound implications for the carbon cycle,” said one of the authors, Di Long, of Tsinghua University in Beijing.

The new paper says this change is likely due to rising temperatures associated with climate change.

Warming of the upper layers of the ocean near the surface has widened the temperature difference with colder depths, which would block the vertical transport of nutrients on which phytoplankton depends.

This confirms theories about the impact of global warming on ocean stratification. Contributing author Michael Mann, of the University of Pennsylvania, said: “This is the first study to robustly demonstrate that, yes, we can confidently conclude that we are seeing a decrease in ocean greenness, indicating a decline in marine productivity, posing yet another threat to humanity associated with the burning of fossil fuels and original global warming human. »

The new research contradicts several previous studies suggesting an increase in algae blooms in the oceans.

The last article indicates that previous studies were less comprehensive. He acknowledges that the situation differs from region to region and may be affected by runoff from agriculture and other human activities, but concludes that the broader picture of a “significant decline” in phytoplankton is clear at low and mid latitudes.

“These changes will profoundly affect the scale and distribution of marine ecosystem functioning,” he says.

The authors said policymakers should analyze the marine ecological environment in coastal areas and formulate countermeasures, including more careful management of agricultural fertilizers, sewage discharge, deforestation and water pollution.

But the biggest challenge will be tackling the climate crisis, as the world’s largest natural carbon absorber loses its strength. The Paris climate agreement, already overdue, may not be enough.

“Based on these results, we are concerned about the future reduction of global emissions. The decline in the carbon sequestration capacity of the oceans means that we may face greater emissions reduction pressure than expected,” Di Long said.