A study reveals that marine animals could die at levels rivaling the greatest mass extinctions in history, if the seas get too warm and retain too little oxygen.
Marine animals could die at a rate rivaling the greatest mass extinctions in geological history if people don’t reduce greenhouse gas emissions.
That’s the conclusion of a study published in the journal Science, that many ocean creatures could face conditions that are too hot and with too little oxygen to survive if we don’t change the situation. The hotter it is, the less species can survive, according to the results.
The new analysis applies to current climate projections what the research team had learned about the “Great Dying” 252 million years ago, when more than two-thirds of all marine life from the Permian period became extinct, along with other historic extinctions. In a high emissions scenario, the results were worrying.
The new models suggest that Earth could approach Permian marine extinction levels by 2300 if emissions continue to rise.
According to the research, as temperatures rise, species richness will decrease near the tropics and some animals will migrate to higher latitudes. Polar species are most at risk, as their habitat becomes an “endangered climatic niche”, the document explains.
But this fate is far from sealed. If emissions stay close to the levels set by world leaders in the 2015 Paris Agreement, marine animals would fare much better, the study finds.
Even so, the analysis reminds us that the current rate of change on Earth may be comparable to that of the most extreme events in history.
Previous work by the team responsible for the new analysis found runaway global warming and loss of oxygen in the ocean to be the causes of the Great Death. His model results matched patterns that paleontologists had observed in the Permian fossil record, giving him credibility.
Before this death, there was only one landmass, Pangea, and the Permian Ocean was teeming with sea creatures. Scientists believe these animals had similar traits to modern animals, such as metabolism and oxygen requirements.
Scientists knew from previous studies of fossil teeth that surface temperatures during this time had soared by around 10°C in the tropics, leading to the extinction of many marine animals. The researchers suspected that volcanic eruptions were causing the changes, so they modeled these conditions.
The results showed that many species were pushed beyond their physiological limits.
As the climate warmed, animals needed more oxygen to perform bodily functions such as breathing. But warmer water doesn’t contain as much dissolved oxygen, making it harder for species to survive.
A similar process is happening now. The Permian event was caused by global warming and the loss of oxygen from the oceans, two environmental changes that are underway today.
Currently, the global average surface temperature is on track to increase by about 3.2°C by the end of the century compared to pre-industrial times. But limiting global warming to 2C, a goal agreed to in the Paris Agreement, would reduce the severity of extinctions by more than 70%, according to the document.
However, if emissions continue to rise, if countries remain divided on climate targets and if temperatures rise to nearly 5°C by the end of the century, marine biodiversity would begin to tend towards the rates observed during the past mass extinctions.
The future of ocean life also depends on tackling other damaging human activities, such as overfishing or pollution, which could have cascading effects in combination with climate change.
More information: www.science.org (English text).