Two marine scientists speaking at a AAAS panel discussion warned that humans and marine life will be forced to adapt to climate change’s effects on oceans already left vulnerable by over-fishing and pollution.
While mitigation efforts reducing greenhouse gas emissions are important, the speakers stressed that the world has already committed itself to decades of climate change, some of which is already underway.
Keith Brander, senior research scientist for the Danish Institute of Aquatic Resources at the Technical University of Denmark, said that changes in ocean temperature and acidity—attributed to the increase in global warming gasses from the burning of carbon-rich energy sources— has led to changes in marine species around Denmark.
He said that the rise in ocean temperature in the North Sea and the Northeast Atlantic Ocean has changed the distribution, abundance, and seasonality of fish, benthos, and plankton—small organisms at the bottom of the food chain vital to the ecosystem’s health—along with animals such as seabirds that use oceans for food and habitat.
“There is no doubt that there are already major changes taking place as a result of global warming,” said Brander, who spoke from Denmark via video link. “The question is, what’s going to happen next”?
Steven Murawski, director of scientific programs and chief science advisor for the National Marine Fisheries Service at the U.S. National Oceanic and Atmospheric Administration, said that climate change in the world’s oceans has affected humanity’s ability to harvest marine resources for food.
As the ocean warms, he explained, some environmentally sensitive species will move toward the poles and to deeper waters where the temperature is within preferred ranges.
“This means that we are going to chase them,” Murawski said, “which will cost more money and time for fishermen and could lead to higher prices.” He called for better marine resources management, which would allow ecosystems to be more resilient in response to climate change while meeting demand for sustainable food from the ocean.
Brander and Murawski spoke 3 December at AAAS headquarters as part of a series entitled “Beyond Copenhagen: Scientific Perspectives on Adaptation and Sustainability,” sponsored by AAAS Center for Science, Technology, and Sustainability; the Embassy of Sweden; and Delegation of the European Commission. AAAS Board Chairman James J. McCarthy, who moderated the event, said that ocean science has grown exponentially over the past half-century.
“It wasn’t until 40 years ago that researchers even considered that fishing stocks could be exhausted,” said McCarthy, the Alexander Agassiz Professor of Biological Oceanography at Harvard University. He added that the use of satellite imagery in marine science “profoundly” affected perceptions of the temporal and spatial scales of ocean production. Moreover, for the first time the major changes across broad ocean areas, such as the bleaching of corals, can now be observed, said McCarthy.
Brander said the rise in ocean temperatures has resulted in new species moving into the warmer North Sea, which has increased biodiversity. While some may think this is a benefit of warming oceans, he cautioned that the new fish could upset the ecosystem by preying on the native species, or that native fish haven’t fully left the newly intolerable conditions.
Brander added that the warming in the North Sea is not outside historical ranges. As recently as 7,000 to 10,000 years ago, the North Sea was warmer by 2 degrees Celsius.
This is helpful for researchers, he explained, as scientists can use historical, archaeological, and fossil records to anticipate new species and conditions in the North Sea during warmer water temperatures. He quickly cautioned that unlike the previous warming trend, the current one is primarily driven by humans and is occurring much more rapidly.
Murawski said that other side-effects of climate change could include unprecedented sea-level rise, sea-ice melting at both poles, and decreased access to fresh water, which could lead to the loss of freshwater breeding and nursery grounds for species like salmon. He added that ocean acidification will affect the well-being of organisms with calcium shells or exoskeletons, which comprise 50% of the value of domestically-caught seafood consumed by Americans as well as the ecosystems that support fisheries.
While the warming trends are currently within historical record, Brander warned that the oceans have not been this acidic in 600,000 years. As the acidity rises, it reduces the ocean’s ability to absorb atmospheric carbon, which in turn will cause more global warming.
Despite the challenges, both speakers said that proper management of oceans resources will allow marine species to thrive while meeting human dietary habits. By reducing fishing pressure, habitat disturbance and pollution, the speakers agreed that oceans could become more resilient and adapt to the effects of climate change.
“If we can maintain a healthy ocean,” Brander said, “then we can better meet the world-wide increasing demand for marine-based protein sources.”