“This research helps us quantify the energetic requirements of the southern residents,” said Jacob Lerner, lead author of the study and a doctoral student in the Pelagic Ecosystems Lab at the Institute for the Oceans and Fisheries. “For example, if the southern residents ate just low-lipid salmon, they would have to eat around 80,000 more Chinook salmon every year than if they just ate high-lipid salmon.”

Southern resident killer whales are an iconic species in British Columbia’s Salish Sea and down the northeastern Pacific coast. With black and white markings, these marine mammals can weigh up to 12,000 pounds and be up to 26 feet long. They are fierce, social creatures that live and hunt in family group pods. And, sadly, there are only 73 left in the world.

Critically endangered by a number of anthropogenic factors, including noise pollution and high levels of water contaminants, their decline is mostly based on the limited availability of their preferred prey — Chinook salmon. However, there are many distinct populations of Chinook salmon available throughout the year, some with stock-specific differences in energy density, and not all in decline.

“We began with an initial hypothesis that these salmon were all created equal, that they all have the same value to resident killer whales. And we quickly realized that this is not true at all,” said Lerner. “They all have different levels of lipid content.”

Quantifying that lipid content is important as it directly relates to the caloric value of a salmon, assigning its value as prey. Specific estimates of lipid content for Chinook populations with different distributions, or run-timings, could be used to inform trends in killer whale populations, properly time fisheries closures, or even decide which hatcheries to augment to increase high quality food availability for southern residents, Lerner said.

This is particularly important as southern resident killer whales are a migratory species and often spend their winter months elsewhere. When they return to the Salish Sea for the spring and summer, their arrival often coincides with the arrival of the spring-run Fraser River Chinook salmon.

“Southern resident killer whales used to come here earlier in the spring season when they could eat early migrating Chinook salmon,” said Brian Hunt, associate professor in the Institute for the Oceans and Fisheries. “Those early Chinook were very energy dense as they need to fuel their long freshwater migration back to their spawning grounds, but those stocks have been declining. With the whales coming later, they mainly have access to Chinook from the lower Fraser. These fish don’t migrate very far, and have lower energy density.”

As a major source of prey for southern residents, estimates of lipid content from Fraser bound Chinook salmon may be one of the keys to helping both threatened species. “We identified a spectrum of high, medium and low-lipid Chinook populations from the Fraser that can be used to better inform energetics models and manage both species,” Lerner stated, “We also identified life history parameters for the salmon to predict where on this spectrum they may fall.”

Though the study has quantified lipid content in Fraser River Chinook, and shown new light on its life history drivers, there is still little information on how ocean conditions influence this energy accumulation.

“We plan to keep monitoring Fraser Chinook salmon fat content,” said Hunt. “And one of questions we want to answer is how changing ocean conditions might be affecting their energy accumulation. Our concern is that ocean warming and food web shifts in the North Pacific Ocean are leading to lower energy accumulation in Chinook salmon. This will have implications for both the Chinook themselves — will they have enough energy for return migration and spawning? — and the killers whales that depend on them.”

They note that the findings, published today in the journal One Earth, add urgency to the need to respond to the climate crisis and provide a roadmap for policymakers aiming to avert the most severe consequences of a warming planet.

In climate science, amplifying feedback loops are situations where a climate-caused alteration can trigger a process that causes even more warming, which in turn intensifies the alteration. An example would be warming in the Arctic, leading to melting sea ice, which results in further warming because sea water absorbs rather than reflects solar radiation.

OSU College of Forestry postdoctoral scholar Christopher Wolf and distinguished professor William Ripple led the study, which in all looked at 41 climate change feedbacks.

“Many of the feedback loops we examined significantly increase warming because of their connection to greenhouse gas emissions,” Wolf said. “To the best of our knowledge, this is the most extensive list available of climate feedback loops, and not all of them are fully considered in climate models. What’s urgently needed is more research and modeling and an accelerated cutback of emissions.”

The paper makes two calls to action for “immediate and massive” emissions reductions:

• Minimize short-term warming given that “climate disasters” in the form of wildfires, coastal flooding, permafrost thaw, intense storms and other extreme weather are already occurring.
• Mitigate the possible major threats looming from climate tipping points that are drawing ever-closer due to the prevalence of the many amplifying feedback loops. A tipping point is a threshold after which a change in a component of the climate system becomes self-perpetuating.

“Transformative, socially just changes in global energy and transportation, short-lived air pollution, food production, nature preservation and the international economy, together with population policies based on education and equality, are needed to meet these challenges in both the short and long term,” Ripple said. “It’s too late to fully prevent the pain of climate change, but if we take meaningful steps soon while prioritizing human basic needs and social justice, it could still be possible to limit the harm.”

Ripple, Wolf and co-authors from the University of Exeter, the Potsdam Institute for Climate Impact Research, the Woodwell Climate Research Center and Terrestrial Ecosystems Research Associates considered both biological and physical feedbacks. Biological feedbacks include forest dieback, soil carbon loss and wildfire; physical feedbacks involve changes such as reduced snow cover, increased Antarctic rainfall and shrinking arctic sea ice.

Even comparatively modest warming is expected to heighten the likelihood that the Earth will cross various tipping points, the researchers say, causing big changes in the planet’s climate system and potentially strengthening the amplifying feedbacks.

“Climate models may be underestimating the acceleration in global temperature change because they aren’t fully considering this large and related set of amplifying feedback loops,” Wolf said. “The accuracy of climate models is crucial as they help guide mitigation efforts by telling policymakers about the expected effects of human-caused greenhouse gas emissions. While recent climate models do a much better job of incorporating diverse feedback loops, more progress is needed.”

Emissions have risen substantially over the last century, the researchers note, despite several decades of warnings that they should be significantly curbed. The scientists say interactions among feedback loops could cause a permanent shift away from the Earth’s current climate state to one that threatens the survival of many humans and other life forms.

“In the worst case, if amplifying feedbacks are strong enough, the result is likely tragic climate change that’s moved beyond anything humans can control,” Ripple said. “We need a rapid transition toward integrated Earth system science because the climate can only be fully understood by considering the functioning and state of all Earth systems together. This will require large-scale collaboration, and the result would provide better information for policymakers.”

In addition to the 27 amplifying climate feedbacks the scientists studied were seven that are characterized as dampening — they act to stabilize the climate system. An example is carbon dioxide fertilization, where rising concentrations of atmospheric CO₂ lead to increasing carbon uptake by vegetation.

The effects of the remaining seven feedbacks, including increased atmospheric dust and reduced ocean stability, are not yet known.

The paper in One Earth has a corresponding website (https://scientistswarning.forestry.oregonstate.edu/climate_feedbacks) that features more about climate feedback loops, including infographics and interactive animations.