Marine ecosystem models may greatly underestimate future climate change impacts

Protecting marine ecosystems and fisheries from climate change is a global priority but a new QUT-led, international study finds that our lack of understanding for how marine systems function is muddying the waters.

Researchers from Australia, the United States, Europe, and Canada suggest while marine ecosystem models are the key tool used to understand how climate change could impact the world’s food web and fisheries in the future, representation of key processes that drive the marine ecosystem’s response to climate change differ widely among them. They believe this uncertainty could be causing models to underestimate future climate change impacts on the world´s marine ecosystems.

Dr Ryan Heneghan from QUT’s School of Mathematical Sciences joined forces with 23 other researchers representing the international marine ecosystem modelling community to produce a milestone paper for marine climate change impact projections.

The result – Disentangling diverse responses to climate change among global marine ecosystem models – has now been published in the journal Progress in Oceanography.

“Global warming is already driving significant changes in the structure of marine ecosystems across the world’s oceans. Marine ecosystem models give us insight into how these changes could impact larger animals and societal services such as fisheries,” said Dr Heneghan.

“The models in our study generally agree that climate change will cause the world’s marine animal biomass to decline. However, we don’t yet have a clear picture on how large these declines could be across the world’s oceans through the 21^st century.

“Millions of people depend on the world’s oceans for food and incomes. In light of the recent release of the report from the Intergovernmental Panel on Climate Change (IPCC) saying that at least 83% of the world’s oceans will very likely warm further this century, it is essential we find a way to be more accurate in such modelling.

“As a community of marine modellers, we undertook this study to get an honest picture of what we’re missing in our models that could be driving inter-model variation.”

“We know the impact of climate change on both water temperature and primary production will alter marine ecosystems in fundamental ways. Fish and other marine animals will burn more energy in warmer waters, leaving less scope for growth and reproduction. At the same time, in regions where primary production from phytoplankton decreases there will be less food, which will drive marine biomass down further.”

Dr Heneghan’s co-authors included Professor Eric Galbraith from McGill University, Montreal (Canada), Associate Professor Julia Blanchard from the Institute for Marine and Antarctic Studies, University of Tasmania, and Associate Professor Derek Tittensor from Dalhousie University, Canada.

They explored the mechanisms behind the diversity of responses to warming and changes in primary production in eight global marine ecosystem models from the Fisheries and Marine Ecosystem Model Intercomparison Project (FishMIP).

“Climate change impacts in our models primarily come through temperature and primary production changes, so we isolated the impacts of warming and primary production changes on our model projections of marine animal biomass and ecosystem structure,” said Dr Heneghan

“Between now and 2100, the change in global marine animal biomass across our models varied between a 30% decline and a small increase of 5%. Across all the models, there were biomass declines across most of the world’s oceans, but the models disagreed on where, why and by how much marine biomass would decline under climate change.

“We are also now aware that many of the models take an optimistic approach to how energy moves through the marine food chain, which overlooks the possibility that climate change could further undermine ecosystem function and cause greater biomass declines than what our models are currently projecting.

“Attempting to summarise the vast complexity of the global marine ecosystem in a handful of equations is enormously difficult and global marine ecosystem modelling is a relatively new field of research; our oldest models are just over 10 years old, whereas the climate modelling community were developing their first models over 40 years ago.

“There is a lot of work to do, and we’re excited at the roadmap this study provides the scientific community for increasing our understanding of the world’s magnificent marine ecosystems.”

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A PDF is available or read the full paper online: Disentangling diverse responses to climate change among global marine ecosystem models.

Climate change is also on the agenda during QUT’s Sustainability Week (23-27 August).

Media contact:

Amanda Weaver, QUT Media, 07 3138 3151, amanda.weaver@qut.edu.au

After hours: Rose Trapnell, 0407 585 901, media@qut.edu.au