[2017] The ups and downs of marine plankton in response to El Nino tell us that climate change will weaken the biological production of tropical oceans in the coming decades

Marine primary production by phytoplankton provides the main source of food and energy to the marine food web, and influences the concentration of atmospheric CO2.

Projections of how such primary production will respond to climate change are currently highly uncertain – some models indicate that climate change may boost primary production, whereas others project declines of up to 20% by 2100. This uncertainty is mainly driven by the sensitivity of tropical ocean primary production to climate change.

A new study lead by researchers at the Pierre-Simon Laplace Institute and published in the journal Nature Climate Change identifies a novel way to reduce the uncertainty associated with projections of marine primary production.

That study shows that across a large ensemble of models there is a consistent relationship between the long-term sensitivity of ocean primary production to climate change and the sensitivity of primary production associated with El Niño/Southern Oscillation (ENSO) variability. Models that are highly sensitive to interannual climate variability are also highly sensitive to long-term climate change. By using this relationship in combination with satellite-based observations of the historical interannual sensitivity of primary production, the authors were able to constrain projections of the long-term climate impact on primary production.

“Using our approach we estimate that under a business-as-usual emissions scenario there will be approximately an 11% decline in tropical marine primary production and a 6% decline in global marine primary production by 2100” said lead author Lester Kwiatkowski.

Study co-author Laurent Bopp added, “This work substantially reduces uncertainty in model projections. Without strong action to reduce emissions of greenhouse gases, climate change will almost certainly result in a long-term decrease in ocean phytoplankton. This is likely to have negative consequences for already pressured global fisheries.”

Reference: Kwiatkowski, L., Bopp, L., Aumont, O., Ciais, P., Cox, P.M., Laufkotter, C., Li, Y., and Seferian, R. (2017). Emergent constraints on projections of declining primary production in the tropical oceans. Nat. Clim. Chang. 7, 355 – 358.

Press release: http://www.insu.cnrs.fr/node/6445

Figure: Emergent constraints on the sensitivity of tropical marine primary production to climate change. For each model (cross with letter), the long-term sensitivity of tropical primary production to climate change is plotted against the interannual sensitivity of tropical primary production to El Niño. The black line is derived from all models and depicts what scientists call « an emergent constraint ». It is then used to project what is observed (sensitivity to ENSO, on the x-axis) to the y-axis (climate projection).