A guide to climate tipping points: the oceans

Making sense of a world on edge

Image Credit: Environmental Defense Fund

3. The Oceans

In addition to local effects experienced in the Arctic and Antarctic, the oceans are heating and absorbing more CO2 on a global scale. This drives cascading effects on marine life and, to a lesser extent, methane deposits, both of which drive further emissions of greenhouse gases.

How is it affected by climate change? The marine carbon pump is being disrupted by climate change in multiple ways. As the ocean absorbs more CO2 from the atmosphere, increasing concentrations of primary producer algae have been observed. However, rising temperatures are also causing the ocean to acidify, making algae less effective at storing carbon and making calcifying organisms like corals and certain phytoplankton less effective at maintaining their skeletons (see #3.2). Lastly, disruption to thermohaline circulation could reduce the extent to which primary producers at the surface receive essential nutrients and circulate carbon to deeper levels (see #1.3 and #2.2).

What are the tipping points? Multiple potential tipping points have been predicted. One threshold could occur when primary producer populations shift from large diatoms to small-celled flagellates and cyanobacteria, diminishing energy transferred to the rest of the food web. Another would occur if the ocean becomes undersaturated in calcium carbonate, accelerating acidification and reducing the viability of calcifying organisms.

What is the timeline? The extent and timescale of these thresholds are uncertain. A tipping point for ocean acidification has been predicted at 450 ppm of atmospheric CO2 (2 °C global increase).

Steve Daniels, Climate Conscious, 11 May 2021. Full article.

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