How Low Does CO2 Go?

by Emil Morhardt

Atmospheric CO2 levels are always lower during glacial periods than during interglacials like the one we are in now. During the last glacial maximum 20,000 years ago, for example, they were at 190 parts per million (ppm), whereas during the most recent 10,000 years, almost up to the present, they have been about 280 ppm. [We have now succeeded in raising them to over 400 ppm and still counting, but that’s a different story.] Eric Galbraith and S. Eggleston (Galbraith and Eggleston, 2017) argue that as far as we know, atmospheric CO2 levels have never gone below the typical glacial levels of 190 ppm, even in extended snowball earth conditions. Why not? Well, a carefully-reasoned 2009 paper they cite (Pagani et al., 2009) suggests that even in the mostly warm conditions of the last 24 million years, when CO2 levels fell below 190 ppm, terrestrial plants stopped effectively photosynthesizing, thus they not only stopped removing CO2 from the atmosphere directly, but they also stopped the active root growth which increases the acidity of soils and enhances chemical silicate weathering from the rocks which removes CO2 from the soil, and ultimately from the atmosphere. Galbraith and Eggleston argue that the same thing has been happening during the glacial periods of the last 800,000 years, and extend the argument to the photosynthesis of oceanic phytoplankton. To wit, when CO2 levels get below 190 ppm, CO2 removal from the atmosphere by photosynthesis and chemical weathering is sharply reduced, so they decline no further. Continue reading

Blooms at Lower pH Levels Could Upset Ocean’s Acidification Cycle

by Max Breitbarth

Ocean acidification—the absorption of atmospheric CO2 by the ocean—has increased due to anthropogenic emissions of CO2, resulting in growing concentrations of CO2 in our oceans. Flynn et al. (2015) created models based on projections of increasing ocean acidity to explore the effects of algae blooms at decreasing pH levels and the effects of these blooms on phytoplankton populations that keep the ocean’s acidity within a manageable spectrum. Continue reading

Big Fish With a Bigger Problem: The Yellowtail Tuna Faces Difficulty in More Acidic Oceans

by Max Breitbarth

Anthropogenic emissions of carbon dioxide (CO2) have resulted in increased concentrations of CO2 in ocean waters that subsequently result in ocean acidification. Bromhead et al. (2015) explored the effects of elevated CO2 levels on the development of yellowfin tuna, Thunnus albacares in their March 2015 Deep-Sea Research article. Tuna represent some of the largest predators in the ocean, and cover vast expanses across several of the earth’s oceans—meaning the effects of ocean acidification could have ramifications for the species and their ecosystems around the world. The researchers found that ocean acidification levels have a strong negative effect on growth, hatch time, and larval survival in the experimental trials. These findings show that future ocean conditions may reduce the survivability of this fish in the future and lead to drastic marine ecosystem changes—as well as affect fishing practices by humans around the world that currently depend on yellowtail as a main source of food. Continue reading