Climate change: Ocean acidification amplifies global warming

It is common knowledge that fossil fuel emissions of CO₂ lead to global warming. The ocean, by taking up significant amounts of CO₂, lessens the effect of this anthropogenic disturbance. The "price" for storing CO₂ is an ongoing decrease of seawater pH (ocean acidification1), a process that is likely to have diverse and harmful impacts on marine biota, food webs, and ecosystems. Until now, however, climate change and ocean acidification have been widely considered as uncoupled consequences of the anthropogenic CO₂ perturbation2.

Recently, ocean biologists measured in experiments using seawater enclosures (mesocosms)3 that DMS concentrations were markedly lower in a low-pH environment. When DMS is emitted to the atmosphere it oxidizes to gas phase sulfuric acid, which can form new aerosol particles that impact cloud albedo and, hence, cool Earth's surface. As marine DMS emissions are the largest natural source for atmospheric sulfur, changes in their strength have the potential to notably alter Earth's radiation budget.

Based on the results from the mesocosm studies the researchers from the MPI-M have established relationships between pH changes and DMS concentrations in seawater. They projected changes in DMS emissions into the atmosphere in a future climate with enhanced ocean acidification using the MPI-M Earth system model4. In the journal Nature Climate Change it is demonstrated, that modeled DMS emissions decrease by about 18 (±3)% in 2100 compared to preindustrial times as a result of the combined effects of ocean acidification and climate change. The reduced DMS emissions induce a significant positive radiative forcing of which 83% (0.4 W/m2) can, in the model, be attributed to the impact of ocean acidification alone. Compared to Earth system response to a doubling of atmospheric CO₂ this is tantamount to an equilibrium temperature increase between 0.23 and 0.48 K.

Simply put, their research shows that ocean acidification has the potential to speed up global warming considerably.