What goes around comes around. Our greenhouse gas emissions do not just warm the planet, they also acidify the oceans; however, it is a fact that most people are not aware of. Now it turns out that the changes in ocean chemistry they cause will feed back into the climate, further driving up temperatures. This was not always thought to be true. Climatologists had considered that carbon dioxide (CO₂) absorbed by the ocean was stored, and unable to affect the climate. But a study now suggests that the acidification it causes will rebound on the entire planet, by acting on tiny marine plants called phytoplankton. These plants produce a chemical called dimethyl sulphide (DMS) that drifts up into the air and reflects sunlight back into space, cooling the planet. Katharina Six and her team at the Max Planck Institute for Meteorology in Hamburg gathered experimental data showing that phytoplankton produce less DMS as seawater becomes less alkaline due to acidification. After entering these figures into climate models, they estimate that 18 percent less DMS will be released from the oceans by the year 2100, compared to pre-industrial times. If the concentration of CO₂ in the atmosphere doubles, which is likely to happen later this century, temperatures are expected to rise between 2 and 4.5°C. Ocean acidification will add between 0.23 and 0.48°C to that figure, Six estimates.