Measurements of the climate system show that the Earth is fast becoming a hotter planet than anything yet experienced by humans. Processes that would normally regulate climate are being driven to amplify warming. Such feedbacks, as well as the inertia of the Earth system—and that of our response—make it doubtful that any of the wellintentioned technical or social schemes for carbon dieting will restore the status quo. What is needed is a fundamental cure. The oceans, which cover more than 70% of the Earth’s surface, are a promising place to seek a regulating influence. One approach would be to use free-floating or tethered vertical pipes to increase the mixing of nutrient-rich waters below the thermocline with the relatively barren waters at the ocean surface.(We acknowledge advice from Armand Neukermans on engineering aspects of the pipes.) Water pumped up pipes—say, 100 to 200 metres long, 10 metres in diameter and with a one-way flap valve at the lower end for pumping by wave movement—would fertilize algae in the surface waters and encourage them to bloom. This would pump down carbon dioxide and produce dimethyl sulphide, the precursor of nuclei that form sunlight-reflecting clouds. Such an approach may fail, perhaps on engineering or economic grounds. And the impact on ocean acidification will need to be taken into account. But the stakes are so high that we put forward the general concept of using the Earth system’s own energy for amelioration. The removal of 500 gigatonnes of carbon dioxide from the air by human endeavour is beyond our current technological capability. If we can’t ‘heal the planet’directly, we may be able to help the planet heal itself.