In 1910, Dr Crippen, an American homoeopathic physician living in London, attempted to dispose of the remains of his wife, Cora, by dissolving her torso in a bath of acid. It might be hard to imagine, but the world's ocean is turning into a warm acid bath because of excess carbon dioxide in our atmosphere.

Carbon dioxide gas not only creates a greenhouse effect but also dissolves in seawater to form carbonic acid. Fortunately for humankind, the capacity of the sea to absorb the gas has offset the problem of warming from fossil-fuel emissions.

But now there are signs that the oceans can't take much more carbon dioxide.

In the evolutionarily fine-tuned oceans, a small change in acidity is enough to shift an organism's physiology from building up bony and stony body parts to breaking them down. Coral polyps are the world's most avid skeleton-builders, but they can't build in an acidic sea. Without maintenance from the organisms that build them, coral reefs start to crumble. Coral reefs protect large areas of tropical coastlines and blunt the effects of typhoons and tsunamis, as well as being an important source of food for fish. Many of the world's largest cities are built on tropical coasts.

It doesn't take much to work out that raising our atmospheric carbon-dioxide levels and thereby acidifying oceans will have grave consequences for human societies as well as wild ecosystems.

The trouble is that the 1.4 quintillion cubic metres of the world's ocean is chewed up, processed and spat out again and again by organisms we can't see with the naked eye, and that we know almost nothing about. We do know that these life forms are the most important on the planet for converting carbon dioxide into living matter by the most significant chemical reaction of them all - photosynthesis. In fact, photosynthetic micro-organisms live in a compulsory symbiosis with reef-building corals, but the cohabiting microbes are very sensitive to the overheated water resulting from carbon dioxide's greenhouse effect. It's double jeopardy for coral, therefore.

Apart from reinventing life, the American biologist Craig Venter has more usefully attempted to find out more about these ocean-living microbes. Venter likes to go sailing, and his state-of-the-art yacht is geared up for regular microbe sampling during voyages. The microbial DNA is extracted, and from the sequences he can obtain indications of what kinds of chemical reactions the sea's microbes can participate in.

Obtaining a DNA sequence nowadays is almost trivial, but it is not so easy to work out how bacteria interact, not even in one cubic millimetre of surface water. Once you have the data from the myriad necessary observations, it has to be fed into some sort of plausible model to explain what is happening on the scale of an ocean basin. The latest issue of Science magazine calls for urgent investment in long-term, systematic and international ocean research collaborations so that we can join up more of the dots in the great unknown of the world ocean.

To understand what we are doing to the world's vast oceans we first need to understand the very, very small. If we don't keep the oceans alive and change our sinister energy consumption habits will we, like Dr Crippen's wife, dissolve in an acid bath of our own making?

Caroline Ash is senior editor of Science magazine.

Mark Lynas will return in August.