Water and life

Water makes life on Earth possible.  It unites the living world like nothing else.  From the lunar tides, ocean currents and seasons to the molecules that build us all, it permits and regulates all life.  Embedded within this big picture, subject to the rules of ecology but often careless of them, are people.  Almost all the world’s water is salty but we live on land, where a regular supply of fresh, clean water is utterly precious. It is the single most important of the ‘on/off’ switches that are hidden under the floorboards of our lives.  But we have allowed these sources of fresh, clean water to be abused, diverted, polluted, or dried up.  Repair is possible, but only by focusing on the ways of nature and the needs of the weak. And now climate change is demolishing the very fabric of our home, making everything worse.

Water has a special structure in which its molecules, each made up of two atoms of hydrogen and one of oxygen, have a different charge on each side, so the molecules attract one another.  This attraction is called a hydrogen bond, and it is strong enough to join water molecules into a swarm that behaves like a supermolecule, but weak enough that the bonds continually form and break depending on how much energy there is in the system.  When there is very little energy, the molecules freeze together into ice; when there is much more, they break apart into steam.  But at middle energies, they ‘shimmer’ in a way that makes life work at the level of cellular structures and chemical metabolism.

Because water molecules are polar – each with a positive and a negative side – they can get a grip on all sorts of other molecules, so water dissolves and mixes with more things than any other liquid.  Then, the hydrogen bonds also do weird things to how water behaves under different conditions, which make life possible at the level of organisms, ecosystems, and the whole biosphere.  They allow water to absorb or lose a lot of energy before it changes from liquid to ice or steam, so blood and ocean currents carry a lot of heat.

Put these things together, multiply them by a couple of billion cubic kilometres of water, each weighing a trillion tonnes, and stir using the energy of a vast thermonuclear reactor (the Sun), and you have the main unifying theme of our living world.  But because of the hydrogen bonds, ice needs 80 times more energy to melt than liquid water does to warm up.  This alone puts water among the most important things right now, since the ice in the Arctic Ocean has been absorbing the extra heat of global warming for decades, and every summer there is less ice up there.  When it finishes melting, only a few years from now, a sudden heating of the Arctic is inevitable, along with a surge of methane and other greenhouse gases. This is what people mean when they talk about ‘tipping points’ and ‘runaway climate change’, and it could spell the end of the only living world that we have ever known.

© Julian Caldecott