But there’s more. When the sun is able to warm the top layer of the ocean - between 30 and 100m deep - into a single layer, it forms a stable layer that fails to mix with the denser cold water beneath. Lovelock explains what happens then:
The formation of the surface layer exerts a powerful constraint on ocean life; primary producers that seed the newly formed warm layer in early spring soon go through a succession that uses up nearly all the nutrients of the layer. The dead bodies of this spring bloom sink to the ocean floor, and soon the suface layer is empty of all but a limited and starving population of algae. This is why warm and tropical waters are so clear and blue; they are the deserts of the ovean, and just now they occupy 80 per cent of the world’s water surface. In the Arctic and Antarctic, the surface waters remain below 10C and so are well mixed from the bottom to the surface and nutrients are available anywhere.Similarly on land, once the temperature gets above about 25C the rate of evaporation is so great that without almost continuous rain the soil dries out and you have a desert. Rainforests to some extent overcome this by creating their own microclimate of cloud above the trees, but Lovelock quotes a study in the Amazon suggesting that a 4C increase in temperature would disable this system and reduce the great forest to scrub or desert.
But temperature of course is not straight physics; there’s also chemistry – and carbon dioxide. And we’re taking the carbon that Gaia has stored over the ages in petrochemicals, and pumping it into the air. And models suggest that past 500 parts per million suggest a temperature rise of about 3C. That’s difficult but not impossible, were it not for positive feedback mechanisms: ice albedo (whereby less ice means less of the sun’s heat is reflected into space), a fall in algal numbers, meaning they are not absorbing carbon dioxide, and not generating marine stratus clouds; tropical forests collapsing; the spread of boreal forests in Canada and Siberia (being dark, they absorb heat); methane (24 times as potent a greenhouse gas as carbon dioxide – and used in its early history by Gaia to heat the earth through “detritophores”) is stored in ice crystals.
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