Climate models have to cope with a big uncertainty: how rapidly, and in what ways, human beings respond to the threat they face
climate scientists are charged with a difficult task: to create a crystal ball with which to skry a future that promises to be hotter than today. But exactly how much hotter depends on innumerable factors, both natural and human. Creating the crystal ball is thus a two-stage process. First, you have to build a simulacrum of how Earth’s climate works. Then, you try to perturb this simulacrum with plausible future human actions, to see what picture appears.
Plants absorb carbon from the air during photosynthesis and then return it during respiration. Animals that eat those plants also respire. Bacteria and fungi similarly break down dead plants and animals to pillage materials and energy from them, releasing carbon dioxide and methane into the atmosphere as they do so. Some organic matter, nevertheless, gets buried rather than broken down, and is thus removed from climatic consideration.
Other parts of the globe suffer from a similar lack of observations. The oceans, for example, are reckoned to absorb more than 90% of the heat trapped by man-made greenhouse-gas emissions. But serious collection of data on the marine processes that underpin this, using networks of autonomous buoys, began only in the early 2000s.
Ocean currents also look susceptible to non-linear effects. These currents are propelled by a phenomenon called thermohaline circulation that depends, as its name suggests, on the salinity and temperature of seawater, and thus its density. Cold or saline water sinks, while warm or fresher water rises, and large bodies of sinking or rising water provide the engine that drives currents around the world.
Both negative emissions and carbon capture and storage could work in principle. But, unlike alternative ways of generating electricity, which, once mastered, will be profitable, they offers little prospect of turning a profit without subsidy. Given the threat, asking for such subsidies is perfectly reasonable. Taxpayers are called on to pay for wars against human enemies, so might be expected to stump up for one against a less tangible foe.
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