Sometimes, it's true, science predicts the future reliably enough. For example, if you'd said on any day during the last four and a half billion years that "tomorrow the sun will rise in the East," you'd have been proved correct. Moreover, much else about astronomy is highly predictable. But that's because everything in the vast emptiness of space happens, well, in space. In other words, astronomical events are highly predictable because the objects about which predictions are made, planets, satellites, stars, and galaxies, are affected by their environment in very few and very predictable ways. These bodies exist in gravitational and electromagnetic fields the properties of which are well understood and which, on astronomical scales, change in strength and conformation incredibly slowly.
But on the surface of the Earth, things are very different. They are, in fact, chaotic because all kinds of complex things are in constant and instantaneous interaction with other complex things. Molecule of air, the behavior of which determine climate, are in violent and repeated collision with other molecules of air, absorbing and emitting radiation, in a vastly complex radiation field that changes continually, as the sun rises and sets, as the earth warms and cools, as clouds form and dissipate.
Added to these effects, the effects of constant additions and removals of components of the atmosphere: removal of water by condensation and precipitation, removal of carbon dioxide by photosynthesizing plants, addition of carbon dioxide from the decomposition of organic matter, the emission of methane from swamps and leaky pipes, the addition of nitrogen oxides from forest fires and the combustion of motor fuels
Then take into account the way that the whole mix is stirred on a massive scale by forces of convection and the motion of the Earth (Coriolis force); and much, much else beside. There you have the underlying challenge of the so-called science of climate change — it is the challenge of understanding how all these variables, including human activity, will affect the weather tomorrow, next week, next year, in the next decade and the next hundred years.
The challenge looks like a scientific question, yet not sensible scientists should presume to answer it. All that one can do, in the face of such a question is to say, if this, then all other things being equal, that. The "that" being what happens by the end of the week, or the decade, or the century. But all other things will never be equal. Over the period for which you have calculated the effect of a particular variable, say increased atmospheric carbon dioxide concentration, the radiant output of the sun may decrease by a tiny fraction of a percent, or it may increase. Or because coal-fired power plants have been replaced by natural-gas-burning power plants, which means less sulfur is being emitted to the atmosphere, which reduces the abundance of white sulfate particles in the air, which increases the reflection of sunlight to outer space, which thus have a cooling effect on the climate.
|Climate models versus reality. Source|
If "climate science" cannot tell us what the effect of human activity on climate will be, what should we do? Stop worrying and just carry on pouring into the atmosphere millions of tons of carbon oxide, soot, sulfur, refrigerant gases, natural gas? I think not. The best bet would be to rename Climate Science "Climate Policy Studies" or some such thing and start looking at worst case scenarios, and practical means to watch for and minimize the risks that those studies reveal. The outcome of such studies would thus be to: (a) identify the greatest risks; (b) watch for evidence of the realization of anticipated risks; and (c) devise actions to growing risks should they emerge.
Daniel Sarewitz: Saving Science
CanSpeccy: Rising Atmospheric Carbon Dioxide Concentration, Part I: Carbon Dioxide Is Not a Greenhouse Gas
CanSpeccy: Rising Atmospheric Carbon Dioxide Concentration, Part II: Ecosystem Disruption
CanSpeccy: Rising Atmospheric Carbon Dioxide Concentration, Part III: Induced Stupidity and the Decline of the West
CanSpeccy: Rising Atmospheric Carbon Dioxide Concentration, Part IV: Reversing the Trend