Global warming is junk science

Overview
One widely-propagated opinion is that arguments for global warming are junk science, i.e. either:
 * based on spurious reasoning but including scientific-sounding phrases and figures designed to sound believable
 * (or) deliberately selecting only data that agree with pre-determined conclusions

at junkscience.com
''Skimming of this site is incomplete; responses are also incomplete. In particular, the "take-home messages" are worth further examination.''
 * the Earth's atmosphere does not behave like an actual greenhouse
 * argument: greenhouses operate by acting as a barrier to convection; the atmosphere does not block convection, and therefore cannot be acting as a greenhouse; there is no "greenhouse effect".
 * response: This is partly true. (It is also an incomplete explanation of how a greenhouse works, in that greenhouses also allow radiation to enter; without that element, a greenhouse would just be a house.) The point about convection is irrelevant in that the atmosphere cannot block convection because there can never be convection between an atmosphere and the vacuum of space. Put another way, the convection is already blocked by the lack of air outside the atmosphere. The entire argument is misleading because the greenhouse effect operates solely through radiation and reflection, not convection.
 * counterargument: Convection containment is critical to the function of physical greenhouses. Greenhouse gases categorically do not inhibit convective activity and so are not like a physical greenhouse.
 * response to counterargument: The greenhouse effect does not operate like a physical greenhouse. It operates by constraining radiation; convection is already restrained.
 * the greenhouse effect does not actually cause that much harm
 * argument:
 * greenhouse gases are not really like a blanket around the earth; they don't block convective activity: there are two parts to this:
 * greenhouse gases are not really like a blanket around the earth: they are a blanket in the sense that they completely enclose the earth, but not in the sense that they are made of cloth and good for wrapping yourself up in on a cold winter day. So this may be true depending on your definition of "like a blanket", but it is irrelevant either way.
 * greenhouse gases do not block convective activity: irrelevant; the greenhouse effect involves radiation and reflection, not convection
 * greenhouse gases do not trap the sun's radiation/'heat
 * argument: Greenhouse gases could be fairly described as delaying the energy transfer from Earth to space. "Trapping heat" implies that the energy is stuck in the system forever; this is a false notion. Greenhouse gases do not emit energy in the same bandwidth that they absorb energy, and thus emissions from carbon dioxide are not absorbed by carbon dioxide. While energy may be delayed on its inevitable journey back to space, it will eventually be emitted regardless of the number of intervening stages.
 * response: This argument makes no sense; see Chewbacca defense
 * it is not accurate to say that greenhouse gases 'reradiate' the infrared radiation they absorb
 * argument: "Absorbed radiation is transformed to either kinetic or potential energy and, as such, no longer exists in its original form -- hence, it cannot be 'reradiated.'"
 * response: The "potential" energy is otherwise known as "heat", which causes radiation. "Kinetic" energy is otherwise known as "motion", which causes either convection or friction. Within a closed system (in this case, the earth), all kinetic energy eventually becomes heat or is radiated away. At the relatively low temperatures under discussion in this case, the radiation is mostly infra-red, which is where most of the absorption takes place.
 * the "greenhouse effect" is not the same thing as "global warming"
 * the "greenhouse effect" is not the same thing as "climate change"
 * argument: The global mean temperature over which there has been so much obsession is only one part of climate – for example, how wet or dry the climate happens to be is probably of far greater significance than a simple mean temperature – in fact, it's not even clear that a global mean temperature is a particularly useful metric.
 * response:
 * convection keeps the planet more than 60 Â°C cooler than would otherwise be the case
 * argument: more detailed explanation not found
 * response: This is impossible; in order for convection to cool a body, it must exchange material (in this case, gas) with a cooler body (e.g. in the case of a malfunctioning greenhouse, the "cooler body" would be the surrounding air). There can be no exchange of gas between the earth and space because there are no other environmentally significant concentrations of gas near the earth's atmosphere.
 * we can't tell if the surface temperature is rising because the data aren't accurate enough
 * argument: The global mean temperature is very difficult to calculate; any claims of rising global temperatures based on such figures are therefore suspect.
 * response:
 * the greenhouse effect does not cause global warming because the net energy in equals the net energy out
 * argument: There's a lot of energy bouncing around, but the amount of energy entering the system and the amount leaving is fairly tightly constrained. The atmosphere is acting as a kind of check valve, slowing the loss of energy to space but the net incoming (324 + 168 Wm-2) = net outgoing (390 + 78 + 24 Wm-2).
 * response:
 * "Global warming" is really just an increased delay in energy loss to space
 * argument: "Global warming" is really just a sort of enhanced greenhouse effect, which means that the additional delay in energy loss to space induced by the fraction of carbon dioxide and other greenhouse gases released by humans before those gases are removed from the atmosphere by breakdown and/or biological activity.
 * response: This is an explanation for global warming, not a refutation.
 * The greenhouse effect has nothing to do with carbon dioxide (CO2); most of the effect (about 90%) is caused by water vapor
 * argument:
 * response:
 * Increased CO2 is essential; increased concentrations of CO2 are environmentally beneficial.
 * argument: Carbon dioxide is an essential trace gas that underpins the bulk of the global food web. Estimates vary, but somewhere around 15% seems to be the common number cited for the increase in global food crop yields due to aerial fertilization with increased carbon dioxide since 1950. Commercial growers deliberately generate CO2 and increase its levels in agricultural greenhouses to between 700ppmv and 1,000ppmv to increase productivity and improve the water efficiency of food crops far beyond those in the somewhat carbon-starved open atmosphere. CO2 feeds the forests, grows more usable lumber in timber lots meaning there is less pressure to cut old growth or push into "natural" wildlife habitat, makes plants more water efficient helping to beat back the encroaching deserts in Africa and Asia and generally increases bio-productivity.
 * response: This may be true, but just because something is good in some ways doesn't mean it can't be extremely harmful too. (At the risk of repeating a clich&eacute;: Water is essential, but too much water can drown you.) Saying it is "essential" does not weaken the point that it can become a problem if its atmospheric concentration becomes increased too far above the naturally-occurring "essential" levels.
 * Even if CO2 is responsible for global warming, humans are only responsible for a very tiny proportion of increased CO2 emissions and thus couldn't possibly be the cause of global warming.
 * argument: Humans can only claim responsibility, if that's the word, for abut 3.4% of carbon dioxide emitted to the atmosphere annually, the rest of it is all natural (you can see the IPCC representation of the natural carbon cycle and human perturbation here or a simple schematic from Woods Hole here). Half our estimated emissions fail to accumulate in the atmosphere," "disappearing" into sinks as yet undetermined. Humans' total accumulated carbon contribution could account for perhaps 25% of the total non-water greenhouse gases. Of the total greenhouse effect, water vapor accounts for about 70% and clouds (mostly water droplets) accounts for another 20%, thus water in its various forms is 90% of the greenhouse effect, leaving 10% for non-water greenhouse effect. Of this remaining 10%, mainly atmospheric carbon, humans might be responsible for 25% of the total accumulated atmospheric carbon, thus 0.25 x 0.1 = 0.025 x 100 = 2.5% of the total greenhouse effect, at most.
 * response:
 * '''Even a 2.5% additional contribution to the greenhouse effect via CO2 seems improbable, since the best estimates are that this would require a toxic amount of CO2 in the atmosphere.
 * argument: Theoretically, in a dry atmosphere, CO2 could absorb about three times more energy than it actually does, as could clouds in the absence of all other greenhouse gases. The temperature effect of atmospheric carbon dioxide is logarithmic (that means there is a diminishing response as you keep adding more. If we consider the warming effect of the pre-Industrial Revolution atmospheric carbon dioxide (about 280 parts per million by volume or ppmv) as 1, then the first half of that heating was delivered by about 20ppmv (0.002% of atmosphere) while the second half required an additional 260ppmv (0.026%). To double the pre-Industrial Revolution warming from CO2 alone would require about 90,000ppmv (9%) but we'd never see it – CO2 becomes toxic at around 6,000ppmv (0.6%).
 * response:
 * It is still disputed whether water acts to enhance the greenhouse effect.
 * argument: There is still dispute over whether water would (does) act as a positive or negative "feedback" (multiplier effect) since water vapor and droplets (clouds) affect both incoming Solar radiation and outgoing Earth radiation.
 * response:
 * The large estimates of global warming effects come primarily from computer models, a disputed method of prediction.
 * argument: "...the big warming numbers come not from measurements but from computer models. These computer models and their output are passionately defended by the modeling clique and frequently derided by empiricists -- but the bottom line is that models make an enormous range of assumptions. Whether all the assumptions, tweaks and parameter adjustments really collectively add up to a realistic representation of the atmosphere is open to some conjecture (current climate models do not model "natural" climatic variation very well), but there is no evidence yet that they can predict the future with any greater certainty than a pack of Tarot cards. Moreover, humans do a lot besides emitting greenhouse gases, changing vegetation and transpiration rates through agriculture, for example, and many effects expected to both increase and decrease regional temperatures are not included in these models."
 * response:
 * Computer-based climate models are especially questionable due to the use of "multiplier" (positive feedback) effects, producing an exponential rather than logarithmic response.
 * argument: "...climate models are made interesting by the inclusion of 'positive feedbacks' (multiplier effects) so that a small temperature increment expected from increasing atmospheric carbon dioxide invokes large increases in water vapor, which seem to produce exponential rather than logarithmic temperature response in the models. It appears to have become something of a game to see who can add in the most creative feedback mechanisms to produce the scariest warming scenarios from their models but there remains no evidence the planet includes any such effects or behaves in a similar manner."
 * response:

Reference

 * Greenhouse, global warming - and some facts at junkscience.com