I haven't been posting much over the last few days because I was busy reading lots of articles about Climate Science and watching YouTube videos, most were from Warmenists and a few from Deniers, for balance. No links, for the time being as I have dozens.
The Warmenist articles/videos look to be about 90% correct, but they all contain a couple of logical/mathematical errors, inherent contradictions or over-simplifications, not to mention that they contradict each other. Most of the Denier articles and videos have similar inconsistencies.
What their explanation boils down to, having stripped away the errors and taking the rest at face value, is this:
1. The two main Greenhouse Gases are
a) water vapour (not to be confused with condensed water droplets, which cool the atmosphere) at an average of 20,000 parts per million (within a wide range between zero and 40,000, that's the assumed average).
b) Carbon dioxide at an average of 420 ppm, up from 280 ppm in pre-industrial era.
Molecule-for-molecule, these have a very similar effect (AFAIAA). Water is self-regulating, as once it hits saturation point, it condenses and falls as rain or snow, removing itself from the atmosphere and cooling things down.
Carbon dioxide is not self-regulating, rain washes some of it out of the atmosphere, but it then most of it re-evaporates and only some goes into the oceans (which is where limestone cliffs come from) or into plants (which eventually die and rot again).
(The Warmenists shift the goal posts here a bit. up to current levels, they accept that H20 is self-regulating and can be ignored (most of them do), but magically, if C02 increases, then H20 and C02 will interact and temperature increases due to the H20 element will somehow become self-reinforcing. This seems highly unlikely to me.)
2. The entire additional 33C average temperature of the earth's surface compared to what you'd expect from sunlight alone is down to greenhouses gases. Apparently nitrogen and oxygen would have no such effect (although you'd still get the steady fall in temperature with decreasing pressure/increasing altitude). This gradient is much the same for all planets in the solar system, regardless of what kind of gas makes up an atmosphere.
3. If you increase greenhouse gas concentrations from average 20,280 (H20 plus pre-industrial C02) to 20,420 (H20 plus modent CO2), that's a 0.7% increase in Watts hitting each square meter of the earth's surface. Existing greenhouse effect is 33C, increase that by 0.7% = 33.23 C i.e. an extra 0.2C* compared to what it would be at 280 ppm C02, everything else being equal.
* The increase in surface temperature relative to increases in Watts/m2 is logarithmic not linear, so let's round that 0.23C down to 0.2C.
4. It appears to be accepted by both sides that global average temperatures go in lots of overlapping and fairly regular cycles. The most relevant one as at today is a roughly thousand-year cycle i.e. Roman Warm Period, Mediaeval Warm Period and Modern Warm Period. That explains the other rest. let's not bicker about what a sensible starting point is, looking at the increase since pre-industrial era means you are looking at the increase since the Little Ice Age, however defined, when temperatures were 1 or 2C lower than the very long run average.
Debate Magazine
