A friend recently made, on Facebook, what I thought was a fairly innocuous comment about a confused news story on global warming, only to get the incredulous reply, ‘What, you don't believe in Climate Change?’. Sigh. But this is the sort of buffoonery I have come to expect from those who fancy themselves as enlightened about ‘Climate Change’. ‘Enlightenment’ is rarely illuminating.
Leaving my friend out of it, here's what I believe with reasonable confidence:
- From the end, in the mid-19th century, of the Little Ice Age, to the end of the 20th century, Earth's atmosphere warmed slightly, well less than 2° C but the exact figure depends on whose data you use and how you run the numbers.
- The planet has probably warmed, on average, since the mid-20th century, although that picture is clouded a bit by siting issues and dubious ‘adjustments’ to the surface temperature data set. In any case, the majority of 20th-century warming happened previous to 1940, i.e. previous to the majority of human emissions of greenhouse gases (GHGs). (Note to the Associated Press: The correct plural form is GHGs, not GHG. Also, RBIs and WMDs. Thank you.)
- The warmest temperatures on record were in the 1930s.
- There has been no statistically detectable warming since the mid-1990s, 1996 or 1997 for sure and possibly back to 1993 depending on the dataset and how it is processed.
- Human action has contributed to global warming, but increased greenhouse effect due to human GHG emissions is probably less than 50% responsible, with or without ‘amplification’. The urban heat-island effect is a significant player, too.
- Natural variability (e.g., the end of the Little Ice Age and changes in El Nino patterns, probably not human-induced) is a significant factor.
- BEST was a bust.
- The overall temperature effects of increased concentration of atmospheric water vapor, clouds included, are at most nearly neutral. Cloud effects, plus and minus, are significant, but are on balance a strong negative feedback. The postulated ‘amplification effect’ due to water vapor has not been observed. (A recent study, claiming the opposite, contained several glaring errors.)
- To date, ‘climate change’ as a result of anthropogenic GHGs is mostly limited to the increase in temperatures. There is no evidence that we are significantly affecting severe-weather patterns. Indeed, there is no evidence that severe-weather patterns are changing at all. (The effect of severe weather on increasing human populations is a different question.)
- All other things being equal, climate sensitivity to changes in CO2 concentration is logarithmic, i.e. not a straight line. Climate sensitivity to increased concentrations (from present) of CO2 is currently and will be slight. Future climate change as a result of increased anthropogenic CO2 will therefore be slight and practically negligible. The IPCC study that projected great cataclysm was based on the high end of IPCC temperature projections. At the low end – which, according to the IPCC, is more likely – they admit that climate effects will be minor.
- All of this is consistent with the ‘97% consensus’ figure, which has been fundamentally misreported and therefore generally, indeed wildly, misunderstood. (For what it's worth, if the proposition is that the planet has warmed significantly since the mid-19th century and that human action has contributed to this change, then 97% is probably a significant underestimate. On that point, even the ‘skeptics’ agree.)
But I have this nasty habit of reading past the headline and lede, and not just getting my information from press releases and news reporters. My bad.