Russ Daggatt (guest post)
BTW, Popular Mechanics (of all publications) has an excellent summary of the meaning of the climate email contretemps:
https://www.popularmechanics.com/science/earth/4338343.html?page=1
It ends with this nice bit:
What We Know for Sure
Leaving the model predictions aside, I’d like to end this by taking stock of the data. Please keep in mind that this is just the view of a nonspecialist, who has not read all of the many papers on global climate written over the past decades.
The atmosphere is well mixed on a year-long time scale. It is not necessary to cover the globe with sensors to determine how the average atmospheric CO2 concentration is changing over periods of years. All data show that atmospheric CO2 is going up. This increase is very strongly correlated with the historical increase in human CO2 emissions. Ice-core gas samples show that the current concentration in CO2 is unprecedented for at least 500,000 years (and probably many millions of years, based on other data). There have been many other periods in the glacial record when atmospheric CO2 went up without any help from humans, but they show a much slower rate of increase of CO2, and much lower maximum concentrations.
For these reasons, and based on carbon isotope data, it is all but certain that the present, unprecedented rise in CO2 is due mainly to human output. But one cannot rule out with complete certainty other factors, for example, global warming itself, that could also be significantly contributing to the atmospheric CO2 increase.
CO2 (and methane) in the atmosphere are nearly transparent to UV and visible radiation, but absorb in the infrared, creating a “greenhouse.” If it were not for this, the surface of the Earth would be much colder. This leads to the inference that increasing CO2 will lead to increasing warmth. Also, high CO2 concentration in the air leads to ocean acidification, which is probably bad for coral and perhaps also for plankton that make their shells from calcium carbonate (soluble in acid) and form the base of the ocean food chain.
A good-faith effort has been made to determine average global temperature using the instrumental record, with increasing accuracy and precision as the data become more comprehensive. For sure, the average temperature of the atmosphere has been rising for most of the last 50 years. This is consistent with the greenhouse theory, though one cannot rule out with complete certainty that other factors—variation due to sunspot activity, or the last gasp of a long warming trend caused by variation in the Earth’s orbit—might also be contributing to temperature change.
The Arctic ice cap is getting smaller, in apparent response to this global temperature increase. Sea level is rising, due to the thermal expansion of the oceans and, increasingly, to melting of the Greenland and/or Antarctic ice caps. It has been shown to most people’s satisfaction that the Greenland ice cap is getting smaller.
There may be other factors, not yet accounted for, which could more or less suddenly emerge, and offset some or all of the future CO2 increase, the warming, the melting and the acidification that are predicted from these simple, well-known observations and the inferences and projections from models based on these observations. That’s the nature of science in general. It is really almost impossible to prove beyond all doubt that nothing important is missing from a theory. As a trail sign in Yosemite used to say, “Caution, unknown hazards may exist.” In addition, the ecological, economic and social consequences of global warming are also uncertain, adding another layer of unpredictability to this whole scenario.
Most scientists know and acknowledge these uncertainties, and reason as follows. We’re in an unprecedented situation, with regard to the concentration of CO2 in the atmosphere and the rate at which it is rising. Because this is unprecedented, we are not sure what is going to happen. But global warming is very likely, and reasonably probable outcomes could be fatal. Ignoring it would be like Russian roulette. Want to play? I do not.
The so-called “One-Percent Doctrine,” attributable to Dick Cheney, is described thusly:
“If there’s a 1% chance that Pakistani scientists are helping al-Qaeda build or develop a nuclear weapon, we have to treat it as a certainty in terms of our response.”
This is a variation of the “precautionary principle“: ” If an action or policy might cause severe or irreversible harm to the public or to the environment, in the absence of a scientific consensus that harm would not ensue, the burden of proof falls on those who would advocate taking the action.”
If there is a one-percent chance that continuing to pump anthropogenic carbon dioxide into the atmosphere would cause catastrophic climate change, the burden of proof falls on those who would continue to engage in those activities.