When Did Anthropogenic Global Warming Begin?

by John Hinderaker in Climate
If you read pretty much any climate alarmist literature, you will see the claim that the Earth’s warming over the last 100 years is due overwhelmingly to the burning of fossil fuels. But this is disingenuous: even under the defective models on which the alarmists rely, it cannot be claimed that prior to 1950, human contributions of CO2 to the atmosphere could have had any significant effect. So why do the warmists keep talking about the last century?
Because they have to. Once again, we turn to Watts Up With That for the explanation. During the 20th century, there were two periods of warming, separated by a time of mild cooling. The first warming period lasted roughly from 1910 to 1940, while the second was from 1975-1998; there has been no warming since then. The second warming period was not statistically different from the first, yet the first could not have been due to human activity.

Hmm. The problem is obvious. If the first temperature increase was not due to more CO2 in the atmosphere, what is the basis for being confident that the second one was?

In fact it was not until approximately 1975 that temperatures began to rise. However, this doesn’t mean that CO2 based Anthropogenic Global Warming began in 1975, because as Phil Jones noted during a 2010 BBC interview, “As for the two periods 1910-40 and 1975-1998 the warming rates are not statistically significantly different.” As such, the warming from 1910 – 1940, before Anthropogenic CO2 became potentially consequential, is “not statistically significantly different” from the warming during the period from 1975 – 1998 when the IPCC AR5 claims to be ” extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century”. Given that “causes of the earlier warming are less clear,” our understanding of Earth’s climate system is rudimentary at best, and our historical record is laughably brief, it is confounding how the IPCC can be so “extremely” sure “that human influence has been the dominant cause of the observed warming since the mid-20th century”, which is “not statistically significantly different” from the natural warming that occurred between 1910 – 1940.
Regardless, claims that “Global warming is the unusually rapid increase in Earth’s average surface temperature over the past century” are erroneous and indicative of either ignorance or duplicity on the part of NASA’s Earth Observatory, NASA’s Climate Consensus page, The Daily Mail, the EPA and many others.

The Earth has been warming naturally for some time, although not in a straight line, as it recovers from the Little Ice Age. Average temperatures are still relatively low compared to the last 10,000 years, so it is plausible that warming may continue. But until the alarmists can explain how they differentiate–scientifically!–the 1975-1998 warming from the 1910-1945 warming, their apocalyptic theories will continue to be a bad joke.

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