Climate alarmists Michael Mann and Katharine Hayhoe have been caught using dubious, revisionist temperature data in their attempt, as one Climategate email author put it, to “deal a mortal blow” to the extensively documented Medieval Warm Period.
Before climate change became a political issue, it was scientifically well-established that a significant global warming event occurred between approximately 900 AD and 1200 AD. For example, the United Nations Intergovernmental Panel on Climate Change (IPCC) First Assessment Report presented a temperature history and visual graph documenting that the Medieval Warm Period existed and that it brought temperatures at least as warm as today (at pg. 7). Multiple peer-reviewed studies provided additional confirmation of the Medieval Warm Period.
The warming climate of the Medieval Warm Period spurred abundant crop production, fewer extreme droughts and floods, growing human population, and improving living standards. The Little Ice Age terminated the Medieval Warm Period and brought devastating weather extremes, widespread crop failures, famines, plagues like the Black Death, and a contracting human population. (For a good summary of the extensive benefits of the Medieval Warm Period and the devastating harms of the Little Ice Age, see the excellent book, “In the Wake of the Plage: The Black Death and the World It Created.”)
The existence of large historical temperature fluctuations, warmer temperatures than today, and many documented benefits of those warmer temperatures presented a powerful obstacle in alarmists’ attempts to brand our current modest warming an unprecedented climate crisis. One of the many embarrassing emails leaked in the Climategate scandal showed how alarmists deliberately set a goal of eliminating the historical existence of the Medieval Warm Period. Alarmist climate scientist Jonathan Overpeck wrote in an email to fellow alarmist Keith Briffa, “I get the sense that I’m not the only one who would like to deal a mortal blow to the misuse of supposed warm period terms and myths in the literature.”
Also, scientist David Deming testified to Congress that a prominent figure working in the field of climate change asserted to him, “We have to get rid of the Medieval Warm Period.”
We have often been told that the science is settled. Apparently, that doesn’t apply to scientific data and evidence invalidating climate alarmism. Mann last month favorably retweeted an assertion that present temperatures are the warmest they have been for at least the past 5,000 years. Hayhoe earlier this year gave a presentation in which she presented a graph (without any scientific citation) asserting temperatures steadily and consistently declined for 4,000 years – without any significant variation – prior to the warming of the past 120 years that finally and mercifully brought an end to the Little Ice Age (at 7:41).
As documented above, the existence of substantial historical climate variations such as the Medieval Warm Period and the Little Ice Age were scientifically well-documented and not in dispute before climate activism politicized the issue. Alarmist scientists were on record searching for justifications to eliminate these inconvenient climate variations that blew gaping holes in their alarmist theories. Now, conveniently, alarmists like Mann and Hayhoe claim the Medieval Warm Period, the Little Ice Age, and other well-documented warm and cold periods simply did not exist.
An old sarcastic saying goes, “When the facts doesn’t fit the theory, change the facts.” Mann and Hayhoe provide perfect real-world examples of such perniciousness. Powerful scientific evidence supported near-universal agreement about the existence of the Medieval Warm Period. Then Mann and Hayhoe, supported by little or no compelling evidence, waved a magic wand and made the Medieval Warm Period conveniently disappear.
Climate realists, however, will stick with the powerful scientific evidence, the long-established scientific “consensus,” the peer-reviewed scientific literature, and the findings of the IPCC. Sorry, Mann and Hayhoe, but you have been caught red-handed.