The world would have warmed throughout the 20th Century even without carbon dioxide emissions from the industrial revolution, according to a new study.

“This suggests that even if there had been no industrial revolution and burning of fossil fuels, there would have still been some warming through the twentieth century – to at least 1980,” according to lead author Jennifer Marohasy.

The world was about as warm in 1980 as it was during the Middle Ages when the Vikings settled Greenland and “when men dressed in tunics and built grand cathedrals with tall spires,” Marohasy wrote in The Spectator Australia on Tuesday, summarizing her study’s results.

Climate scientists Marohasy and John Abbot used a sophisticated artificial intelligence-like computer system to see what temperatures may have done since 1830 without human influence based on proxy climate records going back to 50 A.D.

The ANN system is a “form of machine learning: think big data and artificial intelligence,” which she says has been used to more accurately predict rainfall than models used by Australia’s meteorological agency, Marohasy wrote in a blog post.

“The difference between output from the ANN models and the proxy records is at most 0.2 °C; this was the situation for the studies from Switzerland and New Zealand. So, we suggest that at most, the contribution of industrialization to warming over the twentieth century would be in the order of 0.2°C,” she wrote.

Their findings challenge the mainline conclusion of the Intergovernmental Panel on Climate Change (IPCC), which also found the Earth warmed about 1 degree Celsius since before the industrial revolution. The IPCC just attributes all that warming to humans.

What’s interesting is Marohasy’s study, like most proxy data, shows temperatures declining after 1980. That’s in direct conflict with actual temperature observations, which show a continued rise in global average temperature through to 1998 before it leveled off for about 15 years.

This is called the “divergence problem,” Marohasy wrote. “Rather than address this issue, key climate scientists, have been known to graft instrumental temperature series onto the proxy record from 1980 to literally ‘hide the decline.’”

Marohasy isn’t the first scientist to argue the so-called Medieval Warming Period was about as warm as the late 20th Century.

A 2013 Swedish study suggested the planet was warmer in ancient Roman times and the Middle Ages than today based on radiocarbon data on where tree lined were in Scandinavia.

The study found “the pine tree line (and summer temperatures) was consistently higher than present, as it was also during the Roman and Medieval periods.”

Marohasy recently made headlines when she and meteorologist Lance Pidgeon called out Australia’s Bureau of Meteorology for changing temperature readings in the Snow Mountains.

Government meteorologists removed temperature readings below 13 degrees Fahrenheit as part of a “quality control” system to filter out temperatures dipping below that mark.

Bureau Chief Executive Andrew Johnson said the faulty reading was due to an equipment malfunction, rejecting the notion his agency was trying to manipulate temperature records.

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