Historical fluctuations in climate like the "Little Ice Age" and the "Medieval Warm Period" are frequently used by climate change deniers to dispute the reality of human-caused climate change.

But this thinking is flawed – research recently published in Nature Geoscience has shown (for the first time) that these climatic anomalies (or "phases") were regional, not worldwide. In comparison, the changes we are seeing in global temperatures today is just that. Global.

Evidence of the "Little Ice Age" (approximately 1300-1850 CE) can be found in art and the environment, with paintings of European frost fairs held on frozen rivers, and temperature reconstructions using tree rings. Because these reconstructions can be made in North America as well as in Europe, scientists previously assumed that these temperature fluctuations (caused by natural events) were felt globally.

Now, scientists at the University of Bern in Switzerland have conducted a thorough investigation into historical climate variations with data from the last 2,000 years stored in an international research consortium (PAGES). This includes data on tree rings, ice cores, lake sediments, and corals. Using six different statistical models, the team calculated the probability of exceptionally warm and cold decades and centuries – not just absolute temperatures.

The results show that there was no globally coherent picture in any of the five pre-industrial climate epochs – "Roman Warm Period", "Late Antique Little Ice Age", "Dark Ages Cold Period", "Medieval Warm Period", and "Little Ice Age". Or as lead author Raphael Neukom puts it, "The minimum and maximum temperatures were different in different areas."

"It's true that during the Little Ice Age it was generally colder across the whole world," Neukom said in a statement. "But not everywhere at the same time. The peak periods of pre-industrial warm and cold periods occurred at different times in different places."

In comparison, climate changes we are seeing in modern times show a completely different pattern – one of consistent warming across the planet.

The study found the 20th century was most likely the warmest period of the past two millennia for more than 98 percent of the globe. This, the study authors say, shows it cannot be explained by random fluctuations. Instead, it is further proof that greenhouse gas emissions are triggering temperature rises.

If current trends continue, the 20th century could soon be overtaken by the 21st. Last month broke global records to become the hottest June on record, while this month is predicted to be not just the hottest July, but the hottest month ever recorded. 

Indeed, the last five years have been the hottest on record – and at this rate, it doesn't look like 2019 will buck the trend.