No doubt. There has not been a period as globally warm as the current one in the last 2,000 years. According to scientists, this near-universal warming, which occurs in unison across the planet, is unique to this era. In contrast, other well-known cold and warm snapshots of the past, such as the Little Ice Age or the Medieval Warm Period, were in fact regional rather than global events.
Furthermore, the rate at which temperatures are now increasing far exceeds any previous fluctuations in temperature measured in the last two millennia. Those are the findings of three new studies examining temperature trends over the past 2,000 years and published in the journals Nature and Nature Geoscience . Previous climate fluctuations were mainly due to natural causes, including powerful volcanic eruptions, rather than man-made greenhouse gas emissions.
The findings, which are based on recently available global paleoclimatic data , reinforce an inescapable conclusion: “The current period of warmth is unprecedented in its global reach in the last 2,000 years,” says Michael Mann, climate scientist at Penn University. State (USA) that did not participate in these works.
Thermal evolution
In the study ofNature, a team led by Raphael Neukom, a climate scientist at the University of Bern, Switzerland, used many different types of temperature records from around the world to create thousands of climate reconstructions of the last two millennia, from year 1 to 2000 Those data were compiled by an international group of scientists calledPAGES 2k Consortiumand includetemperatures derived from tree rings, glacial ice cores, lake and ocean sediments, cave deposits such as stalactites and stalagmites, and historical documents.
Using that data, as well as direct temperature measurements collected in some places since the 19th century and some climate simulations, the team producedmore than 15,000 different climatic reconstructions of past global temperatures.The researchers then took a closer look at the precise timing of warming or cooling in four previously identified “climatic epochs”: the Roman warm period from about AD 1 to 300, the cold period of the dark ages from 400 to 800, the medieval warm period. . from about 800 to 1200 and the Little Ice Age from 1300 to 1850.
Although the same data sets were fed into the climatic reproductions, the scientists used different methodologies, which vary widely in computational complexity, to process the data and calculate past temperatures. Regardless of which method they used, history repeated itself:no past climatic epoch was a simultaneous global event.
Climatic seasons
TheLittle Ice AgeFor example, it was a cold snap that is believed to have lasted from about 1350 to 1850, but it did not occur everywhere at the same time. The team found that northwestern Europe and southeastern North America reached their coldest temperatures during the 17th century, while the area encompassing the central and eastern Pacific Ocean was colder two hundred years earlier, during the 15th century.
TheMedieval Warm Period,Also called the Medieval Climate Anomaly, it showed the warmest temperatures in northwestern Europe and eastern North America during the 11th century. But the moment of maximum heat occurred several hundred years later in central South America, and several hundred years earlier in the eastern and central Pacific Ocean.
This finding contrasts with the team’s conclusions on the current era of warming:is occurring simultaneously around the world, and the highest temperatures in the study were found to be correct in the late 20th century. “It’s consistent in a way that we haven’t experienced in the last 2,000 years,” says Nathan Steiger of Columbia University.
Because the study’s temperature data only goes as far as 2000, the last two decades of temperatures were not included in the research, but NASA and the National Oceanic and Atmospheric Administration (NOAA) reported in February that 9 of the 10 warmest years have been on record since 2005, and the last five years have been the five warmest on record. Scientists have repeatedly cited human activities as the cause of these record temperatures.
Anthropogenic warming
A second study, published inNature Geoscience, addresses the issue of anthropogenic warming more explicitly. The study, written by Neukom and other members of the PAGES 2k consortium, used the same temperature balances as the Nature study, but instead of comparing spatial patterns of warming and cooling around the world, they looked at the average global temperature across the globe. time, which revealed thatthe current rate of warming is much faster than that observed in the last 2,000 years, which can be attributed to natural variability.
A third study, also published in Nature Geoscience,It added another layer of context, looking at what natural forces might have been behind large regional fluctuations in temperature, such as the Little Ice Age.
Led by University of Bern (Switzerland) climate scientist Stefan Brönnimann, the researchers found thate before the start of the Industrial Revolution in the mid-19th century, powerful volcanic eruptions were the main driver of such large-scale temperature fluctuations. For example, five major eruptions, including the Mount Tambora eruption in 1815, occurred towards the end of the Little Ice Age.
The eruptions initially triggered cooling and climatic upheaval, and then a recovery period as the planet warmed up again.The recovery coincides with the start of the Industrial Revolution, where greenhouse gases became the main driver of warming, the researchers note.
These studies are undoubtedly the most comprehensive assessment of Earth’s climate in the past 2,000 years and show how unusual the climate we live in today is.
Referencia: R. Neukom et al. No evidence for globally coherent warm and cold periods over the preindustrial Common Era. Nature. Vol. 571, July 25, 2019, p. 550. doi: 10.1038/s41586-019-1401-2.
S. Brönnimann et al. Last phase of the Little Ice Age forced by volcanic eruptions. Nature Geoscience. Published online July 24, 2019. doi: 10.1038/s41561-019-0402-y.
PAGES 2k Consortium. Consistent multidecadal variability in global temperature reconstructions and simulations over the Common Era. Nature Geoscience. Published online July 24, 2019. doi: 10.1038/s41561-019-0400-0.
