2,500 years of wild climate change in southern Europe

By Joanne Nova September 17th, 2023 174 Comments @CFACT

The new study on stalagmites in caves of the Pyrenees shows that modern climate change is nothing compared to normal fluctuations in the last 2,500 years when it was, at times, much hotter, colder, and more volatile. Rapid shifts between temperatures were common.

The researchers looked at eight stalagmites in four caves and local lake levels, but they also compared their results with other European temperature proxies and reconstructions, and the pattern is consistent across the region. The Roman Warm Period was much hotter than today, and for hundreds of years as well, even though coal plants were rare. Apparently, there was a reason Romans were dressed in togas.

The Dark Ages were very cold, especially around 520 – 550 AD — which may be related to what the researchers call a “cataclysmic” volcanic eruption in Iceland in 536 AD. It was followed by two other massive volcanic eruptions in 540 and  547 AD. This effect is visible in European tree rings, which showed “an unprecedented, long-lasting and spatially synchronized cooling”.

Indeed, the researchers declare that volcanoes and solar variability appear to be the main drivers of the climate in South Western Europe.

So, finally, we see one long continuous proxy record from ancient Greek times through until 2010. The big question is why these sorts of studies are not done everywhere and all the time. It’s not like we don’t have plenty of caves with stalagmites to analyze. If the climate really was “the biggest threat to life on Earth”, why are these extraordinary datasets not the top item on the wish-list of every institution claiming they care about the climate?

There will be more to say about this remarkable paper:

Click to enlarge. Oxygen isotopes are used to estimate temperatures.

Some passages from the paper discuss how these results match other studies from Europe:

The cold event at ca. 540 AD (the coldest of the speleothem record) may be related to a cataclysmic volcanic eruption that took place in Iceland in 536 AD and spewed ash across the Northern Hemisphere, together with the effect of two other massive eruptions in 540 and 547 AD (Sigl et al., 2015). An unprecedented, long-lasting, and spatially synchronized cooling was observed in European tree-ring records associated with these large volcanic eruptions, corresponding to the LALIA period (Büntgen et al., 2016).

Some passages from the paper discuss how these results compare with many other European studies and stark moments in history.

5.2.2. Temperature variability in W Europe and the W Mediterranean during the last 2500 years
There are very few high-resolution speleothem records in Europe covering the CE (Comas-Bru et al., 2020). We compare the Central Pyrenean speleothem composite with nine selected speleothems records in Europe and northern Africa which cover with robust chronology and decadal resolution of the last 2500 years (Fig. 5). One of these records is interpreted as NAO variability (Baker et al., 2015), three are paleo-precipitation reconstructions (Ait Brahim et al., 2019; Cisneros et al., 2021; Thatcher et al., 2022) and the other five are reflecting paleo-temperature variations (Affolter et al., 2019; Fohlmeister et al., 2012; Mangini et al., 2005;  Martín-Chivelet et al., 2011; Sundqvist et al., 2010). Considering these differences in the interpretation and the fact these records are from different regions with different climates (from Sweden to Morocco), dissimilar profiles of paleoclimate variability can be expected. Still, some features are comparable and can be discussed to obtain a super-regional picture.

A. The Roman period in Europe-W Mediterranean. In Europe, particularly in the Mediterranean region, the RP is well-known as a warm period (e.g., McCormick et al., 2012). The average sea-surface temperature in the western Mediterranean Sea was 2°C higher than the average temperature of the late centuries (Margaritelli et al., 2020). Our composite, with high values of normalized  18O values during the whole RP, and particularly from 0-200 AD, agrees with the scenario of warm temperatures (Fig. 5i). Speleothem data from the Balearic Islands (Cisneros et al., 2021) indicate a transition from humid to dry conditions along the Iberian-RP (Fig. 5c). The dry period at the end of the RP in the Balearic record appears in agreement with a new speleothem record from northern Italy (Hu et al., 2022), suggesting that the observed drying trend was a possible contribution to the collapse of the Roman Empire in 476 AD. Record from Morocco (Ait Brahim et al., 2019), contrarily, marks a humid trend at the end of the RP (Fig. 5d). Similarly, an increase in humidity was observed in southern Iberia during the Iberian-Roman Period (Jiménez-Moreno et al., 2013; Martín-Puertas et al., 2009) thus reflecting a large spatial heterogeneity in precipitation during the RP when comparing records from the north and south of the Mediterranean basin.

REFERENCES

Bartolomé, M., Moreno, A., Sancho, C., Cacho, I., Stoll, H., Haghipour, N., Belmonte, Á., Spötl, C., Hellstrom, J., Edwards, R. L., and Cheng, H.: Reconstructing land temperature changes of the past 2,500 years using speleothems from Pyrenean caves (NE Spain), Clim. Past Discuss. [preprint], https://doi.org/10.5194/cp-2023-54, in review, 2023.

Author

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  Joanne Nova

  A prize-winning science graduate in molecular biology. She has given keynotes about the medical revolution, gene technology and aging at conferences. She hosted a children’s TV series on Channel Nine, and has done over 200 radio interviews, many on the Australian ABC. She was formerly an associate lecturer in Science Communication at the ANU. She’s author of The Skeptics Handbook which has been translated into 15 languages. Each day 5,000 people read joannenova.com.au

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