Paper Reviewed
Toth, M., Magyari, E.K., Buczko, K., Braun, M., Panagiotopoulos, K. and Heiri, O. 2015. Chironomid-inferred Holocene temperature changes in the South Carpathians (Romania). The Holocene 25: 569-582.

Analyzing fossil chironomids obtained from sediments of Lake Brazi, a shallow mountain lake in the South Carpathian Mountains of Romania, Toth et al. (2015) developed a Holocene summer air temperature history based on a Swiss chironomid-to-temperature transfer function (Sw-TF) and a merged Norway-Swiss chironomid-to-temperature transfer function (NS-TF), which effort revealed that between about 11,500 and 10,980 cal. yr BP, reconstructed summer temperatures increased rapidly by about 1.2°C and 0.8°C when using, respectively, the two different transfer functions (NS-TF and Sw-TF) that pushed them to mean values of 9.3 and 9.7°C. And the six scientists report that these values were followed by additional similarly-derived temperature increases of 2.2-2.5°C that led to corresponding mean values of 10.8-12.3°C and 11.5-12.9°C between about 10,980 and 10,220 cal. yr BP.

Later, after about 10,220 cal. yr BP, the six scientists determined that "inferred temperatures fluctuated strongly above present-day July temperatures by about 1.4°C (NS-TF) and 2.5°C (Sw-TF)." And finally, as they write, "in samples younger than ca. 1500 cal. yr BP, reconstructed temperatures fluctuated strongly between 9.7 and 11.6°C, close to the modern mean July temperature."

What is especially interesting about these findings is the fact that during many of these earlier periods, when reconstructed summer temperatures were significantly warmer than they have been throughout the modern industrial period of human history, the atmosphere's CO2 concentration hovered around a mean value of 250 ppm, which is much lower than today's mean value of approximately 400 ppm. And this observation clearly demonstrates that the lesser warmth of today need not be attributed to the historical increase in the air's CO2 content, which has had absolutely nothing to do with the significantly warmer-than-present temperatures that have been experienced at various times and places throughout the world over the past several millennia.

See also, in this regard, the many related items archived under the general headings of Holocene, Medieval Warm Period and Roman Warm Period in our Subject Index.