Two recently published studies confirm that the climate thousands of years ago was as warm or warmer than today’s – a fact disputed by some believers in the narrative of largely human-caused global warming. That was an era when CO2 levels were much lower than now, long before industrialization and SUVs.
One study demonstrates that the period known as the Roman Warming was the warmest in the last 2,000 years. The other study provides evidence that it was just as warm up to 6,000 years ago. Both studies reinforce the occurrence of an even warmer period immediately following the end of the last ice age 11,000 years ago, known as the Holocene Thermal Maximum.
The first study, undertaken by a group of Italian and Spanish researchers, reconstructed sea surface temperatures in the Mediterranean Sea over the past 5,300 years. Because temperature measurement using scientific thermometers goes back only to the 18th century, temperatures for earlier periods must be reconstructed from proxy data using indirect sources such as tree rings, ice cores, leaf fossils or boreholes.
This particular study utilized fossilized amoeba skeletons found in seabed sediments. The ratio of magnesium to calcium in the skeletons is a measure of the seawater temperature at the time the sediment was deposited; a timeline can be established by radiocarbon dating. The researchers focused on the central part of the Mediterranean Sea, specifically the Sicily Channel as indicated by the red arrow in the figure below. The samples came from a depth of 475 meters (1,550 feet).