Over the past 150 years, global warming has more than undone the global cooling that occurred over the past six millennia, according to a major study.
The recent findings show that the millennial-scale global cooling began approximately 6,500 years ago when the long-term average global temperature topped out at around 0.7°C warmer than the mid-19th century. Since then, accelerating greenhouse gas emissions have contributed to global average temperatures that are now surpassing 1°C above the mid-19th century.
Before global warming, there was global cooling, previous work has shown convincingly that the world naturally and slowly cooled for at least 1,000 years prior to the middle of the 19th century, when the global average temperature reversed course along with the build-up of greenhouse gases. This study, based on a major new compilation of previously published data, combined with new statistical analyses, shows more confidently than ever that the millennial-scale global cooling began approximately 6,500 years ago.
Investigating the patterns of natural temperature changes over space and time helps us understand and quantify the processes that cause the climate to change, which is important as we prepare for the full range of future climate changes due to both human and natural causes.
Our future climate will largely depend on the influence of human factors, especially the build-up of greenhouse gases. However, the future climate will also be influenced by natural factors, and it will be complicated by the natural variability within the climate system. Future projections of climate change will be improved by better accounting for both anthropogenic and natural factors.
Since the mid-19th century, global warming has climbed to about 1°C, suggesting that the global average temperature of the last decade (2010-2019) was warmer than at any time during the present post-glacial period. The last time that happened was back around 125,000 years ago when sea level was around 20 feet higher than today.
Darrell Kaufman, Nicholas McKay, Cody Routson, Michael Erb, Christoph Dätwyler, Philipp S. Sommer, Oliver Heiri, Basil Davis. Holocene global mean surface temperature, a multi-method reconstruction approach. Scientific Data, 2020; 7 (1) DOI: 10.1038/s41597-020-0530-27
Northern Arizona University. "Major new paleoclimatology study shows global warming has upended 6,500 years of cooling: Comprehensive compilation of pre-historic temperature records shows that global warming is reaching levels not seen for at least 6,000 years." ScienceDaily. ScienceDaily, 30 June 2020. <www.sciencedaily.com/releases/2020/06/200630072044.htm>