The unprecedented Medieval Warming Period is again confirmed by new Switzerland research - the MWP and subsequent cooling are both products of natural forces and not a result of large human CO2 emissions
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Read here. The vast majority of scientific research documents the major warming and cooling periods prior to the 20th century. These periods of climate change exhibited large temperature swings across many regions of the world, well before the growth of industrial/consumer CO2 emissions.
A new study by Larocque-Tobler et al. provides more evidence that the Medieval Warming was not only significant, but remains unprecedented in some regions. Likewise, the subsequent Little Ice Age cooling was significantly colder than experienced in the 20th century.
"Working with a lake sediment core extracted in AD 2005 from the deepest point of Seebergsee in the northern Swiss Alps,... mathematically analyzed the taxonomy of chironomid assemblages they identified in the sediments and used the results to reconstruct mean July air temperatures for the past 1000 years. This work revealed a Medieval Warm Period that began some time before AD 1000 (where their temperature history had its beginning) and lasted until about AD 1250, the peak temperature of which was approximately 0.9°C greater than the peak temperature near the end of their record..." [I. Larocque-Tobleration, M.M. Stewart, R. Quinlan, M. Trachsel, C. Kamenik, M. Grosjean 2012: Quaternary Science Reviews]
Conclusion: Natural climate variation can cause dramatic climate change, which the unprecedented Medieval Warming Period represents. This level of extreme climate change can happen regardless of the amount and growth of human CO2 emissions.