I don't need to answer how I came across some source. That's irrelevant. If you have conflicting sources of information, I'll gladly purview them, but don't be condescending or patronizing. It's super counter-productive.

We still don't understand what caused D-O events, but we know one thing for sure: CO2 was an independent variable in those events. Warming occurred in times when CO2 concentrations were decreasing. We know that during these events, global temperatures bounced as much as 8 degrees Celsius in as little as a few dozen years, indicating that rapid climate change is naturally possible. We can speculate that whatever natural forcing caused those changes to occur could potentially occur at any time.

I'm going to show you several sources (that are not Nurtaev) that indicate swings of 4+ degrees Celsius in the past 10,000 years and that bears some level of investigation. I don't know why there's differences between these sources and the one you are quoting.

Peta J. Mudie, Andre Rochon & Elisabeth Levac (2005) Decadal-scale sea ice changes in the Canadian Arctic and their impacts on humans during the past 4,000 years, Environmental Archaeology, 10:2, 113-126, DOI: 10.1179/env.2005.10.2.113 https://doi.org/10.1179/env.2005.10.2.113

The actual temp variations from the ice core on above paper: https://www.researchgate.net/figure/Core-006-from-Coburg-Pol...

Loehle, C. (2007). A 2000-Year Global Temperature Reconstruction Based on Non-Treering Proxies. Energy & Environment, 18(7), 1049–1058. https://doi.org/10.1260/095830507782616797 (shows past 2000 years including Medieval Warming Period and Little Ice Age with much greater perturbations than indicated by Marcott et al.)

Actual PDF for above article: https://www.asc.ohio-state.edu/mcculloch.2/AGW/Loehle/Loehle...

Quansheng GeHaolong LiuXiang MaJingyun ZhengZhixin Hao (2017). Characteristics of temperature change in China over the last 2000 years and spatial patterns of dryness/wetness during cold and warm periods. Advances in Atmospheric Sciences. August 2017, Volume 34, Issue 8, pp 941–951. https://link.springer.com/article/10.1007%2Fs00376-017-6238-...

^^ shows Medieval Warm Period just as warm today "as data show records for the periods AD 981–1100 and AD 1201–70 are comparable to the present"

Holocene volcanic history as recorded in the sulfate stratigraphy of theEuropean Project for Ice Coring in Antarctica Dome C (EDC96)ice core. Holocene volcanic history as recorded in the sulfate stratigraphy of theEuropean Project for Ice Coring in Antarctica Dome C (EDC96)ice coreE. Castellano,1S. Becagli,1M. Hansson,2M. Hutterli,3J. R. Petit,4M. R. Rampino,5M. Severi,1J. P. Steffensen,6R. Traversi,1and R. Udisti. https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/200...

^^ evidence of Medieval Warm Period in Antarctica (offset by about 150 years from Northern hemisphere's warming period)

Yi, S., Saito, Y., Chen, Z. et al. Geosci J (2006) 10: 17. https://doi.org/10.1007/BF02910329 Palynological study on vegetation and climatic change in the subaqueous Changjiang (Yangtze River) delta, China, during the past about 1600 years.

^^ Research indicating 1-2 degrees Celsius warmer in China during Medieval Warming Period.

So the research above depends on both ice cores and tree rings, analyzed completely independently of each other in completely different regions around the world. They all indicate a strong Medieval Warm Period just as warm as today and a strong Little Ice Age, probably 1-2 degrees colder than today, in just the past 1000 years.