Michael Mann's infamous 'hockey stick' graph, used by the IPCC "experts" as propaganda to convince gullible elites that modern warming was unprecedented, has had its science and respectability torn asunder by a multitude of experts over the years.
The graph's lack of both science creditability and statistical robustness eventually caused the UN's IPCC to throw in the towel and exclude it from future climate reports.
Climate research in recent years has confirmed that the hockey stick deserved the ash heap of bad paleo-science it now resides in.
This has again been proven in the latest study, which shows the non-existence of the 'hockey stick' and the rather similar (yet less) modern warming versus that of the Medieval Period. The study's summer temperature reconstruction is adjacent.
More charts indicating modern warming is not unprecedented. A fantastic book regarding the 'hockey stick' and the IPCC.
Other peer-reviewed articles.