Here's an interesting story of work done to resolve apparent conflict between tree ring temperature chronologies and those from ice cores.
The one thing I would like to know more about is this part of the story:
In 2012, Miyaki et al. discovered a rapid increase of radiocarbon (14C) in Japanese cedar, precisely dated to AD 774-775. The cause of this increase was possibly due to a very high energy solar proton event (Usoskin et al., 2013), and its effect on radiocarbon has been observed in tree ring chronologies in both hemispheres (Güttler et al., 2015). Another rapid, slightly smaller (~60%), radiocarbon production event has been dated to AD 993-994 (Miyake et al., 2013).Do we know what causes "very high energy solar proton events"?