Why does FGOALS-gl reproduce a weak Medieval Warm Period but a reasonable Little Ice Age and 20th century warming?

An Overview of CMIP5 and the Experiment Design

(2011) Karl E. Taylor et al.   BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY

Forced response of atmospheric oscillations during the last millennium simulated by a climate system model

(2011) WenMin Man et al.   CHINESE SCIENCE BULLETIN

A comparison of the Medieval Warm Period, Little Ice Age and 20th century warming simulated by the FGOALS climate system model

(2011) TianJun Zhou et al.   CHINESE SCIENCE BULLETIN

Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly

(2009) M. E. Mann et al.   SCIENCE

A fast version of LASG/IAP climate system model and its 1000-year control integration

(2008) Tianjun Zhou et al.   ADVANCES IN ATMOSPHERIC SCIENCES

Mechanisms of Low Cloud–Climate Feedback in Idealized Single-Column Simulations with the Community Atmospheric Model, Version 3 (CAM3)

(2008) Minghua Zhang et al.   JOURNAL OF CLIMATE