Extreme global cooling and global warming are natural phenomenon, which have occurred with regularity - multiple studies have confirmed these extreme climate change events, including a new Iceland study
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Read here. Research out of Hvítárvatn, Iceland confirms that over the past 8,000 years, there have been five extreme, natural climate phases: the Roman warming, the Dark Ages cooling, the Medieval warming, the Little Ice Age and the current warming.
The analyzed evidence indicates that the Little Ice Age (LIA) was the coldest period over the last 8,000 years. Since the LIA was the coldest, it would not be unusual for the natural climate rebound to exhibit significant warming, which the Modern Warming period has.
"...the Holocene has experienced alternating multi-century periods of relative cold and warmth, the most recent and repeatable of which sequences is composed of the pre-DACP period (which is typically referred to as the Roman Warm Period), which was followed by the DACP, which was followed by the MWP, which was followed by the LIA, which was followed by the Current Warm Period or CWP...the LIA was the coldest period of the last 8 thousand years, which suggests that starting from such an unprecedented low temperature, it is only natural that the warming that produced the CWP should have been one of the most significant warmings of the current interglacial...it would have been an aberration of natural history if the warming of the past century or so had not occurred as it has..."