Example:

Tebenkof Glacier in Alaska has been receding fairly rapidly. As it is receding, it is exposing tree trunks from a forest it advanced through in the cold period after the Roman Warm Period and trunks from another forest it advanced through during the Little Ice Age. During the Roman Warm Period, that glacier was smaller than it is today and it was that small long enough for a forest of 300 year old trees to become established before the glacier advanced through them between 430-670 AD and killed the trees. This period also corresponds to a massive climate change (drier) in the middle east and a huge drop in Dead Sea shorelines and glacial advance in the European Alps.

The glacier then advanced through another forest in the LIA between 1300 and 1630 AD with most of the trees being killed around 1430 AD. NO forests have yet reestablished in those areas since. It hasn’t been warm enough for long enough.

In the relatively recent (in geological terms) time the Earth has been warmer for much longer than it is now. The LIA was the coldest period in at least 7000 years.

We are 150 years into this period of warming. These warm and cold periods tend to last about 250-300 years or so. The LIA was sort of a “double dip” period that lasted longer and got colder than previous ones. We are about 160 years into this warm period so if this one is like recent ones, we are probably already past the peak of this warm period. That 1933 was warmer than 1998 would seem to indicate that 1933 was the peak of the current warm period and we have a long period, about another 300 years or so, of cooling temperatures. During that time there will be periods of warming and cooling but the warm periods will be cooler and the cold periods colder. In other words, in this negative cycle of the PDO, I would expect to see temperatures cooler than they were in the late 1960’s early 1970’s but then it will warm again.