China’s climate history includes multiple climate warming and cooling fluctuations of 4°C within centuries, with cold periods aligning with declines in solar irradiance.
According to a new study (Zhang et al., 2021), northern China’s coldest temperatures of the last 5000 years occurred 300 calibrated years before present (cal yr BP), coinciding with the Little Ice Age and a decrease in solar irradiance. This frigid period was was followed by a ~4°C warm-up (from about 3.5°C to 7.5°C) within the span of about 150 years during the middle of the Qing Dynasty (1644-1912 CE), which was well before anthropogenic CO2 emissions began sharply rising.
The warmest temperatures of the last millennium occurred during the Medieval Warm Period (Song Dynasty, 960-1279 CE).
Rapid cooling periods of multiple degrees per century also coincided with the collapse of ancient civilizations, or dynasties, as wars and social unrest were often associated with competition for access to natural resources (such as water during droughts).
Image Source: Zhang et al., 2021
The Zhang et al. study above only uses a 30-year (climate-length) sampling resolution to document temperature changes over the last 5000 years.
Another new study (Chen et al., 2021) assigns an annual temperature value for each year since 1200 A.D. in Southern High Asia.
Interestingly, since the end of the Medieval Warm Period there have been 23 total “extremely warm years” in this region. Seven occurred in the 1400s. Six in the 1600s. Five in the 1700s. And there were five “extremely warm” years in the 2000s.
In other words, since 1200 A.D., 18 of the 23 warmest years in Southern High Asia occurred between the 1400s and 1700s A.D.
It is now generally acknowledged that the upper atmosphere is cooling steadily, the AGW supporters say it is because of the “Thermal Opacity” caused by CO2; those who support the solar influence will say it is down to the reduction in solar activity over the past few years.
Either way, we can see the result in the behaviour of the jet stream. What is generally referred to as “Sea-Land Differential” has become the dominant factor in the behaviour of the upper atmosphere temperatures and profiles, the result being the “Heat Dome” over US and Canada. A classic, self reinforcing structure. Some discussion here : –
https://howtheatmosphereworks.wordpress.com/observations-2021/
usually paleoclimate reconstructions produce no more than noise… this is because of the weak interactions of the examined proxies to the property in question.
probably tree rings is a nice proxy for ground humidity, not temperature. this correlates to temperature only in tropical regions where we have tropical rains…
probably other proxies do even worse correlating to temperatures.
for example sediment proxies vary according to groundwater quantity and makes for decades long variations. this is multiparametric varying according to precipitation volume and ice melting. a flood can cause decades long sediments cover. so it is inaccurate.
OK, that makes more sense than dismissing them out of hand.
Some factors affecting tree rings:
Temperature
Humidity
Insects/Disease
[CO2]
Ambient Light
Nutrient Availability
Any one or combination could lead to a false conclusion about another. So I think tree rings are probably a very good proxie for assessment of overall favorability of past growth conditions, perhaps requiring more information to decide what they mean, specifically.
That said, I guess the assumption is that people who use tree rings as proxies are aware of the limitations and don’t come to hard conclusions when they aren’t warranted.
There are, of course, some who abuse them, not realizing that tree wood is better for making hockey sticks than poor data and faulty statistics. //:)
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