Jo Nova in another great post draws our attention to: Bao Yang et al, (2024) "The influence of proxy selection on global annual mean temperature reconstructions during the Common Era," Science China Earth Sciences. DOI: 10.1007/s11430-024-1348-3. According to this study, while tree ring data does indicate a hockey stick type of curve for long term temperatures, other methods do not, and in fact temperatures have fallen for 2,000 years and have only in comparatively recent times has warming re-commenced. Even here, the temperature has not reached the Roman Empire levels. And as Jo Nova notes, other research indicates that warming began before the industrial era kicked in, probably around the late 1600s. There is no accepted explanation of this, but it is likely due to natural variation factors.
If natural variation was responsible for warming centuries ago, there is no reason not to suppose that it is a major factor operating today, and that placing all the blame upon fossil fuels is misplaced.
"How much money has the world wasted because of some tree ring studies?
A Chinese group has looked at all the different kinds of 2,000 year long proxies in the PAGES dataset and found that history looks quite different depending on which proxy you pick. Only the tree rings show the HockeyStick shape that matches the climate models. In other proxies, temperatures have fallen for most of the last 2,000 years, especially in the Southern half of the world. And even after the recent warming, we are not yet back to the temperatures the Romans lived through.
So yet again, we see that that current temperatures are not unusual except according to tree rings, which we know are affected by rising levels of CO2. (The paper does not mention CO2 or carbon or fertilizer).
"All the evidence points out that we are still far from a complete understanding of the Common Era temperature variability at hemispheric and global scales," says Professor Yang."
"We show that the millennial cooling of annual mean temperatures is likely a global phenomenon."
The world according to tree-rings is at the top, and other proxies, below:
The paper looked closely at how all the proxies responded to volcano eruptions, and tree rings do seem to be useful. But without acknowledging that trees love carbon dioxide and grow faster with the fertilization effect of extra CO2, it feels like they are dancing around the point. They said tree rings capture the variability of shorter periods (less than 200 years) but that non tree ring proxies were better for variations longer than 200 years. The news that matters the most to mum and dad voters is that they found a significant long term cooling trend, but that information is buried in the text.
And as so many proxies have shown, global warming started back in the late 1600s, long before human emissions of CO2 started.
UPDATE: Look at the non-tree-ring proxy — the warming began in the Southern Hemisphere before 1700AD. See also the 120 proxies of Christiansen and Ldundqvist, and the signal in China. What started that? Climate modelers have no idea. It wasn't cars and coal power. It wasn't man-made CO2. We don't understand the big forces that drive our climate, yet we make you pay for your imaginary sins anyway.
PhysOrg: "… we wanted to know how our understanding of climate in the past is dependent on proxies," says Professor Bao Yang. A paper on this topic is published in the journal Science China Earth Sciences.
To do so, the research team led by Professor Yang integrated the longest millennial paleoclimate data in the PAGES proxy network into new versions of global and hemispheric reconstructions of annual temperatures. The results show that the rate of pre-industrial millennial cooling in global and hemispheric temperatures varies according to proxy combination, with the strongest cooling revealed by non-tree-ring proxies.
Yang and colleagues compared the volcanic responses and spectral characteristics of tree-ring and non-tree-ring records. They found that the properties of tree-ring and non-tree-ring data differ significantly.