No evidence for globally coherent warm and cold periods

[gmax137]

No evidence for globally coherent warm and cold periods over the preindustrial Common Era

This is being reported in the popular news, here's a link to the Nature abstract.

https://www.nature.com/articles/s41586-019-1401-2

Earth’s climate history is often understood by breaking it down into constituent climatic epochs1. Over the Common Era (the past 2,000 years) these epochs, such as the Little Ice Age, have been characterized as having occurred at the same time across extensive spatial scales5. Although the rapid global warming seen in observations over the past 150 years does show nearly global coherence6, the spatiotemporal coherence of climate epochs earlier in the Common Era has yet to be robustly tested. Here we use global palaeoclimate reconstructions for the past 2,000 years, and find no evidence for preindustrial globally coherent cold and warm epochs. In particular, we find that the coldest epoch of the last millennium—the putative Little Ice Age—is most likely to have experienced the coldest temperatures during the fifteenth century in the central and eastern Pacific Ocean, during the seventeenth century in northwestern Europe and southeastern North America, and during the mid-nineteenth century over most of the remaining regions. Furthermore, the spatial coherence that does exist over the preindustrial Common Era is consistent with the spatial coherence of stochastic climatic variability. This lack of spatiotemporal coherence indicates that preindustrial forcing was not sufficient to produce globally synchronous extreme temperatures at multidecadal and centennial timescales. By contrast, we find that the warmest period of the past two millennia occurred during the twentieth century for more than 98 per cent of the globe. This provides strong evidence that anthropogenic global warming is not only unparalleled in terms of absolute temperatures5, but also unprecedented in spatial consistency within the context of the past 2,000 years.

 

[Genava]

This is a part of the PAGES 2k initiative:
http://pastglobalchanges.org/products/journal-articles

For the media coverage:
Ancient global climate events rippled unevenly across the globe
https://www.sciencemag.org/news/2019/07/ancient-global-climate-events-rippled-unevenly-across-globe
New study identifies causes of multidecadal climate changes
https://phys.org/news/2019-07-multidecadal-climate.html
The climate is warming faster than it has in the last 2,000 years
https://phys.org/news/2019-07-20th-century-unmatched-years.html

 

[Wellwisher]

Part of the problem is we measure the past by different methods than we do the present. It is like one person digs with a shovel; modern data, and the other person digs with a spoon; ancient data, and we call this fair.

What would happen if we stopped all modern measurement techniques for one year, and only use tree rings and ice core samples to do daily weather. Would we get the same results?

 

[Genava]

Part of the problem is we measure the past by different methods than we do the present. It is like one person digs with a shovel; modern data, and the other person digs with a spoon; ancient data, and we call this fair.

What would happen if we stopped all modern measurement techniques for one year, and only use tree rings and ice core samples to do daily weather. Would we get the same results?

Proxies give you information about the temperature but with a lower resolution, generally an average for a few decades. For example Vinther et al. 2009 used a smoothing on 20 years for instrumental records of the temperature to match the resolution of the ice cores. You are confusing the purpose of these records, it is not to predict weather but to compare the average climate between different period.

 

[Wellwisher]

One potential problem is it would be hard to find ice cores samples, along the equator, or over the open ocean, so we can get a true global average from ice core data. Climate can change in one geographical location, more than in another. Records are not broken everywhere at the same time. Satellite data, from a bunch of satellites, can take an average everywhere, including where there is no ice core data; oceans and equator.

This is why I said to be fair, why not try to do modern climate science with only last year's ice core data and tree rings. This technique is far more limited than satellites and allows us to compare apples to apple, and not apples to oranges. This way we can see if this parallel is valid, or part a stage setting for a climate change magic trick.

Here is a home experiment to show how one can set the stage such a science magic trick . One weekend, organize a group of students to go to a local park to count the number of birds in the park. The team will spend a weekend, with each student having a cell phone camera in hand, to record the birds they see.

When we ae done, compile the data and claim the team has recorded the most birds, ever in the history of that park. This claim does not mean that there have never been more birds in the park, at any time in its history. All it means is nobody or no team has ever recored more bird in an official scientific capacity. The old timers; ice core data, may remember differently, but they may not be able to offer more than anecdotal evidence, that can be refuted.There are semantics involved, but technically, in science terms, the claim is valid.

To continue, the local university hears of our experiment and is intrigue by the record setting number of birds that our research showed. They decide to redo our experiment, but this time with a group of bird experts with the latest tools, way beyond students with cell phone cameras. They record ever more birds.

Again, this may not be because there are more birds in the second experiment, but rather simply because the experts are more thorough, due to their targeted expertise and tools. Nevertheless, this is official data and the new record conclusion is correct, with that data.

They then take the two data sets and plot these on a curve and draw the conclusion the birds are flocking to this park an an alarming rate. It could be due to the popcorn vender who opened a booth a few years back at the park. Nevertheless, at this rate of growth, by the year 2060, there will too many birds, so we need to plan ahead and move some of the birds or the popcorn vender. This can build into a nice political magic trick, especially if they offer to fund an ALL Star Team of experts to try this a third time.

 

[Genava]

One potential problem is it would be hard to find ice cores samples, along the equator, or over the open ocean, so we can get a true global average from ice core data. Climate can change in one geographical location, more than in another. Records are not broken everywhere at the same time. Satellite data, from a bunch of satellites, can take an average everywhere, including where there is no ice core data; oceans and equator.

This is why the Pages initiatives have been created, to include more and more other proxies at different locations and to upgrade the database and the temperature reconstruction.

"Most comprehensive database on past global changes is online"
https://www.sciencedaily.com/releases/2017/07/170711125604.htm
And the uncertainties are addressed in each publication. The National Academies published a good introduction on the methodological limits in this chapter:
https://www.nap.edu/read/11676/chapter/12

This is why I said to be fair, why not try to do modern climate science with only last year's ice core data and tree rings. This technique is far more limited than satellites and allows us to compare apples to apple, and not apples to oranges. This way we can see if this parallel is valid, or part a stage setting for a climate change magic trick.

I do not know what you are thinking by using the term "modern climate science" and if you are not confusing it with weather forecast and atmospheric sciences in general. First of all, it takes time for ice to stabilize and there is no reliable ice core data for the temperature of the past year. There are indeed some ice core data going close to the recent warming period as you can see here:

But it is still missing most of the warming occurring after the 1970s.

So to clarify, what methods and techniques you are suggesting to do through "modern climate science"? Global temperature reconstructions with the recent data for the proxies?

 

[mfb]

Part of the problem is we measure the past by different methods than we do the present. It is like one person digs with a shovel; modern data, and the other person digs with a spoon; ancient data, and we call this fair.

What would happen if we stopped all modern measurement techniques for one year, and only use tree rings and ice core samples to do daily weather. Would we get the same results?

Ice core samples are not used to track the weather. They are used to track the climate.

Comparing them in regions where we have other measurements is exactly how these methods are calibrated.

 

[Nik_2213]

Hence the urgency to get ice-cores from Kilimanjaro and other low-latitude locations...