Roman warm period was...warm

Perhaps my old eyes but their temperature data doesn't seem to closely match the ice core data found in Wiki. But it may be we need to compare ice core data closer to Scandinavia to see how closely these match.

Bob Wilson

 

I'm not going to bite this time.

 

There's a good discussion of this on Realclimate:

RealClimate: Tree Rings and Climate: Some Recent Developments

I think the key is as stated above, "(in Lappland at least)". The realclimate article expands on that. Pretty much, you'd expect to see different behavior of high norther latitude summer wood vis-a-vis hemispheric or global trends.

So it would have been nice to have seen some type of apples-to-apples comparison. What we have now is this one small area, with this new technique, versus global and hemispheric multi-proxy reconstructions, with a wide variety of techniques (some of which use no tree ring data at all).

At least, that's how it looks to me. I see no mention of doing the estimates two ways, with old (ring-width) and new (wood-density) methods. Would it have killed them to have done a side-by-side, for the same set of trees, showing old and new techniques? Given that orbital forcing is, in fact, larger for summertime, for northern latitudes (e.g., Holocene Thermal Maximum), it would have been nice to have known whether the old method would, in fact, give a different answer from the new method, for these trees in this location. And then go on to the larger question of whether or not it calls current multiproxy hemispheric reconstructions into question.

 

Nice stuff, tropical glacier melt will reduce albedo giving more forcings, but if true this data shows the world has cooled off a great deal from current temperatures in the recent past.

I'm sure Thopson will discount it, and make the claim that tree rings aren't good proxies If this data stands up though, its bad news for mann. He can't criticize it without reversing a great deal of his previous positions. It especially makes his over reaching arguments in the past look bad.

I'm sure our polarized media will blow reporting on this. I expect some to claim its proof that we are doomed, and others to claim its proof against climate change, while it really makes neither of these points.

One must remember that the ice core proxies average temperatures, and these get quite blurred over many decades when looking back 2000 years. Good reconstructions of global temperatures going back more than 400 years take a number of different proxies to make their estimates. This is one more data point, another proxie that should have data confirmed and added to the temperature reconstruction model. Mann had attempted to discount many of these proxies and historic writings showing the MTA warm period and RWP claiming this was local not global warming. More and more proxies are being found that indicate these were global events. This is just one more data point.

 

It probably is best to read the study, instead of the real-climate interpretation of it. Real-climate authors have some real skin in the game with competing theories that some of this data contradicts.

The data in the construction is for Northern Europe, it does not attempt to do reconstruct american or southern hemisphere temperatures. You would not expect papers from this research to over reach like that. We can compare this with other models to see if they accurately reconstructed Northern Europe though. Many of these models tried to show that the roman warm period in northern europe was much colder than this new proxy shows. Those at real-climate may need to redo some of their modeling to account for this and the Spanish proxies that show hotter past local temperatures.

I am distrustful of tree ring data, especially that in MBH '98. Those rings displayed a high correlation with co2 and rainfall, and thus were bad temperature proxies. This seems like the data was more accurately constructed, but it is only one type of proxy, tree ring, and would be just one part of a global reconstruction.

It does allow one to look to other factors and according to Esper the interpretation is this

This could be interpreted as the solar forcing is less with a negative net impact, which may mean the ghg impact has been higher when properly calculated. I would expect alley to chime in and see if it changes his forcing model.

 

I did not understand your comment. First you say you would not expect papers to overreach like that. Then you literally quote the overreach, i.e., that large-scale reconstructions by the IPCC are wrong (because of this result for trees in Lappland).

It's the overreach that the Realclimate discussion pointed out. It's well worth reading, in addition to reading the underlying paper, as of course we all have done.

 

This is not an over reach, it is an interpretation of the results. That interpretation is that some of these other models may not have taken solar forcing into account. Indeed according to Real Climates own survey of literature other studies have found even a greater millennial cooling trend. This is not part of the graph. It does nothing like MBH'98 and conclude that MWP didn't really happen. It nearly is suggesting that other results need to be looked at. This is a theory, not a conclusion. Real climate instead of saying, hmm let us check to make sure our models are correct with this new proxy, goes on a long winded answer saying their past models must be right. Not very scientific.

A good answer might have been from a neutral scientific source.

IMHO other proxy data has not shown this long term cooling trend from reduced solar forcings. It might be interesting to reanalyze XYZ to see if the cooling trend can be found in proxies in the southern hemisphere. Instead of the scientific method, real climate simply rejected the hypothesis. Esper says small but significant, Real climate says insignificant in some places, or already there in others, but I have seen no re analysis to quantify this.

No problem with reading realclimate along with the underlying paper. Real climate seemed to find the authors found better ways to use tree ring data proxies.

This may be the pertinant point from the paper.
Orbital forcing of tree-ring data : Nature Climate Change : Nature Publishing Group

They then do research in one area, and the data from that one area using one proxy TRW (tree ring width) supports their hypothesis. They leave it to the future and others to analyse the data - solar forcings versus temperature to confirm, or reject the hypothesis with data. Real climate was attempting to reject the hypothesis with innuendo, not data. It certainly is in the interest of peer review to bring up points that may make this interpretation of the data wrong.​

From the paper

Note this is the point where the authors talk about hemispheric trends. It is not an over reach, it is a data based criticism supported by their research.

This needs to be tested like any good hypothesis. Mann's own research included in the real climate article, states explicitly that some of his TRW is not accurate with some cooling data.

 

Heres a link to hundreds of peer reviewed studies.They are from all over the globe using various proxies and all say the MWP was hotter than today.
You guys are not up to speed if you only read RealClimate.

C3: ? Are Modern Temperatures Unprecedented

Are there any peer reviewed studies that support the Hockey Stick?Lets see them.

 

The whole business of finding a 'proxy' reminds me how 'modern' the thermometer is. We grew up with it and in one respect, it and modern science arrived just in time to document anthro-warming. After all, the CO{2} spike we are seeing now spans the age of the thermometer.

What might be interesting would be to map the dates of the replaced, warming records. This would give another metric for how the current weather compares to earlier, thermometer measured, stretches. Granted, weather is 'in the noise' but it rides the larger trends. With enough data points, the fundamental signal can be found. It would need to include the EU and Asian records.

Bob Wilson

 

The thermometer has been around since the early 1600s. Fahrenheit put a modern scale on them in the early 1700s. It has been recording then non-ghg rise in temperatures since lows in the little ice age. This includes much non ghg related warming. Certainly thermometers have been around longer than the industrial revolution.

The authors of this paper talk about 1750, which may be when thermometers were wide spread enough in europe. Global distribution of the temperature record seems to start around 1850.

The qualitative record had the roman warm period, then a cooling, mideaval warm period, and little ice age. This includes things like harvests, floods, famines, droughts, sea ice. Temperature reconstructions in 1990 had these features. In the late 1990s proxies were used to try to say these things were local and did not exist, but did the certainty of the proxies over ride the qualitative historic record? Recently ice cores, and other proxies have been showing the historical documents to be accurate. This study is one more that confirms these features. These proxies also show that the earth doesn't heat and cool uniformly. For those interested in Asian SST

New Temperature Reconstruction from Indo-Pacific Warm Pool : Woods Hole Oceanographic Institution

 

Tested? What do you mean, tested? Like, say, dropping all the (presumably biased) tree ring data out of hemispheric temperature reconstructions, then seeing what happens to the estimated temperature trend? Like comparing existing temperature reconstructions that don't use tree rings, to those that do? Would those be considered tests of the hypothesis that the tree-ring data bias the overall hemispheric temperature trend?

Well, that's what they did in the Realclimate posting. They quickly tested it, and found that the hypothesis was wrong. Based on the comments, they've already submitted a response to the Nature Climate Change article regarding that.

 

The idea I would have, from reading esper is to build a global climate reconstruction of at least twice the period, and model solar and ghg forcings, to get a base line. Then add the proxies that do not go back as far to fine tune the model. The suposition is that trw sometimes do not lay rings in cold climates. This can lead to systemic errors in temperature. Since they only record in summer they also can distort winter temperatures.

No they took a single study without tree rings. They did not add in the newer data from the waters around indoneasia or antartica which also contains detailed long term temperature trends.