RUS New site

Advanced search

[ New messages · Forum rules · Members ]
Page 15 of 15«12131415
Forum » SpaceEngine » Off-topic Discussions » General Global Warming / Climate Change Discussion (because a thread for this was long overdue)
General Global Warming / Climate Change Discussion
midtskogenDate: Saturday, 24.09.2016, 19:35 | Message # 211
Star Engineer
Group: Users
Norway
Messages: 1672
Status: Offline
Quote Watsisname ()
So, what are comparable changes through the Holocene, what was the forcing mechanism, and where are they in the climate record?

You argue as what we measure as climate (a thin section of air above the ground) is a function of forcing solely. There also is internal, unforced variability, which can amplify, cancel or reverse the effects of forcing changes.

Quote Watsisname ()
You're sure you don't want to protest the cosmic distance ladder? We stitch together totally different data from totally different methodologies all the time in science.

The issue is comparing something measurable in one methodology with something much less measurable in another methodology. It's not just a matter of calibration when you stitch together things measured differently. Though matching ice cores with global temps probably takes clever calibration, that is not what I point at. A lot more internal variability is visible in the instrument record than in the proxy record. Just because much internal variability doesn't show in the proxy record, it doesn't mean that it didn't exist.

So what is the internal variability in the instrumental record? Since we think we know a lot about forcings and feedbacks, a good guess would be that the internal variability is what the models tell us given the actual forcings minus observations. But you can't then say that this is the variability and it proves that the observations match what we know about the forcings. That's circular.

Quote Watsisname ()
We do not see ~1C global temperature change on century timescales

No wonder, if the proxy has no details shortert than 200 years, like the xkcd graph. Anyway, you can't dismiss such changes without showing that internal variability of that scale is impossible.

One interesting case for this question is the Younger Dryas.

Even if we're confident about the calibration of individual proxies and about the insignificance of internal variability, a proxy for global temperatures is still a leap of faith away. If it wasn't warmer in central Greenland 10 to 6k years ago than today, is it a good proxy when we can be pretty sure that other places were warmer than today? As mentioned before, like the Arctic ocean (fossil beaches at the northern coast of Greenland), or Scandinavia (known from old flora).





NIL DIFFICILE VOLENTI
 
WatsisnameDate: Saturday, 24.09.2016, 22:36 | Message # 212
Galaxy Architect
Group: Global Moderators
United States
Messages: 2611
Status: Offline
Quote midtskogen ()
You argue as what we measure as climate (a thin section of air above the ground) is a function of forcing solely. There also is internal, unforced variability, which can amplify, cancel or reverse the effects of forcing changes.


Internal variability does not dominate the Holocene climate record. As you have seen, the first order effects are the volcanic and solar forcings, and what humans do.

This is basic climate dynamics. Forcings, whether internal (like albedo, carbon cycling, aerosols) or external (like solar variations) tend to dominate the climate system because they directly affect the balance of energy into and out of the system. Internal variability matters too, but all that does is redistribute energy within the system.

For example, ENSO can change global temperature based on whether the Pacific ocean puts out warmer or cooler water. Warmer than usual puts extra heat in the atmosphere, cooler than usual takes heat out of the atmosphere. But even ENSO doesn't dominate over anthropogenic forcing, especially through the 21st century.

For internal variability to have a big effect on global climate, it needs a profound change in how the energy is redistributed, such as by changing the ocean circulation. This can happen, but you have to look back beyond the Holocene to see an example. This is the Younger Dryas -- caused by a huge influx of fresh water into the oceans, that had been dammed up behind the ice sheets.

Quote midtskogen ()
No wonder, if the proxy has no details shortert than 200 years, like the xkcd graph.


You have been shown that the paleoclimate record displays variations on timescales of years to decades, that it records the effects caused by volcanoes and solar variations, and that those effects agree with our understanding of how those forcings actually changed. So you should already know that this argument -- that the climate reconstructions are artificially flat because of the methodology or limitations of what they record -- is wrong.

Graphics like the XKCD comic present it in a form which smooths out variations which are either small or brief to give the broader context. You may recall that I said I prefer the unsmoothed reconstructions, with the uncertainties, because this gives better impression of what we do understand about what the climate system does across a variety of timescales.

Would you like to try reviewing and revising your views of this field? You've presented a lot of arguments about why you think the hockey-stick reconstruction of paleoclimate is unphysical, and we've found that many of those were based on misconceptions. Which is fine; I know this is a difficult subject with a lot of information and misinformation out there. I'm happy to try to help you understand it better. smile





 
midtskogenDate: Sunday, 25.09.2016, 16:12 | Message # 213
Star Engineer
Group: Users
Norway
Messages: 1672
Status: Offline
I had a longish answer, then I accidentally hit a key combination that closed Firefox. Sigh.

Quote Watsisname ()
Internal variability does not dominate the Holocene climate record.

The shorter variability can't, as long as the climate record has low temporal resolution. For instance, if you want to study a period during which the real temporal resolution is 50 years, basic signal theory tells you that you'll have zero knowledge about things lasting 100 years or shorter.

Quote Watsisname ()
You have been shown that the paleoclimate record displays variations on timescales of years to decades, that it records the effects caused by volcanoes and solar variations

I think the records showing year to year variation rely heavily on tree rings. Tree rings are interesting, but do not provide a direct mapping to global temperature, and in my book this falls in the realm of educated guessing.

Quote Watsisname ()
Would you like to try reviewing and revising your views of this field?

I'm the one ready to review and revise here. You have made up your mind. wink For instance, when the modern warming shows up in the ice core record, we'll know more about how well the record picks up internal variability and we'll also get a firmer calibration. That could take centuries. Meanwhile, we'll learn more about the multidecadal variability. I hope I've been clear that I don't reject the hockey stick because the record can't be like that, but because we don't know that.

Further reading on uncertainty in climate science.





NIL DIFFICILE VOLENTI
 
Forum » SpaceEngine » Off-topic Discussions » General Global Warming / Climate Change Discussion (because a thread for this was long overdue)
Page 15 of 15«12131415
Search: