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General Global Warming / Climate Change Discussion
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| Watsisname | Date: Monday, 12.09.2016, 22:04 | Message # 196 |
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| Quote midtskogen (  ) And when you match the end with the early instrumental record, you get a hockey stick.
No, that's not how it works. It's good to apply skepticism but at the same time you have a deep misunderstanding of this field and you are drawing very wrong conclusions from that.
Paleoclimate data is a bunch of numbers over time. A curve with some definite shape. But it's not temperature over time, it's something else which is related to temperature. Maybe it's fractionation of an oxygen isotope relative to hydrogen in an ice core. So you look at these data over a period with the instrumental record and say "okay, this value of δD/δO appears to correspond to this true value of temperature".
Doing this mapping does not change the curve. It only assigned true temperature values to it. If the mapping says temperature was flat and then changed rapidly, it's because δD/δO was also flat and then changed rapidly.
Now you would be quite right to be doubtful of this, if that was all there was to it. But notice there is opportunity for further hypothesis testing.
"If this relationship between isotopic abundances and temperature is correct, then I should be able to go out and study the physics of temperature and isotopic fractionation in the ice to see if that happens and find out why that happens, and characterize the relationship."
In the particular example I chose, there is actually a very nice linear relationship between mid to high latitude temperature, and δO18 in Antarctic Ice. It works.
We can go further:
"If these reconstructions of paleoclimate temperature are valid, then I should be able to model it with my understanding of the chemistry and the physics of the system, and reproduce what we observe and make sense of what goes on." This works beautifully, as you see in the graphic I posted.
And further still:
"If these reconstructions are valid, then I should be able to use them to make sense of things I see happening through the geologic record. This works beautifully. We have an amazing understanding of Earth's geologic and climate history. 
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| midtskogen | Date: Tuesday, 13.09.2016, 06:54 | Message # 197 |
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| Quote Watsisname ( ) So you look at these data over a period with the instrumental record
You can't always do that. They don't always match and you have to make assumptions. For instance, for ice cores and CO2 there is a lag. It is assumed that the sealing takes 83 years or thereabouts, which might seem somewhat arbitrary, but the sealing is obviously an issue and we're left with a few problems. Our instrument record isn't that good if we go 83 years back, and if the sealing takes 83 years, then the ice cores only give a rough average for that time, which makes up a serious smoothing. Basic signal theory states that you cannot correlate with something shorter, so the recent CO2 emissions aren't enough. The calibration doesn't really give an independent confirmation of the correspondence with temperature, since the sealing time was selected to make it fit with the data we have. Since the 83 years or whatever is a very long time, it will also take a very long time to know the correlation for sure.
We also know from the "hide the decline" controversy that proxies and instrument records are difficult to harmonise.
Quote Watsisname ( ) Doing this mapping does not change the curve. It only assigned true temperature values to it. If the mapping says temperature was flat and then changed rapidly, it's because δD/δO was also flat and then changed rapidly.
My point was about stitching two data sets together that measure things in entirely different ways. In this case proxies and the instrument record. It's a dangerous thing to do, special care must be taken.
The most famous hockey stick caused quite a bit of controversy.
NIL DIFFICILE VOLENTI
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| midtskogen | Date: Tuesday, 13.09.2016, 08:42 | Message # 198 |
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| I digitised the xkcd graph from -20000 to 2016 and tried used different moving averages. No differences were visible for windows up to 2-300 years, so the reconstruction does not appear to catch any fluctuations on such timescales. The trouble is that with that kind of smoothing, the modern global warming signal disappears.
Compare the two graphs below. The top graph is the original xkcd data, the bottom graph is the same using "just" a 100 year average.
NIL DIFFICILE VOLENTI
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| Watsisname | Date: Tuesday, 13.09.2016, 12:03 | Message # 199 |
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| Quote midtskogen ( ) I digitised the xkcd graph from -20000 to 2016 and tried used different moving averages. No differences were visible for windows up to 2-300 years, so the reconstruction does not appear to catch any fluctuations on such timescales. The trouble is that with that kind of smoothing, the modern global warming signal disappears.
Of course it does. What do you think you have shown?
Quote midtskogen ( )
You can't always do that. They don't always match and you have to make assumptions.
Which we test, particularly in proportion to how important that assumption is, or have some other source of confidence for making them, or otherwise don't use them if we can't confidently justify it. It is very easy to summarily dismiss something because of "having to make assumptions", and so hard to understand what actually goes on in that process.
And we're not talking about CO2 here. We're talking about reconstruction of temperature. Your suggestion was that temperature reconstruction's hockey-stick figure may be an artifact due to matching of the proxy data with instrumental data, and you basically said you don't believe it. Which tells me that you misunderstand where this curve comes from, what 'matching' actually means here, and why we are confident in these results. Again, skepticism is good, but at least understand the field first. This seems to be a common thing in our discussion of various of topics, including astronomy with dark matter/energy and gravitational wave detection.
Here's an example of the relationship between the isotopic content of snowfall to surface temperature. This is something which we can directly measure and understand the physics behind it. Isotopic ratios reveal tons of information about conditions. Much like your radioactivity measurements telling you about precipitation rate. Then we apply this knowledge toward the isotopic measurements in the ice core record. The only big assumption here is that the relationships here are also true in the past. Which sounds like a very dangerous assumption, but it's the basis of essentially everything we do in geology, and it works. It is conducive for making predictions which we can go out and test. The predictive and explanatory power here is enormous.
I'd like to refer you back to these comments about "further hypothesis testing". Seriously stop to think about them. Why do the ice core data show these deviations in δD/δO if you think the hockey-stick in temperature is an artifact? Why does our understanding of the chemistry and physics of the system yield models which reproduce this? Why do these methods yield sensible explanations of the interplay of climate and geologic change throughout Earth history?
Quote midtskogen ( ) The most famous hockey stick caused quite a bit of controversy.
Indeed, and it led to further research of climate reconstruction by many more groups, more gathering of data, improved methods of analysis and robustness checking, an ultimately led to even better understanding with essentially the same conclusion.
Quote midtskogen ( ) My point was about stitching two data sets together that measure things in entirely different ways.
An interesting point. So where's your proposal that we should avoid all study of cosmology based on the cosmic distance ladder?
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| midtskogen | Date: Tuesday, 13.09.2016, 20:03 | Message # 200 |
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| Quote Watsisname ( ) Of course it does. What do you think you have shown?
That either 1) the climate did not have fluctuations showing up in timescales less than 2-300 years until the 18th century or so, or 2) that, for various reasons, the record simply doesn't have that kind of information.
1) seems like a bold claim. Either by extraordinary coincidence it happened just as we were beginning to deploy instruments, or somehow the 18th century population was able to make an unprecedented impact on global climate.
2) means that there's nothing to compare the change rates of the recent record with.
It bothers me that climate scientists seem so allergic to missing data or observations and seem driven by some kind of compulsion to fill in the gaps.
Quote Watsisname ( ) It is very easy to summarily dismiss something because of "having to make assumptions", and so hard to understand what actually goes on in that process.
I'm not dismissing. When you do compare apple and oranges, however, it should be perfectly clear that this is what you do rather than making claims about unprecedented orange apples.
If the idea is to compare the recent temperature changes with what we know of temperature changes in the past 20000 years, then for it to have any value you would have to figure out how the instrument record so far would look in ice cores, sediments whatever in your proxy in a few thousand years. Then you can compare, if that is the purpose.
Quote Watsisname ( ) And we're not talking about CO2 here.
Just an illustration of the problems involved grafting two different techniques together. But I think temperature has similar mixing issues.
Quote Watsisname ( ) This is something which we can directly measure and understand the physics behind it.
I love it, but it only gives local temperatures.
But again, these records have a lag. By themselves they don't tell much about the modern warming. This is what I get if I plot GISP2:
Quote Watsisname ( ) An interesting point. So where's your proposal that we should avoid all study of cosmology based on the cosmic distance ladder?
I never said we should avoid anything depending on different measuring methods. Just that we have to be careful. And extending a proxy record with an instrument record requires special care.
NIL DIFFICILE VOLENTI
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| Watsisname | Date: Tuesday, 13.09.2016, 22:29 | Message # 201 |
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| Quote midtskogen ( ) or somehow the 18th century population was able to make an unprecedented impact on global climate.
Yes, by radiative forcing.
And you know that 2) cannot be the explanation, because you know that the climate record record does show shorter global changes like those caused by volcanic eruptions.
Quote midtskogen ( ) It bothers me that climate scientists seem so allergic to missing data or observations and seem driven by some kind of compulsion to fill in the gaps.
I do not know why, because in my experience they aren't. They are continuously gathering new data and doing hypothesis testing.
Your concern of reconstructing climate history is closely analogous to concern of reconstructing geologic history. There are gaps in our knowledge of it for sure. There are extinction events for which we still have no idea what caused them. There are unconformities in locations for which we have no idea why the record was either not recorded or subsequently erased. Yet it would be disingenuous to say our understanding of Earth history is 'educated guesses'. We have an amazing understanding of it and that understanding comes through very rigorous science.
Quote midtskogen ( ) I love it, but it only gives local temperatures.
If you know conditions at a given point by this method, determining temperatures of surrounding points is often very straightforward, and can be tested. In this particular example with snow deposition, it works very closely by lapse rate. There's also a nice relationship of Antarctic temperature recorded in the ice and global temperature over mid and high latitude. Finally, the isotopic fractionation also reveals much more than conditions at snow deposition -- it also tells us about the conditions where the moisture originally evaporated from, and how it got there.
If you're still doubtful, then think about why a set of local temperatures should lead to a record of global change which is sensible and consistent with our knowledge of the physics of the system and what we observe through the geologic record.
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| midtskogen | Date: Wednesday, 14.09.2016, 06:22 | Message # 202 |
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| Quote Watsisname ( ) Yes, by radiative forcing.
So, in the 18th century ~750 million humans changed the global climate more than, say any natural multidecadal shift over the past 20k years? And we know because the temperature reconstructions tell us?
Quote Watsisname ( ) They are continuously gathering new data and doing hypothesis testing.
I'm a firm believer in observations, but the more layers of interpretation applied to them, the more the hypothesis testing becomes educated guessing. Ultimately, we cannot fully escape indirect measurements. We do say we measure temperature even if what we actually measure is the volume of mercury inside a tube. But indirections can go deep or shallow. I'm just asking for quality. There are so many scientific papers published these days, and most are likely quite forgettable.
Quote Watsisname ( ) Your concern of reconstructing climate history is closely analogous to concern of reconstructing geologic history.
My concern isn't so much about reconstructing climate history, but about comparing that reconstruction with the best precision that we can get with modern instrumentation.
We can reconstruct the geological past to see how continents have moved, how ancient mountain ranges formed and crumbled away, how sea level rose and sank, etc. But would you make claims about whether the current Mount Everest, which we now can measure precisely, is the highest mountain that ever was in the geological history of Earth, and not call it an educated guess?
Quote Watsisname ( ) If you're still doubtful, then think about why a set of local temperatures should lead to a record of global change which is sensible and consistent with our knowledge of the physics of the system and what we observe through the geologic record.
No doubt that it's reasonable to think that agreeing changes in wildly different locations follow a global pattern, but we're not merely speaking of the direction of trends here, but about absolute levels globally at 1/10 degree resolution.
NIL DIFFICILE VOLENTI
Edited by midtskogen - Wednesday, 14.09.2016, 06:29 |
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| Watsisname | Date: Thursday, 15.09.2016, 06:56 | Message # 203 |
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| There is compelling evidence that humans have made an impact on global climate since about six or seven thousand years ago. Do the rates of change dominate over short period variations? No, but I feel that you should understand this.
When we compare the trends of greenhouse gas concentration through the Milankovitch cycles, the atmospheric concentrations did not follow their usual track during the Holocene. When we analyze the possible causes for this divergence, the only explanation that seems to work is a change in carbon cycling by agriculture. This has actually acted as a kind of thermostat, balancing out some of the natural tendency for the planet to cool during the interglacial periods. We can also see this by comparing the warming trends by latitude, since the effect of Milankovitch cycles is to redistribute the sunlight over the Earth. It's basically the same idea as you saw in the presentation about how CO2 globalized the temperature change through the glacial cycles, even though the actual solar forcing which drives the cycle is not globally uniform.
What does this have to do with modern warming and your moving time averages? Not a whole lot. Just don't think humans have only been affecting climate very recently. The atmosphere is thin and the climate cares a lot about what's in it. So much so that it is not impossible for pre-industrial civilization to leave a mark in the record.
If you're interested in when we dominate over short period variations, then that begins to happen around 1800. This is when the change in anthropogenic forcing starts becoming significant. The only natural forcing more powerful than this is from volcanoes, which are brief, sharp blips in the record. You can see this in the graphic shown earlier. Another one, going back 1000 to 2000 years, can be seen here.
So, what do you think explains your finding that the modern warming vanishes with 100+ year smoothing? You know that it is not because the climate record does not record shorter variations than this. And you know the warming is most significant during the 20th century. Oh. There's your answer. It's the most simple thing in the world.
Maybe it is a coincidence that this roughly coincides with the start of the instrumental record. Maybe it is also a coincidence that it happens to coincide with the changes in radiative forcing. Maybe it is a coincidence that our understanding of physics happens to explain that. Maybe it is a coincidence that this understanding, when applied to Earth history, makes sensible explanations with excellent predictive power. Lots and lots of coincidences.
Quote midtskogen ( ) But would you make claims about whether the current Mount Everest, which we now can measure precisely, is the highest mountain that ever was in the geological history of Earth, and not call it an educated guess?
Of course not. In this analogy that would be confusing weather with climate. We do not use proxies to determine instantaneous weather conditions at a point, we use them to determine climate conditions over a region, and we have the tools and techniques to be able to do that, as I have shown you. If the regional climate changes, then proxies over that region tend to show it. If the global climate changes, then the proxies everywhere tend to show it. With mountains, there is no geologic record of individual mountain heights. But there is geologic evidence which tells you where the mountain ranges were, when they formed, and you can make very good inferences about how tall they were from the volume of eroded sediments and how the ranges affected the neighboring climates (rainshadow).
Would you like to try coming up with a better analogy?
Quote midtskogen ( ) No doubt that it's reasonable to think that agreeing changes in wildly different locations follow a global pattern, but we're not merely speaking of the direction of trends here, but about absolute levels globally at 1/10 degree resolution.
I don't think we do have 1/10 degree confidence in global temperature, and the farther back in time you go the worse it gets. But we know the temperature now is about the same as the warmest during the rest of the Holocene, and we know before the industrial revolution it was about the coldest during the Holocene. The change in temperature in the last couple centuries is comparable to that entire difference. In the rest of the period, there are variations which are that big, and they can even happen faster (volcanoes again). But they are so fast that they don't last long. The climate record still shows them.
This is why I like the 'unsmoothed' graphics, with all the short term variations, and the uncertainty, over graphics like XKCD's. Those graphics aren't "wrong", they're just emphasizing a broader picture. They don't show you the whole depth of our understanding about how the climate does change on shorter intervals.
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| Watsisname | Date: Thursday, 15.09.2016, 07:03 | Message # 204 |
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| I know that's a big post, and I apologize, but it was just a lot I wanted to review and explain. I know it takes time to read and more time to write, and I'll try to keep them shorter and more concise in the future.
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| midtskogen | Date: Thursday, 15.09.2016, 21:20 | Message # 205 |
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| Quote Watsisname ( ) I know that's a big post, and I apologize, but it was just a lot I wanted to review and explain. I know it takes time to read and more time to write, and I'll try to keep them shorter and more concise in the future.
By no means, as long as your patience endures it. I find scientific methodology and epistemology very interesting.
Quote Watsisname ( ) When we compare the trends of greenhouse gas concentration through the Milankovitch cycles, the atmospheric concentrations did not follow their usual track during the Holocene.
Assuming that what is found was caused by human activity, the effect on the climate cannot have been larger than the natural changes, since the greenhouse gases went up and the temperature went down, unless you add implausible hypotheses for how humans could have cooled the climate even more. Everything humans do influence, but by "unprecedented impact" I meant unprecedented rate of change, not unprecedented cause (and however small effect).
The projected warming until the mid third millennium is surely a good candidate for an unprecedented impact, but it's a bit early to announce that as a fact.
During the Holocene the world has seen many natural changes that had far greater effects locally than what humans could make. Like the desertification of Sahara, loss and appearance og glaciers (partly due to temperature, partly to changed sea/land level), loss of Ancylus lake, etc. Globally, however, the climate was fairly stable. I consider a variation of a couple of degrees stable.
Quote Watsisname ( ) In this analogy that would be confusing weather with climate.
Ok, the analogy needs improvement. It would be like saying that the highest recorded temperature of 56.7 C in Death Valley is the highest temperature that ever was during the Holocene, which is not the kind of statement I wanted address (though I do not doubt that such claims would have been made had this been observed in 2013 and not in 1913).
How about a claim that the world has not in any geological period had more mountains (average elevation) than in the Holocene? We can measure that pretty accurately today, and we have a good understanding of the geological past, so such a claim would be more than an educated guess? Or surely we can if we get thousands of researchers to do rigorous science, continuously gathering new data and doing hypothesis testing?
Quote Watsisname ( ) But we know the temperature now is about the same as the warmest during the rest of the Holocene, and we know before the industrial revolution it was about the coldest during the Holocene
Right. "About". But these were long periods. Long enough to melt all glaciers in Scandinavia, and long enough to reestablish them. The current warming hasn't even melted the Arctic sea ice to earlier Holocene extents, which unlike glaciers only takes a few years.
Comparing modern decades with prehistoric centuries has limited use.
NIL DIFFICILE VOLENTI
Edited by midtskogen - Thursday, 15.09.2016, 21:21 |
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| midtskogen | Date: Wednesday, 21.09.2016, 06:42 | Message # 206 |
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| Alternative cartoonist's timeline. Not to be taken with more confidence, though.
NIL DIFFICILE VOLENTI
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| JackDole | Date: Wednesday, 21.09.2016, 14:55 | Message # 207 |
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| Quote midtskogen ( ) Alternative cartoonist's timeline.
I agree of course, the real development of climate change can not be predicted, but if I extrapolate the solid black line, I would expect something like the solid red line. 
But of course I'm also not a meteorologist. Amongst other things. 
Don't forget to look here.
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| Watsisname | Date: Thursday, 22.09.2016, 09:59 | Message # 208 |
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| Quote The current state of climate science means that future climate projections are dominated by uncertainty - of that we can probably be certain.
This is a very misleading statement on the comic, especially coupled with the example projection curves. A more correct statement would be:
The current state of climate science says that future climate projections are dominated by uncertainty due to what humans decide to do.
The projection curves should follow SRES or RCP scenarios, and everyone should know what those look like.
There are zero models predicting general cooling over the next 500 years under business as usual scenarios. The only way we could expect such a result is by concerted efforts by humanity to achieve it. The consensus is that unless we change our course we're headed for the PETM.
By the way, this is what the PETM temperature change looks like in the climate record:
The PETM was discovered by geologists in the fossil record (it delineates the Eocene and Paleocene, hence the name) before paleoclimate science understood what caused it. Now we're essentially repeating that event, and we seem to be doing it even faster.
Quote midtskogen ( ) Right. "About".
What "about" means is shown by the blue curve.
The current warmth is not statistically different from the warmest periods in the Holocene. But both are very significantly warmer than the coldest periods of the Holocene, which were at the very beginning (coming out of the glacial) and the very end before anthropogenic forcings became important. That general cooling throughout the Holocene is the consequence of the Milankovitch cycles. Recent human activities completely reversed that trend, and we did it an order of magnitude faster. The climate system can (and does) make similar magnitude changes even faster than we do, but the only way it does so is through volcanoes and the effect lasts only a few years.
The red curve shows projection for 2100 under business as usual. If the above comic showed this projection, it would be the warmest period on it.
Quote midtskogen ( ) How about a claim that the world has not in any geological period had more mountains (average elevation) than in the Holocene? We can measure that pretty accurately today, and we have a good understanding of the geological past, so such a claim would be more than an educated guess? Or surely we can if we get thousands of researchers to do rigorous science, continuously gathering new data and doing hypothesis testing?
This would be a better analogy, though I'd suggest refining it to total mountainous land area, since again it is the orogeny and mountain ranges that is recorded, not the individual mountains. I don't know offhand if it would actually be correct or not (probably not), but I would trust our ability to do science on it and come up with confident solutions back to at least 600 Mya.
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| midtskogen | Date: Thursday, 22.09.2016, 18:52 | Message # 209 |
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| Quote Watsisname ( ) What "about" means is shown by the blue curve.
I still protest at stitching totally different data together like that. To illustrate the nonsensical result it can lead to, I present the yearly mean temperature as measured by my weather station until today and at the end I add the forecast noon temperature tomorrow.
Your and my graph aren't equally nonsensical, but one just can't stitch together data with entirely different smoothing and make claims about unprecedented change.
Quote Watsisname ( ) The climate system can (and does) make similar magnitude changes even faster than we do, but the only way it does so is through volcanoes and the effect lasts only a few years.
How do you know [that there can't be such changes (0.8 deg in a century) not related to volcanos or humans]?
Quote Watsisname ( ) I would trust our ability to do science on it and come up with confident solutions back to at least 600 Mya
I trust science when the extent of the knowledge it builds on is well constrained. Sometimes data are simply lost and likely irrecoverable, but I'm comfortable with that.
NIL DIFFICILE VOLENTI
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| Watsisname | Date: Saturday, 24.09.2016, 00:17 | Message # 210 |
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| Quote midtskogen ( ) How do you know [that there can't be such changes (0.8 deg in a century) not related to volcanos or humans]?
The record we observe is very well explained through our understanding of what the volcanoes did and what the Sun and Earth's orbit did. Besides volcanoes, there's nothing that compares to the forcing now caused by humans. Fortunately volcanoes aren't organized, so they only make brief spikes in the record. If volcanoes were organized we'd be in a lot of trouble.
Changes in solar irradiance are the next closest thing to volcanoes, but even the Maunder Minimum only changed northern hemisphere temperatures by about 0.4C, and global temperature by less than that. The Sun is remarkably nice to our climate -- if it changes fast, it only changes a little. If it changes a lot, it changes slowly, and the climate system naturally compensates for it. Anthropogenic forcing totally overwhelms what the Sun does. A powerful demonstration of this can be seen by comparing projections from a given emission scenario with high and low solar variation.
Changes due to Earth's orbit and obliquity are big, but slow.
The only thing besides volcanoes which we know can change the global climate that quickly is a meteorite impact, and we've not been met with a major one of those during the Holocene.
So, what are comparable changes through the Holocene, what was the forcing mechanism, and where are they in the climate record?
Quote midtskogen ( ) I still protest at stitching totally different data together like that.
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.
What's important is how it is done, what it is used for, and what's the confidence you have with what you conclude from that, which you are fine to question. This is what this graphic is showing:
Blue curve:
Instruments tell us that the global temperature right now is within the statistical bounds of the warmest periods during the rest of the Holocene, which is about as much warmer from the coolest periods of the Holocene as the extent by which it has changed by anthropogenic forcing. There may be excursions above and below that range, but the larger they are the briefer they must be. We do not see ~1C global temperature change on century timescales in the climate record. We see ~1C temperature drops on timescales of years to about a decade from volcanoes.
Red curve:
Where we are going in the next 100 years under business as usual. Natural variations are too small to significantly affect this curve. Uncertainty in climate sensitivity either makes it a little smaller or a lot larger. 100-year smoothing will not make it vanish. Monte-Carlo perturbation of proxy data by future climatologists through the method employed by Marcott will not make it vanish.
Confidence in this projection comes from our understanding of physics, climate dynamics, and climate history. The PETM shows us what happened when a comparable amount of CO2 was added to the atmosphere. The climate responded, big time. We see it in the climate record -- it's a giant spike that stands out from everything else. It affected life everywhere on Earth, and left a mark in the geologic record big enough for geologists to change the name of the Epoch.
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