For a little while I was interested in paleoclimatology and I started studying how researchers developed these historical temperature reconstruction curves. Basically you take “proxies” for temperature, things like tree rings, coral growth, sediment layer thickness, etc. and you posit a relationship between the proxy measurements and temperature. Measurements that better fit the hypothesized model get more weight in the temperature reconstruction.
The main problem is that no one knows if the hypothesized models (temperature vs. tree ring thickness, sediment layer thickness, etc.) have any validity. Why should tree rings grow linearly with temperature- what about a huge number of other variables? The temperature “signal” is at best very weak. Decoupling the temperature signal from other variables (humidity, elevation, tree species, CO2 concentration, etc.) is a hugely difficult multivariate statistics problem and most of the researchers I've corresponded with do not seem to appreciate this fact.
Another major problem is that proxies get weighted in the temperature reconstruction based on how well they fit the hypothesized temperature model. The weighting is where things get really shaky. Right away, you have biased your results in such a way that that nonconforming data is discarded / de-weighted. Note that there is not anything wrong with these nonconforming samples that invalidates them; they just don't fit the proposed models very well. Typically researchers develop their own methods for weighting samples in the temperature reconstructions and many of these methods would make a statistician cringe. Often during the weighting phase you find that a handful of proxy samples (out of a sample size of hundreds) get the vast majority of the weight in the temperature reconstructions. Sometimes the weight of a temperature reconstruction in a location is almost completely computed from a few proxy samples taken halfway around the world at a completely different elevation.
If you try to discuss these fundamental problems with climate scientists you'll typically get told that you're not a scientist (not true) or that you're a "denialist" being paid by big oil (not true). I am convinced that these temperature reconstructions are useless at best.
I worked in a dendrochronology/dendroclimatology lab[1] for several years and can assure you that the researchers involved are well aware of the issue of multiple influences on tree ring growth. There are a couple of ways that they go about dealing with it. NB I was more involved in precipitation reconstructions than temperature reconstructions, but I know enough about the process to discuss it here.
The first is experimental design, much like is necessary in any aspect of science: Annual tree growth is definitely a response to a variety of regional, site-specific, and tree-specific factors for any given species in a location. So in order to increase the 'signal to noise' ratio for a given signal (temperature, precip, fire, disease or whatever reconstructions), you look for combinations of species and sites for which the factor you want to study is the limiting growth factor; in other words, other things the tree needs to grow are present in abundance and one is in shortage. If you want to make a precipitation reconstruction, you find a site that has very little soil moisture storage, such as trees basically growing out of fractures in steep bedrock. If you want to study temperature, you pick species like Bristlecone Pine that grow at high elevations (which are typically relatively wet), so that the temperature/length of growing season is the annual limiting growth factor. That sort of thing.
The second is that researchers use many other forms of measurements than simply ring width to tease these problems out. For example, many people use oxygen isotopic ratios[2], latewood (the dark outer part of the tree ring) density measurements[3], and other measurements in tree rings, both because of the unique and accessible response of the tree, and because (unlike, say, sediment cores) the tree rings are much more quickly, accurately and reliably dated at the single-year precision.
Third, there is a lot of statistical analysis thrown at the problem. I didn't work a lot with this, or see people in my lab do it, but I am aware of researchers doing multivariate statistics techniques such as principal component analysis[4]. I'm sure there is a lot more, but you can do a Scholar search as easily as I can.
Fourth, one of the strengths of the multiproxy technique is that many of them are independent, and they all show a lot of correlation to the temperature records during the instrumental calibration period. There is some divergence before this period, but not as much as would be expected otherwise. There is also the problem of weighting, like you mention, and I don't think anyone is comfortable with it but I don't think it's as ad-hoc as you make it out to be. A review (by a statistician) that discusses this is here[5]; I didn't read it in depth.
You know, nearly everything is a "proxy". Kitchen thermometers use bending metal as a "proxy" for temperature. All that matters is accuracy and precision. This is how science works, at its base. There's no such thing as "sense data".
True, the signals from tree rings (etc.) are noisier than those from kitchen thermometers. Let's consider, for a moment, how you could verify the precision and come to a conclusion as to the accuracy of those signals: well, when you get the same information coming from multiple seemingly independent sources, it greatly increases your confidence in that information. Hence, if you're doing your modeling right, if you get tree ring data from all over the world, and soil samples from all over the world, and find that, sure enough, there is a common signal visible across all of them, then you say "well, the only thing that can explain this global correlation is the modulation of some global parameters". And you present your data and conclusions to a bunch of people whose job it is to poke holes in it and prove you wrong, and after a bunch of time eventually people whose job it is to prove each other wrong end up roughly agreeing on a small sliver of information that lies at the intersection of all their understandings of the world.
Signals in physics can be noisy too (fortunately, in physics you can take millions of samples). But to say "well, these error bars are too big, so therefore we shouldn't pay any attention to the trend at all -- we can decide to do something when we have much higher confidence in the precise figures. In the meantime, I'm going to oppose tighter fuel economy standards for vehicles, and revenue-neutral carbon taxation, and aggressive subsidization of alternative energy R+D, ... " because god forbid we should all drive around in smaller cars, or that we should stop subsidizing air travel, or that we should too quickly improve solar cell efficiency.
It's definitely not the case that climate scientists are uninterested in discussing methodological problems with paleoclimate proxies. A considerable amount of the literature is taken up with doing precisely that, and it takes up a good portion of the Paleoclimatology section of the IPCC report: http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-cha...
I know that some folks in paleoclimatology are interested in these core methodology problems. But these concerns are not conveyed to a wider audience. When a temperature reconstruction graph is released to the public there is no mention at all of these problems and one can easily get the impression that these reconstructed temperatures can be known almost as accurately as going outside and taking a reading from a thermometer.
Okay. What do you say of purely geological phenomena, like glacier coverage. You can look at hydrostatic rebound, erosion patterns, etc to see where glaciers usually are. And you just have to look at pictures within the last 50 years to see where they're not. Much harder data. Same for ecological ones like flora and fauna existing in and being habituated in environments that are no longer very compatible climatologically. And for anyone in their forties or older, there's always your own damn lying eyes.
There's a billion pieces of supporting evidences for global warming. As far as I have ever heard, there's not a single piece of evidence against it, just piles and piles of FUD thrown at each model that tries to explain it.
How accurately can we track CO2 concentration over long timespans? I get that climate science is hard and produces nebulous answers based on arguably nebulous data, but when I read about about ocean acidification and see the long-term graphs from respected organizations [1] as a layman it's really quite alarming.
I.e. maybe the climate won't spiral out of control, but it seems reasonable to be concerned about the alarming levels of CO2. As a new parent I'd love to have my dire fears of catastrophe awaiting future generations assuaged by rational hard science, but (as a layman) everywhere you look the picture is pretty bleak.
AFAIK one of the main ways to reconstruct CO2 concentration is to study samples of air trapped inside old ice. This looks like a pretty direct and reliable method to me.
The figure itself is a new plot by Potsdam University researchers for realclimate.org, though, using the same dataset, but not a graphic taken directly from the paper (the paper's Fig. 1 has some alternate versions).
I think this stinks. The Science paper says their reconstruction is smoothed and has low time resolution. They say it preserves no variability at all on timescales <300 years, and attenuates even 1,000 year variations. Superimposing this with the 30-year Hadley data seems misleading, because it is on a very short timescale which is suppressed from the paleologic data.
(edit):
"Because the relatively low resolution and time uncertainty of our data sets should generally suppress higher-frequency temperature variability, an important question is whether the Holocene stack adequately represents centennial- or millennial scale variability. [...] The results suggest that at longer periods, more variability is preserved, with essentially no variability preserved at periods shorter than 300 years, ~50% preserved at 1000-year periods, and nearly all of the variability preserved for periods longer than 2000 years (figs. S17 and S18)."
The realclimate.org post discusses that as a potential issue, yes. See the section following the sentence: Because the proxy data have only a coarse time resolution – would they have shown it if there had been a similarly rapid warming earlier in the Holocene?
1) I think that we, as the human population, should actively move toward more efficient, less destructive industry on principle, not just because of the threat of climate change. I think making it about climate change gives too many opportunities for argument derailment. Think about when "tree hugger" was a pejorative term; i mean, who DOESN'T want to hug a tree? I think it's a lot harder for people to argue against the idea of "leave a place as you found it" than to find flaws a data set. It also allows for much broader regulation. For example, we could then start focusing on legislation against pharm manufacturers allowing meds to seep into the water supply rather than just the air pollution they're producing.
2) I'm starting to wonder why we're not focusing more on adaptation to than prevention of climate change. I've been watching a lot of TED talks lately (thanks, Netflix!) about the impact of climate change, and the one that I'm thinking of was a researcher who spent time in the arctic studying the wildlife there, and made the case that we should prevent climate change so that we can save arctic wildlife. But I wonder, if we were alive in the age of dinosaurs, would we be saying that we need to clean up the atmosphere to prevent the impact winter that would inevitably kill them? While I love wildlife, I almost feel like it's not our responsibility as humans to tamper with natural processes like extinction. In our prevention efforts, we may also be preventing natural selection and, by extension, adaptation. It could be a reality that we'll face an extinction event that wipes out all other non-domesticated mammalian life. While we can all agree that an Earth like that would suck, we know that, 600 million years from now, EVERYTHING will be wiped out. People speculate that, at this time, humans themselves will either become extinct or will have migrated off the planet. So, my question is, are we prepared to jump ship if Earth becomes uninhabitable? Is it realistic to try to change all 5,000,000,000,000,000,000 kilograms of atmosphere, or should we starting thinking about building habitats for space living?
While I love wildlife, I almost feel like it's not our responsibility as humans to tamper with natural processes like extinction.
The fundamental premise is not that extinction is bad, but that extinction we cause is bad. If a fox tramples your neighbor's garden, that's too bad. If you trample your neighbor's garden, you should fix it.
Loss of diversity is bad. Everything else is all right, as long as in the long term there is no loss of diversity.
The trouble is, that at the current state of science and technology we can not engineer and control ecosystems. We can not even model ecosystems. As a result we are breaking things and we even have no idea how badly we are breaking things when we are extracting resources. Like when we are turning diverse ecologies into monocultures, when forests are being turned into these 'beautiful' fields of golden wheat.
It does NOT have to be that way. There is no natural law that says that it is necessary to destroy diversity if one wants to grow food or extract resources. It is just that our technology is very primitive and that's the only way we've been able to do it so far. With right technology one can have it both ways. But we don't have it. Not yet.
And meanwhile, well. Conservation, common sense and minimizing our damage to the ecology is probably a best that we can do...
Humans are either fully part of the natural process, or everything we do interferes with it.
There's a very real choice about how we want to change the environment of the earth, but lets not couch it in meaningless terms like natural vs. unnatural.
Hunter gatherer societies are no more natural/unnatural than cities.
I used to agree completely with you, but now I realize that, given the second law of thermodynamics, it's impossible to restore an entire ecosystem back to a previous state. From what I hear, one goal of ending climate change is to allow icecaps to re-form and to last longer throughout the year, which ostensibly will end the suffering of polar bears "stranded" at sea. However, even if we did remove all excess amounts of greenhouse gases from the atmosphere (which, as of today, is something that's barely discussed seriously), it's not going to suddenly reverse the adapted behavior of polar bears. This is a totally hypothetical and unscientific story, but let's pretend that the ice caps melted such that polar bears were forced inland and began foraging for food in human-populated areas. In response, the government of Canada single-handedly puts up the money to remove all excess greenhouse gases from the atmosphere. Over a period of decades, the ice grows back, but: do we really expect the polar bear population, which has now adapted to foraging for garbage, to suddenly move back to their initial habitat? Chances are, food will be more plentiful for them in a human-populated area. Now let's assume that polar bears play a significant role in seal population control. Well, now that the polar bears have adapted and are now living further inland, the seal population booms in the arctic region. In fact, it gets so big, that now penguin populations are in rapid decline! So, at this point, we've spent probably trillions of dollars, haven't really helped the polar bears at all, and have directly contributed to the endangerment of penguins. And this is all assuming that our plan even works! Not to mention the fact that there may be other species that died off that played a huge impact on balancing the ice-filled arctic ecosystem.
So, given that scenario, I think the better question to ask is, what benefit would we, as humans, get from a return to a cooler Earth? IMO wildlife will take care of itself: adapt, die off, etc. the same way it always has. BUT, I think that too often the focus is put on sad-looking animals and melted snowcaps, which makes it seem like global warming is just an "environmentalist" issue rather than a serious threat to human life.
While I love wildlife, I almost feel like it's not our responsibility
Two points:
1. The conditions on Earth which support other megafauna also, largely, are beneficial to humans. Change those conditions and it's likely that the extinctions aren't so much bad for humans as indicators of changing conditions which are bad for humans.
2. Conservation biologists have recognized that the Earth and its biosphere isn't a static system, and that conservation efforts shouldn't be aimed at "holding back the tides" so to speak. But noting when changes are happening at scales which are likely to have strongly negative impacts for humans, civilization, and the almighty economy, and deciding to take preemptive action, could be a very good thing.
There's a huge difference between wiping out all life (or much of it) within the next 200 years, and the next 800 million.
Assuming you've got an 85 year lifespan, that's the difference between living for your full life, or just 25 minutes.
My own definition of "sustainability" is "so long as the extrinsic conditions are conducive to human survival". Even with genetic drift, that's likely a few millions to tens of millions of years.
> why we're not focusing more on adaptation to than prevention of climate change
The reality is that prevention is cheaper (there is also an issue of distribution of the cost, though). Prevention of climate change effectively means not using energy from fossil fuels, while adaptation means paying extra energy cost for each unit of energy you get from fossil fuels.
This extra cost is actually greater than extra cost that would be incurred if you used non-fossil fuel source. So if you decide to continue to use fossil fuel sources at all, the total cost (savings due to cheap fuel + mitigation costs) will always be higher than the non-fossil energy sources (higher cost to get the energy but savings on mitigation).
There are enough gigatons of carbon (oil, coal, methanhydrates) available and ready to burn to render this planet uninhabitable in a time frame of centuries. That's nothing someone can adapt to. We can adapt to +2°C, likely to +4°C and perhaps even to +6°C, but there has to be an upper limit, otherwise you simply keep adapting until you run out of money.
Why is it so hard to imagine changing our lifestyle might be the easiest thing to do?
How on earth is this ludicrous wall of text the top comment? "We should look into moving into outer space once we've destroyed the planet" -- are you for real?
I'm with you on #2. One way to look at this chart is that if we 'correct' all of our input into the system then the system will revert to its previous norm, i.e. we'll plunge into an ice age and glaciers will begin to move south over North America and Europe. On the other hand our ability to 'fine tune' our control is all but impossible on these large scales so "control" of the climate is still beyond our reach.
So perhaps investing in keeping old people alive during hot and cold snaps might be a good investment and infrastructure that is impervious to same.
1) CO2 concentration has a long half-life in the atmosphere, so even if we immediately stopped emitting every molecule of fossil fuel-derived CO2 into it, we'd still see the effects of what we've done for the past century for at least another couple centuries.
2) People mostly hope to lower the rate at which our CO2 emissions rate increases, and maybe in certain countries make it negative. Both of those, however, are derivatives of the relevant value for purposes of the greenhouse effect and ocean acidification: the absolute level in the atmosphere. Which has zero chance of decrease even under the most aggressive conceivable prevention efforts.
3) The graph doesn't even cover the last major glaciation event: the last glacial maximum was around 20k years ago.
4) Biggest issue: the people who will be most adversely effected by climate change are people who don't have the resources to adapt. I don't dismiss the idea out of hand that it might be cheaper to put efforts into mitigation than prevention: we're definitely going to have to do some mitigation work. But you are not going to convince Western countries to spend trillions of dollars building levees in Bangladesh.
Your #2 reminds me of something Bjorn Lomborg (yeah yeah, I'm not a fan either - nor a hater, in fact, I just don't know enough about the nuances of the issues involved to have an opinion that's well thought out enough to defend) said in an interview on Dutch television years ago.
He said the money spent on implementing Kyoto was much better spent combating the direct effects of global warming, for example by building dikes in areas that were too poor to build them themselves and that were likely to be affected by rising sea levels, like Bangladesh.
To my layman's ears, that sounded quite reasonable.
How do you fairly raise those revenues that'd fund the trillions of dollars worth of mitigation efforts? People who disproportionately generate CO2 emissions are disproportionately responsible for the need for mitigation efforts.
So Lomborg's argument isn't so much against putting a Pigouvian tax on carbon emissions, as it is earmarking the revenues derived from those emissions for mitigation efforts instead of using it to pay down deficits or pay for other services. Which is certainly something I can agree with, but it seems politically implausible. First lets get a carbon tax.
I think that we, as the human population, should actively move toward more efficient, less destructive industry on principle
That's definitely a must. But I'm not sure if it's doable, seeing the global population just keeps on growing: as long as industry is destructive and always more of it is needed, the net result still is destructive. Might sound bold, but a lot of problems would be solved by combining clean industry with a _lot_ less people to serve.
Right, lets just "cope" with climate change the same way we did 425,000 years ago. By dying, I guess?
What's wierd is that despite that fact that's you've done your best to make AGW look like a non-issue, the chart for the 100 last years looks extremely worrying.
Fact is there's a 125,000 year cycle. We're at the high of one, due for a long drop. When I bring out this long term data, funny how many people shriek at it - but there it is, and the "warmers" won't produce any graphs covering the same (or longer) periods.
Yes, the data is limited. BUT - I hunted it down, put it together, gave it what I considered fair context, and there it is. Don't like it? counter with your own half-million year graph, not snide religious insults.
It's really important to consider the well established cycles in climate, not because they are proof that human changes don't exist, but to put our change in context.
Anthropogenic climate change is IMHO indisputably real and startlingly fast in geological terms, BUT it is dwarfed by the natural variations in climate over the long term and may even (if we don't overdo it) have saved us from another ice age in the long term. I'm not sure anyone understands what the climate is doing enough in order to make concrete predictions or to know what the interaction of our global warming with the long term cycle's cooling will do. It's great that attention is becoming more and more focused on this topic, but we don't need dire predictions and polarisation which have taken place - it is counterproductive.
It startles me how people pick sides and start using labels like denier and apologist on this topic - surely there is room for debate on what we should do about climate change? Do we have to be either for or against AGW and therefore for or against mitigating it? Isn't it reasonable to suggest looking at AGW in context, and also to show that humanity is going to have to deal with far greater swings over the long term in climate than just a few degrees?
If anything I'd say this long-term chart indicates we have to redouble our efforts to understand climate change, and if we can't control it, work on ways to mitigate its effects, because even if we control our own short term effects, long term the earth will move from ice age to tropical and we'll have to adapt.
His chart is based on a single data set (the vostok ice core) for the majority of that period (plus modern temp records slapped on at the end, but it's not visible in the 10,000 year graph) which is not representative of global climate. Correlating proxy records with modern instrument records of temperature is not trivial either (which becomes far more apparent once you look at more than a single proxy record).
It's just cherry picked data to make a cheap political point. The scale of the vertical axis makes it very hard to see what is happening during interglacials, which is what we are in at the moment. If we were worried about an ice age arriving in the next couple of centuries the choice of scale might have some merit, to show how much colder it could possibly get. But we are worried about rapid heating, which that scale does a good job of hiding.
Possibly because it's a three word AGW denying blog post, and includes only from ice core data from Antarctica, whereas the 11,000 year data in the original post is compiled from multiple combined sources.
I'd hate to assume bad faith on the part of a climate change denier, but I can't help but speculate that the data source was chosen specifically because it made the point s/he wanted to make.
Different data set. The 10,000 year chart is only Antarctic ice cores. The 11,000 year chart is a composite of a number of temperature records - tree rings, etc.
My skepticism in climate change is based on a long history of censuses in the scientific community that later proved to be completely wrong.
I'm not saying we should not try to understand the world. I'm saying we should realize we have limits. The more complex the system we seek to understand, the more we should be skeptical. The climate of the entire planet and to the degree one particular species impacts it seems extremely complex to me. Hence, I am highly skeptical.
No one is saying that we should devote 100% of GDP to mitigating global warming. Go ahead, factor in the uncertainty. What % of GDP should we spend to avert the very real possibility catastrophic warning occurs? What % are we spending?
If it were left up to me, I would say we should have zero forced spending and an unlimited amount of voluntary spending to avert a potential global warming catastrophe.
Let me remind you, that at any time you are free to donate any amount of your own money to thwart global warming. That's not what some people really want though. They don't want to spend their own money on the problem. They want to spend other people's money on the problem. And I contend we don't know nearly enough about the issue to cross that line.
Out of idle curiosity, can anyone tell me more about what a 0.4 (0.6, 1, 2...) °C anomaly feels like, maybe with reference to cities that have climates with differing annual averages? I mean, is it like shifting every city 5 ° in latitude closer to the equator, or what?
(I know this wouldn't capture the whole story, I'm just curious.)
Think of it more as extra energy being imparted to the global weather system. This will have all sorts of fun and exciting effects, and as I understand the warming will be greatest at the poles. Alaska has warmed by about 1.6[0] in the last 60 years, and the interior of Alaska by 1.4° C in the last 100[1], compared to a global temperature rise of .8° C over the same period. This has resulted in the melting of thousands of cubic kilometers of glacial ice, with this study[2] suggesting that this is the largest glaciological factor in rising sea levels.
To the eyes of the native inhabitant, the glacial retreat is shocking, with the lower altitude glaciers most affected. We've built glacier overlooks in some places, where once the glacier was a stone's throw away, and now it's barely visible, and in another few decades the only thing they'll be able to show anyone there are photos. I've seen photos from the early 1900s of glacial termini which towered over the masts of a sail-rigged steamer. Today there is a fjord there, and the glacier is more than 13km away.
And you want to know what that feels like?
How about instead you imagine how it feels to watch the Arctic melting around you, while an endless circus of millions deny that it's even happening.
In the maps linked below, each isotherm represents a 2 C difference. So a global rise of 2 C would be equivalent to a 100-200 km or so shift towards the equator, for a given location. Or nearly equivalent to the temperature difference in the center of a major city compared to its suburbs.
If the temperatures are be equally distributed plus 1°C feels like 1°C plus. But that's not the case neither in space nor time. I worry more about the peaks.
googling "industrial revolution averted iceage" returns a few conservative blogs, smugly pleased with the possibility
the only credible commentary i can find is in a nytimes article:
"Scientists say that if natural factors were still governing the climate, the Northern Hemisphere would probably be destined to freeze over again in several thousand years. 'We were on this downward slope, presumably going back toward another ice age,' Dr. Marcott said."
I cannot cite the exact words, but in discussions professors have indeed expressed the opinion that a next ice age won't be of concern for us.
Those charts, especially those going back further, are a good argument for why we will need to control the climate at some point in the future (but please not when we have not figured out how to without significant risk).
Over the last decades, numerous researchers have
painstakingly collected, analyzed, dated, and calibrated
many data series that allow us to reconstruct climate
before the age of direct measurements. Such data come e.g.
from sediment drilling in the deep sea, from corals, ice
cores and other sources. Shaun Marcott and colleagues for
the first time assembled 73 such data sets from around the
world into a global temperature reconstruction for the
Holocene, published in Science. Or strictly speaking, many
such reconstructions: they have tried about twenty
different averaging methods and also carried out 1,000
Monte Carlo simulations with random errors added to the
dating of the individual data series to demonstrate the
robustness of their results.
Marcott et al.'s graphic states that their model reflects historical temperatures so accurately that it can measure the average temperature of the entire globe continuously back to 8000 years ago, to within a small fraction of 1 degree Celsius (i.e. the 1-sigma error bars). That is simply an extraordinary claim given:
1) The "divergence problem". The lack of correlation between model inputs like tree rings and the instrumental record over the last few decades is acknowledged by all; climate scientists generally state that it is due to anthropogenic factors, arguably assuming the consequent.
In other words, key model inputs used in climate reconstructions do not strongly correlate with the instrumental record over the last 30-40 years ("the divergence problem") and climate models have so far had a poor track record over the last 15 years, with average temperatures winding up below the envelope of model predictions. These predictive failures in the datasets we can check bode ill for the prospect of hindcasting global average temperatures to within 1 degree more than 8000 years ago.
In the same article, they explicitly mention that the study is not based on tree ring proxies. In fact, all the global reconstructions are based on many different proxies.
I also think you misrepresent the 2nd article. The question is what and on what time scale are you trying to predict. I believe they are talking about more precision more short-term models. Just like we can predict winter and not predict weather, we can predict warming due to human forcing, but not the specific details.
In the end, however, it's completely irrelevant to AGW if there was a higher temperature in the past or not. The theory of AGW doesn't stand just on that argument (nor any other single argument, for that matter).
Well, there are a certain number of explicit and implicit caveats that don't make it into the made-it-to-the-top-of-HN pretty graph.
One is that this is based on other people's work, as the GP mentioned. Updates to those works will affect this one; the hope is that those 73 underlying datasets aren't systematically biased and any errors will cancel out. Another is that those error bars are probably 95% confidence. So we fully expect that about 550 out of the 11,000 years in this chart will fall outside of that range. A final bit is that we're only reconstructing averages here; it's a lot easier to guess the average number of shoes owned by 1000 people than the exact number of shoes owned by 1.
These extra caveats don't invalidate the data or render it useless, they just qualify it. You shouldn't look at the graph and think, "Here is the exact temperature for the last 11,000 years", you should think, "Given our current best understanding of the available data, the average global temperature for 10,450 out of the last 11,000 years probably fell into this 0.4 degree C range."
Readit News
The main problem is that no one knows if the hypothesized models (temperature vs. tree ring thickness, sediment layer thickness, etc.) have any validity. Why should tree rings grow linearly with temperature- what about a huge number of other variables? The temperature “signal” is at best very weak. Decoupling the temperature signal from other variables (humidity, elevation, tree species, CO2 concentration, etc.) is a hugely difficult multivariate statistics problem and most of the researchers I've corresponded with do not seem to appreciate this fact.
Another major problem is that proxies get weighted in the temperature reconstruction based on how well they fit the hypothesized temperature model. The weighting is where things get really shaky. Right away, you have biased your results in such a way that that nonconforming data is discarded / de-weighted. Note that there is not anything wrong with these nonconforming samples that invalidates them; they just don't fit the proposed models very well. Typically researchers develop their own methods for weighting samples in the temperature reconstructions and many of these methods would make a statistician cringe. Often during the weighting phase you find that a handful of proxy samples (out of a sample size of hundreds) get the vast majority of the weight in the temperature reconstructions. Sometimes the weight of a temperature reconstruction in a location is almost completely computed from a few proxy samples taken halfway around the world at a completely different elevation.
If you try to discuss these fundamental problems with climate scientists you'll typically get told that you're not a scientist (not true) or that you're a "denialist" being paid by big oil (not true). I am convinced that these temperature reconstructions are useless at best.
The first is experimental design, much like is necessary in any aspect of science: Annual tree growth is definitely a response to a variety of regional, site-specific, and tree-specific factors for any given species in a location. So in order to increase the 'signal to noise' ratio for a given signal (temperature, precip, fire, disease or whatever reconstructions), you look for combinations of species and sites for which the factor you want to study is the limiting growth factor; in other words, other things the tree needs to grow are present in abundance and one is in shortage. If you want to make a precipitation reconstruction, you find a site that has very little soil moisture storage, such as trees basically growing out of fractures in steep bedrock. If you want to study temperature, you pick species like Bristlecone Pine that grow at high elevations (which are typically relatively wet), so that the temperature/length of growing season is the annual limiting growth factor. That sort of thing.
The second is that researchers use many other forms of measurements than simply ring width to tease these problems out. For example, many people use oxygen isotopic ratios[2], latewood (the dark outer part of the tree ring) density measurements[3], and other measurements in tree rings, both because of the unique and accessible response of the tree, and because (unlike, say, sediment cores) the tree rings are much more quickly, accurately and reliably dated at the single-year precision.
Third, there is a lot of statistical analysis thrown at the problem. I didn't work a lot with this, or see people in my lab do it, but I am aware of researchers doing multivariate statistics techniques such as principal component analysis[4]. I'm sure there is a lot more, but you can do a Scholar search as easily as I can.
Fourth, one of the strengths of the multiproxy technique is that many of them are independent, and they all show a lot of correlation to the temperature records during the instrumental calibration period. There is some divergence before this period, but not as much as would be expected otherwise. There is also the problem of weighting, like you mention, and I don't think anyone is comfortable with it but I don't think it's as ad-hoc as you make it out to be. A review (by a statistician) that discusses this is here[5]; I didn't read it in depth.
[1] http://www.uark.edu/misc/dendro/
[2] http://link.springer.com/article/10.1007/s00382-013-1674-3
[3] http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-11-00139....
[4] http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0706.2010.... [5] http://www.stat.unc.edu/postscript/rs/Sensitivities-Submitte...
True, the signals from tree rings (etc.) are noisier than those from kitchen thermometers. Let's consider, for a moment, how you could verify the precision and come to a conclusion as to the accuracy of those signals: well, when you get the same information coming from multiple seemingly independent sources, it greatly increases your confidence in that information. Hence, if you're doing your modeling right, if you get tree ring data from all over the world, and soil samples from all over the world, and find that, sure enough, there is a common signal visible across all of them, then you say "well, the only thing that can explain this global correlation is the modulation of some global parameters". And you present your data and conclusions to a bunch of people whose job it is to poke holes in it and prove you wrong, and after a bunch of time eventually people whose job it is to prove each other wrong end up roughly agreeing on a small sliver of information that lies at the intersection of all their understandings of the world.
Signals in physics can be noisy too (fortunately, in physics you can take millions of samples). But to say "well, these error bars are too big, so therefore we shouldn't pay any attention to the trend at all -- we can decide to do something when we have much higher confidence in the precise figures. In the meantime, I'm going to oppose tighter fuel economy standards for vehicles, and revenue-neutral carbon taxation, and aggressive subsidization of alternative energy R+D, ... " because god forbid we should all drive around in smaller cars, or that we should stop subsidizing air travel, or that we should too quickly improve solar cell efficiency.
There's a billion pieces of supporting evidences for global warming. As far as I have ever heard, there's not a single piece of evidence against it, just piles and piles of FUD thrown at each model that tries to explain it.
I.e. maybe the climate won't spiral out of control, but it seems reasonable to be concerned about the alarming levels of CO2. As a new parent I'd love to have my dire fears of catastrophe awaiting future generations assuaged by rational hard science, but (as a layman) everywhere you look the picture is pretty bleak.
1: http://www.esrl.noaa.gov/gmd/ccgg/trends/history.html
The Science paper: http://www.usu.edu/geo/physical/MarcottEtal_Science_2013.pdf
Online supplemental material: http://www.sciencemag.org/content/suppl/2013/03/07/339.6124....
The figure itself is a new plot by Potsdam University researchers for realclimate.org, though, using the same dataset, but not a graphic taken directly from the paper (the paper's Fig. 1 has some alternate versions).
(edit):
"Because the relatively low resolution and time uncertainty of our data sets should generally suppress higher-frequency temperature variability, an important question is whether the Holocene stack adequately represents centennial- or millennial scale variability. [...] The results suggest that at longer periods, more variability is preserved, with essentially no variability preserved at periods shorter than 300 years, ~50% preserved at 1000-year periods, and nearly all of the variability preserved for periods longer than 2000 years (figs. S17 and S18)."
1) I think that we, as the human population, should actively move toward more efficient, less destructive industry on principle, not just because of the threat of climate change. I think making it about climate change gives too many opportunities for argument derailment. Think about when "tree hugger" was a pejorative term; i mean, who DOESN'T want to hug a tree? I think it's a lot harder for people to argue against the idea of "leave a place as you found it" than to find flaws a data set. It also allows for much broader regulation. For example, we could then start focusing on legislation against pharm manufacturers allowing meds to seep into the water supply rather than just the air pollution they're producing.
2) I'm starting to wonder why we're not focusing more on adaptation to than prevention of climate change. I've been watching a lot of TED talks lately (thanks, Netflix!) about the impact of climate change, and the one that I'm thinking of was a researcher who spent time in the arctic studying the wildlife there, and made the case that we should prevent climate change so that we can save arctic wildlife. But I wonder, if we were alive in the age of dinosaurs, would we be saying that we need to clean up the atmosphere to prevent the impact winter that would inevitably kill them? While I love wildlife, I almost feel like it's not our responsibility as humans to tamper with natural processes like extinction. In our prevention efforts, we may also be preventing natural selection and, by extension, adaptation. It could be a reality that we'll face an extinction event that wipes out all other non-domesticated mammalian life. While we can all agree that an Earth like that would suck, we know that, 600 million years from now, EVERYTHING will be wiped out. People speculate that, at this time, humans themselves will either become extinct or will have migrated off the planet. So, my question is, are we prepared to jump ship if Earth becomes uninhabitable? Is it realistic to try to change all 5,000,000,000,000,000,000 kilograms of atmosphere, or should we starting thinking about building habitats for space living?
The fundamental premise is not that extinction is bad, but that extinction we cause is bad. If a fox tramples your neighbor's garden, that's too bad. If you trample your neighbor's garden, you should fix it.
The trouble is, that at the current state of science and technology we can not engineer and control ecosystems. We can not even model ecosystems. As a result we are breaking things and we even have no idea how badly we are breaking things when we are extracting resources. Like when we are turning diverse ecologies into monocultures, when forests are being turned into these 'beautiful' fields of golden wheat.
It does NOT have to be that way. There is no natural law that says that it is necessary to destroy diversity if one wants to grow food or extract resources. It is just that our technology is very primitive and that's the only way we've been able to do it so far. With right technology one can have it both ways. But we don't have it. Not yet.
And meanwhile, well. Conservation, common sense and minimizing our damage to the ecology is probably a best that we can do...
There's a very real choice about how we want to change the environment of the earth, but lets not couch it in meaningless terms like natural vs. unnatural.
Hunter gatherer societies are no more natural/unnatural than cities.
So, given that scenario, I think the better question to ask is, what benefit would we, as humans, get from a return to a cooler Earth? IMO wildlife will take care of itself: adapt, die off, etc. the same way it always has. BUT, I think that too often the focus is put on sad-looking animals and melted snowcaps, which makes it seem like global warming is just an "environmentalist" issue rather than a serious threat to human life.
Two points:
1. The conditions on Earth which support other megafauna also, largely, are beneficial to humans. Change those conditions and it's likely that the extinctions aren't so much bad for humans as indicators of changing conditions which are bad for humans.
2. Conservation biologists have recognized that the Earth and its biosphere isn't a static system, and that conservation efforts shouldn't be aimed at "holding back the tides" so to speak. But noting when changes are happening at scales which are likely to have strongly negative impacts for humans, civilization, and the almighty economy, and deciding to take preemptive action, could be a very good thing.
There's a huge difference between wiping out all life (or much of it) within the next 200 years, and the next 800 million.
Assuming you've got an 85 year lifespan, that's the difference between living for your full life, or just 25 minutes.
My own definition of "sustainability" is "so long as the extrinsic conditions are conducive to human survival". Even with genetic drift, that's likely a few millions to tens of millions of years.
The reality is that prevention is cheaper (there is also an issue of distribution of the cost, though). Prevention of climate change effectively means not using energy from fossil fuels, while adaptation means paying extra energy cost for each unit of energy you get from fossil fuels.
This extra cost is actually greater than extra cost that would be incurred if you used non-fossil fuel source. So if you decide to continue to use fossil fuel sources at all, the total cost (savings due to cheap fuel + mitigation costs) will always be higher than the non-fossil energy sources (higher cost to get the energy but savings on mitigation).
Why is it so hard to imagine changing our lifestyle might be the easiest thing to do?
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So perhaps investing in keeping old people alive during hot and cold snaps might be a good investment and infrastructure that is impervious to same.
1) CO2 concentration has a long half-life in the atmosphere, so even if we immediately stopped emitting every molecule of fossil fuel-derived CO2 into it, we'd still see the effects of what we've done for the past century for at least another couple centuries.
2) People mostly hope to lower the rate at which our CO2 emissions rate increases, and maybe in certain countries make it negative. Both of those, however, are derivatives of the relevant value for purposes of the greenhouse effect and ocean acidification: the absolute level in the atmosphere. Which has zero chance of decrease even under the most aggressive conceivable prevention efforts.
3) The graph doesn't even cover the last major glaciation event: the last glacial maximum was around 20k years ago.
4) Biggest issue: the people who will be most adversely effected by climate change are people who don't have the resources to adapt. I don't dismiss the idea out of hand that it might be cheaper to put efforts into mitigation than prevention: we're definitely going to have to do some mitigation work. But you are not going to convince Western countries to spend trillions of dollars building levees in Bangladesh.
http://en.wikipedia.org/wiki/Wife_acceptance_factor
He said the money spent on implementing Kyoto was much better spent combating the direct effects of global warming, for example by building dikes in areas that were too poor to build them themselves and that were likely to be affected by rising sea levels, like Bangladesh.
To my layman's ears, that sounded quite reasonable.
It still does, in fact.
So Lomborg's argument isn't so much against putting a Pigouvian tax on carbon emissions, as it is earmarking the revenues derived from those emissions for mitigation efforts instead of using it to pay down deficits or pay for other services. Which is certainly something I can agree with, but it seems politically implausible. First lets get a carbon tax.
That's definitely a must. But I'm not sure if it's doable, seeing the global population just keeps on growing: as long as industry is destructive and always more of it is needed, the net result still is destructive. Might sound bold, but a lot of problems would be solved by combining clean industry with a _lot_ less people to serve.
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Clear cutters are given lumber rights temporarily, but since they don't own the lot, they gain nothing from replanting and controlled burning.
Another great asset of private ownership is the inherent drive toward efficiency, which has been great as far as environmental impact reduction goes.
What's wierd is that despite that fact that's you've done your best to make AGW look like a non-issue, the chart for the 100 last years looks extremely worrying.
Yes, the data is limited. BUT - I hunted it down, put it together, gave it what I considered fair context, and there it is. Don't like it? counter with your own half-million year graph, not snide religious insults.
Anthropogenic climate change is IMHO indisputably real and startlingly fast in geological terms, BUT it is dwarfed by the natural variations in climate over the long term and may even (if we don't overdo it) have saved us from another ice age in the long term. I'm not sure anyone understands what the climate is doing enough in order to make concrete predictions or to know what the interaction of our global warming with the long term cycle's cooling will do. It's great that attention is becoming more and more focused on this topic, but we don't need dire predictions and polarisation which have taken place - it is counterproductive.
It startles me how people pick sides and start using labels like denier and apologist on this topic - surely there is room for debate on what we should do about climate change? Do we have to be either for or against AGW and therefore for or against mitigating it? Isn't it reasonable to suggest looking at AGW in context, and also to show that humanity is going to have to deal with far greater swings over the long term in climate than just a few degrees?
If anything I'd say this long-term chart indicates we have to redouble our efforts to understand climate change, and if we can't control it, work on ways to mitigate its effects, because even if we control our own short term effects, long term the earth will move from ice age to tropical and we'll have to adapt.
It's just cherry picked data to make a cheap political point. The scale of the vertical axis makes it very hard to see what is happening during interglacials, which is what we are in at the moment. If we were worried about an ice age arriving in the next couple of centuries the choice of scale might have some merit, to show how much colder it could possibly get. But we are worried about rapid heating, which that scale does a good job of hiding.
I'd hate to assume bad faith on the part of a climate change denier, but I can't help but speculate that the data source was chosen specifically because it made the point s/he wanted to make.
Also, note the scales are totally different, and that the original link at least states sigma (uncertainty.)
I'm not saying we should not try to understand the world. I'm saying we should realize we have limits. The more complex the system we seek to understand, the more we should be skeptical. The climate of the entire planet and to the degree one particular species impacts it seems extremely complex to me. Hence, I am highly skeptical.
Let me remind you, that at any time you are free to donate any amount of your own money to thwart global warming. That's not what some people really want though. They don't want to spend their own money on the problem. They want to spend other people's money on the problem. And I contend we don't know nearly enough about the issue to cross that line.
(I know this wouldn't capture the whole story, I'm just curious.)
EDIT: I guess the state of New York has a range of annual average temperatures from 4 °C to 12 °C, so maybe this isn't useful at all. http://en.wikipedia.org/wiki/Climate_of_New_York#Temperature...
To the eyes of the native inhabitant, the glacial retreat is shocking, with the lower altitude glaciers most affected. We've built glacier overlooks in some places, where once the glacier was a stone's throw away, and now it's barely visible, and in another few decades the only thing they'll be able to show anyone there are photos. I've seen photos from the early 1900s of glacial termini which towered over the masts of a sail-rigged steamer. Today there is a fjord there, and the glacier is more than 13km away.
And you want to know what that feels like?
How about instead you imagine how it feels to watch the Arctic melting around you, while an endless circus of millions deny that it's even happening.
[0] http://climate.gi.alaska.edu/ClimTrends/Change/TempChange.ht... [1] http://oldclimate.gi.alaska.edu/papers/Arctic62-3-295.pdf [2] http://glaciers.gi.alaska.edu/material/arendt_phd.pdf
I said in the original comment that I was well aware this wasn't the entire story.
There are some subjects where I really wish I could ask questions like someone new to the topic and not immediately be branded as some kind of enemy.
http://solargis.info/doc/_pics/SolarGIS-iMaps--World-air-tem...
http://solargis.info/doc/_pics/SolarGIS-iMaps--World-air-tem...
the only credible commentary i can find is in a nytimes article:
"Scientists say that if natural factors were still governing the climate, the Northern Hemisphere would probably be destined to freeze over again in several thousand years. 'We were on this downward slope, presumably going back toward another ice age,' Dr. Marcott said."
http://www.nytimes.com/2013/03/08/science/earth/global-tempe...
Those charts, especially those going back further, are a good argument for why we will need to control the climate at some point in the future (but please not when we have not figured out how to without significant risk).
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1) The "divergence problem". The lack of correlation between model inputs like tree rings and the instrumental record over the last few decades is acknowledged by all; climate scientists generally state that it is due to anthropogenic factors, arguably assuming the consequent.
http://www.skepticalscience.com/Tree-ring-proxies-divergence...
2) Serious climate model prediction failures over the past 10 year period, as acknowledged in Nature:
http://www.nature.com/news/climate-change-the-forecast-for-2...
In other words, key model inputs used in climate reconstructions do not strongly correlate with the instrumental record over the last 30-40 years ("the divergence problem") and climate models have so far had a poor track record over the last 15 years, with average temperatures winding up below the envelope of model predictions. These predictive failures in the datasets we can check bode ill for the prospect of hindcasting global average temperatures to within 1 degree more than 8000 years ago.
I also think you misrepresent the 2nd article. The question is what and on what time scale are you trying to predict. I believe they are talking about more precision more short-term models. Just like we can predict winter and not predict weather, we can predict warming due to human forcing, but not the specific details.
In the end, however, it's completely irrelevant to AGW if there was a higher temperature in the past or not. The theory of AGW doesn't stand just on that argument (nor any other single argument, for that matter).
One is that this is based on other people's work, as the GP mentioned. Updates to those works will affect this one; the hope is that those 73 underlying datasets aren't systematically biased and any errors will cancel out. Another is that those error bars are probably 95% confidence. So we fully expect that about 550 out of the 11,000 years in this chart will fall outside of that range. A final bit is that we're only reconstructing averages here; it's a lot easier to guess the average number of shoes owned by 1000 people than the exact number of shoes owned by 1.
These extra caveats don't invalidate the data or render it useless, they just qualify it. You shouldn't look at the graph and think, "Here is the exact temperature for the last 11,000 years", you should think, "Given our current best understanding of the available data, the average global temperature for 10,450 out of the last 11,000 years probably fell into this 0.4 degree C range."