Arguments
What does past climate change tell us about global warming?
The skeptic argument...
Climate's changed before
Climate is always changing. We have had ice ages and warmer periods when alligators were found in Spitzbergen. Ice ages have occurred in a hundred thousand year cycle for the last 700 thousand years, and there have been previous periods that appear to have been warmer than the present despite CO2 levels being lower than they are now. More recently, we have had the medieval warm period and the little ice age. (Richard Lindzen)
What the science says...
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Climate reacts to whatever forces it to change at the time; humans are now the dominant forcing. |
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A common skeptic argument is that climate has changed naturally in the past, long before SUVs and coal-fired power plants, so humans can't be the cause of the current global warming. Peer-reviewed research shows this is not the case.
It's important to know there are a number of different forces acting on the Earth’s climate. When the sun gets brighter, the planet receives more energy and warms. When volcanoes erupt, they emit particles into the atmosphere which reflect sunlight, and the planet cools. When there are more greenhouse gases in the atmosphere, the planet warms. It's worth remembering that without some greenhouse gas the Earth would be a ball of ice.
These forces are called "forcings" because they force changes in the global average temperature.
Looking at the past gives us insight into how our climate responds to such forcings. Using ice cores, for instance, we can work out past temperature changes, the level of solar activity, and the amount of greenhouse gases and volcanic dust in the atmosphere. Looking at many different periods and timescales including many thousands of years ago we've learned that when the Earth gains heat, glaciers and sea ice melt resulting in a positive feedbacks that amplify the warming. There are other positive feedbacks as well and this is why the planet has experienced such dramatic changes in temperature in the past.
In summary the past reveals our climate is highly sensitive to small changes in heat.
What does that mean for today? Over the past 150 years greenhouse gas levels have increased 40 percent mainly from burning of fossil fuels. This additional "forcing" is warming the planet more than it has in thousands of years. From Earth's history, we know that positive feedbacks will amplify this additional warming.
The Earth's climate has changed in the past and ice cores and other measures tell us why. Based on this knowledge, and other types of evidence we know the human emissions of greenhouse gases are warming the climate.
Last updated on 19 March 2013 by Stephen Leahy. View Archives
Normally, cosmic rays strike the oceans, increasing water-vapor in the atmosphere, and thus causing it to absorb more sunlight and warm slightly; but when solar-plasma ejection reduces, then the earth's water-vapor increases.
And as your site says, solar activity has decreased. This means that the Earth is being subjected to greater cosmic winds, and this explains the increased water-vapor and temperatures.
http://en.wikipedia.org/wiki/Pleistocene
yet the climate history is telling us that there were some severe spikes and troughs during that period.
http://en.wikipedia.org/wiki/Paleoclimatology
Is the current increase in global warming greater than those experienced during Pleistocene periods? Can you provide me with a peer-reviewed paper that would help me to combat this denialist rubbish.
In contrast, humans did not invent agriculture, cities, or civilization until the Holocene. There is a reason for that based in climate. During the Pleistocene climate was very variable over short time spans, with variations in temperature of up to half a degree C occurring in the space of a few hundred years, a condition likely to be inimical to agriculture. And certainly there is much in the potential consequences that will make agriculture much more difficult.
So the question for your denier friend is, does he want all 7 billion of us to go back to being hunter gatherers? And how many of us does he think would survive if we did? Because todate, only Holocene conditions have proved capable of supporting agriculture, and we are rapidly leaving those conditions.
This is always a sobering graphic to ponder. Two degrees C on a global average is a lot - especially if it occurs quickly.
Just be sure to note the non-linear time scale.
Here's the stock version.
--source
I plotted Vostok temperature anomalies along with the Moberg et al 2005 reconstruction's low frequency (LF) component, a smoothed version (LOESS) and GISS temps:
The time scale is calendar year rather than 'years BP.' So the jump up at circa 8000 BP appears at -6000 on the bottom graph. It certainly looks like 8000 years of relatively slow, small temperature variation is over. Anyone who says 'the modern warming is nothing new' clearly doesn't understand the concept of 'rate of change.'
Exit Holocene, enter Anthropocene.
Thank you for the previous graphs.
"The Biggest Control Knob: Carbon dioxide in Earth's climate history"
He's a really engaging speaker too, so this is well worth your time to watch and listen!
Yes, correct. As I understand it, CO2 comprises 0.057% of the Earth's total volume of atmospheric gases, so why all the hoopla about CO2? Presumably industrial CO2 output is a fraction of this tiny fraction (correct me if I'm wrong about this), so even if the atmosphere of the Earth is extremely sensitive to changes in overall composition it cannot be said with the certainty with which it is said that an increase as large as a 'doubling' of CO2 will have 'catastrophic consequences' (as so many in the media would like us to believe).
'However, our climate has feedbacks, both positive and negative. The strongest positive feedback is water vapour.'
Yes, water vapour, we must not forget about that, and yet it is hardly (if ever) mentioned in, for example, the popular press. Why not?
'There are also negative feedbacks - more water vapour causes more clouds which can have both a cooling and warming effect.'
In other words, we just don't know. The truth of the matter is that our atmosphere is such a highly complex and (inherently, over the long term) unpredictable system that we really, in spite of how much progress we have apparently made over the years towards understanding it, know next to nothing about it. Why are the words, 'I don't know' so difficult to utter?
I'll answer one part. You claim CO2 is a tiny fraction of the atmosphere. True. However, about 96-99% of the atmosphere is O2, N2, and Ar. These gases do not absorb/emit radiation in the thermal infrared range, the range within which the sun-warmed Earth emits. If nothing in the atmosphere prevents thermal radiation from escaping Earth, then the Earth should be about 33K cooler than it is. Fortunately, much of the remaining 1% of the atmosphere is composed of gases that do, in fact, absorb/emit within the thermal infrared range. Those gases intercept outgoing thermal radiation, and those gases then emit or conduct the energy in random directions (effectively half up/half down). Increasing the concentration of those gases effectively increases the energy temporarily stored in the system. Energy in temporarily does not equal energy out. The system warms.
As for CO2 vs. H2O as a greenhouse gas, see Lacis et al. (2011).
'Peter, correct yourself. The answers to these questions are all over this website. Read a little before you make claims with the kind of tone that suggests you have access to the absolute Truth (and gosh aren't we all a bunch of idiots).' - DSL
(-snip-). I never claimed to be the bearer of 'absolute truth'; don't quote what I did not write.
[DB] Please refer to this site's Comment Policy before lodging charges of ad hominem (snipped above). The link is adjacent to the comment box.
Further, this site is devoted to advancing the understanding of climate science and exposing the myths and skeptic memes commonly found about it. As such, many thousands of threads and blog posts exist here, all with links to the primary, peer-reviewed literature.
As such, if you differ with the commentary found in a blog post, it is then incumbent upon you to provide a link to the primary, peer-reviewed literature which supports your position. It is insufficient to merely offer up unsubstantiated assertions which run counter to the accepted literature.
Lastly, it is presumed that when placing comments on comment threads here that you will have already read the OP and the previous comments made prior to yours. In many threads, much clarification is given in the comments threads that often subsumes and obviates the need to place a comment or question covering something already asked.
Using a scale of 0 to 10, with 0 being “know absolutely nothing” and 10 being “know absolutely everything”, how do you rate the scientific understanding of the Earth’s climate system?
When you ask a basic question about the relative strength of water vapor and CO2, and then you make a broad claim about what climate science doesn't understand, your broad claim can't be taken seriously.
Statements that you made are considerably at odds with knowledge of all that litterature, hence the reactions you got.
It isn't the case.
A simple Google News search proves that this 'fact' is fiction.
So the real question is... why do you believe things which are plainly untrue? Did you never bother to check?
It purports to show that despite CO2 levels which were often very much higher than at present, temperatures on the planet stabilised around 22C for most of the planet's geological history, with only three 'relatively' short periods, including the present, when temperatures dropped to current levels.
The table included on this site is entitled:
"Global Temperature and Atmospheric CO2 over Geologic Time".
It has a note following saying:
"Late Carboniferous to Early Permian time (315 mya -- 270 mya) is the only time period in the last 600 million years when both atmospheric CO2 and temperatures were as low as they are today (Quaternary Period )".
The table is allegedly sourced as follows:
" Temperature after C.R. Scotese
http://www.scotese.com/climate.htm
CO2 after R.A. Berner, 2001 (GEOCARB III) "
Please don't ask me to study every thread on every page to find out for myself. That would be a bit like saying no-one should make even an implied comment on a subject unless they know every little detail.
From: http://www.geocraft.com/WVFossils/Carboniferous_climate.html
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Similarities with our Present World
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Average global temperatures in the Early Carboniferous Period were hot- approximately 20° C (68° F). However, cooling during the Middle Carboniferous reduced average global temperatures to about 12° C (54° F). As shown on the chart below, this is comparable to the average global temperature on Earth today!
Similarly, atmospheric concentrations of carbon dioxide (CO2) in the Early Carboniferous Period were approximately 1500 ppm (parts per million), but by the Middle Carboniferous had declined to about 350 ppm -- comparable to average CO2 concentrations today!
Earth's atmosphere today contains about 380 ppm CO2 (0.038%). Compared to former geologic times, our present atmosphere, like the Late Carboniferous atmosphere, is CO2- impoverished! In the last 600 million years of Earth's history only the Carboniferous Period and our present age, the Quaternary Period, have witnessed CO2 levels less than 400 ppm.
Global Temperature and Atmospheric CO2 over Geologic Time
Late Carboniferous to Early Permian time (315 mya -- 270 mya) is the only time period in the last 600 million years when both atmospheric CO2 and temperatures were as low as they are today (Quaternary Period ).
Temperature after C.R. Scotese http://www.scotese.com/climate.htm
CO2 after R.A. Berner, 2001 (GEOCARB III)
Compare Oxygen (O2) concentrations.
See an estimate of CO2 concentrations over the past 15,000 years, based on plant stomata.
There has historically been much more CO2 in our atmosphere than exists today. For example, during the Jurassic Period (200 mya), average CO2 concentrations were about 1800 ppm or about 4.7 times higher than today. The highest concentrations of CO2 during all of the Paleozoic Era occurred during the Cambrian Period, nearly 7000 ppm -- about 18 times higher than today.
The Carboniferous Period and the Ordovician Period were the only geological periods during the Paleozoic Era when global temperatures were as low as they are today. To the consternation of global warming proponents, the Late Ordovician Period was also an Ice Age while at the same time CO2 concentrations then were nearly 12 times higher than today-- 4400 ppm. According to greenhouse theory, Earth should have been exceedingly hot. Instead, global temperatures were no warmer than today. Clearly, other factors besides atmospheric carbon influence earth temperatures and global warming.
You need to be very careful comparing much earlier times to today because physics tells us that solar output was much less. In fact, the prediction by physics that the sun was much cooler before yet the geologic evidence showed liquid water on Earth was known as the "Faint Young Sun Paradox" which is resolved precisely by noting that CO2 levels were higher then. In other words, the Earth's temperature is a consequence of all forcings acting on it, and if the solar irradiance is less then higher levels of CO2 are required to maintain temperatures similar to today.
The next question is what happy coincidence was it that caused the Earth to always seem to gravitate towards a certain range of temperatures, rather than e.g. stay stuck in a snowball Earth forever or boil away the oceans? Why were CO2 levels just the right amount higher then to maintain liquid water on Earth? The explanation is absolutely fascinating to me, and explained exceptionally well by Richard Alley in this thoroughly entertaining talk.
Essentially, CO2 acts like a thermostat, automatically adjusting its levels to maintain "nice" conditions on Earth over geologic timescales. When temperatures are too low, ice sheets form, covering the rock -- the same rock that normally CO2 would react with to form carbonates. Since the rock is covered by ice, and CO2 is emitted by volcanos, CO2 levels rise until the greenhouse effect is strong enough to melt the ice, expose the rock, and start reacting with the rock like crazy, bringing CO2 levels down again.
Conversely, if CO2 levels are too high, the rate of rock weathering increases because it is a temperature-dependent reaction. Since the injection of CO2 by volcanos is roughly constant over long periods of time but the removal of CO2 by rock weathering increases with temperature, this acts to bring CO2 levels down and therefore lowers the temperature.
This means that our current massive increase in CO2 will ultimately be corrected by the system but unfortunately it operates on long timescales (compared to what's important for humans) so it doesn't help us with our current problem.
Anyway, watch the video because Richard Alley explains it in much more detail and more entertainingly than I could!
Of course, climate science has always said that, which means your comment "According to greenhouse theory, Earth should have been exceedingly hot" is not correct because "greenhouse theory" is precisely what explains why the temperatures were what they were then despite the fainter sun.
The reason for the focus on CO2 today (and to a lesser extent, other greenhouse gasses) is because they are the main factor influencing the change in Earth temperatures in the recent past. If you look at the official explanation for the early 20th century warming you'll see that much of that is put down to an increase in solar irradiance at that time. If there had been a further increase in solar irradiance in the last 50 years then the temperatures would be even higher and the IPCC reports would have apportioned a greater share of the recent temperature rise to that increase. The fact is, however, that over the last 50 years or so it just happens to have been CO2 that is responsible and, luckily, this is one forcing that we can do something about because it was us that lead to that increase in forcing -- without our CO2 emissions the temperature would have cooled slightly over the last 50 years.
An excellent explanation.
That said, I would be careful in attributing too much of Kiwi Bill's comment as his own. As he notes, he is extracting a commentary from a site (in this case, geocraft) and unless I am mistaken, everything after the line "From: (website link)" is from geocraft.
(Correct me if I am wrong, Kiwi Bill.)
You are right, initially I took the large gap before the last two paragraphs as a "quote delimiter" but afterwards it occurred to me that it might still be part of the quote and checking the page at the URL given confirms this. Sorry Bill.
Looking at what was written on that page, someone has clearly gone to a lot of effort to put together an argument that a little more effort on research would have told them was attacking a strawman. Even a cursory examination of the IPCC reports shows that mainstream science is well aware that "other factors besides atmospheric carbon influence earth temperatures and global warming" because it even quantifies those other factors in the attribution analysis!
That mistake then leads to the erroneous conclusion that all that's required to disprove AGW is to show that other factors must have also influenced climate in the past. The underlying logic is the same as "Lightning has caused fires long before man came along, therefore arson doesn't exist". Or, "murder doesn't exist because people have died of natural causes in the past", used by the defence in a murder trial where the accused was seen by 97 witnesses standing over the body of the victim with a bloody knife in his hand shouting "I'm glad I killed the bastard!". (Apologies to BlackAdder...)
(Three other witnesses aren't sure what they saw and even disagree with each other on what happened, but all agree it couldn't have been murder because that would require the state to raise taxes to employ a police force and one objects strenuously to the 97 others being so certain of what they witnessed.)
Doug H:
If you liked the talk, be sure to check out Ring of Fire. :-) It's hard to reconcile the reality of a funny, geeky climate scientist with the portrayal of them by commentors on sites like WUWT and Climate, Etc.
Touché.
Completely off-topic for this post, but related to the subject of Richard Alley's video:
I recently came across research that showed that some subducting plates may make it all the way down to the bottom of the mantle, literally scraping along and piling up on the core, thousands of km down, because rock is such a poor conductor of heat that they take a really long time to melt. I found this image of plates plunging deep within the earth to be quite fascinating, although I can't remember where I read it now. I just did a quick search and turned up this paper:
http://www.es.ucsc.edu/~ahutko/Publications/HLGR_Nature_2006.pdf
Look at figure 4 in particular.
As Richard Alley's song indicates, and this page confirms, the volcanoes above subduction zones are not actually emitting the melted plate (as I had assumed) but rather magma that has melted due to the water being carried down by the melting plate.
also its very fatalistic, you can make all this effort and then a solar comet is just round the corner at any given moment/ like in the plastacene era. Whats the point of all the scaremongering.
Think of the children guys.
What's the point of all the scare-mongering? Think of the children. You clearly are not. In Europe, the Little Ice Age represented a .5C-.8C drop in temp (from the Medieval Climate Anomaly). It was not pleasant for the children of Europe. Rapid climate change is never pleasant for children, because it usually puts a strain on food supply.
Why, you might wonder, did humans evolve agricultural civilization over the past 10k years instead of some other 10k year period? It's not like we haven't been smart enough. Indeed, a recent study concluded that we've become worse at problem solving over the last 10k years. So what was it? Try climate stability. The Holocene has been remarkably stable, as interglacials go. Human cultural memory, in fact, assumes a stable climate. There are no representations of persistent instability of the type that occurred during glacial periods and previous interglacials. We assume a stable climate. We have trouble imagining anything else. Even when we imagine it--with the help of science even--it's still so unreal that we can't imagine the full range of everyday consequences. Writers have tried.
We're going to get persistent instability for quite a while, dan. If we de-fund education, then we de-fund the means of thinking through the persistent change. You perhaps imagine a world where we drop back and rely on conventional wisdom with regards to the weather and agriculture. No. Weather is changing, and it is not changing from one regime to another. It is persistent change. All systems are changing: climate is everywhere. If you de-fund education, you blind the world just as it is walking across a period that, metaphorically, is the top surface of a glacier.
Of course, we may be blind already, since the "brains" of the world, the political guidance, do not believe their "eyes."
Oh, and dan, imagine living your life according to the comet theory: at any point, a stray bullet could come through the window and kill you. Why do anything? Why post your comment?
Hunter gatherers live in complete harmony with their environment, taking only what they need. Not like modern capitalsitic practice of over supply of mcdonalds beef burgers.whats more, recreation time lead to crackpot theories of gods and the like and more recently the splintered sciences hypotheses. what are they all observing their own little fragmented view of inconsequentiality. Its like in my city, christchurch which had an earthquake. the scientists can only study the after effects, and they get funding for doing that? unbelievable.
whereas we had a moon man who studies the cycles of the supermoons and he actually predicted a big one was coming, the scientific community was upset about it but why can't the moon effect things. last time i heard its the only reason earth is inhabitable due to axis for seasons to be temperate.
people cant see the wood for the trees. theyre observing things but understanding little.
media is a sensationalist scaremongering thoughtless behemouth.start a fire in your backyard and reconnect with the primitive beast.
Back to reality. Physics says that the moon's effects are insufficient to drive large geophysical events, though you're right that we should be grateful to the Moon for stabilising Earth's axial tilt. But crackpots like Ken Ring prey on the superstitious and gullible to garner a little fame for themselves. Don't fall for the astrologers! Real-world geophysical events are not controlled by the Moon, but by much larger forces - motions, stresses and sources of heat within the Earth.
And don't be afraid when the Moon is a wee bit bigger in the sky due to entirely normal and predictable occurrences of lunar perigee. One happened on 14th November during the total eclipse - it was the reason the Moon was big enough to cover the Sun for a beautiful, utterly predictable event. Another will happen in about nine days time, when the moon will be an unspectacular waning crescent in the dawn sky. In fact, 12 have come and gone this year! About once a year, the media gets all excited because perigee roughly coincides with a Full Moon, leading to the so-called "supermoon" (really, nothing special, though some decent spring tides). Do yourself a favour, dan, and ignore the astrologers like New Zealands woeful Moon Man.
I disagree that ag society brought wars of territory and economy. I argue that climate stability brought those features. A long, warm, stable climate allowed territorial expansion and population growth. Eventually, h-g groups would have started to bump into each other, as they undoubtedly did during the glacial periods. Ag culture simply speeded up the process. Ag culture also allows the development of science, which gives us the chance--the chance--to become responsible about what happens next.
dan: "start a fire in your backyard and reconnect with the primitive beast."
Ok, but later on in the evening I'll come back to the internet. The more we disconnect with each other, the more willing we are to cause others pain and misery. If science and then engineering can force us to look into each others' eyes while we have our fingers on triggers (literal or metaphorical), then I'm all for it. If seven billion people go primitive right now, six billion die within two years.
And yes, differences between Perigee and Apogee are irrelevant in geophysical terms, though not for oceanic tides.
Consequently I believe skywatcher's claim withstands scrutiny.
'....It is obviously true that past climate change was caused by natural forcings. However, to argue that this means we can’t cause climate change is like arguing that humans can’t start bushfires because in the past they’ve happened naturally...' is just another absurd comparision.
Comparing a billions of years old eco system and it's natural forcings over eons, to e.g. two neanderthals rubbing two sticks together 10,000 years ago to start a fire, and then accidently starting a bush fire, (proving that even neanderthals had the ability to change the climate!) demonstrates (-snip-).
pcrudy... It's actually a very apt comparison. It's shown over and over in published research that CO2 is the "Biggest Control Knob" (as Dr Richard Alley puts it) for global climate change.
Essentially, what humans are doing is taking that knob, that naturally modulates, and we're turning it rapidly in the warming direction. So, saying that natural climate change precludes humans being able to change climate is fundamentally wrong. And that is the point of the statement.
pcrudy:
The comparison is quite accurate. Arguing that humans can't drive climate change now because humans didn't drive past climate change - in the face of basic physics, backed by empirical evidence, that they can and indeed are - is logically equivalent to arguing that humans can't cause brush fires because they didn't in the past.
The scale of the behaviour being argued is not pertinent.
Another aspect of the "climate has changed before" argument, not covered off in the current answer, is the implication that current climate change should not be considered alarming. "It's changed before, and yet here we are" may be a fair summary of this version.
Is it worth adding some relevant discussion and cross-filing the argument under both the "It's not us" and "It's not bad" taxonomies?
The main responses seem to me to be that a) deep past climate changes were not much fun for living things at the time, being associated with mass extinctions and great upheaval; b) human societies and economies are adapted to the climate they developed in, and so even changes within the range of natural changes of the distant past would be very disruptive; and c) humans now use a very high proportion of potential quality farmland, affordable freshwater and so on to accommodate a large population with high (for many) or rising (for many) living standards; there is not much safety margin to prevent a loss of living standards if climate change erodes availability of some of the resources we depend on.
What was wrong in what Richard Lindzen wrote?
Mark @345 - there's nothing directly wrong with 'the skeptic argument' as articulated by Lindzen here. It's the implication of the statement where the problem lies. Saying 'climate has changed naturally in the past' is like saying 'humans breathe oxygen'. No duh. Everybody knows that. So what's the point in saying it? The answer to that question is pretty clear.
So the "#1 global warming myth" is not really a myth at all...?
Mark, "the climate has changed" before is mostly used to imply that humans arent responsible for current warming and/or that past changes are unforced. As a skeptic argument, it is framed as an excuse to do nothing. In the source where the quote came from, Lindzen tries to touch both bases, along with an a priori assumption that climate sensitivity is low. He has been trying to find some plausible reason for low sensitivity without much success so far. If you want to get down to real myths, then I guess you have to look at what logical step follows from "climate has changed before" but for many, this somehow seems to be enough.
No. There's nothing wrong with the information itself. The myth occurs when the information is voiced--made public. I'd bet you that in 99.99% of the cases in which those facts are strung together and published, the person doing the stringing is attempting to make an implied argument that since climate has changed before without rapid accumulation of atmospheric CO2, and therefore the current climate change is not the result of human CO2 emissions. I've engaged with at least 400-500 people on comment streams using this very implied argument.
So the answer to your first question is "What's wrong is that Lindzen actually wrote it."
In other words, Lindzen thinks you're stupid or at the very least simply ignorant, and willingly so. If you said to him "Duh! What's your point?" he'd probably bluster a little and then show you some really cool graphs.