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anthropogenic
global warming,
and ocean acidity

 

 

 

a briefing document

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click to see all the indexanthropogenic global warming, and ocean acidity is one in a series of briefing documents investigating the indicators, science, analysis and argument surrounding global warming.
One of a grouping of documents on global concerns at abelard.org.
on energy on global warming
On housing and making living systems ecological
sustainable futures briefing documents
Tectonics: tectonic plates - floating on the surface of a cauldron
click to see all the indexIndex
butterfly wings
flat earthers
the case against the accused
looking at the evidence
present road transport highest climate forcer, industry lowest - allegedly
ice and sediment cores
other considerations
february 2007 UN IPCC report 4 part 1 - links
medieval warming, the atlantic conveyor and “the maunder minimum”
explanatory notes on global temperature variation graphs
cloud effects
on paleoclimate
atmospheric CO2
milankovitch cycles
tectonic plates
variations in sun energy output
ocean acidity
table: atmospheric carbon dioxide
bibliography and brief reviews
end notes
 


 



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butterfly wings

Humans love patterns. They seek to simplify the world, which allows them to manage without doing too much thinking or counting. Their simple machines are manufactured to go round and round and round on fixed tracks, like the motor in a car. Humans have tried to apply simple models to the universe in order to simplify, thus the sun goes around the Earth in 365 days. But, of course, it doesn’t, it goes around the sun in 365¼ days and a little bit, and a little bit of that. And then, of course, that timing varies ever so slightly over the millennia; and that little bit of variation starts to mount up over a billion years.

Then, as humans learn more, they learn about variations within variations, as you will see in the Milankovitch cycles section. They look at a few ice ages and think maybe the Milankovitch cycles caused them, so for a century or two they struggle valiantly to make these two things fit together. Every time, a bit more information makes the fit not quite so tidy. Month by month and year by year, our understanding of ice age data increases. The more data we gather, the more untidy the real world looks.

Very small changes in the path of a Mars shot will expand to millions of miles by the time rocket reaches its destination. Very tiny (accidental) differences to where a seed falls in a forest can determine whether the seed becomes a 200-foot giant, or is eaten by a squirrel. Small differences can determine whether a species survives and thrives, or is never heard of again. Small changes can determine whether a tornado gathers and accumulates, finding a path to New Orleans, or whether it peters out in mid-ocean, or takes a slightly different route to a less annoying landfall. Neither do we know much at all what starts or stops an ‘ice age’. Very possibly some trivial or accidental process goes into positive feedback, this leaves plenty of work for the future.

We still struggle to forecast weather a few days ahead, let alone understand a world of hundreds of thousands of years ago - or billions of years - from a few ice or sediment core samples. This is the real world, and the real world of advancing modern science. It is not a world of certainties or a few easy patterns. But despite all these uncertainties, we do expect the sun to rise in the morning and we do believe that we have a reasonable grasp on anthropogenic global warming. Do not become confused between areas of knowledge where we are not completely blind and areas where much that is written is bordering on hubris and speculation.

Human knowledge comes on a scale of knowing rather a lot about rather a little, to knowing very little about rather a lot. It is sane to keep constant awareness of whether you are in the shallow end of a heated swimming pool, or in the middle of the North Atlantic during a raging storm.

flat earthers

Flat earthers make up all sorts of speculative reasons why “there is no anthropomorphic global warming” [AGW]. Many of these ‘reasons’ are based on poorly grasped comments from sloppy fossil media and web sources. The purpose of this subsidiary briefing document is to provide the means for you to follow up these specious claims in more detail, should you wish. There is a great mass of discussion in books and appropriate journals, and increasingly upon the Net.

In a sense, this subsidiary document is a review of the elements that are not primarily emphasised as being relevant to modern anthropogenic global warming concerns!

There is most definitely anthropogenic warming.

  • Empirical statement 1: Greenhouse gases [GHGs] cause global warming.
  • Empirical statement 2: Humans are increasing GHGs considerably.

But we still do not know many of the details. While the consensus is strongly that AGW is a reality, it should be kept in mind that a limited amount of global warming may prove to be a net benefit.

So, moonbats write all sorts of nonsense attempting to ‘be different’ and suggest all manner of mechanisms whereby AGW is not happening,
or it is not significant,
or it’s not faaaair,
or it wasn’t invented here.

Here is an example from the Cato Institute, which is often dubiously supported by all sorts of industrial interests that would rather not change (or pay for) their filthy externalisation of costs.

But there is still that awkward problem - reality!!

There is real global warming with considerable empiric evidence -

the world is getting hotter.

So the moonbats must make all manner of claims that it is really about the sun’s output changing or 101 other excuse-me’s.

Now, every adequate scientist knows full well that, with complicated systems, establishing causal links is no cake-walk.

But when sane scientists see two phenomena tracking each other, they tend to try to work out if there is a linkage.

Meanwhile special interests, for instance the cigarette industry, struggle for decades to dismiss the ever-growing links between illnesses and tobacco.

Or the media industry tries to deny a link between violence on film and violence in the playground.

Or the filthy fossil fuel companies struggle to dismiss any links between their filth and global warming.

But, back to that pesky reality again. The filth also kills millions right now.

Meanwhile, the West is increasingly dependent on a backward area of the world for energy, an area which is also a source of considerable current aggravation.

Among other lies spread by the nay-sayers is the claim that global warming scientists claim more than they know. This is a good way to pretend that there really is ‘no problem’.

But, in fact, serious climate scientists make no such claims.click to return to the index

 

the case against the accused

It has taken decades to bring responsibility home to the tobacco drug pushers, and it ain’t over yet.

We have still a way to go before bringing responsibility home to the media corporations.

How long before sufficient causal evidence is deemed enough to force responsibility on the filthy dangerous fossil fuel industry?

Meanwhile, back in the real world again, planetary temperatures are rising.
Meanwhile, back in the real world, we do know some about the effects of GHGs.
Meanwhile, back in the real world, we do know we are adding considerably to such gases.

But of course, we can’t really be certainly sure, can we? Maybe it’s all to do with university grants, or mickey mouse!

    While the general consensus is that global warming is occurring and is in great part caused by human activity [anthropogenic], anyone who tells you that global warming is easily understood and proven (or disproven), followed by some trite reason, simply does not understand the situation.

    “The most prevalent reasonably scientific question about current climate changes is ‘how do we know that this isn’t natural variability?’.
    [The best answer given was: ]”

    • “[...] the causes of ‘natural variability’ - whether the sun, volcanoes or ocean changes - should be detectable (but haven’t been),

    • and that the anthropogenic ‘hypothesis’ should have consequences that are also detectable (which have been).

    • Add in the modelling studies which indicate that current conditions can’t be explained without including greenhouse gases and you have a pretty solid case that what is happening is in large part anthropogenic.”

Quoted, with enhancements, from realclimate.org. The realclimate.org site is very useful, and well worth visiting.


looking at the evidence

“Natural and anthropogenic substances and processes that alter the Earth's energy budget are drivers of climate change.
Radiative forcing (RF) quantifies the change in energy fluxes caused by changes in these drivers for 2011 relative to 1750, unless otherwise indicated.
Positive RF leads to surface warming, negative RF leads to surface cooling.” [Quoted from IPCC Fifth Assessment Report 2013, p.8]

radiativz forcing factors 2013
From Working Group I Contribution to the IPCC Fifth Assessment Report Climate Change 2013:
The Physical Science Basis Summary for Policymakers [.pdf]

  • Greenhouses gases are by far the most important factor in global warming. This is also the factor for which we have, by far, the highest understanding. See LOSU [Level Of Scientific Understanding] column in diagram above.

  • The second most important is ozone (O3). It is also the second-best understood factor.

  • Next is a group of ‘aerosols’. As a group, these are well understood to have a cooling effect. The cooling effects of each, as components, is not well understood but there is strong empiric evidence of the group effect. See also raising more questions than it answers - on brown clouds over asia.

  • That leaves a couple of factors whose effects are not well understood, but those effects are thought to be minor. These are aviation-induced and solar effects.

present road transport highest climate forcer, industry lowest - allegedly

“The new analysis shows that emissions from the power, biomass burning, and industrial sectors of the economy promote aerosol-cloud interactions that exert a powerful cooling effect, while on-road transportation and household biofuels exacerbate cloud-related warming.”

But this is expected to change:

“The differences are because the impacts of greenhouse gases accumulate and intensify over time, and because they persist in the atmosphere for such long periods," said Unger. "In contrast, aerosols rain out after a few days and can only have a short-term impact." ”

See chart:

Road transport radiative forcing; Image: physorg.com

Error: Thread 1470 does not exist.

Associated notes:

  • Sun energy increases by approximately 5% every billion years.
  • Pre-industrial carbon levels historically were on the very low side.
  • Carbon is absorbed by lowering of ocean temperatures.
  • Carbon was absorbed and buried during the carboniferous era, forming fossil fuels.
  • Fairly small changes in energy balance can push the climate towards ice ages, or towards warming.
  • Tectonic movements can move land masses to the poles, which in turn can increase cooling/ice formation build-up and changing oceanic currents. The land balances are presently toward the poles.
  • Upthrust land (by tectonic action) also allows ice formation.
  • Less land is exposed during warming periods as water levels rise.
  • Milankovich cycles and tectonic movement are regarded as long-term climate drivers. Short-term drivers include dust, as in the ‘year with no summer’ and positive feedback effecting albedo.
  • There are also large releases of methane from permafrost peat areas and from clathrates. As it decomposes, methane is a major contributor to increasing carbon dioxide in the atmosphere.

It remains that we do not know well how all these effects will pan out in the long-term regarding cloud cover and so on. However, we do still know the planet is warming, and we do still believe the main effect is identified.

Nobody sane denies that there are uncertainties, there are uncertainties in virtually all human endeavours. However, of the elements listed, the view is that GHGs have the greatest effect.

click to return to the index

pressing reasons for action

There are other pressing reasons for controlling fossil fuel filth. There are pressing reasons for reducing dependence. The probability/consensus is that the greenhouse gases are highly relevant.

And we have a batch of better alternatives. Why not just get on with improving the situation? Unless, of course, you are involved in the filthy fossil fuel industry.

The arguments for greenhouse gases are far from ‘weak’. They are the most understood effects by a long march.

Perhaps doubters are confusing the level of knowledge of GHG warming contributed to heavily by human activities, with the smaller uncertainties elsewhere.

ice and sediment coresIce core. Image credit: newscientist.com

Increasing quantities of ice-core samples are being obtained. The diagram to the right shows a composite.

The first ice cores were extracted in 1956 to 1957, with techniques that have been steadily advancing since then. Early cores only went back less than 100,000 years, which is less than one glaciation cycle. Ice cores now go back 10 to 20 times further, back to 750,000 years (Vostok). However, their latest cores have not been fully analysed back to the beginning.

Ice core samples provide historic data of the earth’s temperature and its atmospheric composition. There are also (interrupted) sediment core samples that go back as far as 200 million years. Earlier cores were about 3-400 metres long, and the latest are over three kms long. For more on dating.

The atmospheric load for both carbon and methane is now much higher than has been seen during the last 650,000 years, as determined through examining ice cores.

A major part of the analysis of ice cores is checking the 16O/18O ratio. This gives an estimate of how much water is tied up in ice at any time.

“As ocean water evaporates, preferentially more 16O is released, but in non-glacial times is returned almost immediately to the ocean as runoff from the land. In glacial times this excess 16O is stored in ice masses, leading to enrichment of 18O in the oceans.”[1]

According to the analyses, twenty thousand years ago, the sea-level is estimated as being 120 metres below the present sea-level. Today, the equivalent of another 80 metres is still being held in ice sheets, most of that being in the Antarctic.

 

other considerations

There is constant talk of a medieval cooling period and suggestions that this does not fit the overall data. Evidence has now been found - by looking at marine fossils in sediment cores - that that cooling was probably only local to Northern Europe and may be related to a weakening of the Atlantic Conveyor. It could even be argued that the growth of the industrial revolution has offset cooling.

marker at abelard.org

There was also, probably, some cooling in the three decades from 1950 to 1980. General acceptance is this was a cooling affect from dust/aerosols halted by multiple clean air acts in the West, when faced with deteriorating air quality (smogs).

marker at abelard.org

I have seen recent claims from probably unreliable sources that ice core analysis shows a lag of several hundred years between the warming or cooling, and the changes of carbon dioxide trapped in the ice. For the moment, I believe that this is an error in understanding among those making the claim. The general view, in the more academic sources, appears to be that the carbon dioxide and temperatures track each other very closely, so closely that no such distinction can yet be made.

However, ice is laid down and slowly compacts as, year by year, more snow is precipitated on the top of the ice sheet (or glacier). There are minute spaces between snowflakes and within the firn, prior to the mass being so compressed that air communication with the outside world ceases. This process can take several hundred to a thousand years. Thus the air (including the CO2) analysed in the ice can be several hundred years younger than the ice in which it is entrapped. My guess is that those making a claim concerning time lags are, in fact, confused by this anomaly.

marker at abelard.org

This excellent slide presentation [71-page .pdf file - 3.9 Mb] provides more detail on the general discussion than does this current briefing document, which focuses more on particular aspects. The .pdf document comes from one of the world’s premier weather research units.

marker at abelard.org

Warming and sea-level rises are projected to continue increasing for at least another century, due to present levels of anthropogenic greenhouse gases [AGHGs]. Warming is not expected to the same level all around the planet. While average temperatures are rising and expected to rise further, there may still be highly variant local temperatures that are not directly related to AGHGs.

“However, for various reasons, the exact timing and abruptness of the changes are difficult to ascertain in these records, and records of older abrupt changes are even less secure.”
[Quoted from pnas.org]

Keep this constantly in mind when you hear confident assertions and sound bites.J

Do you expect to find loss of ice?

“We actually know from people who have measured our stakes that we have already lost two to three meters of ice from the surface since 2000.

“To me, it's very telling that nothing is accumulating in today's world. If you look at the tropical region in general -- from the Andes to the Himalayas -- many of those glaciers will disappear within 50 years if current rates of mass loss continue. Unfortunately, people in surrounding villages depend on these ice fields for water resources.

“What do you plan to do, ultimately, with the data you've collected?

“My dream is ultimately to piece together a global map of past climate patterns. Right now we have piecemeal evidence reflecting different regional patterns -- we know that some areas are the warmest they've been in 40,000 years, while some are the warmest they've been in 6,000 years. I think it's safe to say that worldwide, the warming trends of today are more dramatic than they have been in at least 5,000 years -- but we must have a more comprehensive map to see how all these trends fit together.”
[Quoted from grist.org]

Here is a none-too-clear description of temperature measurement in ice-cores.
It is, however, recommended reading.

“Methane is of particular interest in studying abrupt changes. It was primarily "swamp gas" in preindustrial times and thus gives an indication of global wetland area (22). Methane destruction occurs globally, but sources may be localized. The residence time in the atmosphere is short enough that when methane sources are predominantly in the Northern Hemisphere, Greenland ice shows significantly higher methane concentrations than similar-age samples from the Antarctic; hence, changes in the concentration difference between Greenland and Antarctica record changes in the latitudinal distribution of methane sources.”

“The Greenland records show that climate changes have been very large, rapid, and widespread. Coolings were achieved in a series of steep ramps or steps and warmings in single steps. The more dramatic of the warmings have involved 8C warming (8, 25) and 2 increases in snow accumulation (9), several-fold or larger drops in wind-blown materials (17), and 50% increase in methane, indicating large changes in global wetland area (5, 24).

“For the best-characterized warming, the end of the Younger Dryas cold interval 11,500 years ago, the transition in many ice-core variables was achieved in three steps, each spanning 5 years and in total covering 40 years (26). However, most of the change occurred in the middle of these steps. The warming as recorded in gas isotopes occurred in decades or less (8). The most direct interpretation of the accumulation-rate record is that snowfall doubled over 3 years and nearly doubled in 1 year (9). Several records show enhanced variability near this.”
[Quoted from pnas.org]

Note: methane is adjudged to remain in the atmosphere for much less time than CO2, that is approximately 14 years against an ‘indeterminate’ time.

“[...] The more dramatic of the warmings have involved 8C warming and 2X increases in snow accumulation, several-fold or larger drops in windblown materials , and 50% increase in methane, indicating large changes in global wetland area. Between 80,000 and 20,000 yr BP, some 20 interstadial events are recorded. These so-called Dansgaard-Oeschger events lasted for about 500-2000 years and therefore cannot be explained by orbital forcing mechanisms. Instead, they are interpreted to reflect feedback mechanisms involving ice sheet/glacier fluctuations, variations in the ocean system and atmospheric circulation fluctuation." ... "The mechanisms of the [many and complex] relationships are poorly understood (7), and it is not known with any certainty which is the drag force of a climate change, especially when talking about an abrupt climate change as testified by the ice cores.”
[Quoted from www.hi.is - 5 page .pdf]

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click to return to the index

February 2007 UN IPCC report 4, part 1 - links
“Climate Change 2007”

An excellent summary [21 page pdf] released today, 2 February 2007. It summarises the current best estimates that were released on 1 February 2007. The summary is also available from here. This is the first part of fourth report in this series. These reports from the IPCC are the bible of current climate science concensus.

The effects that cause global warming will continue for centuries, even if stabilised.
From the summary:

“Warming of the climate system is now unequivocal [...]”

“The updated 100-year trend (1906-2005) of 0.74°C [0.56°C -0.92°C]. The numbers in the square brackets are the 90% confidence range. They are translated as, “there is a 5% possibility of higher or 5% possibility of lower values; that is, values outside the 90% range.”

“The linear trend over the last 50 years, of 0.13 °C per decade [90% confidence range: 0.1°C -0.16°C] is nearly twice the rate for the last 100 years.”

marker at abelard.org

“It also considers the results of new attribution studies that have evaluated whether observed changes are quantitatively consistent with the expected response to external forcings and inconsistent with alternative physically plausible explanations.”

“Increasing atmospheric carbon dioxide concentrations lead to increasing acidification of the ocean. Projections based on SRES scenarios give reductions in average global surface ocean pH17 of between 0.14 and 0.35 units over the 21st century, adding to the present decrease of 0.1 units since pre-industrial times.”

Based on current model simulations, it is very likely that the meridional overturning circulation (MOC) of the Atlantic Ocean will slow down during the 21st century. The multi-model average reduction by 2100 is 25% (range from zero to about 50%) for SRES emission scenario A1B. Temperatures in the Atlantic region are projected to increase despite such changes due to the much larger warming associated with projected increases of greenhouse gases. It is very unlikely that the MOC will undergo a large abrupt transition during the 21st century. Longer-term changes in the MOC cannot be assessed with confidence.”

“Contraction of the Greenland ice sheet is projected to continue to contribute to sea level rise after 2100. Current models suggest ice mass losses increase with temperature more rapidly than gains due to precipitation and that the surface mass balance becomes negative at a global average warming (relative to pre-industrial values) in excess of 1.9 to 4.6°C. [A major element in this uncertainty is feedback effects of cloud cover.] If a negative surface mass balance were sustained for millennia, that would lead to virtually complete elimination of the Greenland ice sheet and a resulting contribution to sea level rise of about 7 m. The corresponding future temperatures in Greenland are comparable to those inferred for the last interglacial period 125,000 years ago, when paleoclimatic information suggests reductions of polar land ice extent and 4 to 6 m of sea level rise.”

Here is the front page of the Intergovernmental Panel on Climate Change [IPCC] site.

The IPCC site is chaotic. abelard.org has managed to extract (eventually) the following information on the three previous Assessment Reports:

  • IPCC Assessment Report 1, August 1990, “Climate Change”
    [This report was published in three volumes, further information at the end of the linked page.]
  • IPCC Assessment Report 2, December 1995, “Climate Change 1995” [73-page .pdf]
  • IPCC Assessment Report 3, September 2001, “Climate Change 2001”
    [This report is widely referred to as TAR - Third Assessment Report. It is in four parts, our link goes to a page giving links to on-line and to .pdf versions. The first part, The Scientific Basis, is referred to most widely.]

Information on IPCC Assessment Report 4, part 2.

The full IPCC4 report is now available. It is in four parts [our links go to IPCC links pages to the sections of each part]:
Climate Change 2007: Synthesis Report
WGI: the Physical Science Basis
WGII: Impacts, Adaptation and Vulnerability
WGIII: Mitigation of Climate Change

Working Group I Contribution to the IPCC Fifth Assessment Report Climate Change 2013: The Physical Science Basis Summary for Policymakers


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medieval warming, the atlantic conveyor and “the maunder minimum”

For longer term effects, see past ice ages and interglacials.

The Atlantic Conveyor (AC), the Gulf Stream, the meridional overturning circulation (MOC), North Atlantic thermohaline circulation (THC), and I believe some other fancy names, all apply to the same thing, one of the great ocean currents of the world. This current transports water from the Caribbean northwards to the Arctic ice. From the surface waters evaporation occurs. Thus, the water increases in salinity and, therefore in density. On freezing to Arctic ice, this leaves the remaining water even more salty and, therefore, more dense, and also colder. Consequently, the cold water sinks, thus drawing up more water from the south to replace the water that sank. This process acts like a giant conveyor belt, and is known as an overturning current. When it reaches the south of its journey, the water coming down from the north warms and rises. This rising water is known as an up-welling current. The up-welling current carries nutrients and is one of the processes by which fisheries and productivity are driven around the world’s oceans.

Global conveyor currents. Courtesy, UNO/IPCC

If the Atlantic Conveyor were to stop, Northern Europe would become, locally, considerably colder. The planet would not become colder (unless this resulted in the spread of ice fields and, therefore, an increased albedo), but the distribution of heat would change; probably with effects upon ocean productivity. There are fears that global warming could, in fact, slow or shut down the Atlantic Conveyor. See also ocean acidity.

Holocene temperature variations graph. Image credit:http://www.globalwarmingart.com
Image credit:globalwarmingart.com

As you can see from the graph above, temperatures have slowly trended downward since the end of the last glaciation (ice age). A few decades ago, when we knew less, there were growing fears of a new expansion of glaciation. It is possible that we may eventually, as we understand more, start to believe that at least a little global warming has come at just the right time!

1000 year temperature comparison. Image credit:http://www.globalwarmingart.com
Image credit:globalwarmingart.com

Let us now telescope in on the last thousand years of the first graph above (Holocene temperature variations), shown in this graph. Understand that what you are seeing is the downward global trend for the past thousand years, followed by a rather violent reversal of that trend. Meanwhile, one of the real world facts impressing itself on climate science is that, while global climate varies over different periods, the recent variation is both rapid and associated with a well-known probable cause. Note also that the slowing and reversal of the cooling trend corresponds with the growing use of fossil fuels.

The warmer, medieval period and the so-called ‘maunder minimum’ (or, ‘Little Ice Age’) in Europe are regarded as a local and relatively minor effects, related to the Atlantic Conveyor and sun variation.

“Shindell noted that the effects of this period of a dimmer Sun were concentrated more regionally than globally. "Global average temperature changes are small, approximately .5 to .7 degrees Fahrenheit (0.3-0.4C), but regional temperature changes are quite large." Shindell said that his climate model simulation shows the temperature changes occurring mostly because of a change in the Arctic Oscillation/North Atlantic Oscillation (AO/NAO).”

“The period of low solar activity in the middle ages led to atmospheric changes that seem to have brought on the Little Ice Age. However, we need to keep in mind that variations in solar output have had far less impact on the Earth's recent climate than human actions," Shindell said. "The biggest catalyst for climate change today are greenhouse gases," he added.” [Quoted from earthobservatory.nasa.gov]

Alongside this rather speculative linked article from NASA is a useful animation showing this effect (Animation of World - 2.2 MB MPEG).

explanatory notes on global temperature variation graphs

On the graphs just above, the various lines are the results of various different workers’ estimates. In such circumstances, one option is to average out the lot. The heavy black lines are such an averaging.

To follow the arguments well, really it is necessary to study statistics. Statistics is one of the most difficult studies of the human mind and is often poorly understood even by statisticians. Intelligence: misuse and abuse of statistics may help that unserstanding..

In statistics there is a phrase, ‘the law of large numbers’ this tends to mean that ‘errors’ will (may!) get lost in large data bases. That is, random errors ‘cancel out’.

One way of dealing with the problems where trends are uncertain is to do what is called a moving average. A moving average is deemed to iron out errors/variations. It is particularly useful if you have a regular variation, like with the 12 months of the year where seasons effect your data, for instance when looking at monthly sales in a shop.

So in summary, there are various ways and reasons to ‘smooth’ out data, as in cases of regularly varing data subject to ‘random’ perturbation. An apposite example is years of temperature data using different worker estimates. Note that ‘random’ is a word that needs much caution!

The point of leaving in the original time series (in those graphs) is to allow more able readers of data to have an idea of how uncertain the data is. Much of the weather data series are estimates based on ‘surrogates’, like tree ring data or ice core analysis. These are surrogates for temperature readings from ‘thermometers’. Otherwise to say, ‘it’ gets complicated.

The NASA animation linked above is of a local effect, that is in the North Atlantic and probably driven by the Atlantic Conveyor. It is vital to clarify the difference between global warming and local weather variations. Some ‘local’ weather variation have very large effects, for instance La Nina and Le Nino. The Nina effects switch quite often. The Atlantic Conveyor is much more stable, but is also capable of switching.

‘Global warming’ is just what it says on the packet. Global, a global average, and with the word ‘average’ we are back to statistics! And that is severe hard work and a lot of experience of reading numbers.

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cloud effects

These are poorly understood at present.
 
Related sections:
Global dimming
Albedo affect

To be developed.click to return to the index

marker at abelard.org

on paleoclimate

In this section, I will focus on the very long-term. You are liable to read about or hear people confusing the anthropomorphic global warming situation by reference to one or another of these long-term changes - atmospheric carbon dioxide, Milankovitch cycles, tectonic plates. One of the most pressing arguments in favour of the AGW analysis is that the change in global warming is happening so rapidly, and particularly the changes in greenhouses gases.

When this is pointed out, rather feeble references will often be made to positive feedback, which may hint at some weak plausibility. Meanwhile, we have the much more immediate and obvious link between greenhouse gases and actual warming. Blue-sky speculation on rather unconvincing ‘theories’ is, naturally, increasingly being discounted by the general scientific consensus.

atmospheric CO2

Excerpt from a excellent page on this subject, with several graphs, and from a site that looks interesting as well.

“For the past ten thousand years, however, the earth's temperature and atmospheric CO2 has been relatively stable - although temperatures have varied over a range of 4ºC (although some of this variation is probably an artifact due to inevitable measurement errors). The causes of these fluctuations are not known with certainty, but are likely to be due to combinations of variation in solar activity and periodic changes in ocean currents.”

“A record of temperature and atmospheric CO2 over the past 400,000 years is preserved in the Vostok Ice Core and is shown in the figure on the right. It can be seen that there have been a series of large fluctuations in temperature (the Ice Ages), accompanied by large changes in atmospheric CO2. It is thought that these large temperature fluctuations are triggered by Milankovitch cycles - variations in the earth's orbit that change the amount of energy from the sun that reaches us. However, on their own, these cycles are not enough to explain the changes in temperature. The full explanation seems to be that the small change in temperature caused by the changing orbit are amplified by natural processes on earth. These cause CO2 to be released from the oceans and the biosphere, causing an increased greenhouse effect.”

 

Milankovitch cycles
Milanovitch cycles involve variations in the earth’s orbit. These variations last tens of thousands of years and, therefore, have little effect in the short run. There are attempts to link these cycles with ice ages, but as yet these attempts are not regarded as highly convincing.

Keep in mind that Milanovitch cycles involve season changes due to the state of the Earth in its journey around the sun. They do not involve differences in the output energy of the sun.

There are three main cycles brought about by eccentricities in the orbit of the Earth around the sun. These cycles last

  • approximately 21,700 years (cycle due to precession),
  • approximately 41,000 years (cycle due to axial tilt),
  • and approximately 95,800 years (cycle due to orbital eccentricity or ellipsicity).

These cycles have not been reliably linked to long-term climate.

These differences are not thought to be great enough to do more than marginally alter the amount of energy reaching the earth from the sun. To claim any effect on earth climate, it is necessary to suggest feedback mechanisms such as, for instance, albedo changes from marginally extra snow fall.

Ellipsicity effects the differences of heat distribution between summer and winter. These differences range from around 6% at one part of the cycle to maybe 25% during the most elliptical phases. We are currently near to the part of least variation in the 95,800 years’ cycle. That is, the least variation between winter and summer.

Axial tilt is currently about half way between its extremes of its 41,000 year cycle. This effects the contrast between the severity of seasons. The part of the theory concerning axial tilt suggests that less tilt may increase snow cover.

Precession is the wobble that can be seen with a spinning gyroscope or top. This 21,700 year cycle moves the winter and summer peaks closer to or further from equilibrium. We are currently in the equilibrium part of the cycle.

Vostok tells us a story of mostly glaciation for the last 400,000 years, with short interglacial periods of up to 20,000 years, very roughly every 100,000 years. (This is part of the reason so many have tried to fit the Milankovitch data to weather.) The recent interglacial period has already lasted around 10,000 years. There was a dip starting around 700 years ago which appears to have started to reverse at about 1800 AD. In other words, we do not know quite why the weather swings over the eons, but we do suspect that we are due to go into another ice-age at any time.

This 100,000 years’ cycle has recently replaced a much shorter cycle, some claim that that earlier cycle was around 40,000 years.

[Note that the Moon also wobbles in its orbit, affecting the height of tides.]

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tectonic plates

The Earth is about 4.6 billion years old. Again, our knowledge of its history has been growing at a rapid and increasing rate for the last couple of hundred years. During that 4.6 billion years, the land areas of the Earth have moved around quite a bit, sometimes pushing land masses to a greater altitude, sometimes to the poles. Naturally, in these latter conditions snow can fall and accumulate, increasing the planetary albedo and generating positive feedback.

As the plates move around, the major currents of the ocean vary. These currents, like El-niño and the Atlantic Conveyor, transfer heat around and, consequently, strongly affect local climates. In the days of Pangea, obviously ocean currents were less complex. Presently two-thirds of global land mass is in the northern hemisphere and, therefore, variations in albedo are expected vary more in the northern hemisphere, thus the northern hemisphere is expected to dominate insolation-driven climate.

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variation in sun energy output

This is little understood as yet, as we have only just started going out into space, and developing sufficiently theory. A minor, eleven-year cycle, which changes the out put of the sun, has been identified in recent times, though it is unlikely to be a long-term trend. However, the difference in energy output is very small compared to the forcing theorised for greenhouse gases, and sun variation is not considered to be a major factor in climate change.

Incidentally, the core of the Earth is also heated by nuclear processes and, while these do contribute to planetary conditions, they are not expected to vary in a relevant manner.

To be developed.

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variation in sun energy output

This is little understood as yet, as we have only just started going out into space, and developing sufficiently theory. A minor, eleven-year cycle, which changes the out put of the sun, has been identified in recent times, though it is unlikely to be a long-term trend. However, the difference in energy output is very small compared to the forcing theorised for greenhouse gases, and sun variation is not considered to be a major factor in climate change.

Incidentally, the core of the Earth is also heated by nuclear processes and, while these do contribute to planetary conditions, they are not expected to vary in a relevant manner.

On very large timescales, the sun and the Earth are estimated to be about four and a half million years old, and the sun’s output is increasing approximately 10% every billion years. In a mere billion years, it is estimated that the Earth will become too hot for liquid water, this may be inconvenient should you live that long.

In about five billion years, the sun will move out of main sequence evolution into a red giant phase.

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ocean acidity

[Abstracted from currents.ucsc.edu]

[...] marine sediments were deposited during a period of extreme global warming 55 million years ago known as the Paleocene-Eocene Thermal Maximum (PETM).

During the PETM, average global temperatures increased by about 9 degrees Fahrenheit (5 degrees Celsius), and the fossil record shows dramatic changes during this time in plant and animal life, both on land and in the oceans.

4,000 billion tonnes of carbon are thought to have been released at that era. Only 250 billion tonnes are thought to have been added since the industrial revolution. If we consume all known reserves, the estimate is close to the 4500 billion tonnes level.

That is how long it took for ocean chemistry to recover from a massive input of carbon dioxide 55 million years ago, according to a study published this week in the journal Science.

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“ The total amount of fossil fuel carbon available to be burnt in the future (approximately 4000 giga-tonnes carbon [Gt C]) is similar to the amount estimated to have been released during the PETM, but the PETM release was much slower, and the surface ocean acidification presumably less as a consequence.”[Quoted from soes.soton.ac.uk]

The Paleocene-Eocene Thermal Maximum (PETM) was a period of extreme global warming, when temperatures rose by as much as 10 degrees in a relatively short time period. Sediment cores drilled out of ocean floors show an sharp change in ocean chemistry when the PETM began 55 million years ago. The following chemistry recovery took at least 80,000 years.

“Increasing atmospheric carbon dioxide concentrations lead to increasing acidification of the ocean. Projections based on SRES scenarios give reductions in average global surface ocean pH17 of between 0.14 and 0.35 units over the 21st century, adding to the present decrease of 0.1 units since pre-industrial times.”[Quoted from ucar.edu]

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“Acidification: It turns out that the sea, through gas exchange, soaks up over 40% of our annual CO2 emissions. (Without the oceans, we’d already be living the global-warming disaster scenarios currently predicted for the second half of the century.) Dissolved CO2 creates carbonic acid (H2CO3) - think teeth dissolving in Coca Cola. More carbonic acid means fewer free carbonate ions, which are a necessary building block of the calcium carbonate (CaCO3) in shells and coral. The bigger significance of this? Coral reefs harbor some of the world’s richest biodiversity; and 25% of all marine life has some part of its life cycle associated with coral. As far as shelled organisms go, it spells potential catastrophe for everything from minuscule zooplankton to lobster.”[Quoted from radioopensource.org]

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“Increasing acidity reduces the availability of calcium carbonate from the water - which the creatures rely on to produce their hard skeletons. Juvenile organisms could be most susceptible to these changes.

“Acidification may also directly affect the growth and reproduction rates of fish, as well as affecting the plankton populations which they rely on for food, with potentially disastrous consequences for marine food webs.

“In addition, nutrient concentrations in surface waters of high-latitude regions are likely to fall, subsurface waters become less oxygenated, and phytoplankton will experience increased exposure to sunlight.”
[Quoted from bbc.co.uk]

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"There is a depth in the ocean above which calcium carbonate shells don't dissolve, and below which they do," says Wallace. The findings suggest that the CO2 pumped into the oceans has pushed up this boundary by 400 m, compared to its level before the industrial age. And the researchers predict that it will be 700 m shallower by 2050 if CO2 emissions continue their fast growth. [Quoted from environment.newscientist.com]

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“Acidity is measured as pH, the negative logarithm to the base 10 of the concentration of hydrogen ion, H+. The scale of pH goes from 0 to 14, pH 7 is neutral, pH greater than 7 is alkaline and less than 7 acidic. The pH of the oceans is slightly alkaline at 8.0 to 8.2; and has dropped 0.1 unit since the industrial revolution. By the end of this century, it will become another 0.3-0.4 unit lower, representing a 100 to 150 percent increase in hydrogen ion concentration.

As pH drops, so does the concentration of carbonate, making it more difficult for marine organisms to form calcium carbonate. There is substantial experimental evidence indicating that calcification rates will decrease in both low latitude corals that form reefs out of aragonite, the metastable form of calcium carbonate, and phytoplankton that form their shells out of calcite, the stable form of calcium carbonate.”

“By year 2100, as atmospheric carbon dioxide reaches 788 ppm (parts per million) under the business as usual scenario, average tropical surface carbonate will decline to 149 +14 mmol/kg, a 45 percent reduction relative to pre-industrial levels, and that agrees with previous estimates. In the Southern Ocean however, surface concentrations will dip to 55 + 5 mmol/kg, which is 18 percent below the threshold (66 mmol/kg) at which aragonite becomes under-saturated. These changes extend well below the sea surface. Throughout the Southern Ocean, the entire water column becomes under-saturated with respect to aragonite. The aragonite saturation horizon shifts from its present average depth of 730 m all the way to the surface. Simultaneously, in a portion of the sub-Arctic Pacific, the aragonite saturation horizon moves from its present depth of about 120 m to the surface. In the North Atlantic, surface waters remain saturated with respect to aragonite, but the saturation horizon shallows dramatically. North of 50 deg N, it shallows from 2 600 m to 115 m. The greater erosion in the North Atlantic is due to deeper penetration and higher concentrations of anthropogenic carbon dioxide, a tendency already evident in present-day estimates based on data and in models." [Quoted from i-sis.org.uk]

Note, these models etc. do not include any feedback allowances.click to return to the index

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bibliography and brief reviews

Glaciers by Hambrey and Alean

Glaciers by Michael Hambrey and Jürg Alean,
Cambridge University Press, 2004, hbk
ISBN-10: 0521828082 / ISBN-13: 978-0521828086

$49.00 [amazon.com]

£36.10 [amazon.co.uk]

Four and a half GoldenYak (tm) award
This book is beautifully illustrated and reasonably well researched. The technical stuff becomes marginally insecure at the edges, and I would have preferred some labelling right on some of the photo illustrations. In other words, this book has the feel of a really serious amateur and enthusiast. This is a good book for those wishing to know what glaciers and their effects look like, and to obtain a reasonable feel for this relevant area of climate science.

The book would have been awarded Five GoldenYaks had the precision been greater, and only Four if the photographs had not been so wonderful. Brilliant coffee-table prize for a young adult learning about the world and interested in this area.


Frozen Earrth by Doug Macdougall Frozen Earth: The Once and Future Story of Ice Ages
by Douglas Macdougall,
University of California Press, 2006
pbk: ISBN-10: 0520248244 / ISBN-13: 978-0520248243
hbk: ISBN-10: 0520239229 / ISBN-13: 978-0520239227

$11.96 pbk [amazon.com] / $40.00 pbk [amazon.com]

£9.98 pbk [amazon.co.uk] / £15.95 hbk [amazon.co.uk]

Three GoldenYak (tm) award
A useful general reader, with history of the science. There is better science and science history around, but not much on this subject. While the book gives a good outline, there is a strong inclination to skip over difficult bits and do a bit of arm-waving. Useful for quick novelish reading.


Paleoclimatology by Raymond Bradley

Paleoclimatology by Raymond Bradley
Academic Press Inc., 1999, hbk
ISBN-10: 012124010X / ISBN-13: 978-0121240103

$66.32 [amazon.com]

£49.99 [amazon.co.uk]

Four GoldenYak (tm) award
This is a book you want if you wish to dig in really seriously. A good first semester reading and on-going reference book for those studying the area. Like so many science books, it could be far better laid out and organised. The illustrations and tables are copious, and useful. However, the paragraphs are often over-long and crammed with too much detail. This book is recommended for someone prepared for serious work.

With over five hundred pages of text and another hundred of bibliography and index, I feel I have my money’s worth, but then I’m a facts freak.

[shorter review]

 

end notes

  1. insolation
    measure of solar radiation on a surface.

  2. The sediment cores eventually turn into sedimentary rock. As they are laid down, they move around. They are dug inot by the animals of the sea, washed around by the tides and storms, distorted by , and transported around the globe. So, as you can imagine, there is a lot of detective work involved. The churning involved during the formation of most sediments results in sediment core analysis being a far less precise source of data than that from ice cores.

  3. firn
    (from German) dense, old snow with its crystals partly joined together, but where the air pockets still communicate with each other.

  4. Emission Scenarios of the IPCC Special Report on Emission Scenarios (SRES)
    Climate studies are immensely complex. There are uncertainties at several levels. Climate can be investigated in historic terms (paleoclimate), present terms and speculative, future terms. A great deal of IPCC reports are about predicting future probabilities. To do this while enabling useful communication, various standardised emission scenarios have been defined. These standardised scenarios are often quoted with additional sub-modifications. At conferences, and in the literature, you will find constant references to these scenarios, according to the workers’ purposes and interests.

    The assumptions in these scenarios are always stated when discussing computer modelling results and IPCC forecasts.

    A1. The A1 storyline and scenario family describes a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies. Major underlying themes are convergence among regions, capacity building and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income. The A1 scenario family develops into three groups that describe alternative directions of technological change in the energy system. The three A1 groups are distinguished by their technological emphasis: fossil intensive (A1FI), non fossil energy sources (A1T), or a balance across all sources (A1B) (where balanced is defined as not relying too heavily on one particular energy source, on the assumption that similar improvement rates apply to all energy supply and end use technologies).

    A2. The A2 storyline and scenario family describes a very heterogeneous world. The underlying theme is self reliance and preservation of local identities. Fertility patterns across regions converge very slowly, which results in continuously increasing population. Economic development is primarily regionally oriented and per capita economic growth and technological change more fragmented and slower than other storylines.

    B1. The B1 storyline and scenario family describes a convergent world with the same global population, that peaks in mid-century and declines thereafter, as in the A1 storyline, but with rapid change in economic structures toward a service and information economy, with reductions in material intensity and the introduction of clean and resource efficient technologies. The emphasis is on global solutions to economic, social and environmental sustainability, including improved equity, but without additional climate initiatives.

    B2. The B2 storyline and scenario family describes a world in which the emphasis is on local solutions to economic, social and environmental sustainability. It is a world with continuously increasing global population, at a rate lower than A2, intermediate levels of economic development, and less rapid and more diverse technological change than in the B1 and A1 storylines. While the scenario is also oriented towards environmental protection and social equity, it focuses on local and regional levels.

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  5. In the graphs, you will see several varicoloured lines. These are from various workers attempting to reconstruct historic temperatures from a variety of sources and surrogates. As you can see, this is no precise science with total, detailed agreement. The black traces in the graphs are averages, calculated by summing the estimates from the different workers.

  6. Surrogate (also proxy, or proxies): There are many surrogates used in this sort of work. A typical surrogate would be tree rings (from around the world) where thicker rings will be taken to reflect warmer and/or extended seasons. Other surrogates are ice cores where years of thicker deposits suggest more snowfall, or greater pollen inclusions suggest more vigorous flowering.

  7. Ice age, what is an ice age? Well, it all depends. Geologists, taking a long view, often regard the present as part of an ice age, which has been coming and going for the last two or three million years. They call it the Pleistocene Ice Age. Geologists regard the current going as an intermission which occurs approximately every hundred thousand years in the present sequence, and then relents for maybe ten or twenty thousand years. Thus, most of familiar human history corresponds with the present easing of the ice. See also past ice ages and interglacials.

  8. The numbers quoted are averages over the last 5,000,000 years. These values can vary to different degrees, sometimes considerably. The numbers also naturally vary over the long-term changes in the universe - that is, once the universe was not even here, or even there. Nature is ever-changing.

    There are varying claims of ‘coincidences’ with phenomena detected in ice cores. Some are more confident than others that these coincide-ences are causal links. As this document starts,“Humans love patterns”. I am a highly cautious entity, others are less so. About this point, you are going to have to start researching for yourself, making judgements and arguing the toss with other interested people. For a start, see the bibliography, join appropriate courses or Internet discussion forums like at realclimate.org.



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