The following information is provided by the British Antarctic Society.
It squares with everything that I have seen on the same subject.
Ice cores don't lie. They also totally demolish all conceivable
arguments made by "young earthers."
Relevant here is what the cores tell us about climate change. In the past
there have, yes, been massive changes in climate. All ( all ) however,
not counting gigantic asteroids and their effects, have been gradual,
with changes spread out over thousands of years.
What we are seeing now is unprecedented rapid atmospheric deterioration.
The start of the process can be traced to the 19th century but takeoff
begins
in about 1900 and has accelerated ever since. Or has accelerated until
very recently with implementation of environmental regulations in the
leading industrial nations since about 1980 or 1990. Data are still fuzzy
about a "leveling off" but some slow down in increases seems obvious
enough. This leaves us at crisis levels even if things are not as dire
as environmental alarmists want us to believe.
The Left, unfortunately, seems to consist of 90 % alarmists.
However, the Right seems to consist of 90 % climate change deniers.
Which is worse ? Take your pick.
Here are the basic facts that ice core evidence provides, with a
short synopsis from the conclusion of the article to lead things off,.
Anyone who insists that climate change is false has the burden
of proof. Where is the evidence that contravenes ice core data ?
It is NOT "proof" to point out that some questionable researchers
(alarmists) have cooked their books in other areas of study.
The question is ice-core specific. What evidence exists that in any way
contravenes ice core evidence ? As far as I know there is no such
counter evidence at all. Therefore deniers necessarily argue on the basis
of ad hominem attacks or evasions or red herrings,
none of which is valid as science.
Anyway, the article recommends itself. And it is consistent with a large
number of other studies, including those from Scientific American,
that are available on the Web.
Billy
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* Ice core. Cylinder of ice drilled out of an ice sheet or glacier.
Most ice core records come from Antarctica and Greenland.
* Ice cores contain information about past temperature, and about
many other aspects of the environment.
* Atmospheric carbon dioxide levels are now nearly 40% higher than
before the industrial revolution. This increase is due to fossil fuel usage
and deforestation.
* The magnitude and rate of the recent increase are almost certainly
unprecedented over the last 800,000 years.
* Methane also shows a huge and unprecedented increase in
concentration over the last two centuries.
--------------------------------------------------------------
Ice cores and climate change
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and climate
change_
(http://www.antarctica.ac.uk/bas_research/science_briefings/icecorebriefing.php)
»
Slices of ice core, drilled from the depths of the Earth’s ice sheets
reveal details of the planet’s past climate
Introduction
Ice cores are cylinders of ice drilled out of an ice sheet or glacier. Most
ice core records come from Antarctica and Greenland, and the longest ice
cores extend to 3km in depth. The oldest continuous ice core records to date
extend 123,000 years in Greenland and 800,000 years in Antarctica. Ice
cores contain information about past temperature, and about many other aspects
of the environment. Crucially, the ice encloses small bubbles of air that
contain a sample of the atmosphere — from these it is possible to measure
directly the past concentration of gases (including carbon dioxide and
methane) in the atmosphere.
Greenhouse gases and the recent past_
Fig 1: Measurements of CO2 from the Law Dome ice core(1) fall onto the
line of annual average atmospheric measurements from South Pole(2)
_
(http://www.antarctica.ac.uk/press/journalists/resources/science/images/001.jpg)
Direct and continuous measurements of carbon dioxide (CO2) in the
atmosphere extend back only to the 1950s. Ice core measurements allow us to
extend
this way back into the past. In an Antarctic core (Law Dome) with a very
high snowfall rate, it has been possible to measure concentrations in air from
as recently as the 1980s that is already enclosed in bubbles within the
ice. Comparison with measurements made at South Pole station show that the
ice core acts as a faithful recorder of atmospheric concentrations (see Fig.
1), although we do have to be cautious, as artefacts can arise at sites
with high concentrations of other impurities.
Antarctic ice cores show us that the concentration of CO2 was stable over
the last millennium until the early 19th century. It then started to rise,
and its concentration is now nearly 40% higher than it was before the
industrial revolution (see Fig. 2). Other measurements (e.g. isotopic data)
confirm that the increase must be due to emissions of CO2 from fossil fuel
usage and deforestation. Measurements from older ice cores (discussed below)
confirm that both the magnitude and rate of the recent increase are almost
certainly unprecedented over the last 800,000 years. _
Fig 2: CO2 and CH4 over the last 1,000 years(1-4)
_
(http://www.antarctica.ac.uk/press/journalists/resources/science/images/002.jpg)
The fastest large natural increase measured in older ice cores is
around 20ppmv (parts per million by volume) in 1000 years (a rate seen
during Earth’s emergence from the last ice age around 12,000 years ago). CO2
concentration increased by the same amount, 20ppmv, in the last 11 years!
Methane (CH4), another important greenhouse gas, also shows a huge and
unprecedented increase in concentration over the last two centuries. Its
concentration is now much more than double its pre-industrial level. This is
mainly
due to the increase in emissions from sources such as rice fields, ruminant
animals and landfills, that comes on top of natural emissions from wetlands
and other sources.
Natural climate changes: glacial-interglacial cycles
(http://www.antarctica.ac.uk/images/image.php?id=53616c7465645f5f4ef4aac34eb4d219edd0574838ac612ba5d2209cc449fcbe)
A slice of ice core containing tiny bubbles of ancient air.
By measuring the ratios of different water isotopes in polar ice cores, we
can determine how temperature in Antarctica and Greenland has changed in
the past. The oldest ice core we have was drilled by the European Project for
Ice Coring in Antarctica (EPICA) from Dome C on the Antarctic plateau. It
extends back 800,000 years and shows a succession of long cold ‘glacial’
periods, interspersed roughly every 100,000 years by warm ‘interglacial’
periods (of which the last 11,000 years is the most recent). This succession
of events is well-known from other records, and the coldest periods in
Antarctica are the times when we had ice ages. Ice sheets extended over North
America as far south as Wisconsin, and over Britain to south of The Wash.
The role of greenhouse gases in glacial-interglacial cycles
_
Fig 3: Ice core data from the EPICA Dome C (Antarctica) ice core:
deuterium ( D) is a proxy for local temperature; CO2 from the ice core air(5,6)
_
(http://www.antarctica.ac.uk/press/journalists/resources/science/images/003.jpg)
From the air in our oldest Antarctic ice core, we can see that CO2
changed in a remarkably similar way to Antarctic climate, with low
concentrations during cold times, and high concentrations during warm periods
(see
Fig. 3). This is entirely consistent with the idea that temperature and CO2
are intimately linked, and each acts to amplify changes in the other (what
we call a positive feedback).It is believed that the warmings out of
glacial periods are paced by changes in Earth’s orbit around the Sun, but the
tiny changes in climate this should cause are amplified, mainly by the
resulting increase in CO2, and by the retreat of sea ice and ice sheets (which
leads to less sunlight being reflected away). Looking at the warming out of
the last glacial period in detail, we can see how remarkably closely
Antarctic temperature and CO2 tracked each other. _
Fig 4: Close-up of deuterium (temperature proxy) and CO2 from the EPICA
Dome C ice core over the warming from the last glacial period.(7)
_
(http://www.antarctica.ac.uk/press/journalists/resources/science/images/004.jpg)
It is often said that the temperature ‘leads’ the CO2 during the
warming out of a glacial period. On the most recent records, there is a hint
that the temperature started to rise slightly (at most a few tenths of a
degree) before the CO2, as expected if changes in Earth’s orbit cause an
initial small warming. But for most of the 6,000-year long ‘transition’,
Antarctic temperature and CO2 rose together, consistent with the role of CO2
as
an important amplifier of climate change (see Fig. 4). In our modern era,
of course, it is human emissions of CO2 that are expected to kick-start
the sequence of events. We see no examples in the ice core record of a major
increase in CO2 that was not accompanied by an increase in temperature.
Methane concentration also tracks the glacial-interglacial changes, probably
because there were less wetlands in the colder, drier glacial periods.
Abrupt climate changes
The climate changes described above were huge, but relatively gradual.
However, ice cores have provided us with evidence that abrupt changes are also
possible. During the last glacial period, Greenland experienced a sequence
of very fast warmings (see Fig. 5). _
Fig 5: Oxygen isotope ratio (temperature proxy) from the NorthGRIP
(Greenland) ice core showing a sequence of rapid temperature jumps.(8)
_
(http://www.antarctica.ac.uk/press/journalists/resources/science/images/005.jpg)
The temperature increased by more than 10°C within 40 years. Other
records show us that major changes in atmospheric circulation and climate
were experienced all around the northern hemisphere. Antarctica and the
Southern Ocean experienced a different pattern, consistent with the idea that
these rapid jumps were caused by sudden changes in the transport of heat in
the ocean. At this time, there was a huge ice sheet (the Laurentide) over
northern North America. Freshwater delivered from the ice sheet to the North
Atlantic was able periodically to disrupt the overturning of the ocean,
causing the transport of tropical heat to the north to reduce and then
suddenly increase again. While this mechanism cannot occur in the same way in
today’s world, it does show us that, at least regionally, the climate is
capable of extraordinary changes within a human lifetime: rapid switches we
certainly want to avoid experiencing.
Summary
Ice cores provide direct information about how greenhouse gas
concentrations have changed in the past, and they also provide direct evidence
that the
climate can change abruptly under some circumstances. However, they provide
no direct analogue for the future because the ice core era contains no
periods with concentrations of CO2 comparable to those of the next century.
Factfile
* Ice core. Cylinder of ice drilled out of an ice sheet or glacier.
Most ice core records come from Antarctica and Greenland.
* Ice cores contain information about past temperature, and about
many other aspects of the environment.
* Atmospheric carbon dioxide levels are now nearly 40% higher than
before the industrial revolution. This increase is due to fossil fuel usage
and deforestation.
* The magnitude and rate of the recent increase are almost certainly
unprecedented over the last 800,000 years.
* Methane also shows a huge and unprecedented increase in
concentration over the last two centuries.
Data sources
1. MacFarling Meure, C., and others: Law Dome CO2, CH4 and N2O ice
core records extended to 2,000 years BP, Geophys. Res. Lett., 33, L14810,
doi:10.1029/2006GL026152, 2006
2. Atmospheric data supplied by NOAA/ESRL
3. Friedli, H., and others: Ice core record of the 13C/12C ratio of
atmospheric CO2 in the past two centuries, Nature, 324, 237–238, 1986
4. Siegenthaler, U., and others: Supporting evidence from the EPICA
Dronning Maud Land ice core for atmospheric CO2 changes during the past
millennium, Tellus Ser. B-Chem. Phys. Meteorol., 57, 51–57, 2005
5. Jouzel, J., and others: Orbital and millennial Antarctic climate
variability over the last 800,000 years, Science, 317, 793–796, 2007
6. Lüthi, D., and others: High-resolution carbon dioxide concentration
record 650,000–800,000 years before present, Nature, 453, 379–382, 2008
7. Monnin, E., and others: Atmospheric CO2 concentrations over the
last glacial termination, Science, 291, 112–114, 2001 with data converted to
the age scale of Parrenin, F., and others: The EDC3 chronology for the EPICA
Dome C ice core, Climate of the Past, 3, 485–497, 2007
8. North Greenland Ice Core Project Members: High-resolution record of
Northern Hemisphere climate extending into the last interglacial period,
Nature, 431, 147–151, 2004
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