Det følgende er litt langt og nok mest for spesielt interesserte i
klimarelatert vitenskap. Det viser hvilken betydning godt kjennskap til
klimahistorien har for vurdering av klimatrusler nå.
Det _finnes_ mer velbegrunnede oppfattelser av at den globale oppvarming kan
ha naturlige årsaker. Denne virker forholdsvis seriøs - i motsetning til mye
tøv om drivhuseffekten benekter den iallfall ikke at det _foregår_ en
oppvarmning, at polisen minker osv. (noe det er håpløst å benekte ut fra fra
dagens omfattende data på mange felter). Denne teoriens innvendinger mot at
menneskelige utslipp påvirker drivhuseffekten og mot at drivhuseffekten
påvirker klimaet er de første jeg har sett som virker noenlunde plausible
(med mitt begrensede kjennskap til atmosfærisk og annen involvert geofysisk
vitenskap):
""At 6 billion tons, humans are then responsible for a comparatively small
amount - less than 5 percent - of atmospheric carbon dioxide," he said. "And
if nature is the source of the rest of the carbon dioxide, then it is
difficult to see that man-made carbon dioxide can be driving the rising
temperatures. In fact, I don't believe it does."
Some scientists believe that the human contribution to carbon dioxide in the
atmosphere, however small, is of a critical amount that could nonetheless
upset Earth's environmental balance. But Essenhigh feels that,
mathematically, that hypothesis hasn't been adequately substantiated.
Here's how Essenhigh sees the global temperature system working: As
temperatures rise, the carbon dioxide equilibrium in the water changes, and
this releases more carbon dioxide into the atmosphere. According to this
scenario, atmospheric carbon dioxide is then an indicator of rising
temperatures -- not the driving force behind it."
IPCCs folk vil sikkert komme med svar på dette. La oss se hva det blir. I
mellomtida fins det en brukbar test: la oss se på temperatur og C02 for
120000-130000 år siden, i forrige mellomistid (varm periode på ca. 10000 år
mellom istidene som i snitt varer ca. 100000 år). Temperaturen var da ifølge
borekjerneanalyser fra innlandsisene (og samme fra havbunnen) ca. 2 grader
over nåværende mellomistid. Det vokste f.eks. trær og busker i området rundt
Scoresbysund langt nord for polarsirkelen på Østgrønland, hvor det i dag er
rent polarklima og bare sparsom høyfjellsvegetasjon som på Svalbard.
Havnivået var noe høyere enn nå, hvilket indikerer mindre breis globalt.
Samtidig viser analyser luft fra av luftblærer i borekjerner fra Antarktis
både høyere innhold av C02 og methan for ca. 130000 år siden enn under
hovedparten av Holocen (= nåværende mellomistid). C02-topp i Eem er ca. 300
ppm
(parts per million), snitt Eem ca. 280 ppm. Snitt for Holocen er ca. 280 ppm
(som Eem). Dvs. det var varmere i Eem og C02 var litt høyere. Nå er C02 over
360 ppm (Økt fra 280 midt 1800-tall), skulle dette skyldes temperaturøkning
i havet burde den nå vært betydelig høyere! Det må altså være andre årsaker,
hvorav menneskets brenning av fossile brensler er en soleklar kandidat. Men
det er fortsatt ikke så varmt som i Eem, og temperaturen stiger saktere enn
C02-innholdet. Utifra dette virker det usannsynlig at det er
temperaturstigning som framkaller den nåværende stigning i C02. Utsvingene i
C02 er nå kommet betydelig raskere enn før i klimahistorien så vidt en kan
se. Men det kan selvsagt være ting som vi ikke ser i borekjerneanalysene på
grunn av for liten tidsoppløsning mv. Alt i alt virker det dog klart
sannsynlig at 1) vi har en temperaturstigning "lagret" i nåværende
C02-mengde og/eller 2) at andre forhold har innflytelse på temperaturen
(og C02).
Essenhighs forklaring på de naturlige temperatursyklene virker mindre
troverdig (og det er rart at han ikke tar hensyn til den "astronomiske
hypotesen" fra Milankovitch som er den gjengse til å forklare 100000-
års-syklene):
"According to this model, when the Arctic Ocean is frozen over, as it is
today, Essenhigh said, it prevents evaporation of water that would otherwise
escape to the atmosphere and then return as snow. When there is less snow to
replenish the Arctic ice cap, the cap may start to shrink. That could be the
cause behind the retreat of the Arctic ice cap that scientists are
documenting today, Essenhigh said."
Det gjengis her som om Essenhigh tror isdekket i polbassenget oppfører seg
som
en bre, hvilket er noe sludder og i tilfelle det er korrekt gjengitt svekker
tilliten til mannens seriøsitet. Oversomrende snø kan nok bidra litt til
havistykkelsen men dette betyr neppe mye. Selvsagt vil mindre snødekke på
havisen og på landområdene rundt (ikke minst på Grønlandsisen) føre til
mindre albedo og dermed mindre utstråling og høyere lufttemperatur, men det
virker ikke troverdigt at lufttemperaturen bestemmer mengden av havis alene,
her har havtemperaturen nok så mye å si. Når temperaturstigningen har åpnet
tilstrekkelig av polbassenget skal det ifølge denne teorien begynne å snø
mye mer - men da er jo temperaturen på kloden en del høyere og mindre av
nedbøren vil falle som snø, og den som faller vil smelte raskere? Jeg tror
ikke dette holder som forklaring alene.
Altså: Det synes å være store huller i Essenhighs hypoteser. Her er det mye
usikkert og uforklart.
Etter min mening endrer alt dette uansett ikke noe ved at vi må følge
føre-var-prinsippet. Så lenge vi ikke vet mer enn vi gjør på vi begrense
energisløseriet: faren for at vi påvirker klimaet irreversibelt og med
uforutsigelige konsekvenser, er for realistisk og alvorlig. SIKKER på-
visning av årsakene til klimaendringene vil vi ikke få, før det er for
seint. Utover dette er det en masse andre veldig gode grunner til å begrense
sløseriet med fossil energi, redusere bilisme osv. Forurensing, begrensede
ressurser mm.
Karsten Johansen
http://www.osu.edu/researchnews/archive/nowarm.htm
VIEWPOINT: GLOBAL WARMING NATURAL, MAY END WITHIN 20 YEARS
COLUMBUS, Ohio -- Global warming is a natural geological process that could
begin to reverse itself within 10 to 20 years, predicts an Ohio State
University researcher.
The researcher suggests that atmospheric carbon dioxide -- often thought of
as a key "greenhouse gas" -- is not the cause of global warming. The
opposite is most likely to be true, according to Robert Essenhigh, E.G.
Bailey Professor of Energy Conservation in Ohio State's Department of
Mechanical Engineering. It is the rising global temperatures that are
naturally increasing the levels of carbon dioxide, not the other way around,
he says.
Essenhigh explains his position in a "viewpoint" article in the current
issue of the journal Chemical Innovation, published by the American Chemical
Society.
Many people blame global warming on carbon dioxide sent into the atmosphere
from burning fossil fuels in man-made devices such as automobiles and power
plants. Essenhigh believes these people fail to account for the much greater
amount of carbon dioxide that enters -- and leaves -- the atmosphere as part
of the natural cycle of water exchange from, and back into, the sea and
vegetation.
"Many scientists who have tried to mathematically determine the relationship
between carbon dioxide and global temperature would appear to have vastly
underestimated the significance of water in the atmosphere as a
radiation-absorbing gas," Essenhigh argues. "If you ignore the water, you're
going to get the wrong answer."
How could so many scientists miss out on this critical bit of information,
as Essenhigh believes? He said a National Academy of Sciences report on
carbon dioxide levels that was published in 1977 omitted information about
water as a gas and identified it only as vapor, which means condensed water
or cloud, which is at a much lower concentration in the atmosphere; and most
subsequent investigations into this area evidently have built upon the
pattern of that report.
For his hypothesis, Essenhigh examined data from various other sources,
including measurements of ocean evaporation rates, man-made sources of
carbon dioxide, and global temperature data for the last one million years.
He cites a 1995 report from the Intergovernmental Panel on Climate Change
(IPCC), a panel formed by the World Meteorological Organization and the
United Nations Environment Programme in 1988 to assess the risk of
human-induced climate change. In the report, the IPCC wrote that some 90
billion tons of carbon as carbon dioxide annually circulate between the
earth's ocean and the atmosphere, and another 60 billion tons exchange
between the vegetation and the atmosphere.
Compared to man-made sources' emission of about 5 to 6 billion tons per
year, the natural sources would then account for more than 95 percent of all
atmospheric carbon dioxide, Essenhigh said.
"At 6 billion tons, humans are then responsible for a comparatively small
amount - less than 5 percent - of atmospheric carbon dioxide," he said. "And
if nature is the source of the rest of the carbon dioxide, then it is
difficult to see that man-made carbon dioxide can be driving the rising
temperatures. In fact, I don't believe it does."
Some scientists believe that the human contribution to carbon dioxide in the
atmosphere, however small, is of a critical amount that could nonetheless
upset Earth's environmental balance. But Essenhigh feels that,
mathematically, that hypothesis hasn't been adequately substantiated.
Here's how Essenhigh sees the global temperature system working: As
temperatures rise, the carbon dioxide equilibrium in the water changes, and
this releases more carbon dioxide into the atmosphere. According to this
scenario, atmospheric carbon dioxide is then an indicator of rising
temperatures -- not the driving force behind it.
Essenhigh attributes the current reported rise in global temperatures to a
natural cycle of warming and cooling.
He examined data that Cambridge University geologists Nicholas Shackleton
and Neil Opdyke reported in the journal Quaternary Research in 1973, which
found that global temperatures have been oscillating steadily, with an
average rising gradually, over the last one million years -- long before
human industry began to release carbon dioxide into the atmosphere. Opdyke
is now at the University of Florida.
According to Shackleton and Opdyke's data, average global temperatures have
risen less than one degree in the last million years, though the amplitude
of the periodic oscillation has now risen in that time from about 5 degrees
to about 10 degrees, with a period of about 100,000 years.
"Today, we are simply near a peak in the current cycle that started about
25,000 years ago," Essenhigh explained.
As to why highs and lows follow a 100,000 year cycle, the explanation
Essenhigh uses is that the Arctic Ocean acts as a giant temperature
regulator, an idea known as the "Arctic Ocean Model." This model first
appeared over 30 years ago and is well presented in the 1974 book Weather
Machine: How our weather works and why it is changing, by Nigel Calder, a
former editor of New Scientist magazine.
According to this model, when the Arctic Ocean is frozen over, as it is
today, Essenhigh said, it prevents evaporation of water that would otherwise
escape to the atmosphere and then return as snow. When there is less snow to
replenish the Arctic ice cap, the cap may start to shrink. That could be the
cause behind the retreat of the Arctic ice cap that scientists are
documenting today, Essenhigh said.
As the ice cap melts, the earth warms, until the Arctic Ocean opens again.
Once enough water is available by evaporation from the ocean into the
atmosphere, snows can begin to replenish the ice cap. At that point, the
Arctic ice begins to expand, the global temperature can then start to
reverse, and the earth can start re-entry to a new ice age.
According to Essenhigh's estimations, Earth may reach a peak in the current
temperature profile within the next 10 to 20 years, and then it could begin
to cool into a new ice age.
Essenhigh knows that his scientific opinion is a minority one. As far as he
knows, he's the only person who's linked global warming and carbon dioxide
in this particular way. But he maintains his evaluations represent an
improvement on those of the majority opinion, because they are logically
rigorous and includes water vapor as a far more significant factor than in
other studies.
"If there are flaws in these propositions, I'm listening," he wrote in his
Chemical Innovation paper. "But if there are objections, let's have them
with the numbers."
#
Contact: Robert Essenhigh, (614) 292-0403; Essenhigh.1@osu.edu Written by
Pam Frost Gorder, (614) 292-9475; Gorder.1@osu.edu
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