Phydeaux
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Posted in post 107. Have at it.
So there are several portions of AGW that I find interesting.
A theory which purports to be global and universal, can't really be either can it when it doesn't hold true for large regions.
Might it better be described as "local warming due to co2 emissions" - why, it might. And honestly, there is tons of records that support that Interstadials may be local phenomenon. Might this explain variations between the anarctic and the equator?
We have had thousands of temperature changes - and they are frequent and sharp. So I'll quote from one such paper
Sudden climate transitions during the Quaternary,by Jonathan Adams (1.), Mark Maslin (2.) & Ellen Thomas (3.)
The time span of the past few million years has been punctuated by many rapid climate transitions, most of them on time scales of centuries to decades or even less. The most detailed information is available for the Younger Dryas-to-Holocene stepwise change around 11,500 years ago, which seems to have occurred over a few decades.
Less intensive, but significant rapid climate changes also occurred during the present (Holocene) interglacial, with cold and dry phases occurring on a 1500-year cycle, and with climate transitions on a decade-to-century timescale. In the past few centuries, smaller transitions (such as the ending of the Little Ice Age at about 1650 AD) probably occurred over only a few decades at most. All the evidence indicates that most long-term climate change occurs in sudden jumps rather than incremental changes.
Climatic variability on the timescale of tens of thousands of years has turned out to be a predominant pattern in earth history. The last two and a half million years have been marked by many global climate oscillations, between warmer and cooler conditions. This trend of oscillations appears to be merely the continuation of a pattern of variability extending back well into the Tertiary period and possibly beyond (e.g., Kennett 1995). During the last few million years, the length and the amplitude of these climate cycles has increased (e.g., Crowley & North, 1991; Hodell and Venz, 1992).
Large global interglacial-glacial-interglacial climate oscillations have been recurring at approximately a 100,000 year periodicity for the last 900,000 years
The Younger Dryas cold event at about 12,900-11,500 years ago seems to have had the general features of a Heinrich Event, and may in fact be regarded as the most recent of these (Severinghaus et al. 1998). The sudden onset and ending of the Younger Dryas has been studied in particular detail in the ice core and sediment records on land and in the sea (e.g., Bjoerck et al., 1996), and it might be respresentative of other Heinrich events. A detailed study of two Greenland ice cores (GRIP and GISP2; Taylor et al. 1997), suggests that the main Younger Dryas-to-Holocene warming took several decades in the Arctic, but was marked by a series of warming steps, each taking less than 5 years. About half of the warming was concentrated into a single period of less than 15 years.
Speaking of DO events:
At least in the North Atlantic region, these changes seem to have been paced according to approximately the same 1500-year rhythm as that found for the last glacial and earlier glacial periods, according to Atlantic sediment records (Bond et al. 1997; Campbell et al., 1998). Generally, at the coldest point of each 1500-year cycle surface temperatures of the North Atlantic were about 2 deg.C cooler than at the warmest part, representing a fairly substantial change in climate. Regional or global fluctuations of this order would be major events if they were to suddenly affect the present-day world with its high population and finely balanced food production. It is uncertain whether these climate cycles indeed extended around the world or were generally confined to the region around the North Atlantic, but the 8,200 ka event (see below) (which fits in as one of the more extreme cold events of this 1500-year pattern) does seem to have been widespread.
III. The mechanisms behind sudden climate transitions.
It is still unclear how the climate on a regional or even global scale can change as rapidly as present evidence suggests. It appears that the climate system is more delicately balanced than had previously been thought, linked by a cascade of powerful mechanisms that can amplify a small initial change into a much larger shift in temperature and aridity (e.g., Rind and Overpeck, 1993). At present, the thinking of climatologists tends to emphasize several key components:
III.1. North Atlantic circulation as a trigger or an amplifier in rapid climate changes.
II.2 Carbon dioxide and methane concentration as a feedback in sudden changes.
The actual importance of carbon dioxide in terms of the climate system is unknown, though computer climate simulations tend to suggest that it directly cooled the world by less than 1 deg.C on average, but due to amplification of this change by various factors within the climate system such as the water vapour content, the resulting change in global climate could have been more than 2 deg.C (e.g., Houghton et al., 1995).
A problem with invoking atmospheric carbon dioxide levels as a causal factor in sudden climate changes is that they seems to have varied too slowly, following on the timescale of millennia what often occurred on the timescale of decades- but the resolution of our records may not be good enough to resolve this question now. Methane, a less important greenhouse gas, was also 50% lower during glacial phases (e.g., Sowers et al., 1993), probably due to reduced biological activity on the colder, drier land surfaces (Meeker et al., 1997)
III.3 Surface reflectivity (albedo) of ice, snow and vegetation.
III.4 Water vapour as a feedback in sudden changes.
III.5. Dust and particulates as a feedback in sudden changes.
III.6. Seasonal sunlight intensity as a background to sudden changes.
These big glacial-interglacial transitions roughly follow the 100,000-year timescale during the last 900 kyr, when the three different rhythms (and possibly the poorly understood factors such as the internal structure of ice-sheets; MacAyeal, 1993a, b) line up to give a big increase in northern summer warmth. However the lesser individual rhythms can also be detected in the temperature record on the 19,000 and 42,000-year timescales, and in fact the timing of interglacial onset tends to more closely follow multiples of the 19,000 year cycle than an exact correspondence to the 100,000 year cycle (Imbrie et al. 1992, 1993).
So a few points:
Carbon contribution is around 1 degree.
Its causality cannot be established due to low correlation between concentrations and temperature.
Further, its important to note the distinction: The paper notes *thousands* of occurences of global warming and global cooling. Carbon dioxide, and methane may be contributing factors. However, IF they contributed they contributed as part of a natural cycle, not anthomorphic - ie., human caused.
As Kent said: This trend of oscillations appears to be merely the continuation of a pattern of variability extending back well into the Tertiary period and possibly beyond (e.g., Kennett 1995). Ie. If we have a trend how do you know the current climate change isn't a reflection of the already established trend?
And carbon is indicated as only one of several forcing behaviors. Not the only one. Not even the predominant one.
Might we be going through a D-O Event, characterized by a 2 degree temperature variation occurring on a cycle of roughly 1500 years? Yes? No? I don't know. But I haven't seen proof either way, and I've looked.
A brief side note about the IPCC climate models. Concentrations of CO2 are well known back about 12000 years. If you plug CO2 concentrations into the models they do not accurately predict either the Roman or the Medieval warming. If they don't model previous data - how do you expect them to predict data?
Oasis or Mirage? Assessing the Role of Abrupt Climate
Change in the Prehistory of the Southern Levant
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