The research paper below puts into practice a much more precise method of measuring atmospheric CO2 retrospectively than is available via ice-cores. The research was done on plant residues in the North Atlantic area and showed repeated fluctuations in CO2 levels -- and that the CO2 levels changed in synchrony with the output of the sun. The paper is rather heavy going for non-scientists but it might help if I note that "cal. yr BP" is fully translatable as "years ago"!
(From Global and Planetary Change 57:247-260, June 2007)
Climate forced atmospheric CO2 variability in the early Holocene: A stomatal frequency reconstruction
By C.A. Jessen et al.
The dynamic climate in the Northern Hemisphere during the early Holocene could be expected to have impacted on the global carbon cycle. Ice core studies however, show little variability in atmospheric CO2. Resolving any possible centennial to decadal CO2 changes is limited by gas diffusion through the firn layer during bubble enclosure. Here we apply the inverse relationship between stomatal index (measured on sub-fossil leaves) and atmospheric CO2 to complement ice core records between 11,230 and 10,330 cal. yr BP. High-resolution sampling and radiocarbon dating of lake sediments from the Faroe Islands reconstruct a distinct CO2 decrease centred on ca. 11,050 cal. yr BP, a consistent and steady decline between ca. 10,900 and 10,600 cal. yr BP and an increased instability after ca. 10,550 cal. yr BP. The earliest decline lasting ca. 150 yr is probably associated with the Preboreal Oscillation, an abrupt climatic cooling affecting much of the Northern Hemisphere a few hundred years after the end of the Younger Dryas. In the absence of known global climatic instability, the decline to ca. 10,600 cal. yr BP is possibly due to expanding vegetation in the Northern Hemisphere. The increasing instability in CO2 after 10,600 cal. yr BP occurs during a period of increasing cooling of surface waters in the North Atlantic and some increased variability in proxy climate indicators in the region. The reconstructed CO2 changes also show a distinct similarity to indicators of changing solar activity. This may suggest that at least the Northern Hemisphere was particularly sensitive to changes in solar activity during this time and that atmospheric CO2 concentrations fluctuated via rapid responses in climate.
...... The relatively new method of stomatal frequency analysis applies the physiological response of certain C3 plants to changing concentrations of CO2 in the atmosphere (Woodward, 1987). Rapidly accumulating lake sediments, if supplied with sufficient numbers of leaves from the surrounding vegetation, allow the reconstruction of atmospheric CO2 changes on centennial to decadal timescales by applying its inverse relationship to stomatal frequency. This paper presents a stomatal frequency reconstruction of atmospheric CO2 at decadal resolution over the time period 11,230 to 10,330 cal. yr BP, supported by a highly resolved AMS radiocarbon chronology from lake sediments of the Faroe Islands (situated in the North Atlantic between south west Norway and Iceland).
As our atmospheric CO2 estimates should reflect the global net effect of carbon transfers between reservoirs responsive on sub-millennial to decadal timescales, we also discuss possible causes for the changes in reconstructed CO2 in relation to evidence of climate variation and solar activity during the early Holocene.....
...... The CO2(SI) reconstruction through the early Holocene bears a striking similarity to reconstructed solar activity changes. This may suggest a rapid response of climate to minor changes in solar activity during this dynamic period, which in turn impacted the global carbon cycle. This can, to some extent, also be seen in the climatic responses associated with the Maunder Minimum in the mid-17th to early 18th centuries.
SOUTHERN HEMISPHERE DATA IMPLICATE OLD SOL TOO
The plant data used by Jessen et al in the paper immediately above are not the only plant data which show apparent effects of solar variability in the Northern hemisphere. But if such effects really were effects of the sun, we would expect similar effects worldwide. So are there Southern hemisphere plant data which give similar conclusions to Northern Hemisphere plant data? There are. See below:
(From Earth and Planetary Science Letters 253:439-444, January 2007)
Globally synchronous climate change 2800 years ago: Proxy data from peat in South America
Frank M. Chambers et al.
Initial findings from high-latitude ice-cores implied a relatively unvarying Holocene climate, in contrast to the major climate swings in the preceding late-Pleistocene. However, several climate archives from low latitudes imply a less than equable Holocene climate, as do recent studies on peat bogs in mainland north-west Europe, which indicate an abrupt climate cooling 2800 years ago, with parallels claimed in a range of climate archives elsewhere. A hypothesis that this claimed climate shift was global, and caused by reduced solar activity, has recently been disputed. Until now, no directly comparable data were available from the southern hemisphere to help resolve the dispute. Building on investigations of the vegetation history of an extensive mire in the Valle de Andorra, Tierra del Fuego, we took a further peat core from the bog to generate a high-resolution climate history through the use of determination of peat humification and quantitative leaf-count plant macrofossil analysis. Here, we present the new proxy-climate data from the bog in South America. The data are directly comparable with those in Europe, as they were produced using identical laboratory methods. They show that there was a major climate perturbation at the same time as in northwest European bogs. Its timing, nature and apparent global synchronicity lend support to the notion of solar forcing of past climate change, amplified by oceanic circulation. This finding of a similar response simultaneously in both hemispheres may help validate and improve global climate models. That reduced solar activity might cause a global climatic change suggests that attention be paid also to consideration of any global climate response to increases in solar activity. This has implications for interpreting the relative contribution of climate drivers of recent "global warming".
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