6 research outputs found
Tree-rings and climate - Standardization, proxy-development, and Fennoscandian summer temperature history
Instrumental meteorological observation are too short for trying to estimate
climate change and variability on multi-decadal and centennial time-scales, and when
trying to evaluate the response of the climate system to human influence, such as
raised concentrations of green house gases (GHG), altered land-use, black carbon etc.
To access information about the climate system predating instrumental observations,
reliable proxy records (natural archives) are necessary. These proxies include for
example tree rings, ice cores, fossil pollen, ocean sediments, corals and historical
documentary data.
Tree rings is one of the most widely used proxy for high-resolution growing season
temperature reconstructions during the last millennium, and in Fennoscandia some of
the best-calibrated records in the world exist. Yet, in this available body of work,
there is limited homogeneity on decadal to centennial scales. Since this tree-ring data
is targeting growing-season temperatures and growing-season temperatures in this
region are very well correlated on annual to decadal scales this is unexpected. This
thesis is concerned with trying to address this issue by 1) developing existing
standardization-tools in order to display centennial scale variability and at the same
time reduce noise arising from internal and external disturbances and mismatches in
actual growth trends compared to the expected growth trend. 2) By developing the
new un-exploited ΔDensity and ΔBlue Intensity proxies (the difference between the
latewood and earlywood for density and blue intensity respectively) to act as
complement or quality control to the established maximum latewood density (MXD)
which is the state of the art proxy for high latitude temperature reconstructions, and
also to the Blue Intensity measurement scheme, that potentially could be an
inexpensive complement to the radiodensitometric methodology.
Results showed that using the Δ parameter for both density and Blue Intensity, give
added value in a more focused annual scale summer temperature signal, and an
improved coherence between different chronologies on decadal to centennial scales.
Methodological protocols such as data analysis and standardization seem to be critical
when trying to attain adequate low-frequency signals from tree-ring data. A more
coherent view of the summer temperature history for the last 900 years in
Fennoscandia is provided using the methodological improvements outlined in this
thesis. Future challenges include trying to extend this excellent network back in time
to not only cover the Little Ice Age (1450-1900 CE) but also to cover the debated
Medieval Climate Anomaly (850-1250 CE)