Masterprosjekt vår 2019 ved GEO - Andreas Born
Reconstructing the climate of the late Holocene using a climate analogues framework
The climate of the last millennia was shaped by multiple forcing components such as variations in solar irradiance, the amount of volcanic aerosols in the upper atmosphere, and a general shift in the length of seasons due to the gradual changes in the earth’s orbit. This superposition of multiple relatively weak external forcings in combination with strong internal variability make simulations of
this period extremely challenging.
Assuming that modern climate models are in principle capable of realistically representing the dynamic equilibrium of the climate system, it is conceivable that the difficulties to accurately simulate the reconstructed climate evolution are primarily due to the presence of high-amplitude internal variations. Because they are stochastic in nature and models do not agree on the spectral density, internal variability is generally out of phase with the proxy record.
We recently developed a new method to compile synthetic transient climate model data that is consistent with proxy reconstructions (Jensen et al., 2017). It identifies fields of climate analogues from the climate model data that best resemble the geological proxy record. Since this method takes advantage of existing climate simulations it is computationally very efficient and large ensembles of reconstructions are feasible to quantify uncertainties and to test various assumptions.
Jensen et al. (2017): A spatio-temporal reconstruction of sea-surface temperatures in the North Atlantic during Dansgaard-Oeschger events 5–8, Climate of the Past Discussions
Hypothesis (scientific problem):
For this project, climate model data from the Norwegian Earth System Model (NorESM) will be used to identify periods with similar temperature anomaly patterns as those inferred from a database of marine proxy reconstructions compiled by collaborators at the Norwegian Polar Institute. The region of interest is the North Atlantic Ocean and the Nordic Seas. Climate anomalies will be selected by an
algorithm that objectively quantifies the similarity of reconstructed and simulated climate fields. The following hypothesis shall be addressed:
1) Can we robustly interpolate North Atlantic marine proxy data from the last millennium with analogues from climate models? Can this be expanded to the mid Holocene?
2) Is it possible to infer NAO anomalies from networks of marine proxy records (pseudo and real proxy)?
3) Consistent changes in Arctic sea ice during the last millennium?
The work consists of two major parts, the implementation of the climate analogue method for which existing python code may be adapted, and the scientific evaluation of the results which will primarily use statistical tools. Although the proxy database already exists, additional work will be necessary to re-sample the data onto a common time axis and to ensure the consistency of age models. One expected outcome are maps of reconstructed variables that include quantifiable information on statistical robustness.
Candidates should have some previous knowledge of computer programing with languages such as python, matlab, R, IDE or similar. Please contact the supervisor before choosing this topic.