Research project Investigating multi-centennial climate variability using the Earth System Model
A crucial goal in climate research is to better understand the mechanisms of observed climate variability and change to assess the relative roles of internal variability and external forcing variations in explaining observed changes in the climate system.
Project description
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Proxy records (488 Kb)
It is difficult to obtain an estimate of internal variability purely from the present-day observations, since observed climate variations arise both from internal variability and from changing forcings. The analysis of instrumental observations and paleo proxy records has revealed important characteristics of multi-centennial climate variability but identifying the underlying cause remains difficult. To provide a further perspective on low-frequency climate variations we can use long climate model simulations. The analysis of these simulations is extremely useful in characterizing the internal variability in the climate system in the absence of changes in external forcing and estimating how the external forcing can modulate/alter these low-frequency variabilities.
In this project we focus on multi-centennial variability on a timescale of 100-500 years, which can also be approximated as a centennial to multi-centennial timescale. The main reason why there are few studies on the multi-centennial timescale is that the length of instrumental observations is with some exceptions less than 200 years. There are no direct observations to confirm the existence of multi-centennial climate variability. It is instead inferred from information retrieved from paleoclimate proxy archives. Another reason is that climate change caused by external forcing is easier to study (at least the ultimate cause is known), while internal variability or periodic oscillations are difficult to clarify the causal relationship (even for natural variability on inter-annual timescales).
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Diagram (549 Kb)
To have a foundation for reliable predictions of future climate change, we need to test the models’ ability on reproducing past climate variability. The coupled climate model has been developed to an Earth System Model (ESM) by introducing more and more components, which can represent a more realistic climate system, and are applied to future climate projection. At the same time, the rapid advance in high performance computation (HPC) offers the opportunity to use such complex ESMs to conduct simulations for several thousand years.
In this project, using an ESM EC-Earth, we will perform and analyse several thousand years long simulations for different past periods and future scenarios, such as an unforced pre-industrial control simulation, forced equilibrium simulations under different forcings, and transient simulation with varied forcings. These simulations allow to detect the mechanism of slow physical processes with robust statistical assessment.
This project intends to answer the following three main questions:
- Is multi-centennial climate variability primarily an intrinsic internal oscillation or is it caused by external forcing?
- How do different external forcings impact the multi-centennial climate variability?
- Do the current state-of-the-art ESMs capture the multi-centennial climate variability seen in paleo-proxy data?
If the multi-centennial variability is an intrinsic internal oscillation in the climate system, this will be very useful for predicting climate changes more than a hundred years into the future. If this variability is caused by external forcing, we need to have a clear understanding of the climate responses and feedbacks to the natural and anthropogenic forcing. Applying the complex ESM on such low-frequency climate variability is very rare. The fundamental scientific issues studied in this project thus stand in the international frontier and have a distinctive lead. Moreover, the long simulations carried out with our ESM will have wider applications on many other aspects in the paleoclimate community as well as for future projections.
Project members
Project managers
Qiong Zhang
Professor
Members
Fredrik Charpentier Ljungqvist
Professor of History, especially Historical Geography
Frederik Schenk
Researcher
Qiong Zhang
Professor