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POSIVA Report 2019-4

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Name:

Modelling Changes in Climate over the Next 1 Million Years

Writer:

Lord, N.S., Lunt, D., Thorne, M.

Language:

English

Page count:

107

ISBN:

978-951-652-274-9

Summary:

The extended timescales involved in the decay of radioactive wastes to safe levels mean that geological disposal facilities must continue to function effectively long into the future. It is therefore essential to consider long-term climate evolution in post-closure safety assessments in order to evaluate a geological disposal system’s response to, and robustness against, a variety of potential environmental changes. In this report, a combination of Earth system modelling techniques has been used to simulate the possible evolution of future climate over the next 1 million years (Myr) for a range of anthropogenic carbon dioxide (CO2) emissions scenarios. Two of these models calculate future changes in variables that drive climate variations: a carbon cycle impulse response function is used to project the future evolution of atmospheric CO2 concentration in response to anthropogenic CO2 emissions, and a conceptual model estimates future changes in global sea level (GSL; as a proxy for the glacial-interglacial cycles) forced by orbital and atmospheric CO2 variations. A statistical climate emulator is then used to project the future evolution of a number of climate variables forced by atmospheric CO2 concentration, orbital variations, and global ice sheet volume changes. Finally, a bias-correction downscaling technique is applied to increase the spatial resolution of the climate projections, with a focus on the regions surrounding Olkiluoto, Finland and Forsmark, Sweden. This is also compared to an alternative physical-statistical downscaling technique in order to assess the uncertainty in the downscaled projections.


Future climate is shown to vary in response to the CO2 (both anthropogenic and natural) and orbital forcings. The period of anthropogenic CO2 emissions in each emissions scenario is accompanied by a period of warming (along with associated climate changes) which lasts for up to 50 thousand years (kyr) into the future. This is followed by an increased dominance of orbital forcing on climate, and fluctuations between interglacial and glacial states. The results suggest that the timing of the next glacial inception, which is a key climate issue in safety assessments performed for the Olkiluoto and Forsmark sites, may be strongly affected by anthropogenic CO2 emissions. Scenarios with relatively low emissions are projected to undergo glacial inception in ~50 kyr (from present), whilst relatively high emissions are suggested to extend the current interglacial for approximately 170 kyr after present-day. It should be noted that, based on a comparison of the climate model and palaeo proxy climate data, the SAT projections for glacial conditions that are presented in this report could be considered as worst-case, i.e. if the palaeoclimate that was reconstructed using proxy data is correct then the cooling and associated impacts (e.g. permafrost) may not be quite as severe as projected in this report. The data presented here can be utilized to inform further modelling studies (e.g. landscape, permafrost, surface denudation, etc.) performed as part of a post-closure performance assessment for a radioactive waste repository.

Keywords:

Climate evolution, glaciation, interglacial, atmospheric carbon dioxide, modelling, emulator

File(s):

POSIVA 2019-04_web (pdf) (7.5 MB)


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