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SUMMARY Mass loss from polar ice sheets is becoming the dominant contributor to current sea level changes, as well as one of the largest sources of uncertainty in sea level projections. The spatial pattern of sea level change is sensitive to the geometry of ice sheet mass changes, and local sea level changes can deviate from the global mean sea level change due to gravitational, Earth rotational and deformational (GRD) effects. The pattern of GRD sea level change associated with the melting of an ice sheet is often considered to remain relatively constant in time outside the vicinity of the ice sheet. For example, in the sea level projections from the most recent IPCC sixth assessment report (AR6), the geometry of ice sheet mass loss was treated as constant during the 21st century. However, ice sheet simulations predict that the geometry of ice mass changes across a given ice sheet and the relative mass loss from each ice sheet will vary during the coming century, producing patters of global sea level changes that are spatiotemporally variable. We adopt a sea level model that includes GRD effects and shoreline migration to calculate time-varying sea level patterns associated with projections of the Greenland and Antarctic Ice Sheets during the coming century. We find that in some cases, sea level changes can be substantially amplified above the global mean early in the century, with this amplification diminishing by 2100. We explain these differences by calculating the contributions of Earth rotation as well as gravitational and deformational effects to the projected sea level changes separately. We find in one case, for example, that ice gain on the Antarctic Peninsula can cause an amplification of up to 2.9 times the global mean sea level equivalent along South American coastlines due to positive interference of GRD effects. To explore the uncertainty introduced by differences in predicted ice mass geometry, we predict the sea level changes following end-member mass loss scenarios for various regions of the Antarctic Ice Sheet from the ISMIP6 model ensemblely, and find that sea level amplification above the global mean sea level equivalent differ by up to 1.9 times between different ice mass projections along global coastlines outside of Greenland and Antarctica. This work suggests that assessments of future sea level hazard should consider not only the integrated mass changes of ice sheets, but also temporal variations in the geometry of the ice mass changes across the ice sheets. As well, this study highlights the importance of constraining the relative timing of ice mass changes between the Greenland and Antarctic Ice Sheets.
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Implications of the Paris Climate Agreement for future sea-level rise from Antarctica
The agreement reached at the 21st Conference of the Parties (COP21) of the United Nations Framework Conven- tion on Climate Change (UNFCC) is aimed at limiting the post-preindustrial rise in global mean temperature to less than 2 oC at the end of this century, and to promote further efforts to limit the warming to 1.5 oC. Here, we use a numerical ice sheet-shelf model, with physics tested and calibrated against modern and past ice-sheet behavior and coupled to highly resolved atmospheric and ocean components, to test the Antarctic Ice Sheet’s response to a range of future climate scenarios representing COP21 aspirations versus a fossil-fuel intensive RCP8.5 emissions scenario. Assuming COP21 temperature targets are achievable and those temperatures will not be exceeded beyond 2100, we find that a global mean temperature rise less than 2 oC substantially reduces both the short term (decadal- century) and long-term risk of catastrophic sea level rise from Antarctica. In contrast, we find that the current, Intended Nationally Determined Contributions (INDCs), allowing global mean temperature to approach ∼3 oC by the end of this century, results in a substantial increase in Antarctica’s contribution to sea-level rise, relative to 1.5 or 2 oC. The results suggest that the current INCDs might not be sufficient to save the West Antarctic Ice Sheet and some East Antarctic outlets from substantial retreat.
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- Award ID(s):
- 1664013
- PAR ID:
- 10066646
- Date Published:
- Journal Name:
- Geophysical research abstracts
- Volume:
- 20
- ISSN:
- 1029-7006
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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