Sea-level variability

This section contains studies that characterize and determine the drivers of past, present and future sea-level variability. Studies featured here examine natural and anthropogenic variability from a regional to a global scale and use a combination of observational data, novel analytical approaches, and numerical modelling.

Committed sea-level rise under the Paris Agreement and the legacy of delayed mitigation action

Matthias Mengel et al., Nat. Commun. 9 601 (2018)

Sea levels respond to drivers on different timescales and even if greenhouse gas emissions ceased today, we are already committed to certain sea-level rise in the coming centuries as a result of such processes. Assuming the Paris Agreement targets are met sea-levels will rise between 0.7 and 1.2m by 2300, depending on the pathway of emissions during this century, with an increase of 0.2m for every 5-years of delayed mitigating action. 

Coralgal reef morphology records punctuated sea-level rise during the last deglaciation

Pankaj Khanna et al., Nat. Commun. 8 1046 (2017)

A paucity of natural archives can make resolving rapid sea level rise induced by ice sheet collapse during past periods of warming difficult. Here the authors show that systematic and common coralgal terraces record punctuated sea level rise events over decades to centuries during the last deglaciation.

Ice volume and climate changes from a 6000 year sea-level record in French Polynesia

Nadine Hallmann et al., Nat. Commun. 8 285 (2017)

Past sea-level records serve as an important baseline of natural variability in sea level and global ice volume prior to the Anthropocene. Here, the authors reconstruct relative sea-level changes over the last 6,000 years based on coral microatolls, which are the most accurate low-tide recorders.

Half-metre sea-level fluctuations on centennial timescales from mid-Holocene corals of Southeast Asia

Aron J. Meltzner et al., Nat. Commun. 8 14387 (2017)

Palaeo sea-level reconstructions characterize natural variability and provide a baseline for comparison with recent and future trends. Proxy reconstructions of past relative sea-levels in East and Southeast Asia have been hindered by accuracy and precision, limiting our understanding of regional deviations from the global average in the region. Here, the authors reconstruct relative sea levels from coral microatolls in Indonesia which reveal 0.6-m fluctuations in relative sea-level over several centuries during the mid-Holocene (between 6850 and 6500 yr BP).

An extreme event of sea-level rise along the Northeast coast of North America in 2009–2010

Paul B. Goddard et al., Nat. Commun. 6 6346 (2015)

Extreme sea-level events are a threat to coastal communities, but their cause on seasonal to interannual time scales has received little attention. Here, the authors analyse long-term tide gauge data to report an extreme and unprecedented sea-level rise event in 2009-10 along the Northeast coast of North America. Combining observational data with models they show that this extreme event was caused by a 30% downturn in the Atlantic overturning circulation and an alongshore wind stress anomaly associated with the negative phase of the North Atlantic Oscillation.

Detecting anthropogenic footprints in sea level rise

Sönke Dangendorf et al.,  Nat. Commun. 6 7849 (2015)

The relative contribution of natural and anthropogenic forcing to rising sea levels since the late 19^th century remains unclear. Here, the authors show that at least 45% of global mean sea-level rise is of anthropogenic origin. However, at the local level, natural trends in mean sea-level may be underestimated, resulting in erroneous enhancement of the anthropogenic contribution in some regions.

Sea-level variability over five glacial cycles

Katharine M. Grant et al.,  Nat. Commun. 5 5076 (2014)

Radiometrically dated relative sea-level indicators provide strong constraints on past sea-levels but are generally unsuitable for reconstructions older than ~150,000 years. Here, the authors present a new, uranium/thorium-dated high-resolution sea-level record from the Red Sea, spanning the past five glacial cycles. Sea-level rise rates below 2 metres per century are observed for periods with up to twice the modern global ice volume and maximum sea-level rise rates were attained within 2,000 years of the onset of deglaciations.

Timescales for detecting a significant acceleration in sea level rise

Ivan D. Haigh et al.,  Nat. Commun. 5 3635 (2014)

The rate of sea-level rise, and whether it is increasing, is still open to debate. Here, the authors use a new approach to identify the timing regarding when accelerations will become apparent for different sea-level projections. They adjust sea-level records to account for natural internal climate variability and show that the earliest possible detection of significant sea-level acceleration can only be achieved once inter-annual and multi-decadal variability is removed.