North Atlantic sea-level variability during the last half-millennium

Lead Research Organisation: University of Plymouth
Department Name: Unlisted

Abstract

Sea-level change is one of the most significant threats facing society over the next 100 years and beyond. Measurements of current sea-level change have shown that there has been a mean global sea-level rise of between 10 and 20 cm over the 20th century. A further rise in sea level of between 20 and 80 cm is predicted by AD 2100 due to future global climate change. However, such predictions of future change are subject to very large uncertainties because our understanding of the past behaviour of sea level is poor. It is essential that we quantify sea-level changes in the recent past if we are to provide more accurate and precise predictions for the future. It is clear from measurements and from sea-level reconstructions based on geological data that there has been a significant increase in the rate of sea-level rise from the 19th to the 20th century. We ask the question: Have similar accelerations of sea-level rise happened in the past? Some of our published geological reconstructions give us good reason to believe that there were pre-industrial sea-level accelerations and these require further investigation. We aim to establish the precise timing and magnitude of these rapid rises of sea level by constructing detailed 500-yr histories of sea-level changes in six sites around the North Atlantic Ocean. These records will be based on the remains of fossil plants and animals buried in coastal sediments which are excellent indicators of the past level of the sea. Timing is key, so we will use the most advanced dating methods, in particular ultra-high precision radiocarbon dating techniques, to find out when the rapid increases in sea-level rise occurred. If the changes we observe occurred in various sites at the same time, then it would imply that hitherto unknown episodes of land-based polar ice melt are responsible. There are important processes that obscure the sea-level signal derived from melting ice that may be observed in coastal sediments and tide gauges. These include changes in the density of sea water - leading to expansion/contraction - due to temperature and salinity variations and vertical movements of the coast. We will correct for these processes separately, using models and available tide-gauge and ocean temperature measurements. First, we will create a model that can calculate steric (density) changes along the coast. Measurements of ocean density are available for the past 50 years, but these were taken in the open ocean, not near the coast. Many processes operating on the continental shelves, such as tides, currents and winds, mix the water column in these areas and so using ocean records may be inaccurate. Our model will help us to predict how the water density changes at the coast following a measured change in the middle of the ocean. A second model can simulate ocean steric changes for the past 500 years, a period for which ocean density and temperature data are not available. Some additional corrections for wind, air pressure and tidal changes, are also necessary but these are relatively easy to do. Second, we need to remove the effects of long-term land movements from our records. We will do this by reconstructing sea-level trends over the last 2000-3000 years and subtracting these from the proxy reconstructions. There are also geophysical models and GPS data that can help with this correction. The 'corrected' records of sea level will be analysed to determine whether synchronous episodes of sea-level rise have occurred in the past 500 years. We believe the work is important because it will, for the first time, enable us to test whether accelerations in sea-level in the North Atlantic have occurred at the same time or not, and if they have, we can determine how big they were. These data will provide important 'baseline' constraints for future sea-level predictions.
 
Description We found evidence that during past centuries sea-level change in the western Atlantic is very different from the eastern Atlantic. The 20th century acceleration, for example, is much more pronounced in the western Atlantic. We have also found a close relationship between centennial scale sea-level changes and the North Atlantic Oscillation. In Iceland this relationship is positive; along the North American East Coast negative.
Exploitation Route The NAO can serve as a proxy for sea level, which provides opportunities for better predictions. Our data can also be used by semi-empirical models to predict future sea-level change.
Sectors Environment

 
Description Barack Obama tweet
Geographic Reach North America 
Policy Influence Type Citation in other policy documents
URL https://twitter.com/barackobama/status/704770760259166208
 
Description US Senate debate
Geographic Reach North America 
Policy Influence Type Citation in other policy documents
URL https://www.youtube.com/watch?v=mBIUIZLXVmA
 
Description NERC Standard Grant
Amount £628,000 (GBP)
Funding ID NE/R010846/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 06/2018 
End 05/2021
 
Description North Atlantic sea-level variability during the last half-millennium
Amount £24,440 (GBP)
Funding ID 1490.0810 
Organisation Research Councils UK (RCUK) 
Sector Public
Country United Kingdom
Start 08/2010 
End 12/2013
 
Description North Atlantic sea-level variability during the last half-millennium
Amount £57,420 (GBP)
Funding ID 1604.0112 
Organisation Research Councils UK (RCUK) 
Sector Public
Country United Kingdom
Start 01/2012 
End 03/2013
 
Description North Atlantic sea-level variability during the last half-millennium
Amount £57,420 (GBP)
Funding ID 1604.0112 
Organisation Research Councils UK (RCUK) 
Sector Public
Country United Kingdom
Start 01/2012 
End 01/2013
 
Description North Atlantic sea-level variability during the last half-millennium
Amount £24,440 (GBP)
Funding ID 1490.081 
Organisation Research Councils UK (RCUK) 
Sector Public
Country United Kingdom
Start 08/2010 
End 03/2013
 
Description North Atlantic sea-level variability during the last half-millennium
Amount £101,440 (GBP)
Funding ID 1566.0511 
Organisation Research Councils UK (RCUK) 
Sector Public
Country United Kingdom
Start 05/2011 
End 12/2013
 
Description North Atlantic sea-level variability during the last half-millennium
Amount £101,440 (GBP)
Funding ID 1566.0511 
Organisation Research Councils UK (RCUK) 
Sector Public
Country United Kingdom
Start 05/2011 
End 03/2013
 
Description Climate Central report 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Climate Central issues a parallel report to our paper in PNAS (Kopp, R.E., Kemp, A.C., Bittermann, K., Horton, B.P., Donnelly, J.P., Gehrels, W.R., Hay, C.C., Mitrovica, J.X., Morrow, E.D., Rahmstorf, S., Temperature-driven global sea-level variability in the Common Era, 2016, Proceedings of the Natural Academy of Sciences, doi:10.1073/pnas.1517056113) which received widespread attention and was cited in most press coverage about the paper. Graphs from the report were used in a US Senate debate about climate change (http://www.c-span.org/video/?c4582233/climate-change).
Year(s) Of Engagement Activity 2016
URL http://www.climatecentral.org/news/study-reveals-acceleration-of-sea-level-rise-20055
 
Description Paper ranks 3rd in 2016 ranking list of climate papers that received most press 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Article shows that our paper reached 186 news outlets, 200 tweeters, and 109 Facebook walls.
Year(s) Of Engagement Activity 2016
URL https://www.carbonbrief.org/analysis-climate-papers-featured-media-2016?utm_content=buffere3464&utm_...
 
Description Press release PNAS paper 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Associated Press press release. Picked up by the NY Times (front page) and Washington Post and about 160 other news outlets. See https://pnas.altmetric.com/details/5963104/news. Currently (10/3/16) #11 of 37,318 PNAS articles in Altmetric ranking.

The Daily Mail was among media outlets that covered the research in the UK. BBC World News interviewed Professor Roland Gehrels about the historical fluctuations of global sea levels.
Year(s) Of Engagement Activity 2016
URL http://bigstory.ap.org/article/7108567e23c44cb68711046f1dfb9ad0/seas-are-rising-way-faster-any-time-...
 
Description Press release PNAS paper 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Media (as a channel to the public)
Results and Impact Press release by University of York press office
Year(s) Of Engagement Activity 2016
URL https://www.york.ac.uk/news-and-events/news/2016/research/sealevel-warming-millennia/