Skip to main content

Uncertain World: Understanding past and future sea level rise

A recent study published in Science Advances suggests that if we burn all attainable fossil fuels (up to 12,000 gigatonnes of carbon), the Antarctic ice sheet is likely to become almost ice-free within 10,000 years. However, what does this mean in terms of sea level rise? To illustrate this we have designed an infographic which shows the likely extent of sea level rise under a range of different scenarios. We have chosen to use the Wills Memorial Building as an example and assume, for the purpose of this exercise, that it resides at sea level (Figure 1).

1) Sea level rise over the next century:

The most recent report by the Intergovernmental Panel on Climate Change (IPCC AR5) indicates that if we continue emitting greenhouse gases under business-as-usual scenarios (i.e. no reduction in emissions), it is likely that global mean sea level will rise between 0.52 and 0.98 m by the year 2100. If we are more optimistic, and we allow greenhouse gas emissions to peak in 2040 and decline thereafter, the range of likely global mean sea level rise is lower, but not insignificant (0.36 to 0.71 m). Both of these estimates are illustrated below and shown alongside the Wills Memorial Building. 

Figure 1: An infographic showing the approximate height of sea level rise depending upon a range of different scenarios (Fretwell et al., 2013; IPCC AR5). This assumes the Wills Memorial Building resides at sea level

Although ~30 to 100 cm of sea level rise may seem insignificant, it is worth considering what this means for other regions. For example, "...since 80% of its 1,200 islands are no more than 1m above sea level", sea level rise has the potential to impact up to 360,000 citizens and lead to widespread migration.

The reason that scientists provide a range of values for sea level rise is that the climate system is very complex. For example, under low emissions scenarios, there is expected to be an increase in moisture content around Antarctica, leading to increased snowfall along the ice sheet margins. However, under higher emissions scenarios, ice sheet discharge overcompensates for an increase in snowfall, leading to a net sea level rise.

2) Sea level rise over 10,000 years:

The variations between these two emission scenarios are less important when looking over longer timescales. Winklemann et al. (2015) have recently simulated changes in the Antarctic ice sheet over the next 10,000 years using a combination of climate and ice sheet models. From these experiments, it is clear that ice loss is driven by two key feedback mechanisms. The first begins with warming and subsequent retreat of the grounding line (Figure 2). The grounding line is the region where ice transitions from a grounded ice sheet to a freely-floating ice shelf. When the grounding line retreats to a point where the ice sheet falls below sea level, then ice sheets can become unstable.

Figure 2: A schematic of an ice sheet showing the position of the grounding line (bottom right). Image credit:

Winklemann et al. (2015) argue that the West Antarctic Ice Sheet (WAIS) becomes unstable when cumulative carbon emissions reach 600 to 800 gigatonnes of carbon (this is equivalent to a 2 degree rise in temperature by 2100). If this part of the Antarctic Ice Sheet becomes unstable, we can expect ~4 m of global sea level rise (Figure 1).Once a specific temperature is reached, a second feedback then kicks in. This destabilises the rest of the Antarctic ice sheet via the so-called surface elevation feedback. On the timescale of 10,000 years this will eventually lead to an almost ice-free Antarctica (Winklemann et al. 2015).

Figure 3: Predicted ice-sheet loss on Antarctica under different carbon emission pathways (Winkelmann et al., 2015: Science Advances).

3) Sea level rise over millions of years:

Palaeoclimatologists can provide insights into the fate of ice sheets over longer timescales. For example, the last time Antarctica was ice-free was during the early Eocene (~56 to 48 million years ago). During this interval, carbon dioxide concentrations were much higher and allowed the development of lush, tropical rainforests along the ancient coastline (Figure 4). Gradual cooling over millions of years eventually culminated in the sudden and rapid establishment of ice-sheets on Antarctica. This occurred ~34 million years ago and was likely driven by a reduction in carbon dioxide (and perhaps some other feedback mechanisms). Although Antarctica has fluctuated in size since then, it has never been completely ice-free since the Eocene. However, under rising carbon emissions, we are rapidly returning to a world that has not been seen for at least 34 million years.

Figure 4: This may be what the East Antarctic coastline looked like during the early Eocene (Pross et al., 2012). 

Further reading:
  • Fretwell et al. 2013. Bedmap2: improved ice bed, surface and thickness datasets for Antarctica. The Cryosphere. v. 7.
  • Winkelmann et al. 2015 Combustion of available fossil fuel resources sufficient to eliminate the Antarctic Ice Sheet. Science Advances, v.1. 
  • Bamber et al., 2009. Reassessment of the Potential Sea-Level Rise from a Collapse of the West Antarctic Ice Sheet. Science. v. 324
  • Church et al. 2013.  Sea Level Change. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA (see Chapter 13; Table 13.5, p. 1182 for 21st Century sea-level rise estimates).
  • Pross et al., 2012. Persistent near-tropical warmth on the Antarctic continent during the early Eocene epoch. Nature. v. 488.
n.b. As with the IPCC, we occasionally use the following terms to indicate the assessed likelihood of an outcome or a result. These are noted in italics: Virtually certain 99–100% probability, Very likely 90–100%, Likely 66–100%, About as likely as not 33–66%, Unlikely 0–33%, Very unlikely 0–10%, Exceptionally unlikely 0–1%.


Correction: the original post incorrectly stated that "... more than 80% of the Maldives lie one metre below sea level". This has since been amended. Thanks to @radicalrodent for spotting this.

This blog was written by Gordon Inglis (@climategordon), a palaeoclimatologist working in the Organic Geochemistry Unit within the School of Chemistry. The infographic was created by Catherine McIntyre (@cathmci), an organic geochemistry PhD student working in same group.

Popular posts from this blog

Are you a journalist looking for climate experts? We've got you covered

We've got lots of media trained climate change experts. If you need an expert for an interview, here is a list of Caboteers you can approach. All media enquiries should be made via  Victoria Tagg , our dedicated Media and PR Manager at the University of Bristol. Email or call +44 (0)117 428 2489. Climate change / climate emergency / climate science / climate-induced disasters Dr Eunice Lo - expert in changes in extreme weather events such as heatwaves and cold spells , and how these changes translate to negative health outcomes including illnesses and deaths. Follow on Twitter @EuniceLoClimate . Professor Daniela Schmidt - expert in the causes and effects of climate change on marine systems . Dani is also a Lead Author on the IPCC reports. Dani will be at COP26. Dr Katerina Michalides - expert in drylands, drought and desertification and helping East African rural communities to adapt to droughts and future climate change. Follow on Twitter @_k

Urban gardens are crucial food sources for pollinators - here’s what to plant for every season

A bumblebee visits a blooming honeysuckle plant. Sidorova Mariya | Shutterstock Pollinators are struggling to survive in the countryside, where flower-rich meadows, hedges and fields have been replaced by green monocultures , the result of modern industrialised farming. Yet an unlikely refuge could come in the form of city gardens. Research has shown how the havens that urban gardeners create provide plentiful nectar , the energy-rich sugar solution that pollinators harvest from flowers to keep themselves flying. In a city, flying insects like bees, butterflies and hoverflies, can flit from one garden to the next and by doing so ensure they find food whenever they need it. These urban gardens produce some 85% of the nectar found in a city. Countryside nectar supplies, by contrast, have declined by one-third in Britain since the 1930s. Our new research has found that this urban food supply for pollinators is also more diverse and continuous

#CabotNext10 Spotlight on City Futures

In conversation with Dr Katharina Burger, theme lead at the Cabot Institute for the Environment. Dr Katharina Burger Why did you choose to become a theme leader at Cabot Institute ? I applied to become a Theme Leader at Cabot, a voluntary role, to bring together scientists from different faculties to help us jointly develop proposals to address some of the major challenges facing our urban environments. My educational background is in Civil Engineering at Bristol and I am now in the School of Management, I felt that this combination would allow me to build links and communicate across different ways of thinking about socio-technical challenges and systems. In your opinion, what is one of the biggest global challenges associated with your theme? (Feel free to name others if there is more than one) The biggest challenge is to evolve environmentally sustainable, resilient, socially inclusive, safe and violence-free and economically productive cities. The following areas are part of this c