Is Worldwide Sea Level Rise Occurring?

Is worldwide sea level rise occurring?

Check out this answer from Consensus:

The evidence overwhelmingly supports the conclusion that worldwide sea level rise is occurring and accelerating. This rise is driven by thermal expansion of seawater and the melting of glaciers and polar ice sheets. While there are regional variations and uncertainties, the overall trend is clear and consistent with the impacts of global warming. Continued monitoring and improved modeling are essential for accurate future projections and effective coastal adaptation strategies.

The question of whether worldwide sea level rise is occurring is critical for understanding the impacts of climate change. Numerous studies have investigated this phenomenon using various methods, including satellite altimetry, tide-gauge data, and climate models. This synthesis aims to present a cohesive overview of the current state of knowledge on global sea level rise.

Key Insights

• Consistent Rise in Sea Levels Over the 20th and 21st Centuries:
  • Multiple studies confirm that global sea levels have been rising consistently over the past century. The rate of rise has varied, with estimates ranging from 1.5 mm/year to 3.4 mm/year depending on the period and method of measurement1 3 5 7.
• Acceleration of Sea Level Rise:
  • There is a significant acceleration in the rate of sea level rise, particularly noted since the late 19th century. This acceleration has been attributed to increased global temperatures and melting ice sheets1 3 6.
• Impact of Thermal Expansion and Ice Melt:
  • The primary contributors to sea level rise are thermal expansion of ocean water and the melting of glaciers and polar ice sheets. Studies indicate that thermal expansion alone cannot account for the observed rise, highlighting the significant role of ice melt7 9.
• Recent Trends and Projections:
  • Recent data from satellite altimetry show that the rate of sea level rise has increased in the past few decades, with current rates around 3.2 mm/year to 4.4 mm/year. Projections suggest that this trend will continue and possibly accelerate further due to ongoing global warming1 4 6 10.
• Regional Variability and Uncertainties:
  • There is considerable regional variability in sea level rise due to factors such as land subsidence, ocean currents, and local climatic conditions. This variability introduces uncertainties in global estimates and necessitates localized studies for accurate predictions2 5 8.

 

 

Is worldwide sea level rise occurring?

Marco Marani has answered Near Certain

An expert from Duke University in Hydrology

Sea-level rise is a fact that is agreed upon by all scientists, even by those that are tepid supporters of anthropogenic climate change (i.e. of the fact that observed changes in the earth system are caused by human activities).

The Intergovernmental Panel on Climate Change (a panel of hundreds of scientists put together by the United Nations and the World Meteorological Organization to which about 195 Countries are contributing) devoted a whole chapter of it 2013 report to analyzing sea-level rise in the past and its projections for the future. The Chapter can be found here:

https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapter13_FINAL.pdf

Figures showing how sea level has changed over time can be found here:

https://www.ipcc.ch/report/ar5/wg1/sea-level-change/

 

Is worldwide sea level rise occurring?

Eigil Kaas has answered Near Certain

An expert from University of Copenhagen in Climatology, Geophysics, Meteorology

This is not “near certain” but “certain”. Numerous theoretical, observational and modeling studies support this.

Our planet is currently losing less radiative energy (in terms of infrared radiation) than it net gets from the sun. Theoretically this should be the case because the composition of the atmosphere is changing. Therefore, we can also with certainty measure increases in the internal energy of the whole climate system: the oceans plus the ice-sheets / glaciers plus soils plus lakes and plus the atmosphere. I.e., the temperature is generally increasing. This said, there are a lot of temporal fluctuations from year to year and from decade to decade – and even more so when regional climate is considered. This is because the climate system is chaotic and re-organizes the heat between its different compartments.

By far the most of the net surplus of heat received by the planet ends up in the oceans, where we nowadays have very good observational coverage via the ARGO fleet. When the oceans are heated they expand, and this is a main contributor to present-day sea level rise. Of course, melting glaciers and ice-sheets are also main contributors (plus others).

Global sea level can be measured very accurately using satellite altimetry, and locally with tide gauges. As for temperature, there are also temporal fluctuations in sea level, which are much larger locally than globally. There are even regions with recent decadal decreases, e.g., related to variations/changes in the ocean currents. It may be that such local measurements have contributed to the misconception that sea level is not rising in general. On average it is currently rising about 3.4 mm each year.

 

Is worldwide sea level rise occurring?

Mark Schuerch has answered Near Certain

An expert from University of Lincoln in Geography

There is a range of different global dataset that evidence global sea level rise, particulary prominent within the last few decades. These datasets include data from global networks of tide gauges, satellite altimetry or sediment records.

 

Is worldwide sea level rise occurring?

Catia M Domingues has answered Near Certain

An expert from University of Tasmania in Oceanography

Many lines of evidence from different in situ and satellite observation-based that, on the global mean, sea level is rising and the rate of rise is accelerating.

 

Is worldwide sea level rise occurring?

Martin Vermeer has answered Near Certain

An expert from Aalto University in Geophysics

I would go for “certain”. It’s really not a hard question. Had it been something like “has sea-level rise accelerated?” or “has sea level ever before risen at the current rate?” or “is sea level rising because of human activity?”, I would have had to give a more conditional answer.

I will not in detail go into the evidence but just give the link to the sea-level chapter in the fifth IPCC assessment:

https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapter13_FINAL.pdf

This is a “meta-review” synthesizing the research in this field, i.e., close to the top of the evidence pyramid:

https://www.library.qut.edu.au/search/getstarted/howtofind/evidencebased/images/evidencepyramid.png

I know many of these people, have worked with some of them, they are professionals and can be trusted to say it like it is. So, not only is sea-level rise occurring, currently at a rate of some 3 mm/a, but it has accelerated, having been 1.2 mm/a or so over the 20th century, and around zero for the several thousand years before that:

https://upload.wikimedia.org/wikipedia/commons/1/1e/Holocene_Sea_Level.png

Before that, coming out of the Ice Age produced a rapid sea-level rise naturally.

 

Is worldwide sea level rise occurring?

Frank Pattyn has answered Near Certain

An expert from Université Libre de Bruxelles in Glaciology

Sea level has been rising continuously at a rate of approximately 2.2 mm/year during the 20th century and the last decades accelerated to 3.4 mm/year. While the past century the rise was dominated by thermal expansion of the oceans (ocean waters getting less dense due to surface warming, hence increasing in volume), the last decades the signal becomes dominated by the loss of glacier ice, melting of the Greenland ice sheet and mass loss from the Antarctic ice sheet.

 

Is worldwide sea level rise occurring?

Stephen F Price has answered Near Certain

An expert from Los Alamos National Laboratory in Earth Sciences

There have been numerous scientific papers published over the past decade (and more) documenting that global sea level rise is happening, largely as a result of ocean thermal expansion and increased mass loss from glaciers and ice sheets. While the rate of sea level rise varies regionally (due to a range of complicating factors, such as ocean circulation, regional variations in earth’s gravity field), averaged over the whole globe it is increasing at a rate of several mm per year.

 

Is worldwide sea level rise occurring?

Eric von Wettberg has answered Near Certain

An expert from University of Vermont in Biology, Ecology, Marine Ecology

Sea level can be measured from satellites and from tide gauges, which have records continuing back into the middle of the 19th century. Although the amount of sea level varies some from place to place, due to factors like glacial rebound in areas closer to the poles, it is a well documented global phenomena of enormous consequences. The two majors causes of sea level rise are melting of ice on land in places like Antarctica, Greenland, and the Himalayas, and thermal expansion of seawater as it warms.

 

Is worldwide sea level rise occurring?

Roxy Mathew Koll has answered Near Certain

An expert from Indian Institute of Tropical Meteorology in Earth Sciences, Atmospheric Science, Oceanography, Meteorology, Climatology

During the 20th century, the sea level increased in the range 10-20 cm per decade. These are based on century long observations from tide gauges. Recent satellite data indicate a change of 26-29 cm per decade, which is consistent with improved tide gauge observations which show a change of 28 cm per decade, since the 1990s. Several studies using multiple observation datasets and climate model simulations have consistently shown that the sea level has been rising monotonously, and that global warming has a major role on it. The sea level rise is due to the thermal expansion of sea water due to increasing temperatures and also due to melting ice/snow/glaciers.

 

Is worldwide sea level rise occurring?

Neil Saintilan has answered Near Certain

An expert from Macquarie University in Environmental Science, Ecology, Marine Science, Marine Ecology

There are two sources of evidence which independently concur that sea-level has been rising at about 3.4 mm per year over the past few decades. First, tide gauges across the world give us a picture of how sea-level is changing in relation to the elevation of land masses. In tectonically stable coastlines (like Australia), tide gauges show a consistent increase in sea-level when analysed over inter-decadal time-scales. The second line of evidence is satellite altimeters, which continuously assess the distrance between the ocean surface and the satellite using active sensors. These provide a global picture of sea-level rise consistent with (a) the tide gauge records, corrected for land subsidence and (b) the projections of models relating sea-level to changes in ocean temperature and volume.

 

Is worldwide sea level rise occurring?

Ki-Weon Seo has answered Near Certain

An expert from Seoul National University in Geophysics

The answer is yes. Global mean sea level has risen about 3.5 mm every year recently based on satellite altimeter data.

 

Is worldwide sea level rise occurring?

Hamish D Pritchard has answered Near Certain

An expert from British Antarctic Survey in Glaciology

Sea level has been directly observed by tide gauges, satellite altimetry and satellite gravimetry. While each technique has measurement uncertainties, the techniques are independent and agree that global mean sea level is rising. Sea level rise is also in agreement with observed losses of water from storage on land, notably from glaciers and the Greenland and Antarctic ice sheets, and possible smaller contributions from other stores such as groundwater. Finally, the rising global mean sea level is also in agreement with ocean thermal expansion, and ocean warming has also been observed.

Any dispute of whether global sea level rise is occurring would have to overturn these independent lines of observational evidence and the established logic that links warming to ice loss and ocean thermal expansion to their effects on sea level. Given that many people in multiple separate fields have been researching this issue for many years without managing this, realistically we can say that it isn’t going to happen. The fact of global sea level rise is here to stay.

There is extensive scientific literature on these topics. Examples include:

Church, J. A. 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 [Stocker, T. F., D. Qin, G. K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P. M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Dangendorf, S. et al., 2017: Reassessment of 20th century global mean sea level rise. Proceedings of the National Academy of Sciences, 201616007.

Nerem, R. S. et al., 2018: Climate-change–driven accelerated sea-level rise detected in the altimeter era. Proceedings of the National Academy of Sciences, doi:10.1073/pnas.1717312115.

Blazquez, A. et al., 2018: Exploring the uncertainty in GRACE estimates of the mass redistributions at the Earth surface: implications for the global water and sea level budgets. Geophysical Journal International, 215 (1), 415-430.

Chambers, D. P. et al., 2017: Evaluation of the global mean sea level budget between 1993 and 2014. Surveys in Geophysics, 38 (1), 309-327.

Storto, A. et al., 2017: Steric sea level variability (1993–2010) in an ensemble of ocean reanalyses and objective analyses. Climate Dynamics, 49 (3), 709-729.

Bamber, J. L., Westaway, R. M., Marzeion, B. & Wouters, B. The land ice contribution to sea level during the satellite era. Environmental Research Letters 13, 063008, doi:10.1088/1748-9326/aac2f0 (2018).

 

Is worldwide sea level rise occurring?

James Baldini has answered Near Certain

An expert from Durham University in Palaeoclimatology, Geochemistry, Climatology

Before this question can be answered it is important to note that sea level rise is complex and spatially heterogeneous. Although global mean sea level (sea level averaged at every location across the globe) is almost certainly rising, in any one given location relative sea level (sea level relative to the land in that location) might actually be dropping. The causes of relative sea level change are complex.

The melting of ice sheets and thermal expansion of the oceans both cause the volume of water in the oceans to increase, causing sea level rise globally. Because temperatures are rising globally, this effect is certainly happening. However, land in places that were previously glaciated was pressed down by the glaciers (which melted ~10,000 years ago) is currently rising, so if you measure sea level in one of these locations (say Hudson Bay, Canada, or Stockholm, Sweden) you would find that the land is rising faster than the sea is rising – i.e., relative sea level is dropping. On the other hand, there are places that were near the ice sheets (but not right underneath them), where the land is dropping and meeting the rising sea, so the relative sea level change is greater than the global average.

Winds also control local sea level. A good example of this is the equatorial Pacific, where the trade winds normally push water towards the western part of the Pacific basin, so that the western Pacific has a higher sea level than the eastern Pacific. During an El Nino event though, these winds slacken and the waters are allowed to slosh back across the basin, dropping sea level in the west and causing dramatic sea level rise in the east. There are many other examples of these sorts of complexities.

Seismically active islands and locations also have different relative sea level change rates compared to other places. So in order to determine a global mean sea level change rate, one must take the mean of many different locations that were far away from the Last Glacial ice sheets and are tectonically stable. Good locations would be places like Bermuda, Tahiti, or the Bahamas. It is very easy to ‘cherry-pick’ locations to suit an argument, and this is something that people arguing that sea level isn’t changing do quite a lot, so these cases need to be ignored. The only estimates that are valid are from multiple sites over longer periods of time. These averages demonstrate that sea level is now rising at more than 3 mm per year. This has been independently confirmed using satellite measurements over the last few decades, which also derive a number of over 3 mm per year global average sea level rise. So in conclusion, global average sea level is almost certainly rising due to the near equal contributions of melting ice sheets and thermal expansion of the oceans, although any one individual location has its own signal where only one component is this global (‘eustatic’) signal.

 

Is worldwide sea level rise occurring?

Kerrylee Rogers has answered Near Certain

An expert from University of Wollongong in Geomorphology, Ecology

The sea is rarely stable, and neither is the land. Together, both of these components lead to changes in the level of the sea with respect to land. Increases in the volume of oceans globally leads to ‘eustatic sea level rise’, whilst declines in land elevations due to sediment consolidation, subsidence or isostasy can lead to ‘relative sea-level rise’. We know that relative sea level has risen in the past, as this has been recorded in substrates by biological markers that indicate prior sea levels. For example, mangrove forests grow at or near sea level, and palaeo or fossilised mangrove material extracted from cores can be used to indicate past sea levels. There is substantial palaeoecological evidence and other physical markers in landscapes that indicate that seas have not been stable and have been changing substantially over geological timescales

It is therefore not surprising that the sea is rising, ratehr the surprise is that the degree of sea-level rise is occurring in association with very high atmospheric carbon concentrations that are well beyond what would be expected. We know that the sea is rising now because we are not only recording rises in eustatic sea level one tide gauges and satellite altimetry that measures the elevation of oceans globally, but we are also seeing that many ecosystems that are positioned along coastlines at certain elevations that correspond to sea level have been changing; these changes are best explained by sea-level rise. Mangrove forests, in particular have globally been expanding across intertidal gradients and these changes have been noted to correspond to changes in sea level. At smaller spatial scales, there are locations where relative sea level has been falling due to hydrological alterations of isostatic uplift; and along these coastlines changes in coastal ecosystem extent correspond to the direction of change in sea level.

In combination, observational evidence from tide gauges and satellite altimetry, as well as biological indicators of sea level all point to large scale changes in sea level that are related to eustatic changes to the ocean volume. Where relative sea level does not indicate a rise at a loca scale, this is typically related to uplift of land surfaces or small-scale hydrological changes, and does not indicate that eustatic sea levels are not rising. There is high certainty that globally the volume of oceans has increased resulting in eustatic sea level rise, which translates to relative sea level rise along most shorelines.

 

Is worldwide sea level rise occurring?

Katherine Hagemann has answered Near Certain

An expert from Miami-Dade County in Environmental Science

We have multiple forms of measurement both from a global network of tide gauges and more recent satellite measurements. These measurements are consistent and indicate the trend is global. we also have direct and satellite measurements of melting ice sheets which directly contributes to sea level rise.

Sea level change is not uniform around the globe and varies by location depending on the vertical movement of the land. This leads to the “relative” sea level rise at each locations. In locations where the land is subsiding or sinking the sea level appears to be rising faster, but it is really an indicator of both a change in the land and the water happening at the same time. Conversely, in some locations the land is “bouncing” back after being depressed by the weight of the ice sheets. Because the land is moving up faster than the sea is rising the relative sea level rise at those locations appears to be falling.