Scientists from five countries have collaborated to analyze the causes of sea-level rise since 1900
Recently, Scientific research teams from five countries including the United States, the United Kingdom, China, Belgium, and Germany have got together to carry out international collaborative research on sea-level observations and the impact factors of their changes.
It is directed by the Jet Propulsion Laboratory of the California Institute of Technology and research is clarifying the reason for the sea level rise in the global and various sea basins since 1900 and the paper was published in “Nature” in August 2020.
Global warming has caused the sea-level rise, bringing significant risks to low-lying, coastal areas, and small island countries.
Sea level rise and related disasters are crucial challenges for the sustainable development of human society and the economy in the future.
There is much evidence that the global sea level has continued to rise since the 20th century.
However, “What caused the sea level rise since 1900?” This issue has long been controversial.
The lack of understanding of past sea level changes has also brought more significant uncertainty in predicting future sea-level changes, which is one of the critical scientific issues of the ocean and global changes.
Scientists said: “We have been discussing this issue since 2016. However, there has been no progress before 2019”.
The biggest obstacle is that there are many factors affecting sea level rises, including thermal expansion, mountain glacier retreat, Greenland, and Antarctic ice sheet melting.
Many contributing factors did not have global observations or reconstructed data for research in the last century.
Associate researcher Cheng Lijing of the Institute of Atmospheric Physics of the Chinese Academy of Sciences said:
“Since the reconstruction data of the contributing factors of sea-level change have been published, these advances are the prerequisite for this research to be carried out and published.”
Based on a series of latest scientific developments, in 2019, 11 authors, including nine young scientists jointly researched the reconstruction of sea-level change and its main contributing factors.
In the end, the study gave the most accurate estimates of the reconstruction of sea-level rise since 1900 and its three main contributing factors.
For example, previous studies underestimated global ocean warming and the resulting specific volume rise due to systematic deviations in observational data and gridding methods.
The latest research data (including atmospheric IAP data) provides a more accurate specific volume.
They estimated sea-level change. For another example, after considering the deviation caused by the land’s vertical movement (such as land subsidence), the new tide gauge-based sea level rise in the 20th century is slightly lower than previous estimates (listed in the IPCC-AR5 report).
The study clarified for the first time in the world from the global and ocean basin scales.
After 1900, the total observed sea level rise is equal to the loss of mass of mountain glaciers and ice sheets, changes in ocean water volume caused by changes in land water reserves, and thermal expansion.
The sum of the effects of the three contributing factors of temperature, salinity changes and land-water reserves. Among them, land-water reserves include three main factors:
- Sea-land water transfer caused by natural variability
- Groundwater loss caused by human use
- The impact of dam storage
The first author of the paper, T. Frederikse, said:
“Our research shows that from 1900 to 2018, the contribution of mountain glaciers and ice sheet mass loss is twice the contribution of ocean warming and thermal expansion, and it is the leading factor in sea-level rise in the past century.”
“However, the main contributors to sea-level rise are not the same in each basin”.
For example, the contribution of the increase in the quality of the seawater in the Northwest Pacific is equivalent to the contribution of changes in temperature and salinity, while the contribution of the increase in the quality of the sea in the East Pacific is greater.
The study also found that the sea level has not risen linearly since 1900, and there are significant interdecadal fluctuations in the rate of rising.
The rapid global sea level rise in the 1940s was mainly due to the loss of quality of mountain glaciers and the Greenland ice sheet leading to the input of freshwater into the ocean.
The slowdown in the rate of sea level rise in the 1970s was mainly due to the increase in land water reserves and the decrease in ocean water as a result of the massive construction of dams on land.
The accelerated sea level rise since the 1990s is mainly due to the accelerated warming of the ocean and the accelerated melting of the Greenland ice sheet.
The contribution of Antarctic ice sheet loss has been increasing since 2000.
The study also found that the sea level has not risen linearly since 1900, and there are significant interdecadal fluctuations in the rate of rising.
The rapid global sea level rise in the 1940s was mainly due to the loss of quality of mountain glaciers and the Greenland ice sheet, leading to fresh water’s input into the ocean.
The slowdown in the rate of sea level rise in the 1970s was mainly due to the increase in land water reserves and the decrease in ocean water due to the massive construction of dams on land.
The accelerated sea level rise since the 1990s is mainly due to the accelerated warming of the ocean and the Greenland ice sheet’s accelerated melting.
Since 2000, the contribution of Antarctic ice sheet loss has been increasing.
The research indicates that the scientific community has fully understood the mechanism of sea-level change over the past 100 years.
The research is joint research on sea-level change by cooperating with international scientific research teams in multiple disciplines, including ocean, land, atmosphere, and cryosphere.
The research was led by Thomas Frederikse and Felix Landerer, Jet Propulsion Laboratory (JPL) of the California Institute of Technology.
Among them, the ocean temperature and salinity data and the specific volume of the sea-level change are handled by Cheng Lijing, Institute of Atmospheric Sciences, Chinese Academy of Sciences, and Laure Zanna, New York University.
Glacier equilibrium adjustment and solid earth processes are handled by Lambert Caron and Surendra Adhikari of JPL.
Belgium University David Parkes is responsible for Leuven handles mountain glaciers data.
California Institute of Technology Vincent W. Humphrey is responsible for land water storage.
Tide-gauge data is provided by Peter Hogarth, UK National Ocean Center.
Sea-level change reconstruction based on tide-gauge stations is provided by Sonke Dangendorf, University of Siegen, Germany.
Yun-Hao Wu from Taiwan, China is responsible for dam storage data.
The research was funded by the National Key Research and Development Program, Global Change and Response Special Project “Observation of Key Parameter Observation Data Processing Methods and Product Development for Marine Environmental Changes,” and other projects, using the ocean temperature and salinity grid data independently constructed by China.
