S u m m a r y :
Sea level rise is not keeping a steady rate: rather, it is accelerating a little every year, says a new study published in PNAS.
Rate of Sea Level Rise Increasing
Global sea level rise has remained a huge problem for decades now, and it might be worse than previously thought. A new research conducted by a team from the University of Colorado Boulder has reviewed 25 years of satellite data to investigate the rate of sea level rise, the results of which are alarming. While it is believed that the increase is happening at a constant 3 mm per year, the findings show that the rate of increase is itself going up by around 0.08 mm per year, implying that the annual rate of sea level rise might reach around 10 mm per year by 2100.
“This acceleration, driven mainly by accelerated melting in Greenland and Antarctica, has the potential to double the total sea level rise by 2100 as compared to projections that assume a constant rate—to more than 60 cm instead of about 30.” says lead author Steve Nerem, a professor of Aerospace Engineering Sciences from the University of Colorado Boulder.
“And this is almost certainly a conservative estimate.”
“Our extrapolation assumes that sea level continues to change in the future as it has over the last 25 years. Given the large changes we are seeing in the ice sheets today, that’s not likely.”
65 cm Rise in Around 80 Years
If the sea level keeps this upward spiralling trend, sea level will have risen to 65 cm by 2100, a figure that promises to threaten the existence of coastal cities.
This study is meant to pave the way to further research to predict future occurrences with greater accuracy so that we are better equipped to deal with them when the time comes.
The Processes Behind Sea Level Rise
Sea level rises because of the increased temperatures of air and water resulting from increasing concentrations of greenhouse gases, such as carbon dioxide, in our planet’s atmosphere. The water in our oceans has become warmer, and has thus expanded more, such that it has contributed to around 50% of the 7 cm global sea level rise that has occurred in the last 25 years. Then, another factor is the melting ice that finds its way into the oceans, adding more volume to it.
Using Data From Satellites, Volcanic Activity, and Tide Gauge Measurements
Nerem and his team used a number of measurements to calculate the rate of acceleration. They analysed satellite altimeter data since 1992, including those from the U.S./European TOPEX/Poseidon, Jason-1, Jason-2, and Jason-3 satellite missions. Also, they had to factor in other natural happenings that might influence sea level such as volcanic activity: they, thus, looked into the variability that was caused by the eruption of Mount Pinatubo in 1991 that is said to have decreased the average global sea level. Furthermore, the sea level can be affected by climate patterns like El Niños and La Niñas through changed ocean temperatures and global precipitation patterns. Additionally, tide gauge data was considered to evaluate any error in the estimate.
“The tide gauge measurements are essential for determining the uncertainty in the GMSL (global mean sea level) acceleration estimate,” says co-author Gary Mitchum. “They provide the only assessments of the satellite instruments from the ground.”
That was how the team was able to reveal the the underlying sea-level rate and acceleration in the last 25 years.
“This study highlights the important role that can be played by satellite records in validating climate model projections,” says co-author John Fasullo. “It also demonstrates the importance of climate models in interpreting satellite records, such as in our work where they allow us to estimate the background effects of the 1991 eruption of Mount Pinatubo on global sea level.”
The findings of this study will now be refined through further investigation to better forecast future events pertaining to seal level rise.