Earth’s crust may seem like a rigid certainty, something that is eternally unyielding, but it’s not. Despite being made of a variety of different but unwaveringly strong rock types, both the continental crust and the oceanic crust can, and have, warped over time. Remember that the record-breaking rainfall dumped on Texas by Hurricane Harvey caused the ground there to warp downwards.
Now, as reported in a pre-Christmas study in the journal Geophysical Research Letters - and as first spotted by Earther - we’ve detected another major deformation in the crust, and this time, it’s planetwide. Thanks to climate change and the mass melting of landlocked ice, the oceans are rising and the seafloors are being significantly deformed.
According to the study led by the Netherlands’ Delft University of Technology, the crust down there has warped so much that the global average sea level rise measurement has been inaccurately measured over the last two decades. Don't worry though: the inaccuracy is so slight that we've still got a solid grasp on how quickly we're affecting the climate and causing the waves to encroach upon our shores.
Sea level rise is primarily measured by satellites these days, but they can’t tell if the seafloor is being deformed or not. When the colossal addition of water was taken into account, the team calculated that satellites have missed out on an extra 8 percent of sea level rise.
This huge redistribution of mass isn’t the only thing that causes the sea level to change, though. This mass addition by meltwater flow is known as barystatic sea level rise, but the thermal expansion of the oceans and changes in salt content (steric sea level rise) also plays a major role.
Additionally, satellites – whose coverage isn't equal across the planet, particularly around the poles – aren’t the only method of measuring sea level change.
The mass balance change is also far from even across the entire planet. As the ice itself melts, some parts of the crust, mostly in the Northern Hemisphere, are actually flexing back upwards. In contrast to this, the Southern Hemisphere’s crust is subsiding faster than the global average.
"The largest differences between relative and geocentric sea level can be found in high-latitude areas close to the major ice melt sources," the authors explain in their study.
"A substantial part of the surface mass redistribution is caused by mass loss from Greenland and the glacierized regions surrounding the Arctic Ocean."
By a separate estimate, the region around the rapidly thawing Greenland ice sheet is rising up by 12 millimetres (0.47 inches) per year - an astounding rebound rate.
When everything is considered together, it appears that barystatic sea level rise has been underestimated by 0.1 millimeters (0.004 inches) per year on average.
Regional variations in the shapes and mechanical properties of ocean basins mean that this can sometimes be far higher in parts. The Arctic Ocean, for example, has had its barystatic sea level rise underestimated by up to 1 millimeter (0.04 inches) per year.
Pushing down the oceanic crusts of every single major oceanic basin in the world is no small feat, and it’s something that will worsen over time as climate change continues to accelerate. At the very least, it’s masking just how badly we’re affecting the planet, and this study attempts to pull away this veil for the first time.
Calculating such a major geological change isn’t easy either. In order to do this, the team used the best estimates possible of how much land-based ice and water is making its way into the oceans. They plugged these numbers into a series of computer models and watched as their virtual oceans bent and pushed at the creaking oceanic crust.
“To increase the accuracy of sea level estimates, the effect of ocean bottom deformation should be taken into account,” the researchers stress in their study.
They suggest using a satellite system similar to the now-terminated GRACE mission. By detecting small localized changes in gravity, the barystatic sea level rise could be properly quantified.
Far stranger things are happening to the planet due to this redistribution of water. As noted by a 2016 study, it’s also altering how Earth rotates on its axis. The northern end of this rotational axis – the North Pole, essentially – is drifting eastwards as a result, and it’s heading toward London.
