Tide models reproduce observed tides once they include the springlike push of internal waves

Internal tides are waves inside the ocean. They form when the surface tide flows over rough seafloor, and the Indonesian archipelago produces strong ones ^[5]. Some break near where they form. Others travel thousands of kilometers first ^[14]. As they travel, they push back on the surface tide. Depending on the timing, that push acts as a brake that drains energy, or as a spring that takes energy in one part of the cycle and returns it later. Most tide models leave the spring out, according to the researchers who wrote the explainer published by phys.org ^[6].

Their recent study added the springlike term, and the models then reproduced observed tides accurately without simulating internal tides directly ^[7]. Simulating them directly takes substantial computing power ^[7]. The design is a shortcut: the model represents what the waves do to the tide, leaves out the waves themselves, and is judged against measured tides ^[7]. The account does not report the model's error against those measurements, or how much, and where, real tides have already changed.

The authors name two uses for a cheaper, reliable model. One is reconstructing past tides, a record of how Earth's rotation and the Moon's orbit have evolved. The other is predicting future tides ^[8].

The future is where warming comes in. Climate change is raising sea level, altering coastlines, warming the upper ocean and making it more stratified, and the authors write that these changes can affect the size of tides ^[9]. Measurements already suggest tides are changing, they write, and changes in stratification may help explain some of it ^[10]. Improved ocean models are also capturing internal tides in greater detail ^[12].

Gravity is only the starting point. Isaac Newton explained tides with gravity in 1687 ^[11]. Real tides, though, slosh back and forth inside ocean basins, often rotating around amphidromic points where the rise and fall is almost zero. Ranges generally grow with distance from those points ^[4]. A bay amplifies the tide when its natural sloshing rhythm, set by its shape and depth, matches the local tide ^[3]. That resonance helps give Canada's Bay of Fundy a range of up to 16 meters ^[2] and Western Australia's Kimberley coast more than 10 ^[1][3]. On the authors' own description, the largest ranges depend on depth and coastline shape, and rising seas and altered coastlines change both ^[3][9].

Going by the authors' account, I'd treat a bay's tidal range as a quantity that can drift with the ocean's state. How strong that claim is depends on measurements the explainer calls only suggestive, with stratification offered as a possible partial cause ^[10].