The First Church of Climate Change demands absolute fealty lest Mother Gaia smite thee mightily with a fearsome blow. This is why, for example, true believers such as Barack Obama only purchase property guaranteed safe from rising sea levels and … oh, wait …
Nevertheless, intrepid defenders of the faith are unceasing in their efforts, demanding who do you believe: them, or your lying eyes and ears. The latest foray involves recently circulated photos of Sydney Harbor taken some 140 years apart.
Let the outrage begin, courtesy of Reuters:
It is not possible to gauge sea level rise simply by comparing two images of a location side-by-side, experts told Reuters, despite claims made online.
Oh, really. Do tell.
The photographs may reflect “different tidal stages,” Gary Griggs, Distinguished Professor of Earth and Planetary Sciences, University of California, Santa Cruz, told Reuters.
An absolute global rate of sea-level rise has been recorded since 1993 by orbiting satellites, Prof Griggs said.
“This rate has averaged 3.42 mm/yr. but over the past decade or so has increased to 4.77mm/yr. over the past 10 years,” he said.
This begs the question of how sea levels are determined via satellite. Since hanging a giant dipstick from one into the ocean would doubtless prove unwieldy, the method involved is described thusly:
Satellite altimetry is all about timing. Sea-surface height can be measured by the time it takes for radar pulses to hit the ocean surface and bounce back to the spacecraft. Laser altimetry works in a similar manner, as laser pulses bounce off land-ice and sea-ice surfaces. But this method requires precise knowledge of satellite altitude, as well as the terrestrial reference frame (see question on how NASA studies sea level change). Extensive calibration is necessary to ensure the accuracy of altimetry measurements.
So, we’re depending on NASA knowing exactly how high their and others’ satellites are flying to keep tabs on the ocean level. Good to know.