Due to melting ice and the expansion of a warming ocean, the global sea level rose at a rate of 1.7mm/year during the 20th century and at a rate of more than 3mm/year since 1993, according to NASA.
Climate scientist Josh Willis explained that the "pothole" was caused by the dramatic shift in natural climate patterns from El Niño to La Niña, which redistributed the globe's water, dumping much of it on land this year. Willis said the drop in sea level doesn't change the long term trend: "We're heating up the planet, and in the end that means more sea level rise ... But El Niño and La Niña always take us on a rainfall rollercoaster, and in years like this they give us sea-level whiplash."
As you can imagine, that key fact won't stop conservative media from employing the well-worn and always wrong tactic of using short-term changes to dismiss the long-term trends driven by human-induced global warming.