A deadly climate change effect is even worse than feared, study finds

Sea level along the world’s coastlines is often much higher than previously assumed, a new study finds.

Climate change may threaten tens of millions more people than previously believed, according to a new study that says previous research used incorrect information about water levels along the world’s coastlines.

The new research, published March 4 in the peer-reviewed British journal Nature, found that more than 90% of the existing sea-level studies use a reference sea level that is lower than the actual sea level along the coast. That means already dire projections about sea level rise might be underestimating the risk.

“Our calculations show that measured coastal sea levels in many places on Earth are higher than is often assumed in coastal impact studies,” said study lead author Katharina Seeger, of the University of Padua in Italy, in a statement. “Our findings make it necessary to re-evaluate and, in most cases, update the underlying methodology of all existing coastal hazard studies," she added.

Sea-level rise, one of the clearest signals of human-caused global warming, is driven by warming and expanding ocean water, as well as the melting of mountain glaciers, ice caps and the vast Greenland and Antarctic ice sheets.

Seas have risen nearly 8 inches worldwide since 1880, but unlike water in a bathtub, they don't rise evenly.