People walk the flooded waters Hopper Rd. on September 19, 2019 in Houston, Texas. Gov. Greg Abbott has declared much of Southeast Texas disaster areas after heavy rain and flooding from the remnants of Tropical Depression Imelda dumped more than two feet of water across some areas.

A new report from the United Nations says surface temperatures for the world's oceans are rising at an alarming pace, causing marine "heatwaves" and accelerating sea levels that threaten fishing economies.

The heat waves occur when the daily sea surface temperature exceeds the local 99th percentile of the temperature between 1982 and 2016.

"Marine heatwaves have doubled in frequency since 1982 and are increasing in intensity," the special report by the Intergovernmental Panel on Climate Change said Wednesday.

The global ocean temperatures have warmed every year since 1970, and the rate has more than doubled since 1993.

"Future shifts in fish distribution and decreases in their abundance and fisheries catch potential due to climate change are projected to affect income, livelihoods, and food security of marine resource-dependent communities," the report said.

Melting ice sheets in Greenland and the Antarctic have also caused sea levels to rise and accelerate. That increases the frequency of extreme sea level events, which causes disasters such as flooding and tropical cyclones.

Some of the biggest victims are coastal communities, fishing economies, and those in polar and high mountains regions. Rising sea levels will render some island nations uninhabitable. The report said that the low-lying coastal zone is currently home to around 680 million people and is projected to reach more than 1 billion by 2050. Around 670 million people live in high mountain regions, which are particularly vulnerable to changes in the ocean, glaciers and ice sheets.

Ocean warming has also caused a drop in fish populations, which compounds the impact of overfishing and has reduced fishery catches. Communities that depend highly on seafood might also face risk to nutritional health and food security.

The report said that in order to protect and restore the ocean and its ecosystems, humans will need to significantly reduce greenhouse gas emissions and be more conscious about how to manage the use of natural resources.