Human-caused
greenhouse gases in the atmosphere create an energy imbalance, with more than 90% of remaining heat trapped by the gases going into the oceans, according to the National Oceanographic and Atmospheric Association.
Ocean heat content, a measure of the amount of heat stored in the upper levels of the ocean, is a key indicator of global warming.
Last year was the hottest on record for the Earth's oceans, with a record high for global heat content in the upper 2,000 meters of the oceans, which broke the record from the year before.
"The heat fuels storms of all sorts and contributes to very heavy rain events and flooding," Trenberth said.
"The observed increases of upper (ocean heat content) support higher sea surface temperatures and atmospheric moisture,
and fuel tropical storms to become more intense, bigger and longer-lasting, thereby increasing their potential for damage."
Warmer oceans mean more moisture is available in a warmer atmosphere.
"It's one of the simplest relationships in all of meteorology," said Michael Mann, professor of atmospheric science and director of the Earth System Science Center at Pennsylvania State University.
For every 1 degree Celsius (1.8 degree Fahrenheit), there is 7% more moisture in the air.
Ocean temperatures around Florence trended 1.5 degrees C (2.7 degrees F) warmer than normal, contributing to about 10% more moisture available in the atmosphere.
This certainly helped make Florence the wettest tropical system to strike the US East Coast, dumping almost 3 feet of rain on parts of North Carolina.
