The amount of energy that's warmed the world's oceans over the past 25 years is the same as if 3.6 billion atom-bombs were dropped into them.
A new report has analysed more than half a century of ocean data - painting a picture of the trends of climate change.
Summer's supposed to be an ideal time for a dip - but so far for much of the country, the water hasn't been so inviting.
Beachgoers Newshub spoke to on Tuesday described the water as "refreshingly cold" and "quite chilly".
And while it might not feel like it at the moment, the oceans are actually getting much warmer.
An Advances in Atmospheric Sciences report published on Tuesday has found the world's oceans warmed four-and-a-half times faster between 1987 and 2019 than they did between 1955 and 1986.
NIWA meteorologist Ben Noll says it's not surprising, but it's still concerning.
"The long-term trend is certainly not our friend at this point in time," says Noll.
Not only was last year's ocean temperature the warmest ever - it was 0.075C higher than the average between 1981 and 2010.
The report says the energy required to warm the world's water that much would be 228 sextillion joules of heat. The same rate as if five Hiroshima atomic bombs were dropped into the water every second over the past 25 years.
Oceans absorb more than 90 percent of the heat trapped by greenhouse gases.
Fourteen international scientists examined data all the way back to the 1950s, using satellites as well as deploying thousands of Argo floats around the world.
"The oceans are a repository of the excess heat that is caused by global warming, and represent one of the best ways that we can measure climate change anywhere on the globe," says Noll.
As for why Kiwi seas haven't provided the goods this summer, it's all a matter of perspective.
The previous two summers we've had marine heatwaves and fewer southerlies.
"We do see some warmer patterns unfolding for the last week of January, that's probably good news if you want to hit the seas and hit the beach," says Noll.
But it's not so good for those long-term trends.