Oceanic Warming? Well, sorta.

Guest Post by Willis Eschenbach

After my last post about the surface warming of the ocean, entitled “How Global Warming Isn’t“, I got to thinking about the warming of the upper part of the ocean. So I got the data for the ocean heat content (OHC) of the top 700 metres of the ocean from the marvelous site, KNMI. If you look under “Monthly Observations” you’ll find a host of most fascinating datasets. Under “Heat Content” on that page, you’ll find the National Oceanic Data Center (NODC) 0-700 metre depth OHC data. And down at the very bottom of that page is a link that will download a 196 megabyte gridded NetCDF file containing the data that I used. (Big file, click at your own risk.)

And what did I find? Well, I’m a visual kind of guy. I mean, I can do the math, but it only makes sense when it comes up as a picture on the silver screen. So here are my graphics. I’m interested in the changes in the oceanic heat content, so these are two views of those trends.

Figures 1 & 2. Decadal trends in oceanic heat content, in exajoules (10¹⁸ joules) per decade.

I love climate science because I’m continually surprised by what I find. What could be better? It’s like Christmas every day.

My first surprise? There’s a line of giant oceanic slow whirlpool-type eddies that I’ve seen before. They start at the southern tip of Africa and extend down under Australia. I knew about them because they’re visible in graphics of satellite sea-surface height data. But what I hadn’t realized is that these eddies are mixing warm surface water down into the depths. This is indicated by the orange/yellow line of increased undersea heat stretching from Africa under Australia.

And when you mix some warm surface water downwards, other cool deep water has to come upwards … as indicated by the corresponding line of areas just south of the eddies encircled by black/white lines, showing areas that have actually lost heat since 1955. Who knew? Certainly not me.

What else surprised me? The turbulence of the Gulf Stream as it interacts with the ocean floor topography along the East Coast of the US is also mixing warm surface water downwards … and the corresponding upwelling of cold subsurface water is occurring just south of Greenland.

I’ve long wondered how less-dense warmer water could mix downwards into denser cooler deeper waters … well, there are a couple of places where it is happening.

To close out, I took a look at the actual temperature change represented by those exajoules of energy changes. I mean, just how big is an exajoule when it’s at home? I’m sure I don’t know.

But like I said, I can do the math. So I converted the slow increase in exajoules of heat content into degrees Celsius of slow warming. Here’s that result:

Figure 3. Global ocean temperature change, surface to 700 metres depth from 1955 to 2020

A quarter of a degree in a half century?

Now I keep reading about how fish are changing their locations in response to oceanic warming. But it seems extremely doubtful to me because the changes have been so small. Over the last fifty years, the ocean has warmed by about 0.005°C per year … and call me crazy, but I’m just not believing that the fishies and other underwater denizens are so temperature-sensitive that a change of a quarter of a degree in half a century will make them leave their happy homes.

For one thing, in the open ocean, the vertical temperature change is often on the order of 1°C per 40 metres vertical or so. Here are some Argo float profiles of the top 200 metres.

Figure 4. Vertical temperature profiles of the North Pacific, Argo float data.

And that means that if a fishie or other subaquatic denizen goes up or down by ten metres or so, it’s already endured the dreaded quarter-degree temperature change …

Add to that the fact that many millions of oceanic fish, shrimp, and copepods migrate every night from 800-1000 metres depth up to around 100 metres depth, and then go back down at dawn … which means they happily endure 5° – 10° of temperature change every night. So I doubt greatly that they will be bothered by a quarter of a degree temperature change in a half-century.

And by tonnage, this daily vertical migration is the largest movement of living creatures on the planet … so we’re not talking about a few fish here and there.

This is the bottom line. If the world’s creatures, both on land and at sea, were as temperature-sensitive as the alarmists would have us believe, those beings (and we humanoids as well) all would have gone extinct long ago. And near as I can tell, that hasn’t occurred … at least yet.

My very best wishes to all living creatures, terrestrial and aquatic alike,

w.

As Always: I ask that when you comment you quote the exact words you are discussing, so we can all know both what and who you are responding to.

A Final Note: In addition to daily traversing the five degrees or more temperature range, it’s worth noting that when the millions of tonnes of aquatic creatures travel from 1000 metres to 100 metres depth and back down every night, they undergo a pH change of about half a pH unit.

In other words, every night they undergo a greater pH change than we’re expected to see in the ocean in the next century under IPCC assumptions. You know … the dreaded pH change that’s supposed to kill oceanic creatures by the millions. But instead, as Darwin is rumored to have mentioned once or twice, living creatures have evolved to … well … survive.