Last March, the seriously high-minded magazine The Economist published a cover story, based on a leak from a draft from the U.N.’s Intergovernmental Panel on Climate Change, reporting that global warming had slowed during the 2000-2010 decade.
The rate of warming over the past 15 years, the story reported, “has been lower than that of the preceding 20 years.” It went on to note that the earth “has heated less than most climate scientists had predicted.”
Shortly thereafter another writer for Forbes chimed in, “Faith in global warming is collapsing,” and chastised global warming “hysterics” who are trying “to shut down capitalist prosperity.”
Last month, the IPCC issued its fifth assessment report in final form, which in fact predicts a “new” slightly lower limit of global temperature increases than the last assessment predicted. Some headlines described the IPCC report as a “retreat” from the threat of global warming.
But actually the bottom line of the report continues to be stark and sobering: Global temperatures are rising, and humans are causing it.
But why has the rate of warming slowed during the past 10-15 years, you might wonder? Remember scientists are not describing a decrease in global temperatures, but only the rate that temperatures are increasing on land.
Some scientists believe that the slowdown is just part of the earth’s natural variability – analogous to a small landing in a tall building’s staircase.
However, one of the most interesting, but least reported, scientific explanations for the slowing of the rate of temperature increase on land has been the increase of ocean temperatures, especially at depth.
To get the gist of this explanation requires a bit of a deep dive, beginning with the fact that we still do not understand much about the planet’s oceans. For instance, there are more than 11,000 temperature recording stations around the globe; but only about 3,000 of these have been deployed in the ocean — and then only since 2007.
Prior to the effort to get a comprehensive picture of world ocean temperatures, satellites had been used extensively to detect sea surface temperature. Satellite measurements, however, are confined to the top half-inch of ocean’s depth and reveal only a small part of what is happening in vast parts of the ocean.
Until relatively recently we knew little about how temperatures in the largest compartment of our planet were reacting to the increases in air temperature.
At the same time, however, in Maine we have more than 5,000 keen observers whose livelihoods depend on reacting to temperature changes in their small piece of the ocean — which is to say lobstermen in the Gulf of Maine. Every time a lobsterman hauls a trap from the bottom, they see another little piece of the jigsaw picture of the changing ocean.
This summer lobstermen in Penobscot Bay have reported finding such warm water species as triggerfish — common in North Carolina — when their traps came to the surface. Several lobstermen have recently found — are you ready for this? — seahorses in their traps. Scientists have also reported finding tropical species such as filefish and the Caribbean-based snowy grouper during sampling expeditions.
Dave Cousens, head of the Maine Lobstermen’s Association, said it’s been “a weird year.” Water temperatures, Cousens said, “have stayed at 58 or 59 from July through October. And it’s been 53-54 on the bottom at 170 feet. But at least it’s not like last year when it was 65 on the surface and we started seeing shell disease.”
The measurements of ocean temperatures will become increasingly important to lobstermen, shippers, offshore oil drillers and others who use the ocean every day, because the behavior of the ocean affects their costs of doing business. We will become ever more mindful of the fact that storms increase in intensity as ocean waters warm.
For the rest of us who live by the sea — today almost half of America’s population — we will be affected not only by warm water storms but by the steady expansion of the ocean as sea levels continue to rise inexorably around us for the next several centuries, regardless of whether we stopped burning carbon fuels today, which to date we have shown few signs of doing.