The tropical Pacific Ocean has been acting as a type of air conditioner for the planet during the past decade and a half by slowing the rate of global warming. Recent research suggests that the “speed bump” is in large part due to cooler-than-average sea surface temperatures.
Although several studies point to volcanic activity, anthropogenic aerosols, stratospheric water vapor and solar minimum, the ocean continues to be the leading candidate for tempering rising global temperatures.
Not too long ago I remember visiting the state of Oregon for the first time. I was in Corvallis getting ready for the start of my postdoc when I mentioned to my wife that we could visit the Pacific coast since it was only an hour and a half away. Knowing the probable cooler temperatures there I suggested we wear jeans because it would be like stepping into a cold room. She did not concur.
The end result of our visit to Oregon’s coast was a 25 degree temperature drop from the Willamette Valley at 85 °F to a cool 60 °F when we reached Newport. It wasn’t a cold front or altitude. It was just the cooler waters of the Pacific Ocean keeping the temperatures lower during the middle of the summer. An air conditioner, so to speak, and my wife was not ready for a walk to the edge of Depoe Bay.
So could this “air conditioner” effect work on a much grander scale, say globally? Yes, as suggested by work published in Science, Nature and other recent publications. In fact, natural variability of the Pacific seems to provide a way to dissipate excess heat and transport it to the upper layers of the ocean and, eventually, deeper still. As was noted in a recent UCS blog post, 90% of the excess heat from global warming resides within the ocean as an incremental increase of heat content.
The Pacific cools Earth’s surface
Continuing with the air conditioner analogy. Let’s consider this: an air conditioner is a “heat engine” that works to cool an environment by providing the engine with energy to run its process. Air conditioner units use an amazing physical law: when a liquid turns to gas it absorbs heat in a process called “phase conversion.” It works like this: the compressor in an AC unit heats up the refrigerant (such as freon) by causing it to condense, which releases heat. The expansion valve does the opposite, using the phase change from liquid to gas to cause the environment around it to cool.
How does this apply to the Pacific Ocean? According to the law of conservation of energy, the total energy of an isolated system is constant; energy can be transformed from one form to another, but cannot be created or destroyed. Thus, as excess energy is trapped in the Earth system by greenhouse gases, it is transformed into ocean heat content. And although it remains unclear as to the exact process, scientists believe that stronger trade winds associated with cold surface temperatures may allow for the penetration of warming below the ocean surface. Thus, the Pacific becomes the expansion valve in our analogy, providing a cool surface to moderate the tide of global warming.
But this “air conditioner effect” is a only a temporary speed bump, just as occurred in the mid twentieth century when aerosols, and possibly the Pacific itself, reduced the warming signal present since the advent of the industrial revolution. This brings us back to our initial analogy, for even in a heat wave, when your air conditioner is on, it has a hard time keeping the temperature down inside your home. That is the case with the Pacific Ocean and why we are still breaking temperature records, even if at a slower rate.
As the Pacific Ocean cycle enters another warm stage, we are likely to see our global temperatures break records two to three times faster than we have experienced during the past decade and a half. In the end, I like to think as our oceans as a blessing, for they may be temporarily shielding us from a more immediate catastrophic rise in the temperature of the planet.
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