Comments On NOAA’s Report Of Deep Ocean Warming

I was alerted by Leonard Ornstein to a NOAA news article titled

Scientists Find 20 Years of Deep Water Warming Leading to Sea Level Rise

The article includes the text

“Scientists analyzing measurements taken in the deep ocean around the globe over the past two decades find a warming trend that contributes to sea level rise, especially around Antarctica.

Greenhouse gases in the atmosphere, such as carbon dioxide, cause heating of the Earth. Over the past few decades, at least 80 percent of this heat energy has gone into the ocean, warming it in the process.

“Previous studies have shown that the upper ocean is warming, but our analysis determines how much additional heat the deep ocean is storing from warming observed all the way to the ocean floor,” said Sarah Purkey, an oceanographer at the University of Washington and lead author of the study.

This study shows that the deep ocean – below about 3,300 feet – is taking up about 16 percent of what the upper ocean is absorbing. The authors note that there are several possible causes for this deep warming: a shift in Southern Ocean winds, a change in the density of what is called Antarctic Bottom Water, or how quickly that bottom water is formed near the Antarctic, where it sinks to fill the deepest, coldest portions of the ocean around much of the globe.

The scientists found the strongest deep warming around Antarctica, weakening with distance from its source as it spreads around the globe….”

I wrote in the paper

Pielke Sr., R.A., 2003: Heat storage within the Earth system. Bull. Amer. Meteor. Soc., 84, 331-335.

“An assessment of the heat storage within the earth’s climate system offers a unique perspective on global change. If the heat actually remains within the earth system in the deeper ocean, for example, while the heat content of the remainder of the heat reservoirs in the earth system remains unchanged, sudden transfers of the heat between components of the system (from the ocean into the atmosphere) could produce rapid, unanticipated changes in global weather. “

Since I wrote that statement, I have become convinced that since deep ocean heating is diffused through relatively large volumes of the ocean (as indicated in the NOAA study), it cannot suddenly reappear in the atmosphere.  Indeed, we can now monitor with the Argo network in order to assess if there are large amounts of heat (in Joules) migrating towards the surface of the ocean.

There are several  comments and questions that result from this study:

  1. First, since the warming is concentrated in the higher southern latitudes, how did was this heat transferred through the upper ocean without being sampled by the Argo network or in the satellite measurements of ocean surface temperatures?
  2. If a significant fraction of the radiative forcing is transferred deep into the ocean, it is effectively “sequestered” and is not easily available to affect atmospheric climate.
  3. The heating of the deeper ocean does assist in part with explaining sea level rise in the absence of upper ocean heating.
  4. The fraction of heating that is within the deeper ocean reduces the magnitude of heat available to increase the global average surface temperature.

Since the data density of this study was relatively coarse, however, further study is needed to confirm their values. Nonetheless, this is the type of diagnosis we need, along with the Argo network, to obtain a more accurate diagnosis of global warming and cooling.

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