Taking the Pulse of the Planet
Exquisite technologies add an "Ocean Pulse" to the Keeling Curve
A good book can be a life-changing experience. We recently lost a brilliant and controversial scientist who wrote a short book that changed my worldview, and apparently did the same for many, many others.
James Lovelock died on July 26 this year at the wonderfully old age of 103.
Lovelock was an independent scientist and, in the 1960s, the inventor of a technology that allowed vastly increased sensitivity in the measurement of trace gases in the atmosphere, including some critical for understanding acid rain, the ozone hole, and climate change.
This innovation is just one of an array of sensor technologies that now allow us to assess the state of the global environment and how we are changing it. Two others related to "taking the pulse of the planet" are described below.
Inventing a new method can also open doors for the scientist-inventor, and Lovelock rode his invention around the world, being invited on research cruises and to remote field sites. He credits his experiences working with scientists across many disciplines and in many different settings for the development of his unique worldview - both of science and of the Earth as an integrated system.
And that worldview was presented in 1979 in a short, brilliant book called Gaia. It was an instant phenomenon.
The book itself presents Gaia as a metaphor for the Earth as a living entity. Scientifically, the metaphor meant that many, many interactive biological, chemical, and physical processes, including some that could now be measured through Lovelock's invention, respond to changes in the chemistry of the atmosphere and oceans in ways that maintain an environment that can support life.
Whether this is by design or just good luck has generated many of the more intense, philosophical disagreements about the concept.
One important step in Lovelock's development of this whole-Earth view was an invitation to work with a science team at NASA developing Mars landers that would test for the presence of life. As he tells it in the book, Lovelock talked with colleagues in search of a definition of life as a planet-level process - how would you detect it? Finding no existing definition, he provided one: life at the planetary level can be said to exist wherever the sun's energy has been used to create an atmosphere that is not in chemical equilibrium. He uses the terms entropy reduction, or chemical disequilibrium.
Earth is clearly alive by this criterion. Our atmosphere, rich in elemental nitrogen and oxygen (together 99% of our atmosphere), is very, very far from chemical equilibrium, reflecting the constant production of oxygen by photosynthesis - life! Without photosynthesis, the highly reactive oxygen in our atmosphere would disappear in a geological heartbeat.
In contrast, even an early understanding of the atmosphere of Mars said the opposite. At 96% carbon dioxide, it is very near chemical equilibrium - hence not alive - at least not now.
Lovelock's passing led me to reread the original Gaia which led in turn to a realization of how much his ideas affected the development of my own scientific worldview. He excelled at simple explanations of complex process and was dedicated to presenting science in understandable terms to general readers (the goal of this Substack site). His chapter on cybernetics, running to all of 15 pages, provided a clear explanation of feedbacks and their importance in any system. Feedbacks take you away from linear thinking. Cause and effect become only the first step in a response to change.
Above all, his view of the Earth as an integrated biological, chemical, and physical system rife with critical feedbacks responding to subtle changes in the chemistry of the atmosphere and the oceans, helped introduce me to the central concepts of what has become Earth System Science. In that field, you look at the whole planet first, and then try to decipher where the most important interactions and feedbacks are hidden in that complex web of direct causes and effects.
While you won't read about "Gaia" in scientific papers, Lovelock was ahead of his time in seeing the Earth as an integrated system.
Which leads in rather a roundabout way to the two technologies and data sets that give this essay its name.
Measurement methods for these two could not be more different. One involves a single measurement in a single location. The other relies on the acquisition of what must be billions of bits of data gathered from all around the world and combined through a set of complex calculations into another single number.
The two data sets are the carbon dioxide concentration in the atmosphere, and the continuing rise in sea level.
I try to put "The Keeling Curve" documenting the increase in carbon dioxide in the atmosphere in front of audiences or readers at every opportunity. It is my nomination for the icon of the climate change era (and has actually been designated as a National Historic Chemical Landmark by the American Chemical Society). No other data set offers so clear and understandable an image of our impact on the global environment, and yet most in any audience will not have seen it.
Measurements of carbon dioxide concentration are made atop Mauna Loa on the big island of Hawaii, at an elevation that represents the well-mixed concentration in the atmosphere of the northern hemisphere. The record begins in 1958 when Charles David Keeling established an observatory at this location.
The technology used in this case is well-established. The ability of carbon dioxide to absorb infrared radiation and so act as a greenhouse gas was discovered by John Tyndall around 1860. The infrared sensor initially used at Mauna Loa was built on similar principles. Current measurements are being augmented with the use of laser-based sensors.
What is revolutionary about the Keeling Curve is that it was the first to provide consistent measurements in a single location continuously over time. And that record shows both a long-term and short-term pattern. The long-term pattern is the continuous increase in carbon dioxide concentration that defines the impact of the burning of fossil fuels on the atmosphere and so also on the steady increase in global temperatures.
The short-term trend is also remarkable in terms of our topic. The measurements are so precise that the seasonal "metabolism" or "pulse" of the biosphere in the norther hemisphere is clearly revealed. Summer brings a draw down in carbon dioxide as photosynthesis in ecosystems, especially forests, ramps up. As summer ends, photosynthesis declines while decomposition and respiration continue, driving concentration up.
Here is the biosphere inhaling and exhaling… Yes, those human analogies are hard to resist.
The second data set is the result of some truly dazzling technologies.
Imagine trying to measure minute changes in sea level. In pre-satellite days, the sea level record was drawn from tide gauges in harbors and other locations all around the world. Affected by storms and waves, as well as tides, measurements in individual locations would be widely variable, making the detection of any trend very difficult.
Still, the number of measurements and locations is huge, and by carefully combining them, there is a data set that presents changes in sea level since 1880. Total estimated rise over that period is 8–9 inches (21–24 centimeters).
How much easier would it be if we could measure sea level continuously and globally, averaging out waves and tides, to develop a more complete and consistent record.
That has been the goal of a series of satellite remote sensing initiatives pursued cooperatively by NASA, NOAA, and space agencies in Europe.
Sequentially named TOPEX, Poseidon and now Sentinel-6 Michael Freilich, the satellites beam microwaves at the ocean surface and measure the time required for the signal to bounce back to the sensor. Combined with a very precise three-dimensional location of the satellite, and corrected for atmospheric conditions, this timing is a measurement of the height of the ocean directly below the satellite.
Imagine how precise both the timing and satellite location need to be to achieve accuracy at the scale of centimeters for sea level. Given this precision and the number of samples (data are recorded continuously and the satellites revisit the same location every 10 days) the NASA scientists on this project say the record is equivalent to half a million tide gauges.
And that precision, along with what is now a 30 year record of measurement, allows a sensitive determination of the rate of sea level rise, currently 3.9 mm (0.15 inches) per year.
The seasonal cycle in sea level is just as intriguing as that for carbon dioxide. Josh Willis, an oceanographer at NASA's Jet Propulsion Laboratory and project scientist for Sentinel-6 Michael Freilich notes that, “Winter rain and snowfall in the northern hemisphere shifts water from ocean to land, and it takes some time for this to runoff back into the oceans,” causing “about 1 centimeter of rise and fall each year. It’s literally like the heartbeat of the planet.” Or the hydrologic pulse.
Willis also points out that the signal is precise enough to notice differences between El Niño and La Niña years. We have reported a similar sensitivity in the Keeling Curve.
The sensitivity also allows Willis to conclude that, “With 30 years of data, we can finally see [that] the rise of sea level caused by human interference with the climate now dwarfs the natural cycles.” The signal (sea level rise) now exceeds annual variation.
Earlier essays have described the role of thermal expansion versus the melting of glaciers and ice caps in driving this rise, and also a suggestion of where this is leading us. The consistent and now inevitable rise in sea level may well be the most crucial long-term impact of global warming.
If the Keeling Curve is the pulse of the biosphere and the global caron cycle, then this sea level data set can be seen as the pulse of the global water cycle. And if both respond to seasonal changes in daylength, temperature and other climatic factors, might they also coincide in their timing?
Well, they do. If you overlay the carbon dioxide and sea level data sets, you will see that they move in opposite directions (carbon down in the summer, sea level down in the winter), but are perfectly synchronized, capturing seasonal dynamics or - can we say it - the pulse of the planet.
I think James Lovelock would be pleased.
Acknowledgement: Thanks to Josh Willis for reading and improving an earlier version of this essay.
Sources
Kudos first to the scientists, engineers, technicians, and their sponsors for making the data and images used here freely available. This Substack site would be much poorer, if it existed at all, without free and open access to these crucial scientific findings.
The original version of Gaia is:
Lovelock, J.E. 1979. Gaia: A New Look at Life on Earth. Oxford University Press.
Reissued in 1995 with a new preface.
The Keeling Curve, data, methods, and history, are here:
https://keelingcurve.ucsd.edu/
The data on sea level rise since 1880 is from:
https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level
The recent NASA story on sea level rise by satellites is here:
https://earthobservatory.nasa.gov/images/150192/tracking-30-years-of-sea-level-rise
and information on the most recent satellite is here:
https://www.nasa.gov/feature/jpl/5-things-to-know-about-sentinel-6-michael-freilich
https://express.adobe.com/page/6AUtOCtuYglX7/
A map of ocean topography can be found here:
