Taking the Temperature of the Earth
Amazing Technologies Give a Sensitive View of a Changing Climate
I am constantly amazed by our technological prowess in measuring the state of the climate system. Accumulating long-term data on key processes in the weather/climate machine with rigorously validated methods is essential to understanding our climate future. It’s also a marvel of the application of a host of modern technologies operated by a large cadre of dedicated scientists and technicians!
Previous posts here presented a four step introduction to the reality of climate change, measured as changes in global temperature, and explored the role of carbon dioxide as an accurate index to what is driving that change:
https://lessheatmorelight.substack.com/p/climate-change-in-four-easy-steps
https://lessheatmorelight.substack.com/p/why-carbon-dioxide-predicts-temperature
Both of those depended on public availability of high quality, long-term, data sets for carbon dioxide in the atmosphere and surface temperatures around the globe. And both suggested that the solar energy received from the sun at the top of the atmosphere was greater than the amount radiated back out to space – a positive energy balance, if you will, or a net energy gain – leading to a warming planet.
What if we could make direct measurements of the actual energy balance of our planet, and even perhaps the major components of the Earth’s climate system? Even better, what if we could check one set of measurements against another independent set as a challenge to the consistency of the numbers?
In fact, researchers have done both of these things.
A colleague has just sent me a reprint of a recent article I had not seen that provides a “we can” to both of those “what if”s. The paper is in Geophysical Research Letters and is titled Satellite and Ocean Data Reveal Marked Increases in Earth’s Heating Rate, with Norman Loeb as first author (complete citation is at the end of this essay).
This concise paper presents two independent estimates of the net retention of heat energy by the entire Earth system as a result of changes we have made to that system. One estimate is based on measurements of the radiation balance of the surface and atmosphere summarized as a net flux at the top. The other is based on changes in temperature, or heat storage, in the oceans, atmosphere, ice, and solid Earth.
Before looking at the results, which are consistent with other measured changes in the Earth system, let’s look at the data sets on which this paper relies. We can’t get into the technical details of each data set here, but Loeb and colleagues provide links to the publicly available descriptions and contents of each. What we can do here is give some indication of the amount of human effort and applied technology that underlie each data set. They include:
- Satellite-based measurements of radiative balance: The sensitivity of data recorded by these flying laboratories is astounding. We have been measuring radiation in the lab and field directly for many decades, but to develop, launch and maintain a system of satellites to do this continuously for the entire Earth is a stunning achievement.
- Ground-based measurements of radiative balance: Measuring radiation balance at the surface is not as inspiring, perhaps, but maintaining a network of cross-calibrated instruments at a representative set of locations all around the globe is.
- Satellite and buoy-based measurements of ocean temperature at the surface and to a depth of 2000 meters: Satellites also measure changes in the temperature of the ocean surface globally and continuously, providing images of the central Pacific, for example, that chart the state of the El Nino oscillation. There now also exists a network of something close to 6,000 tethered and drifting buoys, some with long tentacles reaching down to that 2000 meter depth that support a wealth of sensors. Placing and maintaining this network of buoys, and then collating all the data received is another major challenge.
- Satellite-based and ground-based measurements of changes in the distribution of ice: The areal extent of ice in the Arctic Ocean and on Greenland and Antarctica can be measured by satellite, and the images track some dramatic changes, but comprehending the depth, density and movement of these sheets requires some of the most rigorous field programs in environmental science.
- Ground-based measurement of air temperature: This is the oldest, longest, most intensive and most often cited data set. Maintenance and cross-checking of this data set requires conscientious dedication by a large number of professionals from almost every country in the world.
These words can only begin to convey the actual demands of accumulating these data sets. Three of my favorite popular science books can add some depth and detail to dedication required, and I recommend them to you.
In The Weather Machine, Andrew Blum documents the extensive, world-wide network of people and technologies that gather the real-time data needed to run the computer models that predict tomorrow’s weather. He highlights the intense, deadline-driven process by which the 350 or so people at the European Center for Medium-Range Forecasts convert those data into global weather predictions at 12-hour intervals.
The rigors and hardships, as well as the satisfactions, of collecting and processing ice samples in Greenland is captured well by Richard Alley in The Two Mile Time Machine. Mark Bowen does the same as he documents the added logistical problems of collecting those samples at the tops of tropical mountains, before those retreating ice caps disappear.
We should give a shout out to the large number of scientists, technicians and support staff that make these measurements possible, and applaud their dedication to precision and accuracy.
Returning to the paper by Loeb and colleagues, what they have done is summarize a number of measurements of the energy balance of different parts of the Earth system, combine them into two independent estimates of the planets total energy balance and then compare those estimates.
The two results in this paper that stand out to me are captured in the single diagram below. It is worth noting that it is common in Earth System Science for years of work and collaboration to come down to one or a few high-impact results, often presented graphically. A single graph might suggest a simple project which is why I have described above all of the cumulative effort by the scientific community that underlies this one result. Not simple at all!
This one graph presents two estimates of the net energy gain by the entire Earth System developed in two independent ways. The red line is generated by direct measurement of the actual radiation balance at the top of the atmosphere. The blue line is a summation of the measured heat balance of oceans, atmosphere, land and ice.
The two primary results are:
- There is very good agreement between these two independent measures of the change in the Earth’s energy balance; they are mutually reinforcing
- The balance is consistently positive and trending upward showing that the Earth is warming, and at an increasing rate, with a current net energy gain of about 1 watt per meter square.
For comparison, one estimate from the USEPA of the increase in “radiative forcing” or the increased retention and “recycling” of infrared or “heat” radiation by the atmosphere over this same time period, due to greenhouse gas accumulation, is about 0.6 watts per meter square. A more complete presentation on greenhouse gases and radiative forcing is in the second essay link at the top of this one.
So, we can celebrate our ability to monitor the Earth’s climate system with exquisite sensitivity and accuracy. We can also understand just how critical this technological and human achievement is for charting our current climate path. Based on this paper, and many others that corroborate the basic findings, we can see where our climate system is headed.
One final thought. In the second essay linked at the top of this one, I noted that relatively small changes in energy flows brought about by greenhouse gases and other factors have already led to measured changes in global temperature and the follow-on effects of increased sea level, disappearance of Arctic sea ice and many other changes in the climate system. I will repeat here a conclusion from that previous essay: that our climate system appears to be precariously perched at a state that we have considered “normal” for some time. The entire system shows high sensitivity to small perturbations. This might make us consider being more respectful of that system and all that it provides, and maybe a bit more humble about changing it.
Is that too gentle a statement? I like to avoid exaggeration and hyperbole, but maybe just this once I should close with a famous quote from a pre-eminent climate scientist. Wally Broecker put it this way: The climate system is like “an angry beast and we are poking it with sticks.”
Acknowledgements:
Thanks to Norman Loeb for reviewing an earlier draft of this essay.
Sources:
The Loeb et al article is here:
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL093047.
And a more complete reference is:
Loeb, N. G., Johnson, G. C., Thorsen, T. J., Lyman, J. M., Rose, F. G., & Kato, S. (2021). Satellite and ocean data reveal marked increase in Earth’s heating rate. Geophysical Research Letters, 48,
https://doi.org/10.1029/2021GL093047
The three books cited are:
Richard Alley. 2008. The Two Mile Time Machine. Princeton University Press
Andrew Blum. 2019. The Weather Machine. Harper Collins Publishers
Mark Bowen. 2005. Thin Ice. Henry Holt and Company
The source for the USEPA estimate of increase in radiative forcing due to greenhouse gases is here:
https://www.epa.gov/climate-indicators/climate-change-indicators-climate-forcing
And the Broeker quote is taken from an interview with the New York Times