Deciphering climate messages via the heart of the atom

Vemork Hydroelectric Plant at Rjukan, Norway, which Hans Suess advised on heavy water production, telling Nazi Germany it couldn't make heavy water quickly enough for military use. His expertise with heavy water was part of an interest in nuclear science that led him to become a pioneer in carbon dating.

Vemork Hydroelectric Plant at Rjukan, Norway, which Hans Suess advised on heavy water production, telling Nazi Germany it couldn’t make heavy water quickly enough for military use. His expertise with heavy water was part of an interest in nuclear science that led him to become a pioneer in carbon dating.

When Hans Suess chose to study physical chemistry, he went nuclear, apparently overturning two generations of family tradition. Hans was born in 1909, just as his father Franz succeeded his grandfather Eduard as a geology professor at the University of Vienna. Hans got his PhD from the same university in 1936, but in studying heavy water he was set to aid the historic advances in nuclear science of the time. Yet a transatlantic scientific coincidence would bring him back to more environmental science, and see him help pioneer radiocarbon measurements. With that expertise, Hans showed humans were raising atmospheric CO2 levels, and revealed another surprising source of variations in climate.

The common theme to these achievements was how neutrons and protons combine in an atom’s nucleus. For example, hydrogen atoms found in conventional water have just a single proton in their nuclei. In heavy water, some of these atoms are replaced by a rarer form of hydrogen, known as deuterium, whose atoms have an extra neutron in their nuclei. That gives heavy water properties that can help nuclear reactors, which Nazi Germany notoriously hoped to exploit to make nuclear weapons.

With Hitler’s armies occupying Austria just two years after Hans finished his PhD, his expertise brought him to the attention of the Nazi regime. They called him in to advise a hydroelectric power plant in Vemork, Norway, that was making heavy water. Hans visited several times, reporting that it couldn’t make heavy water quickly enough for military use. Allied forces destroyed it in 1943 anyway, in audacious raids fictionalised in the film “Heroes of Telemark”.

Alongside working with heavy water, Hans studied why the chemical elements exist in the amounts that they do. The answer laid in how stable different numbers of protons and neutrons are when they come together in nuclei. He continued this work after the Second World War in West Germany, helping develop the “Nuclear Shell Theory” explanation, which other scientists won the Nobel Prize for Physics for in 1963. Suess missed out on this acclaim partly because two teams came up with the explanation at the same time. But when the other team, based at the University of Chicago, invited him to visit, Hans’ life changed course towards unravelling the secrets of Earth’s history.

The carbon dating game

A modern carbon-dating setup used to date samples more than 40,000 years old.

A modern carbon-dating setup used to date samples more than 40,000 years old.

Willard Libby, also at the University of Chicago had just invented carbon dating and was just writing his first paper on his method, which would also win him a Nobel Prize. Carbon dating relies on the fact that as well as carbon-12, the dominant and stable form, there’s carbon-14, which is heavier and unstable as it has two extra neutrons. Carbon-14 slowly decays to nitrogen and would soon run out, if cosmic rays from space didn’t keep reacting with nitrogen in the atmosphere to make it. That keeps a fairly steady amount in the air, and so when trees are taking up CO2 to grow, they contain specific ratios of carbon-12 to carbon-14. But when trees die, the ratio in their wood progressively decreases, at around 14 atoms per minute per gram of pure carbon. That regular tick can be used as a clock to work out the time since the tree died.

Hans learned the method from Willard, and set up a lab at the US Geological Survey in Washington, DC, to develop and use it in his own research. His early results came from stumps or logs of trees in the northern US knocked over by sheets of ice that advanced across the country around 20,000 years ago. But when looking at more modern samples, he found a strange effect: the ratios of the types of carbon had been changing. He soon realised that part of the explanation was coal burning. Having taken a very long time to form, coal has no carbon-14, and so neither does the CO2 that it makes when burned. That reduces the ratio of carbon-14 to carbon-12 in air, giving direct evidence that burning fossil fuels adds carbon to the atmosphere. And although radiocarbon dating was still establishing its reliability, the finding lent weight to the idea that human fossil fuel burning was warming the planet, championed by Guy Callendar.

New school thinking

Hans Suess helped understand why and how much radiocarbon dating varied when compared to ages given by counting tree rings. Image from Suess, 1965, used via Creative Commons license, see reference below.

Hans Suess helped understand why and how much radiocarbon dating varied when compared to ages given by counting tree rings. Image from Suess, 1965, used via Creative Commons license, see reference below.

Meanwhile, an oceanographer named Roger Revelle had worked out that the oceans can absorb CO2 from the air. He was also busy growing the University of California, San Diego (UCSD) out of his research institute, the Scripps Institution of Oceanography. Seeing the power of radiocarbon dating, in 1955 he invited Hans to join him as a professor at the new university. Together they worked out that oceans only absorb a limited amount of the CO2 humans add to the air by burning fossil fuels. Their findings made Roger and Hans keen to know more about “the large scale geophysical experiment” burning coal had kicked off. And, powered by their enthusiasm, they helped find the cash that let Charles Keeling go on to do detailed measurements on CO2 in air.

At UCSD, Hans also continued his carbon dating work, particularly on the puzzle of why wrong ages were still regularly cropping up. He resolved this problem by comparing trees’ radiocarbon ages against the age given by counting tree rings. Comparing them showed that carbon-14 production varies regularly, usually rising by about one percent in about 20 years, then decreasing again over a century. That affects the carbon dating ratio, with trees growing when more carbon-14 is being made appearing younger. By 1980, Hans had taken his tree-based calibration curve back 8,000 years, making carbon dating a precise tool for dating organic materials, and tracking carbon’s movement through ecosystems.

The curve also helped confirm a controversial possible cause for the variations in carbon-14 production: changes in the Sun’s activity. A strong piece of evidence came from two periods in the 15th and 17th centuries, during a cold interval known as the ‘Little Ice Age’. This period had been especially hard to carbon-date, and Hans showed that’s because carbon-14 production was particularly high. If the Sun was less active – a shocking idea at the time – perhaps its magnetic field was weaker, letting more cosmic rays through into our atmosphere and turning more nitrogen into carbon-14. Records showed far fewer sunspots than normal during this period, giving the quiet Sun idea extra backing. The cooler temperatures during that time could also have been because the Sun was giving out less heat. So despite seemingly turning away from studying the Earth at an early age, by his retirement Hans had helped highlight two important influences on our climate: CO2 and solar activity.

Variation of carbon-14 levels in the atmosphere over the last 8000 years, as determined by Hans Suess. The bottom axis shows the date, on a scale of hundreds of years BC and AD, and the variation in carbon-14 concentration is along the vertical scale in parts per thousand. Image from Suess, 1980, used via Creative Commons license, see reference below.

Variation of carbon-14 levels in the atmosphere over the last 8000 years, as determined by Hans Suess. The bottom axis shows the date, on a scale of hundreds of years BC and AD, and the variation in carbon-14 concentration is along the vertical scale in parts per thousand. Image from Suess, 1980, used via Creative Commons license, see reference below.

Further reading:

Spencer Weart’s book, ‘The Discovery of Global Warming’ has been the starting point for this series of blog posts on the key players in the history of climate change.

The US National Academies Press has published biographical memoirs of Hans Suess by his coworkers.
Suess, H. (1954). U. S. Geological Survey Radiocarbon Dates I Science, 120 (3117), 467-473 DOI: 10.1126/science.120.3117.467
Suess, H. (1955). Radiocarbon Concentration in Modern Wood Science, 122 (3166), 415-417 DOI: 10.1126/science.122.3166.415-a
Stuiver, M; Suess, H. E. (1966). On The Relationship Between Radiocarbon Dates And True Sample Ages Radiocarbon, 534-540
Suess, H. E. (1980). The Radiocarbon Record in Tree Rings of the Last 8000 Years Radiocarbon, 22, 202-209

About these ads

22 Responses to “Deciphering climate messages via the heart of the atom”

  1. Another Week of Global Warming News, June 16, 2013 – A Few Things Ill Considered Says:

    […] 2013/06/15: SimpleC: Deciphering climate messages via the heart of the atom […]

  2. Martin Says:

    There’s a little twist to the discovery of the so-called “Suess-wiggles”, i.e. the 14C variations caused by decadal to centennial changes in 14C production. His tree-ring data were actually not very accurate (compared to modern methods), hence many colleagues were skeptical. When he presented the variations at a conference in the early 1970s he was asked how he had drawn the smooth wiggly curve through the swarm of measurement points. He responded: “mit kosmischem Schwung” (with cosmic momentum). Later measurements with better accuracy by a group in Belfast and also by Stuiver and colleagues confirmed that Suess’ cosmic inspiration was dead right…

    • andyextance Says:

      Wow, that’s amazing! Is this story written down anywhere else? I’d love to hear/read more about it!

      • Martin Says:

        When I was a student, I got acquainted with Hans Suess who came to visit each summer Hans Oeschger at the Physics department of the University of Bern. Oeschger also made radiocarbon measurements. That’s where I got the story. We were at the time also studying Suess-wiggles, looking for periodicities. Indeed, a colleague student of mine wrote for Suess in the late 70’s a computer program to calculate the smooth curve through his measurements, taking the errors into account. But Suess’ “cosmic” comment on his earlier hand drawn curve is indeed documented in the proceedings of that conference in the early 1970’s – I stumbled over this much later. If you are interested, I can find out which conference this was. But I don’t have the proceedings myself. Suess was quite a character: there are more personal anecdotes to tell…

    • andyextance Says:

      How very intriguing – I hope that somehow I get to hear about them!

  3. What Dave Keeling did ahead of his curve | Simple Climate Says:

    […] the International Geophysical Year (IGY), set to take place from 1957-1958. Roger Revelle and Hans Suess at Scripps had proposed a modest program to measure CO2 during IGY. Meanwhile, the Weather Bureau […]

  4. Continuing the fight for CO2 monitoring | Simple Climate Says:

    […] the same time: Svante Arrhenius, Milutin Milanković, Guy Callendar part I, Guy Callendar part II, Hans Suess, Willi Dansgaard, Dave Keeling part […]

  5. Fossil fuels are more than just a bad habit | Simple Climate Says:

    […] Guy Callendar spotted Earth’s rising temperatures, and blamed them on CO2, as far back as 1938. Hans Suess published evidence that CO2 increases were coming from fossil fuels in 1955. Dave Keeling was […]

  6. The joker who brought climate science out of the cold | Simple Climate Says:

    […] Taking advantage of the slow decay of a rare, radioactive form of carbon – carbon-14 – into the …, radiocarbon dating was in its infancy. The balance between the two is quite steady in CO2 in the air, and also in living plants that take up the gas as they grow. But when plants die, the carbon-14 they contain slowly decays to carbon-12. Measuring the ratio between the two, scientists can tell when the plants had died. But in 1952, Laurence’s lab was getting inconsistent readings, with carbon-14 counts sometimes coming out too high, even after Wally had fixed a problem with the equipment. Then Wally realised the problem came from outside the lab. The extra counts were coming from nuclear tests that had recently started over Nevada. […]

  7. How ocean data helped reveal the climate beast | Simple Climate Says:

    […] acid into seawater, he could convert dissolved carbonate back into CO2 gas that he could then carbon date. And though nuclear weapon tests had previously messed with Wally’s results, they actually turned […]

  8. Braving African piracy reveals abrupt rainfall shifts | Simple Climate Says:

    […] in these waxes tracks rainfall, with more deuterium indicating a drier period. She could then use carbon-dating to work out when the waxes were formed, to create a historical […]

  9. Tundra plants show modern temperatures unmatched in over 44,000 years | Simple Climate Says:

    […] Gifford and Kurt simply had to snip off a bit and take it back to the lab to establish its age by carbon dating. “It told us something we’d never been able to capture precisely before – when the site […]

  10. The underprepared figurehead that led climate science from calculation to negotiation | Simple Climate Says:

    […] same time: Svante Arrhenius, Milutin Milanković, Guy Callendar part I, Guy Callendar part II, Hans Suess, Willi Dansgaard, Dave Keeling part I, Dave Keeling part II, Wally Broecker part I, Wally […]

  11. The man who got the world to agree on climate | Simple Climate Says:

    […] same time: Svante Arrhenius, Milutin Milanković, Guy Callendar part I, Guy Callendar part II, Hans Suess, Willi Dansgaard, Dave Keeling part I, Dave Keeling part II, Wally Broecker part I, Wally […]

  12. The model scientist who fixed the greenhouse effect | Simple Climate Says:

    […] same time: Svante Arrhenius, Milutin Milanković, Guy Callendar part I, Guy Callendar part II, Hans Suess, Willi Dansgaard, Dave Keeling part I, Dave Keeling part II, Wally Broecker part I, Wally […]

  13. Fighting for useful climate models | Simple Climate Says:

    […] the same time: Svante Arrhenius, Milutin Milanković, Guy Callendar part I, Guy Callendar part II, Hans Suess, Willi Dansgaard, Dave Keeling part I, Dave Keeling part II, Wally Broecker part I, Wally Broecker […]

  14. The ice-age U-turn that set the stage for the climate debate | Simple Climate Says:

    […] the same time: Svante Arrhenius, Milutin Milanković, Guy Callendar part I, Guy Callendar part II, Hans Suess, Willi Dansgaard, Dave Keeling part I, Dave Keeling part II, Wally Broecker part I, Wally Broecker […]

  15. When the climate change fight got ugly | Simple Climate Says:

    […] the same time: Svante Arrhenius, Milutin Milanković, Guy Callendar part I, Guy Callendar part II, Hans Suess, Willi Dansgaard, Dave Keeling part I, Dave Keeling part II, Wally Broecker part I, Wally Broecker […]

  16. The warrior who gave his life to climate change | Simple Climate Says:

    […] the same time: Svante Arrhenius, Milutin Milanković, Guy Callendar part I, Guy Callendar part II, Hans Suess, Willi Dansgaard, Dave Keeling part I, Dave Keeling part II, Wally Broecker part I, Wally Broecker […]

  17. How lessons from space put the greenhouse effect on the front page | Simple Climate Says:

    […] the same time: Svante Arrhenius, Milutin Milanković, Guy Callendar part I, Guy Callendar part II, Hans Suess, Willi Dansgaard, Dave Keeling part I, Dave Keeling part II, Wally Broecker part I, Wally Broecker […]

  18. The witness who collided with government on climate | Simple Climate Says:

    […] the same time: Svante Arrhenius, Milutin Milanković, Guy Callendar part I, Guy Callendar part II, Hans Suess, Willi Dansgaard, Dave Keeling part I, Dave Keeling part II, Wally Broecker part I, Wally Broecker […]

  19. The urgent voice who refused to be silenced on climate danger | Simple Climate Says:

    […] the same time: Svante Arrhenius, Milutin Milanković, Guy Callendar part I, Guy Callendar part II, Hans Suess, Willi Dansgaard, Dave Keeling part I, Dave Keeling part II, Wally Broecker part I, Wally Broecker […]


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 191 other followers

%d bloggers like this: