I was lucky enough to be able to persuade the great Stephen Fry to narrate our Adams Event HitchHikers Guide video!
UNSW short video on the Adams Event
Our study is completely novel in finding that strong variations in earth’s geomagnetic field may lead to global climate changes under particular circumstances, which is contrary to current thinking.
This discovery resulted from a major international collaboration between 31 scientists from 7 very different fields of research (geochronology, climate modeling, atmospheric chemistry, solar physics, anthropology, paleontology, genetics). The work was based around a study of preserved NZ kauri trees, whose tree rings recorded changes in atmospheric levels of radiocarbon (carbon-14) through time. This enabled the radiocarbon record to be precisely calibrated through the last major geomagnetic reversal, the Laschamps Excursion, 42-41,000 years ago. Team members used the new dating ability to analyze geological records of past environmental change (e.g. glacier growth, vegetation changes, extinction events). Others analyzed the climatic response to a low geomagnetic field, especially with the additional impacts of solar storms(space weather!), using a state-of-the-art atmosphere-ocean chemistry climate model. The model results predicted major global changes, including shifts in wind patterns, cooling over the North Atlantic, consistent with many contemporaneous enigmatic events and changes in human behaviour.
We had previously noticed that the timing of extinction events in megafaunal animals seemed to be distributed broadly through the past 40-50,000 years, (ie wasn’t human overkill, where the arrival of humans is associated with a rapid extinction), and the pattern showed some strange patterns (groupings) - (Cooper et al. Science 2015,
https://www.researchgate.net/publication/280733346_PALEOECOLOGY_Abrupt_warming_events_drove_Late_Pleistocene_Holarctic_megafaunal_turnover) which had led us to conclude that sudden environmental changes must be driving the extinctions. However, trying to work out what might be causing the environmental changes was difficult. In Australia though, the important clue that tipped us off was that the events appeared at ~42,000 years ago, both on the mainland, and also on Tasmania - which had been an island until just before that point. This seemed very strange - as Aboriginal populations had been in Australia since 50ka (Tobler et al. 2018, https://www.researchgate.net/publication/314306369_Aboriginal_mitogenomes_reveal_50000_years_of_regionalism_in_Australia) so there was at least 8,000 years for human impact, with no major changes, and then a peak in extinction events at 42ka. This timing closely matched major changes across Australia to dry-adapted vegetation and the disappearance of the huge central lakes, telling us that 42ka was the key change - at least in Australia. We quickly found that sedimentary records in subantarctic islands and tropics also showed records of sharp climate change at exactly this point, as major global wind belts had shifted from their position. When we dated all of these events as precisely as possible, we found that they aligned exactly with the geomagnetic excursion. That is what provoked us to start seriously contemplating whether the magnetic changes had impacted climate, as this was widely considered impossible.
The full Laschamps geomagnetic excursion is shown in detail in Figure 1 of the paper, and started around 42.35 and lasted until 40.75ka. The initial phase of pole reversal (when the field strength was lowest) was 42.35-41.45ka, while the reversed polarity period was 41.45-41.05ka, and the transition back to normal polarity occurred 41.05-40.75ka. This was the last time the earth's poles switched position, even if only temporarily.
In order to study the events precisely, we needed to calibrate the radiocarbon dating technique in this time period - as it was previously difficult due to the Laschamps Excursion causing markedly increased rates of 14C generation in the stratosphere, changing the starting ratio of 14C to 12C incorporated by living organisms. The kauri tree ring record provided a way to precisely study the levels of 14C during this period. Although there are many kauri logs scattered through time back beyond even 60,000 years - there were none during the Laschamps. The Ngahwa log was discovered during development around a geothermal power station, and is being preserved as a taonga or treasure, by the local Maori iwi.
Using a cross section of the Ngawha log we were able to closely calculate the levels of 14C across the rings, over 2000 years, providing a precise reading of atmospheric levels of C14 (from the CO2 incorporated by the tree into the wood each year). With that precise record, we could calibrate the radiocarbon curve through the Laschamps - and analyse events around the world using radiocarbon dating. That enabled us to accurately date the changes in climate and environment recorded in sediments, ice cores, bones etc (our team included experts from all these multiple fields) - and show that they aligned exactly with the Laschamps. That was the only reason we were able to identify that the geomagnetic change appeared to be behind it - because supposedly everyone ‘knew’ that geomagnetic changes couldn’t have any impact on climate! It took us a long time to accept that this was what had happened - it was very much against standard thinking - and it will take some time to be considered and tested - science is naturally cautious about accepting big new ideas!
While the polar ice cores provide remarkable records of climate it must be remembered that they record local and seasonal impacts for those areas, which may not reflect changes happening elsewhere on the planet. In the case of Laschamps, the new kauri dating allowed us to precisely align the weak periods in earth’s magnetic field strength with rapid cooling events (Greenland Stadials 11 and 10) recorded in Greenland ice cores. These stadials look similar to surrounding climatic changes, but we suggest they may actually record the sudden cooling predicted by the climate models and have been missed previously due to limitations in dating accuracy.
Outside of the polar ice cores, we show widespread evidence of marked changes in global weather and glacier growth patterns around the Laschamps, including cooling and ice sheet growth of the massive Laurentide Ice Sheet over northern America. We suggest that this acted as a tipping point, locking in a cooling trend for much longer than the geomagnetic changes themselves. We identify that the climate alteration included global changes in wind patterns, changing continental climate systems such as in Australia where the vegetation swaps to an arid system, and was accompanied by widespread megafaunal extinctions.
We currently don’t know whether former geomagnetic reversals had impacts on the Earth as records are not well-resolved, and in many cases this question has not been examined closely. One possibility is that during the Laschamps Excursion, the Earth’s climate was relatively sensitive to external forcings – i.e. a state close to a tipping point. As a result, low geomagnetic activity, together with solar storms could ionize the atmosphere to such a degree that changes in ozone concentration, atmospheric temperature gradients, and subsequent weakening of the polar vortex caused significant changes in surface temperature, wind, and precipitation patterns all over the globe. This may, for instance, also have accelerated the onset of the Greendland stadials that occurred during the weakest periods of geomagnetic field strength. Further research is required to examine the relationship between geomagnetic variation and other climatic patterns, and whether previous geomagnetic excursion events were also impacted by solar storms or whether the coincidence of events during the Laschamps was unique.
Normally, the earth’s magnetic field provides a protective shield around the planet, blocking ionising radiation from deep space and the sun (galactic and solar cosmic rays, respectively). During the transition phases of the Laschamps Excursion, as the magnetic poles are switching position, the magnetic field strength collapsed to <6% of current levels, and potentially to 0%. With no magnetic shield, the levels of ionising cosmic radiation increased markedly. This impact was made far worse during Grand Solar Minima, periods of 50-150 years when solar sunspot activity reduces to a minimum, removing the default magnetic field that the streaming solar wind provides as it passes around each planet in the solar system. To try and work out how and why the loss of the magnetic field might have been able to cause such changes, the world-leading global chemistry-climate change modellers at the ETH constructed full models of the 42ka earth, where they could change the level of magnetic field protection and study the impacts on atmospheric chemistry. This was remarkable, as it confirmed that the strong atmospheric ionisation caused by increased amounts of incoming cosmic radiation (galactic and solar) created NOx and HOx which eroded the ozone layer and altered the energy budget of incoming solar radiation. The model showed that marked changes in global climate occured due to solar energy being distributed differently throughout the atmosphere, causing wind belts to shift - and strengthening the polar vortex, causing cold air to sit above the Laurentide ice Sheet, causing rapid and massive growth. We suggest this is what locked in the cooling climate change, so that even when the magnetism returned to normal the cool dry conditions were maintained in places like Australia. A recent parallel experiment (much smaller) is the climatic shifts caused by the ozone hole in the 1970s (caused by CFCs) where the altered climate patterns (cooling of the stratosphere) is still being felt today. The Laschamps was like this but on a massive scale!
Interestingly, the global chemistry-climate model showed that atmospheric ionisation caused climatic shifts without invoking any increase in cloud formation - which has been a hotly debated topic in climate change circles. We did not have an increased cloud formation factor in the climate model - but if that is in fact correct then our models would likely be underestimates of the level of climatic change. With the climate models, we were confident that we now had a mechanism to explain the changes we could see in the environmental records, occurring globally.
This question is related to the CLOUD experiment performed at CERN to investigate whether ionization of atmospheric compounds might increase cloud formation, as has been suggested. The CERN results were inconclusive, and as a result we did not implement a cloud formation mechanism into our model. The only mechanism simulated is the formation of HOx & NOx from ionization by energetic particles such as galactic cosmic rays (GCR), low energetic electrons (from the solar wind) or from solar proton events (SPE). Using just these factors, the global chemistry-climate model predicts 10-15% ozone destruction and altered atmospheric wind patterns producing considerable cooling impacts, including over the Laurentide Ice Sheet of North America.
It is also important to note that the levels of atmospheric ionisation implied during the Laschamps are several orders of magnitude larger than the minor fluctuations produced by the natural 11-year solar cycle. The latter are so small they have no significant impact on current climate.
As for any study, particularly one proposing such a radial new interpretation as this, there remains much that is unknown. While we suggest it is unlikely that so many different responses would happen around the world so close in time to the Laschamps Excursion (e.g. glacier growth, displacement of major wind belts, extinctions) it is always possible that these might have happened without a geomagnetic reversal and a solar minimum. However, such a high degree of coincidence raises suspicions about an external driver, which is why we decided to perform different climate simulations to determine the effects of simultaneous geomagnetic and solar minima. While many of the observations (such as the growth of the Laurentide ice Sheet) could be confirmed with the model results, things like the extinctions of the Neandertals obviously could not be modelled. Many more studies across multiple fields will be required to fully determine what the impacts of the Laschamps Excursion might have been. For the moment, we have provided a provocative new model explaining a number of seemingly unrelated events. Ongoing scientific research will now test whether this surprising new hypothesis holds, and whether it requires significant adjustment.
The reports of late surviving Neandertals on Iberia and western Europe (eg Spy) are all now considered incorrect due to problems with radiocarbon dating, and the most comprehensive studies of reliable Neandertal dates conclude that the last individuals, who survived longest in westernmost Europe, went extinct around 41-40ka. Studies of the Neandertal extinction have shown that it was a process that was staggered across space and time - starting early in eastern Europe around 50ka and slowly moving across to westernmost Europe by 42-41ka, where the last Neandertals survived. The best explanation appears to be that invading AMH populations were outcompeting the Neandertals - potentially by expanding more rapidly each time after a series of cold stadial events which caused both Neanderthal and AMH populations to shrink down into climate refugia. During these cold events (Greenland Stadials 12-10) archaeological records suggest that many areas were completely abandoned during each event - and then AMH were the first ones back. By repeating this process through each cold cycle, Neandertals lost more and more territory, until they were too small and fragmented to survive. The sharp cold of GS10 - which overlaps with the final polarity transition 41.05-40.75ka, aligns perfectly with the last Neandertals. So while these climatic changes might have driven the last Neandertal populations extinct, the process itself was much longer and appears to have been driven by better adaptability of AMH to rapidly changing climate and the environmental consequences. This was possibly through the use of better technology for hunting (nets, traps, etc), or methods of heat generation etc.
Archaeologists had previously noted the strange coincidence that there was a sudden onset of figurative cave art globally around 40-42ka, from Borneo and Sulawesi to Spain and France, which seemed very odd as these populations were clearly not communicating with each other. We suggest that this actually represents the survival of pre-existing artistic traditions inside caves, as groups took shelter in them during solar storms and Grand Solar Minima, when the impacts of the ionised atmospheric conditions would have been severe (such as high UV). We also suspect that some of the art might actually reflect these conditions, which would have included widespread strong aurora right down to the equator, lightning storms, and other strange visual phenomena. For example, during solar storms it is possible that the night sky lit up as brightly as day.
One intriguing possibility is that the widespread appearance of red ochre hand stencils (negative images of a hand) in cave art might reflect the use of red ochre sunscreens by indigenous groups, which is still practiced today. The ground red ochre is mixed with saliva or fat and applied by blowing from the mouth or through a straw. When a hand is covered using this process the consequence is a red ochre negative outline on any surface behind the hand, and we think that these images might record the use of sunscreen. The image subsequently becomes common in cave art, and anthropologists have suggested the image came to represent a sign that an individual was ‘here’ (ie like a fingerprint, or graffiti).