Radiocarbon and cosmic radiation events

The Sun serves as the primary energy source for Earth's system, and fluctuations in solar activity can have a significant impact on climate. Although direct records of solar activity, such as sunspot observations, date back only about 400 years, cosmic ray-induced radionuclides preserved in tree rings and ice cores provide valuable proxies, allowing scientists to reconstruct solar activity patterns over thousands of years.

However, the low temporal resolution of most existing long, precisely dated cosmogenic nuclide records poses challenges for studies of short-term solar variability, such as the 11-year Schwabe cycle and solar energetic particle events. Here we present several continuous, annually resolved records of atmospheric ¹⁴C concentration from tree rings covering most of the past 6000 years.

The records are extensively analysed to identify the 11-year Schwabe cycle and potential solar energetic particle events. Evidence suggests that the 11-year solar cycle has persisted for thousands of years, at least during grand solar maxima. We will present an analysis, when extreme solar energetic particle events are detected in the context of the sun’s 11-year cycle.

Dr Nicolas Brehm

Federal Institute of Technology Zurich, Switzerland

Dr Nicolas Brehm

Federal Institute of Technology Zurich, Switzerland

Dr Nicolas Brehm is a researcher specialized in high precision radiocarbon analysis at the Laboratory of Ion Beam Physics, ETH Zurich. His work focuses on reconstructing past solar activity by analysing ¹⁴C concentrations in dendrochonologically dated tree rings and modelling the global carbon cycle.

Dr Brehm's work has significantly advanced our understanding of solar variability over the past 10000 years. His research includes the discovery of two strong solar proton events in 7176 and 5259 BCE, as well as the identification and characterization of the eleven-year solar cycle through radiocarbon measurements in tree rings.

The history of solar cycles provides clues to the mechanisms behind the occurrence of anomalous events of solar activity, such as grand solar minima, including the Maunder Minimum in the 17th century. It is therefore essential to derive accurate information on the characteristics of solar cycles. To achieve a cycle-by-cycle examination of solar cycle length, our team has been working on improving the precision of radiocarbon measurements using the Accelerator Mass Spectrometer (AMS) at Yamagata University in Japan.

High-precision radiocarbon measurements also allow the identification of relatively smaller extreme solar proton events (SPEs) than the 774 – 775 CE event, which has been challenging to achieve with conventional analytical precision. Identification of such smaller but more frequent events enable us to explore their occurrence characteristics in relation to long-term solar activity variations, and by integrating these data with reconstructed solar cycles, examine the potential solar cycle dependence of extreme SPE occurrences.

In this presentation, we will discuss our latest progress and findings, highlighting the importance of high-precision radiocarbon measurements in advancing our understanding of solar variability and extreme space weather events.

Dr Hiroko Miyahara

Okinawa Institute of Science and Technology, Japan

Dr Hiroko Miyahara

Okinawa Institute of Science and Technology, Japan

Hiroko Miyahara is an associate professor at Okinawa Institute of Science and Technology (OIST) in Japan. She earned her PhD from Nagoya University and worked as an assistance professor at the Institute for Cosmic Ray Research, the University of Tokyo. After that, she continued her research at Musashino Art University while engaging in science education. In April 2025, she joined OIST and launched the Solar-Terrestrial Environment and Climate Unit. Her research interests include the long-term variability of solar activity, historical extreme solar proton events, changes in the heliospheric environment and galactic cosmic rays, and the influence of solar and cosmic-ray variations on the Earth's climate system.

Humankind's knowledge of extreme solar particle events (ESPEs), although partially informed by the discovery of so called 'Miyake events' remains rudimentary, as does hazard preparedness. I will present a summary of effects from the interval surrounding ground level enhancement (GLE) 70 in mid-December 2006. The particle fluence of reconstruction shown by Usoskin et al. (2023)  indicates that GLE 70's spectral shape was similar to the ESPE of 993-994 CE but at least three orders-of-magnitude less intense. Effects from the Active Region associated with GLE 70 include: 1) a burst of solar energetic neutral atoms at Earth associated with an X.9 solar flare along with quasi-trapped by-products of these observed by the SAMPEX satellite; 2) Protons (250-2000 MeV) arriving at the Ulysses spacecraft within minutes of the subsequent X6.5 flare peak; 3) Solar neutrons (20-70 MeV) in PAMELA data for subsequent X-class flares. Technology effects were numerous. CNES turned off CALIPSO's satellite payload controller and Chandra X-ray Observatory operations team re-planned science activities because of rising radiation levels. Polar flights were re-routed. During GLE 70 geosynchronous operators reported increased noise in a GEO attitude control system and switch-off of a reaction wheel. Closer to Earth, Envisat suspended its Payload Module Computer; PROBA-1 was temporarily unable to process some data; and the lightly shielded ALSat reported > 300 single-bit upsets. Currently thousands of spacecrafts, many operating off-the-shelf hardware and sensors, reside in LEO. Additionally, constellation spacecraft are using onboard autonomous control systems that may be greatly challenged during an ESPE.

Professor Delores Knipp

University of Colorado, USA

Professor Delores Knipp

University of Colorado, USA

Professor Knipp studies the space atmosphere interaction regions where energy from solar and geospace storms tend to concentrate. She earned her PhD from the University of California Los Angeles in 1989. Since then, she has held teaching and research positions at the US Air Force Academy and the Smead Aerospace Engineering Sciences Department at the University of Colorado Boulder, USA. Her research focuses on the space environment and the atmospheric and solar events that disturb it. She also studies historical space weather events to understand the impacts these events have had on society. Searching old data sets to reveal new physical insights about solar storms is her avocation. She is a retired USAF officer, former Editor-in-Chief of Space Weather and a Fellow of the American Meteorological Society.

Ions and electrons generated during flare and coronal mass ejection events at the Sun may escape the solar atmosphere and, guided by the interplanetary magnetic fields, propagate through space to near-Earth locations. These Solar Energetic Particles (SEPs) can be detected directly by spacecraft instrumentation. The highest energy SEPs may also propagate through the geomagnetic field and precipitate to low atmospheric heights, producing secondary particles including neutrons and cosmogenic radionuclides. The space weather effects associated with the SEP ion population (for the most part protons) consist principally of radiation risk to aviation, humans in space and spacecraft. This talk will review the risks to aviation and astronauts and emphasize how the parameters of the SEP event, including peak intensity, fluence and spectrum, affect radiation doses. It will describe space weather effects for events that took place in recent decades, for which a large body of measurements and models exist. It will discuss how the radiation at aviation altitudes and in space may be affected during SEP events of extreme magnitude, such as the ones extrapolated from radionuclide data from the distant past. The influence of propagation effects on the spatial distributions of intensities and magnitude of the events at different locations will be discussed.

Professor Silvia Dalla

University of Central Lancashire, UK

Professor Silvia Dalla

University of Central Lancashire, UK

Silvia Dalla is a Professor of Solar Physics at the University of Central Lancashire. Following a PhD in fusion plasmas, her research focused on solar and space plasmas, with appointments at Imperial College London and University of Manchester. Her main expertise is in the study of how particles are accelerated during solar eruptions and propagate through space to reach Earth. She developed a test particle code to model Solar Energetic Particle (SEP) propagation from Sun to Earth and worked on the analysis of particle events detected by spacecraft. Her research has demonstrated the importance of 3D effects in SEP propagation: these include guiding centre drifts, transport along the heliospheric current sheet and turbulence-induced cross field motion. Space weather forecasting models using the latest understanding in SEP physics have been developed within her group. These include SPARX, forecasting SEP intensities near Earth in real time and FORGE, a ground level enhancement in-progress forecast tool.

Radiocarbon (¹⁴C) dating provides the ultimate clock to study the past 55,000 years – allowing us to better explain our present, and to accurately predict/mitigate our future. However, the variations in past levels of ¹⁴C mean that all radiocarbon measurements need to be adjusted (calibrated) to be understood on a calendar scale. This need for calibration has, until now, limited the dating precision possible using ¹⁴C. Calibrated age estimates are typically uncertain, as well as potentially being complex and multimodal. 

The discovery of ‘Miyake’ events has provided exciting opportunities to obtain more precise calendar dates through radiocarbon. For those studying sites/periods containing known ‘Miyake’ events, calibration of a series of single tree-ring measurements containing the specific ¹⁴C signature can now provide an exact calendar date to anchor a chronology. Those who do not have such material, or who work in other periods, can still leverage the fine-scale ¹⁴C variations identified by the recent wider annual ¹⁴C measurement programmes in their calibration more broadly. 

In this talk, I will aim to give a whistle-stop, introductory, tour of radiocarbon dating and discuss the new opportunities presented by the discovery of these ¹⁴C production spikes, as well as some of the challenges to overcome if we want to optimally harness their use when building chronologies. 

Professor Tim Heaton

University of Leeds, UK

Professor Tim Heaton

University of Leeds, UK

Tim Heaton is an interdisciplinary academic at the University of Leeds where he works at the interface of statistics, the environmental sciences, and archaeology. Originally trained as a methodological statistician, he is now a lead academic on the INTCAL group, providing the internationally ratified radiocarbon (¹⁴C) calibration standards necessary to convert ¹⁴C measurements into calendar ages.

Tim was co-ordinating lead author on the current Marine20 radiocarbon calibration curve for the global surface oceans; led statistical construction for the Northern Hemispheric IntCal20 curve; and was a major contributor to the Southern Hemispheric SHCal20 curve. He also contributed to the recent discovery of the Miyake Event at 14 300 cal yr BP, helping create the absolute chronology to precisely date the event.

Recent clarification on the spatial and temporal structure of the 664 BCE Miyake event has staged the unique opportunity to enhance the precision in calibrating ¹⁴C ages over the Hallstatt Plateau (800-400 BCE) of the International Radiocarbon Calibration curve. Archaeological sites with timbers, charcoals, and floating tree-ring series now have unparalleled tool for achieving more accurate calendar synchronization of historical frameworks of the Iron Age. We present new fundings on dating archaeological timbers of the frozen kurgans of Bes-Shatyr and Shilikty sites erected by the Saka people in the Altai and Tian Shan Mountains of Central Asia (modern Kazakhstan), using the delta ¹⁴C signature of the 664 BCE Miyake event. AMS high-precision radiocarbon measurements, resolved annually and derived from larch and spruce tree rings previously dated using 10-year resolution wiggle matching, overturned the relative chronology of these kurgans and placed them approximately 100 years apart near 652 BCE (Bes-Shatyr k.3) and 555 BCE (Shilikty-III k.1). The discussion on the choking of the "Hallstatt Plateau curse" in calibration of tree-ring radiocarbon outlines the imminent perspective in application of both 664 BCE Miyake event and delta 14C annual series to redefine the chronological systems of Siberian Scythian, Saka, and Hellenistic sites across the Inner Eurasia, encompassing modern Turkmenistan, Kazakhstan, Uzbekistan, Kirgizstan, Russa, and China. This leads to exciting opportunities to precisely synchronize cultural transformations across the Eurasian Steppe, trace interactions with the Greco-Bactrian Kingdom, and link these societal and technological shifts with abrupt climate change events (4.2ka BP and 2.5ka BP).

Associate Professor Irina P Panyushkina, University of Arizona, USA

Associate Professor Irina P Panyushkina, University of Arizona, USA

Irina Panyushkina, a Russian-born physical geographer trained at the Russian Academy of Sciences in Krasnoyarsk, holds a PhD in Forest Ecology and specializes in Dendrochronology. Since 1998, she has been engaged in academic research, with her home base at the Laboratory of Tree-Ring Research, the University of Arizona. Her research spans environmental science, hydrology, paleoclimatology, forest conservation, archaeology, and biochemistry. Dr Panyushkina has developed and led international, multidisciplinary programs, primary in Siberia and Central Asia, focusing on reconstructing past climate variability and its societal and environmental impacts through tree-ring proxies. Irina is also part of an international initiative investigating carbon-14 spikes, Miyake events, and abrupt climate change during the Holocene. 

The potential for high-precision radiocarbon dating using signatures of cosmic radiation events in tree rings is widely acknowledged, with a wealth of new data produced. Recent research utilizing sub-annual samples of trees from different climate zones and growing seasons aids in determining the season of these events. However, cosmic radiation events can cause problems for dating individual samples, particularly short-lived materials formed around such events. Moreover, precise wiggle matching of wood samples requires non-smoothed calibration curves and must consider the cosmic radiation event's season in combination with the local growing season. An unexplored potential lies in dating samples beyond traditional tree ring sequences. Single-year radiocarbon dating is feasible even at sites where no wood is preserved, provided the activity phase is long enough (covering a cosmic radiation event), the deposition rate is sufficient, and stratigraphy is detailed. Urban sites or lake cores could meet these conditions. My presentation will showcase these challenges and opportunities, inviting discussion on advancing radiocarbon dating with cosmic radiation events.

Dr Bente Philippsen

Norwegian University of Science and Technology, Norway

Dr Bente Philippsen

Norwegian University of Science and Technology, Norway

Bente Philippsen is an Associate Professor at NTNU University Museum and the Leader of the National Laboratory for Age Determination in Trondheim, Norway. She holds a PhD in Physics and Archaeology, having studied at Heidelberg University and Aarhus University. Since completing her PhD in 2012, she has held various postdoctoral and short-term positions, focusing on radiocarbon dating and scientific archaeology. Her research primarily involves AMS radiocarbon dating, dendrochronology, and stable isotope analyses, which she applies to answer questions from archaeology, history, and ecology. Philippsen's work aims to place historical events and developments on a timeline, even when they are not documented in written sources. By combining radiocarbon and dendro-dates with contextual information, she enhances dating precision and studies human-environment interactions, subsistence strategies, and ancient dietary habits.