500-year-old Transylvanian diaries show how the Little Ice Age completely changed life and death in the region

Tapping into ‘society’s archive’, researchers have examined written sources from the 16th century that chronicle famine, excessive flooding, and plagues in what today is Romania

From Frontiers in Science and the University of Oradea:

Glaciers, sediments, and pollen can be used to reconstruct the climate of the past. Beyond ‘nature’s archive,’, other sources, such as diaries, travel notes, parish or monastery registers, and other written documents – known at the ‘society’s archive’ – contain reports and observations about local climates in bygone centuries.

In contrast, the second half of the century was characterized by heavy rainfall and floods, particularly in the 1590s.

The western parts of the European continent cooled significantly when in the 16th century a period known as the ‘Little Ice Age’ intensified. During the second half of the century, temperatures dropped by 0.5°C. In Transylvania, however, hot weather was recorded much more frequently than cold weather during the 16th century. “This makes us believe that the Little Ice Age could have manifested itself later in this part of Europe,” said Caciora. Later writings, in which more cold waves and severe winters are mentioned, support this thesis.

Delayed ice age

The sources tell of a particularly hot and dry first half of the century. “One compelling passage comes from a historical document describing the summer of 1540. ‘The springs dried up, and the rivers dwindled to mere trickles. Livestock fell in the fields, and the air was thick with despair as the people gathered in processions, praying for rain,’” said Caciora. “This vivid account underscores the emotional and spiritual dimensions of living through climatic extremes.”

In contrast, the second half of the century was characterized by heavy rainfall and floods, particularly in the 1590s. Compared to the western parts of the European continent, which cooled significantly when in the 16th century a period known as the ‘Little Ice Age’, intensified. During the second half of the century, temperatures dropped by 0.5°C.

In Transylvania, however, hot weather was recorded much more frequently than cold weather during the 16th century. “This makes us believe that the Little Ice Age could have manifested itself later in this part of Europe,” said Caciora. Later writings, in which more cold waves and severe winters are mentioned, support this thesis.

Climate catastrophes

Such weather variations often resulted in catastrophes, related directly or indirectly to the climate. These included 30 years during which the Black Death ravaged the land, 23 years or famine, and nine years during which locust invasions were recorded.

However tragic, weather extremes and resulting calamities could have driven changes in settlement patterns, the researchers said. “Towns might have adopted flood-resistant infrastructure or migrated to more favorable areas. The challenges might also have spurred technological innovations, such as improved irrigation systems or storage facilities,” Caciora explained.

The human element

“Chronicles and diaries reveal how people perceived, responded to, and were impacted by these events,” Caciora continued.

Despite the insights it provides, the study faces several limitations, the researchers pointed out. Few people were literate, reports are often subjective, or only true on local scales. In addition, the records are fragmented. For example, the researchers were not able to include any records about 15 years of the 16th century, either because no records existed, or they were too contradictory for inclusion.  

Nevertheless, these writings not only provide a glimpse into how people in the past might have lived, but are also relevant for modern climate resilience strategies, particularly in understanding the socio-economic consequences of extreme weather events and their role in shaping human history. “Studying climate records from the society’s archive is as crucial as analyzing natural proxies,” Caciora explained. “It provides a human-centric perspective on past climatic events.”

Journal

Frontiers in Climate DOI 10.3389/fclim.2024.1507143 

From the “Why do we care that agricultural pests can’t lay eggs properly? – Oh wait, we don’t!” department…and Eurekalert.

Rising carbon dioxide level disrupts insects’ ability to choose optimal egg-laying sites

Climate change is rapidly reshaping ecosystems across the globe, and new research has identified a previously unrecognized consequence: disrupted insect reproductive behavior. A recent study published in National Science Review reveals that rising atmospheric carbon dioxide (CO₂) levels are interfering with how agricultural pests choose egg-laying sites—posing significant risks to biodiversity, food security, and pest management strategies.

  Insects, despite their adaptability, are especially sensitive to shifts in environmental conditions. As global temperatures rise and atmospheric composition changes, their behavior is changing in ways that ripple through ecosystems. CO₂, the primary greenhouse gas driving global warming, has increased from 278 ppm in 1750 to approximately 420 ppm in 2023. Emerging evidence shows that elevated CO₂ levels—alongside pollutants such as ozone and nitrogen oxides—are disrupting insects’ ability to detect chemical cues essential for reproduction and survival. Until now, the underlying mechanisms remained poorly understood.

  Now, an international collaborative study by scientists from the Chinese Academy of Agricultural Sciences, the Norwegian University of Science and Technology, and the Max Planck Institute has provided key insights. Focusing on Helicoverpa armigera—the cotton bollworm, a major global crop pest—the team discovered that females normally use plant-emitted CO₂ to locate suitable egg-laying sites, particularly favoring younger leaves that emit higher CO₂ gradients. These sites are critical for larval survival and development. However, under elevated atmospheric CO₂ concentrations, this behavior is significantly disrupted. The study found that moths’ CO₂-sensing ability is impaired, causing them to lay eggs in less suitable locations. “This disruption is akin to confusing a key olfactory cue from a GPS system,” said Prof. Guirong Wang, lead author of the study. “Without accurate CO₂ signals, the insects struggle to find ideal egg-laying sites, which could affect pest population dynamics and agricultural damage.”

  To understand the biological basis for this disruption, the researchers identified three CO₂-detecting gustatory receptors—HarmGR1, HarmGR2, and HarmGR3. When any of these receptors were genetically deleted, the moths’ ability to detect CO₂ impaired, resulting in disoriented egg-laying behavior.

  The study’s simulations paint a worrying future: if atmospheric CO₂ reaches 1000 ppm by 2100, moths’ preference for optimal egg-laying sites could drop by up to 75%. This would likely reduce larval survival, destabilize pest populations, and alter biodiversity and ecological balance.

  Beyond the alarming ecological implications, these findings point to new opportunities. “By targeting the CO₂ receptors, we can explore novel, eco-friendly pest control strategies,” said Dr. Qiuyan Cheng, first author of the paper. One promising approach is RNA interference (RNAi), a gene-silencing technique already used in mosquito control, which could disrupt pest reproduction without harmful chemicals.

  The study adds to growing evidence that climate change is influencing insect behavior in complex and unexpected ways—not only through temperature shifts but also via direct changes to atmospheric chemistry. With global CO₂ levels on track to exceed 1000 ppm by the end of the century, researchers stress the urgent need for both emissions reductions and innovative agricultural adaptation.

Journal

National Science Review DOI 10.1093/nsr/nwaf270