Although it is generally accepted today that climate and other environmental factors affected past human societies at different spatiotemporal scales, direct linkages are difficult to determine, and correlation should not be confused with causation. Here, we use a tree-ring width network of multimillennial chronologies from inner Eurasia to reconstruct annual changes in Net Primary Productivity (NPP) back to 200 BCE. Our findings reveal that episodes of reduced NPP around the 70s–100s, 360s–380s, and 470s–560s CE likely contributed to the westward and southward migration of nomadic people from their homelands in northwestern China and Mongolia. Although prolonged multidecadal periods of climate-induced low NPP served as tipping points for agricultural and pastoral subsistence systems, the inherent mobility of nomadic communities not only enabled them to adapt to adverse environmental conditions but also facilitated a widespread dispersal of ethnic groups.

Grain was the most important food source in pre-industrial Sweden. Climate variability is known to have affected grain harvests, but knowledge of Swedish climate–harvest relationships remains patchy prior to the late 19th century. In this study, we conducted statistical and geostatistical analyses of the effects of climate variability on harvest variations across Sweden for the main crops of spring barley and oats and winter rye over the period 1665–1810. We employed parish-level data from tithes, a tax levied on a certain percentage of the harvest, and state-of-the-art palaeoclimate reconstructions and reanalysis data. Geographically consistent positive relationships between summer temperatures and harvests are found in approximately the northern two-thirds of Sweden. This relationship extended further south for rye. Conversely, summer temperatures showed a negative relationship with the harvest of all three grain types in southern Sweden. For barley and oats, this negative relationship also extended throughout central Sweden. Higher May–July precipitation and higher soil moisture improved harvests in all but northern Sweden, and did so to a surprisingly comparable degree in wetter western as well as in drier eastern Sweden. The worst harvest outcomes were observed either during years of extremely dry conditions, very high June–July temperatures or extremely cold summers. In conclusion, climate–harvest relationships during the 1665–1810 period are surprisingly similar to those of today for the same crops and regions. Drought, rather than too low growing season temperatures, was the main constraint on grain cultivation in the major grain-growing regions of Sweden – even during the Little Ice Age.

Earth has reflected progressively less solar radiation since the start of the satellite era (1979), amplifying the planetary energy imbalance. Satellite analyses attribute the trend primarily to circulation-driven contraction of reflective cloud regimes, whereas process-based studies emphasize surface reflectivity changes. We argue that these perspectives are dynamically linked: as cloud cover contracts, diminishing atmospheric masking elevates the realized climatic leverage of surface albedo. This coupling makes surface reflectivity an increasingly important and manageable regulator of solar absorption under clearer-sky conditions. We propose an integrated governance framework that explicitly incorporates albedo management alongside carbon management.

The decline of the Classic Maya civilisation (∼8th–10th centuries CE) occurred in part from drought stress induced by natural climate variability. Using the EC-Earth3 8K simulation, driven by time-varying orbital and greenhouse gas forcing, we show that the convergence of internal hydroclimatic rhythms alone, generated severe, prolonged droughts comparable to, or even greater than, observed extreme events. We identify the interaction of multi-centennial oscillations (∼600 years) and centennial (∼160 years) cycles, superimposed with robust sub-centennial oscillations (∼60–90 years) and persistent multi-decadal and inter-annual variability, created a shifting wet/dry regime over the Yucatán Peninsula. Severe droughts arose when different frequency modulations aligned in their dry phases. Our results provide the first model-based demonstration of how internal climate variability alone can trigger extreme events capable of reshaping societies, revealing key climatic drivers of societal vulnerability, with direct implications for how internal variability may interact with anthropogenic forcing to amplify future climate risks.

Medieval Scandinavia presents ten groundbreaking thematic studies of various aspects of the social and economic history of the three medieval Scandinavian kingdoms, Denmark, Norway, and Sweden.

The contributing archaeologists and historians present a wealth of findings. With new information prompted by methodological advances they give us fresh perspectives on population estimates, coinage, trade and travelling, and building activities reflecting economic and social well-being. There are novel insights into complex topics such as gender dynamics, work and wage structures, and the importance of Saami networks.

The Scandinavian countries are studied individually and together as an entity in a European context. The volume is a contribution to scholarly studies, but at the same time makes fascinating reading for anyone with an interest in medieval history, with facts ranging from the impact of plagues to vernacular architecture.

Northwest China is facing socio-environmental challenges linked to ongoing climatic warming. However, a scarcity of regional paleorecord syntheses limits our understanding of natural long-term climate variability in the region and hinders the contextualization of contemporary warming. Here, we present paleorecord syntheses for both summer and annual temperatures during the Holocene based on a range of lacustrine sediment records from northwest China, with consideration of chronological uncertainties within records. The syntheses show similar summer and annual temperature variations, including peak warmth at ∼9000 years BP, followed by a 2000-year cooling trend, and stable temperatures thereafter. These variations may reflect inter-seasonal impact of summer insolation forcing through climate feedbacks (e.g., Arctic sea-ice cover) that are still not well represented in climate models. The early-Holocene peak warmth was >1.0°C warmer than the 20th century mean warmth, but is expected to be exceeded during the 21st century even under a low emission scenario.

As the sub-Arctic and Arctic regions undergoes rapid changes, understanding its hydroclimate history is more critical than ever. A limited availability of moisture-sensitive proxy data severely constrains our insights, underscoring the urgent need for more hydroclimate reconstructions in the region. Here we present a May–June precipitation reconstruction based on ring width from living and dead trees of Scots pine (Pinus sylvestris L.) growing under drought-stressed conditions at 63° N, near Skuleskogen National Park, on the northern part of the east coast of Sweden. The oldest deadwood sample dates back to the mid-11th century, and the Expressed Population Signal (EPS) exceeds 0.85 from 1320 CE until the present (2021 CE), making this the longest tree-ring-based hydroclimate reconstruction from high-latitude Fennoscandia. Unlike typical high-latitude forests in Fennoscandia, the trees at this site thrive under low-pressure conditions and show strong correlations up to approximately |r| = 0.6 over the period 1920–2021 with drought-related variables such as precipitation, cloud cover, solar radiation, potential evapotranspiration and diurnal temperature range. The climate signal is concentrated to a short window between mid-May and early July but reflects climatic conditions over a broad region. Significant spatial correlations extend over most of Sweden as well as large parts of Norway and Finland, indicating sensitivity to large-scale climate systems. The tree-ring chronology also shows clear cyclic patterns, with a particularly strong ∼ 64-year cycle. The modern era stands out for its variability, with 2018 CE emerging as one of the of the driest year in the entire record. There is potential to extend the chronology further back in time, possibly to 1000 CE or earlier, and to extract additional climate information using other tree-ring parameters such as blue intensity.

The paper explores to which extent narrative documentary records on wine production in Central Europe can be used as a proxy for summer temperatures. Here, we compiled 11 regional series spanning from the early 15th century to 1988. We detrended the data to adjust for long-term biases such as warfare-related population decline. The homogenised regional series were subsequently merged into three supra-regional series: (1) the Mosel series, starting in 1416 and consisting of data from the former city-republic of Metz (France) and the Grand Duchy of Luxembourg; (2) the series for Germany, starting in 1511 and mainly originating from the former city-state of Heilbronn; and (3) the third series, starting in 1529 and representing production on the Swiss Plateau. The residuals of the supra-regional yield series were averaged, divided into seven classes, and multiplied by five quality classes. Yield quality indices (YQI) varying between 35 (large and excellent) and 1 (small and undrinkable) significantly correlated with temperatures between May and July. Regression analysis of the composite series revealed that yield and quality primarily depend on the climate conditions from May to July as well as on those in June of the previous year. Crops with a YQI > 28 (rated “good” by traditional winegrowers) were related to above-average May–July temperatures, early grape harvest dates and high tree-ring maximum latewood density values resulting from frequent anticyclonic weather situations. Crops with YQI > 10 could not be uncritically assigned to cold summers since severe winter conditions, and spring frosts sometimes substantially reduced yields without affecting quality, particularly during the Little Ice Age in the marginal Mosel and German areas. Extreme yield fluctuations challenged winegrowing communities. Overproduction induced wastefulness, while crop failures sometimes triggered witch hunts.