The Baltic Sea catchment area extends from the upper course of the Elbe in the Czech Republic to northernmost Lapland where the Tornionjoki river (Sw. Torneälven = Lake Torne) marks the border between Finland and Sweden today. This article concentrates on the coastal regions of the sea and discusses a mutual dialogue between climate and man. Oxygen isotope 18O and hydrogen isotope 2H in the layers of polar ice sheets indicate climate change in the time span of thousands, even tens of thousands, of years. In northern areas, much climatologic information is based on polar ice drilling data from Greenland. The influence of climate changes on human subsistence is clearly visible in pollen data from the numerous ponds and swamps in the Baltic Sea coastal zone. Accelerator mass spectrometry (AMS) dating of carbon remains in archaeological materials (such as the crusts of ceramic pieces) are used to build detailed chronological sequences. Human adaption to conditions dictated by nature is usually interpreted as innovation and progress in prehistory. But numerous raw materials, once used, cannot be replaced, while land exploitation is often followed by side effects such as erosion and eutrophication. For example, the Neolithic “revolution”—the beginning of crop cultivation and large-scale cattle breeding—is an example of such changes in southern Europe from ca. 6,000 bce. Between ca. 200 bce and 100 ce, during the Early Iron Age, the climate was relatively warm here. Local iron production expanded in the Baltic Sea region and allowed effective slash-and-burn crop cultivation for the first time in prehistory. Since then, human activity has caused damage to forests all around the Baltic Sea. A colder phase followed in 100–600 ce. Even today slight changes in annual temperature have great impact on subsistence in areas with harsh climate conditions, such as close to the Polar Circle. An abrupt and radical fall of temperature surely caused severe difficulties. Hunter-gatherers had to find secondary food resources while societies which were strongly dependent on one single base for economy, like agriculture, had even greater difficulties. In the southern part of the Baltic Sea sphere, considerable areas of land were under cultivation at that time. Harvest failures led to famines. A climate catastrophe, probably caused by volcanic eruption, adversely impacted urban, peasant, nomadic, and hunting populations all over the northern hemisphere in 535–536 ce. Recent archaeological studies and AMS samples have proven there was a demographic crisis in the northern part of the Baltic Sea. Soon after 600 ce, the climate became milder again, and the following centuries were warmer than almost any period during Holocene: the warm phase from 800 to ca.1050 ce perfectly matches a historical and archaeological era: the Viking Period. The Middle Ages and early post-medieval period were relatively mild and human-friendly times. But this was followed by the so-called Little Ice Age, dated approximately to 1275–1870. With the beginning of industrialization in mid-19th century, human impact on climate became obvious all over the globe, and the Baltic Sea region is no exception.
Bradley Skopyk and Elinor G. K. Melville
The onset of Spanish imperial rule in Mexico in 1521 had profound consequences well beyond the political and cultural spheres. It also altered Mexico’s environment, reconstituting the region’s ecology as new fauna, flora, and microorganisms were added and as the population dynamics of native Mexican biota fluctuated in response to Old World arrivals. While the consequences of myriad interactions between native and non-native species were vast and complex, it was the decimation of indigenous persons by pathogens that was one of the first biological consequences of colonization (in fact, occurring first in 1520, one year before the fall of the Aztec state) and one of the most important. Mexican human populations were reduced by 80 to 90 percent, effecting cascading ecological consequences across the physical and biological geography of Mexico. Forests regenerated, terraced slopes degraded, and much of the Mexican landscape lost its anthropogenic aspect. Simultaneously, ungulate introductions transformed Mexican flora and likely initiated soil erosion in some regions that, when transported to fluvial environments, disrupted the flow of rivers. On the other hand, pigs, sheep, goats, horses, and other ungulates altered plant communities through selective seed dispersion. New economic pursuits such as brick making and silver mining increased demand for heat energy that, in an unprecedented manner, encouraged intensive forest usage and, probably, regional deforestation, although empirical data on historical forest cover are still lacking. Severe climate variability, of a scale not experienced for at least five hundred years and perhaps many millennia, occurred simultaneously with colonial-induced ecological change. A significant conquest-era drought was followed by one of the coolest and wettest periods of the Holocene; a strong pluvial in the Mexican context lasted from 1540 to around 1620. Subsequent anomalies of both temperature (cold) and precipitation (either wet or dry) occurred in the 1640s and 1650s, and from the 1690s until about 1705. Together, these climate anomalies are known as the core Little Ice Age, and initiated agrarian transitions, hazardous flooding, prolonged droughts, epidemics, epizootics, and recurring agrarian crises that destabilized human health and spurred high rates of mortality. Soil degradation and suppressed forest cover are also likely outcomes of this process. Although debate abounds regarding the timing, extent, and causes of soil and water degradation, there is little doubt that extensive degradation occurred and destabilized late-colonial and early-Republic societies.