Did the Bronze Age deforestation of Europe affect its climate? A regional climate-model study using pollen-based land-cover reconstructions

Abstract. This paper studies the impact of land use and land-cover change (LULCC) on the climate around 2 500 years ago (2.5 ka), a period of rapid transitions across the European landscape. One global climate model was used to force two regional climate models (RCMs). The RCMs used two land cover descriptions. The first was from a dynamical vegetation model representing potential land cover; the second a land cover description reconstructed from pollen data by statistical interpolation. The two different land covers enable us to study the impact of land cover on climate conditions. Since the difference in landscape openness between potential and reconstructed land cover is mostly due to LULCC, this can be taken as a measure of early anthropogenic effects on climate. The use of two RCMs enables us to study how sensitive climate models can be to land-cover changes. The results show that the simulated 2.5 ka climate was warmer than the simulated pre-industrial (PI) climate. The largest differences are seen in northern Europe, where the 2.5 ka climate is 2–4 °C warmer than PI. In summer, the difference between the simulated 2.5 ka and PI climates is smaller (0–3 °C), with the smallest differences in southern Europe. Differences in seasonal precipitation are mostly within ±10 %. In parts of northern Europe, the 2.5 ka climate is up to 30 % wetter in winter than that of PI. In summer there is a tendency for the 2.5 ka climate to be drier than PI in the Mediterranean region. The results also suggest that LULCC at 2.5 ka significantly impacted the climate in parts of Europe. Simulations including reconstructed LULCC (i.e. those using pollen-derived land cover descriptions) give up to 1 °C higher temperature in parts of northern Europe in winter and up to 1.5 °C warmer in southern Europe in summer than simulations with potential land cover. This relatively strong response implies that anthropogenic land cover changes that had occurred by the late prehistoric period may have already affected the European climate by 2.5 ka.