Regional climate model simulations for Europe at 6 and 0.2 k BP: sensitivity to changes in anthropogenic deforestation

Gustav Strandberg ,Ralph Fyfe ,Laimdota Kalniņa ,Anneli Poska ,Benjamin Smith ,Thomas Giesecke ,Anne Birgitte Nielsen ,H John B Birks ,Anna-Kari Trondman ,Małgorzata Latałowa ,Mihkel Kangur ,Marie-José Gaillard ,Sebastian Wagner ,Jed O Kaplan ,Basil Davis ,Erik Kjellström ,Achille Mauri ,W.o Van Der Knaap ,Anne E Bjune ,Florence Mazier ,Laurent Marquer ,Ulla Kokfelt ,Heikki Seppä ,Petr Kuneš ,S Sugita

doi:10.5194/cp-10-661-2014

Abstract

Abstract. This study aims to evaluate the direct effects of anthropogenic deforestation on simulated climate at two contrasting periods in the Holocene, ~6 and ~0.2 k BP in Europe. We apply We apply the Rossby Centre regional climate model RCA3, a regional climate model with 50 km spatial resolution, for both time periods, considering three alternative descriptions of the past vegetation: (i) potential natural vegetation (V) simulated by the dynamic vegetation model LPJ-GUESS, (ii) potential vegetation with anthropogenic land use (deforestation) from the HYDE3.1 (History Database of the Global Environment) scenario (V + H3.1), and (iii) potential vegetation with anthropogenic land use from the KK10 scenario (V + KK10). The climate model results show that the simulated effects of deforestation depend on both local/regional climate and vegetation characteristics. At ~6 k BP the extent of simulated deforestation in Europe is generally small, but there are areas where deforestation is large enough to produce significant differences in summer temperatures of 0.5–1 °C. At ~0.2 k BP, extensive deforestation, particularly according to the KK10 model, leads to significant temperature differences in large parts of Europe in both winter and summer. In winter, deforestation leads to lower temperatures because of the differences in albedo between forested and unforested areas, particularly in the snow-covered regions. In summer, deforestation leads to higher temperatures in central and eastern Europe because evapotranspiration from unforested areas is lower than from forests. Summer evaporation is already limited in the southernmost parts of Europe under potential vegetation conditions and, therefore, cannot become much lower. Accordingly, the albedo effect dominates in southern Europe also in summer, which implies that deforestation causes a decrease in temperatures. Differences in summer temperature due to deforestation range from −1 °C in south-western Europe to +1 °C in eastern Europe. The choice of anthropogenic land-cover scenario has a significant influence on the simulated climate, but uncertainties in palaeoclimate proxy data for the two time periods do not allow for a definitive discrimination among climate model results.

Highlights

Humans potentially had an influence on the climate system through deforestation and early agriculture already long before we started to emit CO2 from fossil fuel combustion (Ruddiman, 2003)
We focus on two contrasting time periods in terms of climate and anthropogenic land cover change: the MidHolocene warm period (∼ 6 k BP) and the Little Ice Age (∼ 0.2 k BP = ∼ AD 1750)
The additional unforested land predicted by HYDE3.1 and KK10 is negligible in comparison to the potential unforested land simulated by LPJ-GUESS, which explains why the V, V + H3.1 and V + KK10 land cover descriptions do not differ significantly from each other at 6 k

Summary

Introduction

Humans potentially had an influence on the climate system through deforestation and early agriculture already long before we started to emit CO2 from fossil fuel combustion (Ruddiman, 2003). The effect on the global climate is conveyed by the increased amounts of CO2 in the atmosphere from deforestation, and by the regional and local changes of land-surface properties Forster et al, 2007) Such changes have a direct effect on the regional climate, including changes in albedo and energy fluxes between the land surface and the atmosphere (e.g. Pielke et al, 2011). Reduced vegetation cover means reduced evapotranspiration that leads to higher air temperature, but the amplitude of the evapotranspiration changes depend on local conditions, such as soil moisture availability (Ban-Weiss et al, 2011; de Noblet-Ducoudré et al, 2012). The direct effects of past vegetation change have mostly been studied on a global scale The direct effects of past vegetation change have mostly been studied on a global scale (e.g. Brovkin et al, 2006; Pitman et al, 2009; Pongratz et al, 2009b, 2010; de Noblet-Ducoudré et al, 2012; Christidis et al, 2013)

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