Climate change impacts and vulnerability in Europe 2016

Climate change impacts on environmental systems
Box 4.6
Soils under climate change: carbon storage and soil erosion
Climate is one of the factors that determines soil formation and soil processes. Soil functions are equally critical in the soil
system's resilience to climate change effects. Soils can offset other greenhouse gas emissions by capturing and storing
carbon, and the soil's flood regulation function (owing to the structuring effect of soil organic matter) can help in the
adaptation to climate change. Furthermore, soils also help regulate temperature, as the water present in the soil has a
cooling effect. Soils are subject to a range of degradation processes, some of which are strongly influenced by climate
change. For example, erosion by water and wind are affected by extreme climate events (intense rainfall, droughts, heat
waves, storms). In particular, erosion of the upper part of the soil (topsoil) leads to declining soil organic carbon and
nutrient stocks, which influences fertility and has further knock-on effects. Soil organic matter loss leads to a breakdown
of the soil structure and reduced soil water storage, which can lead to an enhanced risk of flooding and landslides in
adjacent areas. Soil organic matter can be a strong indicator of soil biodiversity, which plays a crucial role in carbon and
nutrient cycling. In addition, both soil organic matter and soil organism diversity and activity are affected by temperature
and moisture changes. The interlinkages between the climate and soil system, along with the interaction between humans
and these natural systems, define the degree to which soil can deliver services to society. Land use and land management
(supported by conducive policies) responsive to the challenges of climate change and its impact are thus crucial for the
resulting services.
Soil organic carbon
Estimates derived from the European Soil Database indicate that around 45 % of the mineral soils in Europe have a topsoil
organic carbon content that is very low to low (0–2 %) and 45 % have a medium content (2–6 %) (Rusco et al., 2001). Soil
organic carbon (SOC) stocks in the EU-27 were estimated at 73–79 billion tonnes using the Topsoil Organic Carbon Content
for Europe (OCTOP) model (Jones et al., 2005, 2012). Comparisons of this modelled data with alternative approaches
suggest that the SOC stock may have been both underestimated and overestimated. On the one hand, Baritz et al. (2014)
suggest that the OCTPOP model has underestimated SOC (e.g. in Norway). On the other hand, estimates for north-eastern
Europe, comprising countries with a high proportion of organic topsoils, are presumably overestimated (country data,
Panagos et al., 2013; GEMAS ( 58 ) dataset, Baritz et al., 2014). Modelling results from the CAPRESE ( 59 ) project show a topsoil
(0–30 cm) SOC pool of 17.6 billion tonnes (or Gt) ( 60 ) in agricultural soils at pan-European level ( 61 ) (17.0 Gt for the EU-28)
(Lugato, Panagos et al., 2014). These data suggest that the OCTOP assessment may have overestimated the SOC pool in
agricultural soils by around 24 %. Values for forest SOC stocks in Europe (on a reference forest area of 163 million hectares
(ha)) were estimated at 3.50–3.94 Gt in forest floors (organic sub-layers), and 11.4–12.2 Gt (0–30 cm) or 21.4–22.5 Gt (upper
1 m) in mineral and peat soils (De Vos et al., 2015). These new data point at an underestimation of most existing estimates
for European forest soils, and highlight that a substantial amount of SOC is stored in forest floors.
A recent assessment (using the LUCAS ( 62 ) database along with SOC predictors) shows that predicted SOC contents are
lowest in Mediterranean countries and in croplands across Europe, whereas the largest predicted SOC contents are in
wetlands, woodlands and mountainous areas (de Brogniez et al., 2015). This is in line with the notion that croplands
generally act as a carbon source, while forest soils generally provide a sink (Schils et al., 2008). Nevertheless, some cropping
practices can lead to sequestration in arable soils if given time (see below), while CH 4 emissions from livestock and N 2 O
emissions from arable agriculture may be fully compensated by the CO 2 sink provided by forests and grasslands (Schulze
et al., 2009).
Possible pathways for SOC and CO 2 development in temperate mineral soils involve many possible interrelationships,
making the effects of climate change on SOC stocks and greenhouse gas emissions complex (EEA, 2012). The organic carbon
pool of soils (including deeper layers) in the northern permafrost region is estimated to account for approximately 50 % of
the estimated global belowground organic carbon pool (Tarnocai et al., 2009). There, higher temperatures could increase
the activity of microbial decomposers and indirectly affect organic matter decomposition through other feedbacks, of which
thawing of permafrost (covering about 50 % of the boreal zone) and increased fire frequency are expected to create the
strongest effects (positive and negative, respectively) on microbial CO 2 production (Allison and Treseder, 2011).
( 58 ) GEMAS: 'Geochemical Mapping of Agricultural and Grazing Land Soil'.
( 59 ) CAPRESE: 'CArbon PREservation and SEquestration in agricultural soils: Options and implications for agricultural production'.
( 60 ) Allocated as 7.6 and 5.5 Gt in arable and pasture lands, respectively.
( 61 ) EU-28 + Serbia, Bosnia and Herzegovina, Montenegro, Albania, former Yugoslav Republic of Macedonia and Norway.
( 62 ) LUCAS: 'Land Use/Cover Area frame Statistical Survey'.
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