CMIP5 Models Predict Rapid and Deep Soil Warming Over the 21st Century

Abstract

Despite the fundamental importance of soil temperature for Earth's carbon and energy budgets, ecosystem functioning, and agricultural production, studies of climate change impacts on soil processes have mainly relied on air temperatures, assuming they are accurate proxies for soil temperatures. We evaluated changes in soil temperature, moisture, and air temperature predicted over the 21st century from 14 Earth system models. The model ensemble predicted a global mean soil warming of 2.3 ± 0.7 and 4.5 ± 1.1 °C at 100‐cm depth by the end of the 21st century for RCPs 4.5 and 8.5, respectively. Soils at 100 cm warmed at almost exactly the same rate as near‐surface (~1 cm) soils. Globally, soil warming was slightly slower than air warming above it, and this difference increased over the 21st century. Regionally, soil warming kept pace with air warming in tropical and arid regions but lagged air warming in colder regions. Thus, air warming is not necessarily a good proxy for soil warming in cold regions where snow and ice impede the direct transfer of sensible heat from the atmosphere to soil. Despite this effect, high‐latitude soils were still projected to warm faster than elsewhere, albeit at slower rates than surface air above them. When compared with observations, the models were able to capture soil thermal dynamics in most biomes, but some failed to recreate thermal properties in permafrost regions. Particularly in cold regions, using soil warming rather than air warming projections may improve predictions of temperature‐sensitive soil processes.

Relative humidity predominantly determines long‐term biocrust‐forming lichen cover in drylands under climate change

“…However, the net benefits of mitigation at higher atmospheric CO 2 become smaller if relative humidity decreases (a trend being already observed in Spain in Moratiel et al, 2010). Additionally, there is a general trend towards warmer and dryer soils that can further reduce water availability and increase drought stress for biocrusts (Soong et al, 2020). Field studies on this subject are still very rare, but a study conducted in the Mojave desert suggests that higher atmospheric CO 2 cannot mitigate the negative effects of drought on biocrust cover (Wertin et al, 2012).…”

Massive peatland carbon banks vulnerable to rising temperatures

“…Each sample was analyzed twice, and the average results for each sample were recorded. Analytical precision was 0.2‰ for 13 C.…”

“…1a). Capturing comprehensive peatland responses to climate change requires the use of active surface and deep-soil warming because deep-soil temperatures will naturally increase in concert with rising annual air temperatures [13][14][15] . Based on current greenhouse gas emission rates 16 , forcing estimates in line or greater than the RCP 8.5 scenario are likely to occur.…”

How Much Will Soil Warm?

“…Nevertheless, Soong et al (2020) showed the models do agree on the speed with which the warming signal is propagated through the most biologically active soil layers. Answering the question of whether shallow soils (1–5 cm depth) will warm faster than deep soils (100 cm depth), they showed no difference in warming rate predicted by the models.…”