The impact of nitrogen and phosphorous limitation on the estimated terrestrial carbon balance and warming of land use change over the last 156 yr

Q Zhang,Y P Wang,Y J Dai,P J Lawrence,A J Pitman

doi:10.5194/esd-4-333-2013

Abstract

Abstract. We examine the impact of land use and land cover change (LULCC) over the period from 1850 to 2005 using an Earth system model that incorporates nitrogen and phosphorous limitation on the terrestrial carbon cycle. We compare the estimated CO2 emissions and warming from land use change in a carbon-only version of the model with those from simulations, including nitrogen and phosphorous limitation. If we omit nutrients, our results suggest LULCC cools on the global average by about 0.1 °C. Including nutrients reduces this cooling to ~ 0.05 °C. Our results also suggest LULCC has a major impact on total land carbon over the period 1850–2005. In carbon-only simulations, the inclusion of LULCC decreases the total additional land carbon stored in 2005 from around 210 Pg C to 85 Pg C. Including nitrogen and phosphorous limitation also decreases the scale of the terrestrial carbon sink to 80 Pg C. Shown as corresponding fluxes, adding LULCC on top of the nutrient-limited simulations changes the sign of the terrestrial carbon flux from a sink to a source (12 Pg C). The CO2 emission from LULCC from 1850 to 2005 is estimated to be 130 Pg C for carbon only simulation, or 97 Pg C if nutrient limitation is accounted for in our model. The difference between these two estimates of CO2 emissions from LULCC largely results from the weaker response of photosynthesis to increased CO2 and smaller carbon pool sizes, and therefore lower carbon loss from plant and wood product carbon pools under nutrient limitation. We suggest that nutrient limitation should be accounted for in simulating the effects of LULCC on the past climate and on the past and future carbon budget.

Highlights

The CryosphereHuman activity has modified 42–68 % of the terrestrial surface via deforestation, reforestation, clearing for crops, pasture and urban settlements (Hurtt et al, 2006)
Most of these studies have focused on the biogeophysical impacts of Land use and land cover change (LULCC)
The N and P limitation reduces the capacity of the terrestrial biosphere to take up CO2 such that in the LUC-CNP simulations the land is a weak source of CO2 because emissions from land cover change are not fully offset by land carbon uptake in response to increased atmospheric CO2 (Fig. 3)

Summary

Introduction

The CryosphereHuman activity has modified 42–68 % of the terrestrial surface via deforestation, reforestation, clearing for crops, pasture and urban settlements (Hurtt et al, 2006). There is extensive literature pointing to significant impacts of these changes on regional temperature (Bonan, 1997; Gallo et al, 1999; Zhou et al, 2004; Lobell et al, 2008), temperature extremes (Avila et al, 2012; Pitman et al, 2012), rainfall (Niyogi et al, 2010; Pielke et al, 2011) and in some regions of intensive LULCC perhaps rainfall extremes (Pitman et al, 2012) Most of these studies have focused on the biogeophysical impacts of LULCC. LULCC modifies the leaf area index, root depth, stomatal conductance and aerodynamic roughness length (Bonan, 2008) which combine to change the efficiency of water transfer from within the soil, through the plants and into the atmosphere via the stomata

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