Our Common Future Under Climate Change

International Scientific Conference 7-10 JULY 2015 Paris, France

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Tuesday 7 July - 14:30-16:00 UNESCO Fontenoy - ROOM I

L1.2 - Climate Change and Land Systems: Impacts and Feedbacks

Large Parallel Session

Chair(s): W. Cramer (IMBE, Marseille, France), S. Seneviratne (ETH, Zurich, Zurich, Switzerland)

14:30

Climate change and land systems: Impacts and feedbacks related to drought

S. Seneviratne (ETH, Zurich, Switzerland)

Abstract details
Climate change and land systems: Impacts and feedbacks related to drought

S. Seneviratne (1)
(1) ETH, Institute for atmospheric and climate science, Zurich, Switzerland

Abstract content

Land systems have numerous two-way interactions with the climate system. While they are often strongly affected by climate variability and changes, in particular in relation to droughts and hot extremes, they also impact climate through direct forcing and feedbacks. In particular, the modulation of soil water dynamics by ecosystems is an important factor affecting itself the evolution of droughts and heatwaves in several regions. In addition, human management, e.g. through changes in surface properties associated with agriculture practice, also affects these interactions. This presentation will provide a brief overview of the underlying mechanisms, including insights from new research, and will introduce the main topics addressed in this session.

14:40

Climate and the water-energy-food nexus

C. Dalin (LSE, London, United Kingdom)

Abstract details
Climate and the water-energy-food nexus

C. Dalin (1)
(1) LSE, Grantham research institute,, London, United Kingdom

Abstract content

Water, energy and food are essential for human well-being, and socio-economic development. Global projections indicate that demand for these resources will increase significantly over the next decades, under the pressure of population growth, economic development, urbanisation, diversifying diets, cultural and technological changes, and climate change (Hoff 2011). Annual and seasonal climate variability, as well as climate change, strongly affect all components of the water-energy-food nexus, adding to the challenge of using resources sustainably across sectors. While uncertainties remain high, climate models project decreases in annual precipitation in many developing countries, e.g. by as much as 20% in southern Africa by 2080. These changes would propagate into reduced water availability and crop yields, which, combined with projected population growth, reinforces the need for planners to collaborate across sectors and account for climate variability and change. Recognition of spatial and sectoral interdependencies in the nexus should inform policies, institutions, and investments for enhancing water, energy, and food security, and thus support sustainable development in climate-sensitive environments. This presentation will highlight the importance of recognising these linkages, and identify spatial and topical hotspots in current nexus research.

14:55

Revising the planetary boundary for freshwater use

D. Gerten (Potsdam Institute for Climate Impact Research, Potsdam, Germany)

Abstract details
Revising the planetary boundary for freshwater use

D. Gerten (1) ; J. Heinke, (1) ; A. Pastor (2) ; J. Jägermeyr (1)
(1) Potsdam Institute for Climate Impact Research, Potsdam, Germany; (2) Wageningen University, Wageningen, Netherlands

Abstract content

Nine intertwined ‘planetary boundaries’ demarcate the multidimensional ‘safe’ space for key earth system processes. Leaving this safe space due to the environmental imprint of collective human activities, Earth may be moved out of its Holocene status which up to now enabled the development of a human society of several billion people. While the concept and quantitative basis of planetary boundaries has recently undergone a comprehensive update (Steffen et al., Science, 2015), some boundaries still require a more robust quantification, especially in terms of upscaling regional patterns to the planetary scale and in terms of boundary interactions. Moreover, comprehensive assessments of development pathways for civil society under the constraint of planetary boundaries are still lacking.

 

This talk shows ways to improve the definition and assessment of the planetary boundary for human freshwater use, which is challenging as the regional pattern of water availabilities and limitations and the tight interactions with land cover and use are to be considered. The core approach is to account, spatially explicitly, for the environmental flow requirements of riverine ecosystems, which define local limitations to human water use and serve as a basis for a geographically explicit ‘bottom-up’ estimation of the planetary boundary. A pilot assessment – based on high-resolution simulations with a dynamic global vegetation and water balance model – indicates that the value of the planetary boundary may be lower than suggested earlier. Different estimation methods to assess environmental flows suggest a value between 1,100 and 4,500 km3 consumptive water use per year (original estimate from Rockström et al., Nature 2009: 4,000 km3 per year). Thus, humanity’s current consumptive water use (at least ~1,600 km3 per year), let alone water withdrawal (~3,600 km3/year), already exceeds the lower end of this range that reflects stringent environmental policies. Moreover, local tolerance limits of water use are already exceeded in many places, such as in parts of southern Europe, southern Asia, the Near and Middle East, and in the western US. Building on these results, the presentation elaborates on how the definition and quantification of the freshwater boundary can be further improved, for example by including “green” water, by specifying linkages with other planetary boundaries (such as the one for land-system change), and by water ethical considerations. Initial estimates of the potential of improved on-farm water management to increase crop production while staying within the planetary boundaries for freshwater use and land-system change are also presented.

15:05

Land use changes and their impacts on climate

J. Pongratz (Max-Planck Institute for Meteorology, Hamburg, Germany)

Abstract details
Land use changes and their impacts on climate

J. Pongratz (1)
(1) Max-Planck Institute for Meteorology, Hamburg, Germany

Abstract content

About three quarters of the ice-free land surface have undergone some form of land use change: about one quarter has undergone a change in land cover, in particular deforestation for agricultural expansion; on another one half the vegetation cover has been kept but is managed, as happens e.g. in forestry. This land cover change and land management affects climate through multiple pathways. The political focus mostly lies on land use change as contributor to the human-induced rise in atmospheric CO2 and thus global warming. The local-scale climate, more relevant for adaptation, can show strong effects due to biogeophysical effects such as changes in water and heat fluxes.

 

Land use change (mostly restricted to land cover change) has therefore entered into most Earth system models (ESMs) used to project climate change. With the Coupled Model Intercomparison Project 5 (CMIP5) land use change has for the first time been considered in the climate simulations underlying the IPCC assessment report. However, the spread across model results for both carbon cycle and biogeophysical aspects has been found to be substantial. This initiated a range of studies that aim at understanding the reasons why estimates differ so much. These findings can be arranged along a chain of uncertainties from uncertain land use datasets, differences in their implementation in ESMs, to various definitions of land-use-induced carbon fluxes in models. This talk will discuss these sources of model spread and ways forward to reduce the uncertainties.

 

Understanding the sources of uncertainty is particularly important now: Recent observational studies suggest that land management can have effects on climate that are of similar strength as those of land cover change, yet occur on much larger area. The ESM community is therefore moving beyond land cover change towards land management for a more complete representation of the human impact on climate.

15:15

Terrestrial carbon cycle feedbacks in the climate system

L. Mercado (University of Exeter, Exeter, United Kingdom)

Abstract details
Terrestrial carbon cycle feedbacks in the climate system

L. Mercado (1)
(1) University of Exeter, Exeter, United Kingdom

Abstract content

 

Terrestrial ecosystems take up around a quarter of the human CO2 emissions from fossil fuel burning, land use and land cover changes each year (Le Quéré et al., 2015), mitigating climate change for the present day. Can we rely on this carbon sink in the future?

 

Terrestrial ecosystems store a vast quantity of carbon in biomass and soils and their storage capacity depends on environmental conditions. Elevated CO2 is known to act as a fertilizer, stimulating plant production, and a changing climate (e.g. temperature and precipitation) will alter the lifetime of carbon in plants and soils.  For example, the seminal work by Cox et al., (2000) suggested that future climate warming will lead to a release of carbon from terrestrial ecosystems, through temperature-enhanced soil decomposition, and highlighted the vulnerability of tropical forests to climate change. This represents a positive climate carbon cycle feedback, whereby an initial warming leads to a terrestrial release of CO2, which in turn leads to further warming.

 

Subsequently much research has focused on the role of terrestrial ecosystems and their feedbacks in the Earth system. Here we review the current state-of-the-knowledge drawing from the latest synthesis in the IPCC AR5 WG1 report, and our research at the University of Exeter, Met Office Hadley Centre and Centre of Ecology and Hydrology, UK. In particular, we present the effect of aerosols, implications of plant acclimation to temperature, and the resilience of tropical forests on the future development of the land carbon sink (Mercado et al., 2009, Booth et al., 2012, Huntingford et al., 2013). I will highlight the key uncertainties in our understanding of climate- terrestrial carbon cycle feedbacks, and present recent work on emerging constraints on climate carbon cycle feedbacks (Cox et al., 2013, Wenzel et al 2014). 

15:25

Global impacts of climate change on terrestrial biodiversity and ecosystem service supply

W. Cramer (IMBE, Marseille, France)

Abstract details
Global impacts of climate change on terrestrial biodiversity and ecosystem service supply

W. Cramer (1)
(1) CNRS, Imbe, Aix-en-Provence, France

Abstract content

Impacts of recent climate change have been observed and attributed worldwide. Many of these affect land ecosystems, their function and the diversity of organisms in them. Scenarios of future warming, changes in rainfall patterns, and sea-level rise all indicate significant impacts on biodiversity in natural and managed landscapes, despite uncertainties regarding spatial patterns and confounding drivers such as land use and land management change, and urbanisation. While biodiversity loss may be considered a major impact of climate change in its own right, concerns are growing that the supply of essential services to humanity, where these depend on intact ecosystems, is also at risk. For certain key ecosystem services, such as climate regulation, food and timber production, water purification and others, the global nature of possible losses has been considered widely (also by the IPCC), but other ecosystem services are less easily quantified. I will summarise the state of knowledge for more comprehensive assessments of future global biodiversity loss and changes in ecosystem service provisioning, and thereby indicate the need for interaction between assessments of risks made by the IPCC and the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES).