Climate change and energy - Carbon sinks

Title

The carbon footprint of urban green space—A life cycle approach

Reference

Landscape and Urban Planning
Volume 104, Issue 2, February 2012, Pages 220–229

Author(s)

Michael W. Strohbach, Eric Arnold, Dagmar Haase

Study type

Peer Review Journal    

Abstract

Cities play an important role in the global carbon cycle. They produce a large proportion of CO2 emissions, but they also sequester and store carbon in urban forests and green space. However, sequestration by urban green space is difficult to quantify and also involves emissions. The carbon footprint analysis is an established method for systematically quantifying carbon sinks and sources throughout the lifetime of goods and services. We applied this method to an urban green space project in Leipzig, Germany. To the best of our knowledge it is the first application in this field. We simulated carbon sequestration by growing trees and contrasted it with all related carbon sources, from construction and maintenance over the lifetime of 50 years. In addition, we explored alternative design and maintenance scenarios. Total net sequestration was predicted to be between 137 and 162 MgCO2 ha−1. Park-like design and maintenance is less effective than forest-like design and maintenance. Much uncertainty is linked to tree growth and tree mortality. Increasing annual tree mortality from 0.5 to 4% reduces sequestration by over 70%. In conclusion, urban green space can act as a carbon sink and the design and maintenance have a strong influence on the carbon footprint. The carbon footprint analysis is a valuable tool for estimating the long-term environmental performance of urban green space projects. Compared to emissions from people, the overall potential for carbon mitigation is limited, even in cities such as Leipzig with widely available space for new urban green space.

Policy theme(s)

Biodiversity >> Habitats >> Green Infrastructure
Climate change and energy >> Climate change mitigation >> Carbon sinks
Urban environment >> Urban biodiversity

Keywords

Carbon sequestration; Urban forestry; Life cycle assessment; Urban decline;
Urban reconstruction

Entry Source:

Selected for Science for Environment Policy News Alert

View this study at:

http://www.sciencedirect.com/science/article/pii/S016920461100301X
There is a fee to view this study in full    

Contact the study author at:

strohbach@eco.umass.edu

Title

Increasing net CO₂ uptake by a Danish beech forest during the period from 1996 to 2009

Reference

Agricultural and Forest Meteorology
Volume 151, Issue 7, 15 July 2011, Pages 934-946
EU funded

Author(s)

Kim Pilegaard , Andreas Ibrom, Michael S. Courtney, Poul Hummelshøj, Niels Otto Jensen

Study type

Peer Review Journal

Abstract

The exchange of CO₂ between the atmosphere and a beech forest near Sorø, Denmark, was measured continuously over 14 years (1996-2009). The simultaneous measurement of many parameters that influence CO₂ uptake makes it possible to relate the CO₂ exchange to recent changes in e.g. temperature and atmospheric CO₂ concentration. The net CO₂ exchange (NEE) was measured by the eddy covariance method. Ecosystem respiration (RE) was estimated from nighttime values and gross ecosystem exchange (GEE) was calculated as the sum of RE and NEE. Over the years the beech forest acted as a sink of on average of 157 g C m-2 yr-1. In one of the years only, the forest acted as a small source. During 1996–2009 a significant increase in annual NEE was observed. A significant increase in GEE and a smaller and not significant increase in RE was also found. Thus the increased NEE was mainly attributed to an increase in GEE. The overall trend in NEE was significant with an average increase in uptake of 23 g C m-2 yr-2. The carbon uptake period (i.e. the period with daily net CO₂ gain) increased by 1.9 days per year, whereas there was a non significant tendency of increase of the leafed period. This means that the leaves stayed active longer. The analysis of CO₂ uptake by the forest by use of light response curves, revealed that the maximum rate of photosynthetic assimilation increased by 15% during the 14-year period. We conclude that the increase in the overall CO₂ uptake of the forest is due to a combination of increased growing season length and increased uptake capacity. We also conclude that long time series of flux measurements are necessary to reveal trends in the data because of the substantial inter-annual variation in the flux.

Policy theme(s)

Climate change and energy >> Climate change mitigation >> Carbon sinks

Keywords

Carbon dioxide exchange; Deciduous forest; Eddy covariance; Multi-years; Trends

Entry Source:

Shortlisted for Science for Environment Policy News Alert

Referred to in EC doc:

N/A

View this study at:

http://www.sciencedirect.com/science/article/pii/S0168192311000797
There is a fee to view this study in full

Contact the study author at:

kipi@risoe.dtu.dk

Title

Soil water repellency and its implications for organic matter decomposition - is there a link to extreme climatic events?

Reference

Global Change Biology
Volume 17, Issue 8, pages 2640-2656, August 2011
EU funded

Author(s)

Marc-O Goebel, Jorg Bachmann, Markus Reichstein, Ivan Janssens, Georg Guggenberger

Study type

Peer Review Journal

Abstract

Earth system models associate the ongoing global warming with increasing frequency and intensity of extreme events such as droughts and heat waves. The carbon balance of soils may be more sensitive to the impact of such extremes than to homogeneously distributed changes in soil temperature (T_s) or soil water content (θ_s). One parameter influenced by more pronounced drying/rewetting cycles or increases in Ts is the wettability of soils. Results from laboratory and field studies showed that low θ_s, particularly in combination with high Ts can increase soil water repellency (SWR). Recent studies have provided evidence that the stability of soil organic matter (SOM) against microbial decomposition is substantially enhanced in water repellent soils. This review hypothesizes that SWR is an important SOM stabilization mechanism that could become more important because of the increase in extreme events. We discuss wettability-induced changes in soil moisture distribution and in soil aggregate turnover as the main mechanisms explaining the reduced mineralization of SOM with increasing SWR. The creation of preferential flow paths and subsequent uneven penetration of rainwater may cause a long-term reduction of soil water availability, affecting both microorganisms and plants. We conclude that climate change-induced SWR may intensify the effects of climatic drought and thus affects ecosystem processes such as SOM decomposition and plant productivity, as well as changes in vegetation and microbial community structure. Future research on biosphere-climate interactions should consider the effects of increasing SWR on soil moisture and subsequently on both microbial activity and plant productivity, which ultimately determine the overall carbon balance.

Policy theme(s)

Climate change and energy >> Climate change mitigation >> Carbon sinks
Soil >> Soil carbon and nitrogen

Keywords

aggregate stability; carbon cycle; carbon sequestration; climate change; extreme climatic events; hydrophobicity; microbial respiration; soil organic matter; soil water repellency; substrate availability

Entry Source:

Selected for Science for Environment Policy News Alert

Referred to in EC doc:

N/A

View this study at:

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2011.02414.x/abstract
There is a fee to view this study in full

Contact the study author at:

goebel@ifbk.uni-hanover.de

Title

Permafrost carbon-climate feedbacks accelerate global warming

Reference

PNAS September 6, 2011 vol. 108 no. 36 14769-14774

Author(s)

Charles D. Koven , Bruno Ringeval, Pierre Friedlingstein, Philippe Ciais, Patricia Cadule, Dmitry Khvorostyanov, Gerhard Krinner, and Charles Tarnocai

Study type

Peer Review Journal

Abstract

Permafrost soils contain enormous amounts of organic carbon, which could act as a positive feedback to global climate change due to enhanced respiration rates with warming. We have used a terrestrial ecosystem model that includes permafrost carbon dynamics, inhibition of respiration in frozen soil layers, vertical mixing of soil carbon from surface to permafrost layers, and CH₄ emissions from flooded areas, and which better matches new circumpolar inventories of soil carbon stocks, to explore the potential for carbon-climate feedbacks at high latitudes. Contrary to model results for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4), when permafrost processes are included, terrestrial ecosystems north of 60°N could shift from being a sink to a source of CO₂ by the end of the 21st century when forced by a Special Report on Emissions Scenarios (SRES) A2 climate change scenario. Between 1860 and 2100, the model response to combined CO₂ fertilization and climate change changes from a sink of 68 Pg to a 27 + -7 Pg sink to 4 + -18 Pg source, depending on the processes and parameter values used. The integrated change in carbon due to climate change shifts from near zero, which is within the range of previous model estimates, to a climate-induced loss of carbon by ecosystems in the range of 25 + -3 to 85 + -16 Pg C, depending on processes included in the model, with a best estimate of a 62 + -7 Pg C loss. Methane emissions from high-latitude regions are calculated to increase from 34 Tg CH₄/y to 41-70 Tg CH₄/y, with increases due to CO₂ fertilization, permafrost thaw, and warming-induced increased CH₄ flux densities partially offset by a reduction in wetland extent.

Policy theme(s)

Climate change and energy >> Climate change mitigation >> Carbon sinks
Climate change and energy >> Greenhouse gas emissions >> Terrestrial emissions
Soil >> Soil carbon and nitrogen

Keywords

carbon cycle:  land surface models: cryosphere: soil organic: matter active layer

Entry Source:

Selected for Science for Environment Policy News Alert

Referred to in EC doc:

N/A

View this study at:

http://www.pnas.org/content/108/36/14769.abstract
There is a fee to view this study in full

Contact the study author at:

cdkoven@lbl.gov

Title

Increased forest ecosystem carbon and nitrogen storage from nitrogen rich bedrock

Reference

Nature 477, 78-81 doi:10.1038/nature10415

Author(s)

Scott L. Morford, Benjamin Z. Houlton & Randy A. Dahlgren

Study type

Peer Review Journal

Abstract

Nitrogen (N) limits the productivity of many ecosystems worldwide, thereby restricting the ability of terrestrial ecosystems to offset the effects of rising atmospheric CO₂ emissions naturally. Understanding input pathways of bioavailable N is therefore paramount for predicting carbon (C) storage on land, particularly in temperate and boreal forests. Paradigms of nutrient cycling and limitation posit that new N enters terrestrial ecosystems solely from the atmosphere. Here we show that bedrock comprises a hitherto overlooked source of ecologically available N to forests. We report that the N content of soils and forest foliage on N-rich metasedimentary rocks (350-950 mg N kg^-1) is elevated by more than 50% compared with similar temperate forest sites underlain by N-poor igneous parent material (30-70 mg N kg^-1). Natural abundance N isotopes attribute this difference to rock-derived N: 15N/14N values for rock, soils and plants are indistinguishable in sites underlain by N-rich lithology, in marked contrast to sites on N-poor substrates. Furthermore, forests associated with N-rich parent material contain on average 42% more carbon in above-ground tree biomass and 60% more carbon in the upper 30cm of the soil than similar sites underlain by N-poor rocks. Our results raise the possibility that bedrock N input may represent an important and overlooked component of ecosystem N and C cycling elsewhere.

Policy theme(s)

Soil >> Soil carbon and nitrogen
Climate change and energy >> Climate change mitigation >> Carbon sinks

Keywords

Earth science, Ecology, Geology and geophysics, Climate science

Entry Source:

Shortlisted for Science for Environment Policy News Alert

Referred to in EC doc:

N/A

View this study at:

http://www.nature.com/nature/journal/v477/n7362/full/nature10415.html  
There is a fee to view this study in full

Contact the study author at:

slmorford@ucdavis.edu