A.M.R. Petrescu

Verifying Greenhouse Gas Emissions: Methods to Support International Climate Agreements

As a reference work on compilation, monitoring and verification of emission inventories on global scale, this book provides emission inventory scientists with a comprehensive literature overview. Moreover anybody can download it free of charge fromwww.nap.edu/catalog.php?record_id=12883. A prerequisite for an international assessment of greenhouse gas (GHG) emission inventories is a list of clear definitions, for which this report chose the UNFCCC standard terms and summarized them in a clarifying box in the introductory chapter. Not only methods but also uncertainties are addressed with an exhaustive list of references. This book can significantly contribute to re-assess the scientific robustness behind the UNFCCC rules for emission inventorying, as they are applied by the roster experts reviewing the national reports. To each of the relevant GHG emission inventory topics a separate chapter is dedicated: (i) national inventory reports, (ii) land-use sources/sinks fluxes and (iii) atmospheric and oceanic measurements and inverse modelling. All three chapters describe the technical/scientific details for GHG emissions inventory assessments concisely and provide references for the reader to allow further investigation. Chapter 2 on national inventory reports familiarizes the reader with the framework and current practices for developing the National Inventories/Communications of GHG emissions. International sector-specific reporting is synthesized such that it presents an overview on the contribution of each sector and on the lead of data gathering institutions and research centres. Often the national systems behind GHG inventories are not fully appreciated because the efforts improving accuracy and decreasing uncertainty are overshadowed by problems of consistency and the 1990 global base year. An overlooked issue is the generally low comparability of national estimates caused by the unharmonized use of different methods and proxy definitions. The report tends to underestimate the potential for reporting with default data for non Annex I countries in the short term. Instead, near-term measures that should be taken as capacity building in developing countries including associated costs, further extension of independent verification of ‘self-reported’ emissions data, as well as assessment and means to reduce the uncertainties are highlighted. Recommendations are given mainly on extending the inventory reporting and reviewing to all UNFCCC parties, on improving methods and on facilitating cross-comparisons of ‘self-reported’ data with data derived from other monitoring sources. Support to IPCC, UN, IEA and FAO to improve their statistics is thereby underlined. Chapter 3 addresses agriculture, land use and forestry activities, focusing mainly on the situation in the USA, and does not assess the experience achieved by other Annex I parties or international organizations to address also global land cover changes. The method proposed of combined statistical sampling and remote sensing seems indeed the most appropriate for LULUCF GHG inventories on land remaining in the same category, but more might be needed for detecting conversions. Relatively large uncertainties (above 10% to be realistic) and difficulties in reporting small pools are to be anticipated. Harmonization opportunities (of definitions, and computational methods) could have been pointed out as a great potential to achieve a complete and consistent global dataset. The list of international efforts could include not only the NASA-sponsored FluxNet network, but also the EU FP6 and FP7 research projects such as NitroEurope and CarboEurope on the nitrogen and carbon cycles. Chapter 4 provides an overview of the potential and limitations of using atmospheric measurements and inverse modelling for verification of ‘self-reported’ (‘bottom-up’) emission inventories. This chapter focuses mainly on CO2, which is clearly the most important anthropogenic GHG but at the same time probably the most difficult one for verification by

Modeling regional to global CH4 emissions of boreal and arctic wetlands

Methane (CH4) emission from boreal, arctic and subarctic wetlands constitutes a potentially positive feedback to global climate warming. Many process-based models have been developed, but high uncertainties remain in estimating the amount of CH4 released from wetlands at the global scale. This study tries to improve estimates of CH4 emissions by up-scaling a wetland CH4 emission model, PEATLAND-VU, to the global scale with a spatial resolution of 0.5 degrees for the period 2001-2006. This up-scaling was based on the global circum-arctic distribution of wetlands with hydrological conditions being specified by a global hydrological model, PCR-GLOBWB. In addition to the daily hydrological output from PCR-GLOBWB, comprising water table depths and snow thickness, the parameterization included air temperature as obtained from the ECMWF Operational Archive. To establish the uncertainty in the representations of the circum-arctic distribution of wetlands on the CH4 emission, several existing products were used to aggregate the emissions. Using the description of potential peatlands from the FAO Digital Soil Map of the World and the representation of floodplains by PCR-GLOBWB, the average annual flux over the period 2001-2006 was estimated to be 78 Tg yr(-1). In comparison, the six-year average CH4 fluxes were 37.7, 89.4, 145.6, and 157.3 Tg yr(-1) for different estimates of wetland extends based on the studies by Matthews and Fung, Prigent et al., Lehner and Doll, and Kaplan, respectively. This study shows the feasibility to estimate interannual variations in CH4 emissions by coupling hydrological and CH4 emission process models. It highlights the importance of an adequate understanding of hydrology in quantifying the total emissions from northern hemispheric wetlands and shows how knowledge of the sub-grid variability in wetland extent helps to prescribe relevant hydrological conditions to the emission model as well as to identify the uncertainty associated with existing wetland distributions. (Less)

The uncertain climate footprint of wetlands under human pressure

Significance Wetlands are unique ecosystems because they are in general sinks for carbon dioxide and sources of methane. Their climate footprint therefore depends on the relative sign and magnitude of the land–atmosphere exchange of these two major greenhouse gases. This work presents a synthesis of simultaneous measurements of carbon dioxide and methane fluxes to assess the radiative forcing of natural wetlands converted to agricultural or forested land. The net climate impact of wetlands is strongly dependent on whether they are natural or managed. Here we show that the conversion of natural wetlands produces a significant increase of the atmospheric radiative forcing. The findings suggest that management plans for these complex ecosystems should carefully account for the potential biogeochemical effects on climate. Significant climate risks are associated with a positive carbon–temperature feedback in northern latitude carbon-rich ecosystems, making an accurate analysis of human impacts on the net greenhouse gas balance of wetlands a priority. Here, we provide a coherent assessment of the climate footprint of a network of wetland sites based on simultaneous and quasi-continuous ecosystem observations of CO2 and CH4 fluxes. Experimental areas are located both in natural and in managed wetlands and cover a wide range of climatic regions, ecosystem types, and management practices. Based on direct observations we predict that sustained CH4 emissions in natural ecosystems are in the long term (i.e., several centuries) typically offset by CO2 uptake, although with large spatiotemporal variability. Using a space-for-time analogy across ecological and climatic gradients, we represent the chronosequence from natural to managed conditions to quantify the “cost” of CH4 emissions for the benefit of net carbon sequestration. With a sustained pulse–response radiative forcing model, we found a significant increase in atmospheric forcing due to land management, in particular for wetland converted to cropland. Our results quantify the role of human activities on the climate footprint of northern wetlands and call for development of active mitigation strategies for managed wetlands and new guidelines of the Intergovernmental Panel on Climate Change (IPCC) accounting for both sustained CH4 emissions and cumulative CO2 exchange.

Sensitivity analysis of a wetland methane emission model based on temperate and arctic wetland sites

Modelling of wetland CH4 fluxes using wetland soil emission models is used to determine the size of this natural source of CH4 emission on local to global scale. Most process models of CH 4 formation and soil-atmosphere CH 4 transport processes operate on a plot scale. For large scale emission modelling (regional to global scale) upscaling of this type of model requires thorough analysis of the sensitivity of these models to parameter uncertainty. We applied the GLUE (Generalized Likelihood Uncertainty Analysis) methodology to a well-known CH 4 emission model, the Walter-Heimann model, as implemented in the PEATLANDVU model. The model is tested using data from two temperate wetland sites and one arctic site. The tests include experiments with different objective functions, which quantify the fit of the model results to the data. The results indicate that the model 1) in most cases is capable of estimating CH4 fluxes better than an estimate based on the data avarage, but does not clearly outcompete a regression model based on local data; 2) is capable of reproducing larger scale (seasonal) temporal variability in the data, but not the small-scale (daily) temporal variability; 3) is not strongly sensitive to soil parameters, 4) is sensitive to parameters determining CH 4 transport and oxidation in vegetation, and the temperature sensitivity of the microbial population. The GLUE method also allowed testing of several smaller modifications of the original model. We conclude that upscaling of this plot-based wetland CH4 emission model is feasible, but considerable improveCorrespondence to: J. van Huissteden (ko.van.huissteden@geo.falw.vu.nl) ments of wetland CH4 modelling will result from improvement of wetland vegetation data.

Assessing CH4 and CO2 emissions from wetlands in the Drenthe province, The Netherlands: a modelling approach

Assessment of land use related greenhouse gas (GHG) emissions on larger spatial scales is usually achieved by modelling. Surface flux measurements are expensive and measurement locations too widely scattered to serve as spatially reliable flux estimates. Here we assess CO2 and CH4 fluxes from wetland nature reserves in the Dutch province of Drenthe, using the PEATLAND-VU model. Since surface flux observations in the province are absent and cannot be obtained in a short (