A. Anthony Bloom

Large-Scale Controls of Methanogenesis Inferred from Methane and Gravity Spaceborne Data

Measuring Methanogenesis After carbon dioxide, methane is the second most important greenhouse gas, and an important species in terms of its role in atmospheric chemistry. The sources and sinks of methane, particularly the natural ones, are too poorly quantified, however, even to explain why the decades-long, steady increase of its concentration in the atmosphere was interrupted between 1999 and 2006. Bloom et al. (p. 322) use a combination of satellite data, which indicate water table depth and surface temperature, and atmospheric methane concentrations to determine the location and strength of methane emissions from wetlands, the largest natural global source. The constraints placed on these sources should help to improve predictions of how climate change will affect wet-land emissions of methane. Satellite measurements allow the strength of wetland emissions of methane to be determined. Wetlands are the largest individual source of methane (CH4), but the magnitude and distribution of this source are poorly understood on continental scales. We isolated the wetland and rice paddy contributions to spaceborne CH4 measurements over 2003–2005 using satellite observations of gravity anomalies, a proxy for water-table depth Γ, and surface temperature analyses TS. We find that tropical and higher-latitude CH4 variations are largely described by Γ and TS variations, respectively. Our work suggests that tropical wetlands contribute 52 to 58% of global emissions, with the remainder coming from the extra-tropics, 2% of which is from Arctic latitudes. We estimate a 7% rise in wetland CH4 emissions over 2003–2007, due to warming of mid-latitude and Arctic wetland regions, which we find is consistent with recent changes in atmospheric CH4.

Global methane emission estimates from ultraviolet irradiation of terrestrial plant foliage

SUMMARY *Several studies have reported in situ methane (CH(4)) emissions from vegetation foliage, but there remains considerable debate about its significance as a global source. Here, we report a study that evaluates the role of ultraviolet (UV) radiation-driven CH(4) emissions from foliar pectin as a global CH(4) source. *We combine a relationship for spectrally weighted CH(4) production from pectin with a global UV irradiation climatology model, satellite-derived leaf area index (LAI) and air temperature data to estimate the potential global CH(4) emissions from vegetation foliage. *Our results suggest that global foliar CH(4) emissions from UV-irradiated pectin could account for 0.2-1.0 Tg yr(-1), of which 60% is from tropical latitudes, corresponding to < 0.2% of total CH(4) sources. *Our estimate is one to two orders of magnitude lower than previous estimates of global foliar CH(4) emissions. Recent studies have reported that pectin is not the only molecular source of UV-driven CH(4) emissions and that other environmental stresses may also generate CH(4). Consequently, further evaluation of such mechanisms of CH(4) generation is needed to confirm the contribution of foliage to the global CH(4) budget.

The decadal state of the terrestrial carbon cycle: Global retrievals of terrestrial carbon allocation, pools, and residence times

Significance Quantitative knowledge of terrestrial carbon pathways and processes is fundamental for understanding the biosphere’s response to a changing climate. Carbon allocation, stocks, and residence times together define the dynamic state of the terrestrial carbon cycle. These quantities are difficult to measure and remain poorly quantified on a global scale. Here, we retrieve global 1° × 1° carbon state and process variables by combining a carbon balance model with satellite observations of biomass and leaf area (where and when available) and global soil carbon data. Our results reveal emergent continental-scale patterns and relationships between carbon states and processes. We find that conventional land cover types cannot capture continental-scale variations of retrieved carbon variables; this mismatch has strong implications for terrestrial carbon cycle predictions. The terrestrial carbon cycle is currently the least constrained component of the global carbon budget. Large uncertainties stem from a poor understanding of plant carbon allocation, stocks, residence times, and carbon use efficiency. Imposing observational constraints on the terrestrial carbon cycle and its processes is, therefore, necessary to better understand its current state and predict its future state. We combine a diagnostic ecosystem carbon model with satellite observations of leaf area and biomass (where and when available) and soil carbon data to retrieve the first global estimates, to our knowledge, of carbon cycle state and process variables at a 1° × 1° resolution; retrieved variables are independent from the plant functional type and steady-state paradigms. Our results reveal global emergent relationships in the spatial distribution of key carbon cycle states and processes. Live biomass and dead organic carbon residence times exhibit contrasting spatial features (r = 0.3). Allocation to structural carbon is highest in the wet tropics (85–88%) in contrast to higher latitudes (73–82%), where allocation shifts toward photosynthetic carbon. Carbon use efficiency is lowest (0.42–0.44) in the wet tropics. We find an emergent global correlation between retrievals of leaf mass per leaf area and leaf lifespan (r = 0.64–0.80) that matches independent trait studies. We show that conventional land cover types cannot adequately describe the spatial variability of key carbon states and processes (multiple correlation median = 0.41). This mismatch has strong implications for the prediction of terrestrial carbon dynamics, which are currently based on globally applied parameters linked to land cover or plant functional types.

Are inventory based and remotely sensed above-ground biomass estimates consistent?

Carbon emissions resulting from deforestation and forest degradation are poorly known at local, national and global scales. In part, this lack of knowledge results from uncertain above-ground biomass estimates. It is generally assumed that using more sophisticated methods of estimating above-ground biomass, which make use of remote sensing, will improve accuracy. We examine this assumption by calculating, and then comparing, above-ground biomass area density (AGBD) estimates from studies with differing levels of methodological sophistication. We consider estimates based on information from nine different studies at the scale of Africa, Mozambique and a 1160 km2 study area within Mozambique. The true AGBD is not known for these scales and so accuracy cannot be determined. Instead we consider the overall precision of estimates by grouping different studies. Since an the accuracy of an estimate cannot exceed its precision, this approach provides an upper limit on the overall accuracy of the group. This reveals poor precision at all scales, even between studies that are based on conceptually similar approaches. Mean AGBD estimates for Africa vary from 19.9 to 44.3 Mg ha−1, for Mozambique from 12.7 to 68.3 Mg ha−1, and for the 1160 km2 study area estimates range from 35.6 to 102.4 Mg ha−1. The original uncertainty estimates for each study, when available, are generally small in comparison with the differences between mean biomass estimates of different studies. We find that increasing methodological sophistication does not appear to result in improved precision of AGBD estimates, and moreover, inadequate estimates of uncertainty obscure any improvements in accuracy. Therefore, despite the clear advantages of remote sensing, there is a need to improve remotely sensed AGBD estimates if they are to provide accurate information on above-ground biomass. In particular, more robust and comprehensive uncertainty estimates are needed.

Seasonal variability of tropical wetland CH 4 emissions: the role of the methanogen-available carbon pool

Abstract. We develop a dynamic methanogen-available carbon model (DMCM) to quantify the role of the methanogen-available carbon pool in determining the spatial and temporal variability of tropical wetland CH4 emissions over seasonal timescales. We fit DMCM parameters to satellite observations of CH4 columns from SCIAMACHY CH4 and equivalent water height (EWH) from GRACE. Over the Amazon River basin we found substantial seasonal variability of this carbon pool (coefficient of variation = 28 ± 22%) and a rapid decay constant (φ = 0.017 day−1), in agreement with available laboratory measurements, suggesting that plant litter is likely the prominent methanogen carbon source over this region. Using the DMCM we derived global CH4 emissions for 2003–2009, and determined the resulting seasonal variability of atmospheric CH4 on a global scale using the GEOS-Chem atmospheric chemistry and transport model. First, we estimated that tropical emissions amounted to 111.1 Tg CH4 yr−1, of which 24% was emitted from Amazon wetlands. We estimated that annual tropical wetland emissions increased by 3.4 Tg CH4 yr−1 between 2003 and 2009. Second, we found that the model was able to reproduce the observed seasonal lag of CH4 concentrations peaking 1–3 months before peak EWH values. We also found that our estimates of CH4 emissions substantially improved the comparison between the model and observed CH4 surface concentrations (r = 0.9). We anticipate that these new insights from the DMCM represent a fundamental step in parameterising tropical wetland CH4 emissions and quantifying the seasonal variability and future trends of tropical CH4 emissions.

PHYSICAL EXCHANGES AT THE AIR-SEA INTERFACE UK-SOLAS Field Measurements

As part of the U.K. contribution to the international Surface Ocean–Lower Atmosphere Study, a series of three related projects—DOGEE, SEASAW, and HiWASE—undertook experimental studies of the processes controlling the physical exchange of gases and sea spray aerosol at the sea surface. The studies share a common goal: to reduce the high degree of uncertainty in current parameterization schemes. The wide variety of measurements made during the studies, which incorporated tracer and surfactant release experiments, included direct eddy correlation fluxes, detailed wave spectra, wind history, photographic retrievals of whitecap fraction, aerosol-size spectra and composition, surfactant concentration, and bubble populations in the ocean mixed layer. Measurements were made during three cruises in the northeast Atlantic on the RRS Discovery during 2006 and 2007; a fourth campaign has been making continuous measurements on the Norwegian weather ship Polarfront since September 2006. This paper provides an overview of the three projects and some of the highlights of the measurement campaigns.

Competing uses for China's straw: the economic and carbon abatement potential of biochar

China is under pressure to improve its agricultural productivity to keep up with the demands of a growing population with increasingly resource‐intensive diets. This productivity improvement must occur against a backdrop of carbon intensity reduction targets, and a highly fragmented, nutrient‐inefficient farming system. Moreover, the Chinese government increasingly recognizes the need to rationalize the management of the 800 million tonnes of agricultural crop straw that China produces each year, up to 40% of which is burned in‐field as a waste. Biochar produced from these residues and applied to land could contribute to Chinas agricultural productivity, resource use efficiency and carbon reduction goals. However competing uses for Chinas straw residues are rapidly emerging, particularly from bioenergy generation. Therefore it is important to understand the relative economic viability and carbon abatement potential of directing agricultural residues to biochar rather than bioenergy. Using cost‐benefit analysis (CBA) and life‐cycle analysis (LCA), this paper therefore compares the economic viability and carbon abatement potential of biochar production via pyrolysis, with that of bioenergy production via briquetting and gasification. Straw reincorporation and in‐field straw burning are used as baseline scenarios. We find that briquetting straw for heat energy is the most cost‐effective carbon abatement technology, requiring a subsidy of

Contrasting carbon cycle responses of the tropical continents to the 2015–2016 El Niño

7 MgCO2e−1 abated. However Chinas current bioelectricity subsidy scheme makes gasification (NPV

Remote‐sensing constraints on South America fire traits by Bayesian fusion of atmospheric and surface data

12.6 million) more financially attractive for investors than both briquetting (NPV

Contribution of regional sources to atmospheric methane over the Amazon Basin in 2010 and 2011

7.34 million), and pyrolysis (