12 research outputs found
The carbon cycle in Mexico: Past, present and future of C stocks and fluxes
We modeled the carbon (C) cycle in Mexico with a process-based approach. We used different available products (satellite data, field measurements, models and flux towers) to estimate C stocks and fluxes in the country at three different time frames: present (defined as the period 2000–2005), the past century (1901–2000) and the remainder of this century (2010–2100). Our estimate of the gross primary productivity (GPP) for the country was 2137±1023 TgC yr and a total C stock of 34 506±7483 TgC, with 20 347±4622 TgC in vegetation and 14 159±3861 in the soil.
Contrary to other current estimates for recent decades, our results showed that Mexico was a C sink over the period 1990–2009 (+31 TgC yr) and that C accumulation over the last century amounted to 1210±1040 TgC.We attributed this sink to the CO fertilization effect on GPP, which led to an increase of 3408±1060 TgC, while both climate and land use reduced the country C stocks by -458±1001 and -1740±878 TgC, respectively. Under different future scenarios, the C sink will likely continue over the 21st century, with decreasing C uptake as the climate forcing becomes more extreme. Our work provides valuable insights on relevant driving processes of the C cycle such as the role of drought in drylands (e.g., grasslands and shrublands) and the impact of climate change on the mean residence time of soil C in tropical ecosystems
The global methane budget 2000-2017
Understanding and quantifying the global methane (CH4) budget is important for assessing realistic pathways to mitigate climate change. Atmospheric emissions and concentrations of CH4 continue to increase, making CH4 the second most important human-influenced greenhouse gas in terms of climate forcing, after carbon dioxide (CO2). The relative importance of CH4 compared to CO2 depends on its shorter atmospheric lifetime, stronger warming potential, and variations in atmospheric growth rate over the past decade, the causes of which are still debated. Two major challenges in reducing uncertainties in the atmospheric growth rate arise from the variety of geographically overlapping CH4 sources and from the destruction of CH4 by short-lived hydroxyl radicals (OH). To address these challenges, we have established a consortium of multidisciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate new research aimed at improving and regularly updating the global methane budget. Following Saunois et al. (2016), we present here the second version of the living review paper dedicated to the decadal methane budget, integrating results of top-down studies (atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up estimates (including process-based models for estimating land surface emissions and atmospheric chemistry, inventories of anthropogenic emissions, and data-driven extrapolations). For the 2008-2017 decade, global methane emissions are estimated by atmospheric inversions (a top-down approach) to be 576 Tg CH4 yr-1 (range 550-594, corresponding to the minimum and maximum estimates of the model ensemble). Of this total, 359 Tg CH4 yr-1 or ĝ1/4 60 % is attributed to anthropogenic sources, that is emissions caused by direct human activity (i.e. anthropogenic emissions; range 336-376 Tg CH4 yr-1 or 50 %-65 %). The mean annual total emission for the new decade (2008-2017) is 29 Tg CH4 yr-1 larger than our estimate for the previous decade (2000-2009), and 24 Tg CH4 yr-1 larger than the one reported in the previous budget for 2003-2012 (Saunois et al., 2016). Since 2012, global CH4 emissions have been tracking the warmest scenarios assessed by the Intergovernmental Panel on Climate Change. Bottom-up methods suggest almost 30 % larger global emissions (737 Tg CH4 yr-1, range 594-881) than top-down inversion methods. Indeed, bottom-up estimates for natural sources such as natural wetlands, other inland water systems, and geological sources are higher than top-down estimates. The atmospheric constraints on the top-down budget suggest that at least some of these bottom-up emissions are overestimated. The latitudinal distribution of atmospheric observation-based emissions indicates a predominance of tropical emissions (ĝ1/4 65 % of the global budget, < 30ĝ N) compared to mid-latitudes (ĝ1/4 30 %, 30-60ĝ N) and high northern latitudes (ĝ1/4 4 %, 60-90ĝ N). The most important source of uncertainty in the methane budget is attributable to natural emissions, especially those from wetlands and other inland waters. Some of our global source estimates are smaller than those in previously published budgets (Saunois et al., 2016; Kirschke et al., 2013). In particular wetland emissions are about 35 Tg CH4 yr-1 lower due to improved partition wetlands and other inland waters. Emissions from geological sources and wild animals are also found to be smaller by 7 Tg CH4 yr-1 by 8 Tg CH4 yr-1, respectively. However, the overall discrepancy between bottom-up and top-down estimates has been reduced by only 5 % compared to Saunois et al. (2016), due to a higher estimate of emissions from inland waters, highlighting the need for more detailed research on emissions factors. Priorities for improving the methane budget include (i) a global, high-resolution map of water-saturated soils and inundated areas emitting methane based on a robust classification of different types of emitting habitats; (ii) further development of process-based models for inland-water emissions; (iii) intensification of methane observations at local scales (e.g., FLUXNET-CH4 measurements) and urban-scale monitoring to constrain bottom-up land surface models, and at regional scales (surface networks and satellites) to constrain atmospheric inversions; (iv) improvements of transport models and the representation of photochemical sinks in top-down inversions; and (v) development of a 3D variational inversion system using isotopic and/or co-emitted species such as ethane to improve source partitioning. The data presented here can be downloaded from https://doi.org/10.18160/GCP-CH4-2019 (Saunois et al., 2020) and from the Global Carbon Project
Multi-messenger observations of a binary neutron star merger
On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta
Assessing methane emissions from tropical wetlands: Uncertainties from natural variability and drivers at the global scale
This is the author accepted manuscript. The final version is available from the American Geophysical Union via the DOI in this recordData Availability Statement:
The data base created in this work, with the compilation of 101 publish works and 328 direct
measures of CH4 emissions from tropical wetlands is available as supplementary information and
deposited in a repository with the link: 10.5281/zenodo.8226694Methane (CH4) emissions from tropical wetlands represent half of the global wetland emissions,
but uncertainties remain concerning the extent of tropical methane sources. One limitation is to
conceive tropical wetlands as a single ecosystem, especially in global land surface models. We
estimate CH4 emissions and assess their environmental and anthropogenic drivers. We created a
dataset with 101 studies involving 328-point measurements, classified the sites into four wetland
types, and included relevant biological and environmental information. We estimate the global
CH4 emission rate from tropical wetlands as 35 (5-160) mg CH4 m-2 d-1 (median, first and third
quartile) and an annual global rate of 94 (56, 158) Tg y-1
. Fluxes differed among the wetland
types, but except for anthropogenic factors, significant environmental drivers at the global scale
could not be quantitatively identified due to high flux variability, even within wetland types.
Coastal wetlands generate median emissions of 12(5-23) Tg y-1
. Inland deep-water wetlands emit
53 (32-114) Tg y-1
, with highly variable areal extent. Emissions from inland shallow-water
wetlands are 52(33-78) Tg y-1 with variation due to seasonal changes in water table level.
Human-made wetlands emit 17 (10-4) Tg y-1
. Pollution and N inputs from agriculture are
significant anthropogenic drivers of emissions from tropical wetlands. Specific drivers of change
need to be considered according to wetland type when estimating global emissions, as well as
their specific vulnerability to global change. Additionally, these differences should be
contemplated when implementing wetland management practices aimed at decreasing methane
emissions.European Research CouncilDirección General de Asuntos del Personal Académico, Universidad Nacional Autónoma de Méxic
Soil Methanotrophy Model (MeMo v1.0): a process-based model to quantify global uptake of atmospheric methane by soil
Soil bacteria known as methanotrophs are the sole biological
sink for atmospheric methane (CH4), a potent greenhouse gas that is
responsible for ∼ 20 % of the human-driven increase in radiative
forcing since pre-industrial times. Soil methanotrophy is controlled by a
plethora of factors, including temperature, soil texture, moisture and
nitrogen content, resulting in spatially and temporally heterogeneous rates
of soil methanotrophy. As a consequence, the exact magnitude of the global
soil sink, as well as its temporal and spatial variability, remains poorly
constrained. We developed a process-based model (Methanotrophy Model; MeMo
v1.0) to simulate and quantify the uptake of atmospheric CH4 by soils at
the global scale. MeMo builds on previous models by Ridgwell et al. (1999)
and Curry (2007) by introducing several advances, including (1) a general
analytical solution of the one-dimensional diffusion–reaction equation in
porous media, (2) a refined representation of nitrogen inhibition on soil
methanotrophy, (3) updated factors governing the influence of soil moisture
and temperature on CH4 oxidation rates and (4) the ability to evaluate
the impact of autochthonous soil CH4 sources on uptake of atmospheric
CH4. We show that the improved structural and parametric representation
of key drivers of soil methanotrophy in MeMo results in a better fit to
observational data. A global simulation of soil methanotrophy for the period
1990–2009 using MeMo yielded an average annual sink of
33.5 ± 0.6 Tg CH4 yr−1. Warm and semi-arid regions
(tropical deciduous forest and open shrubland) had the highest CH4
uptake rates of 602 and 518 mg CH4 m−2 yr−1, respectively.
In these regions, favourable annual soil moisture content ( ∼ 20 %
saturation) and low seasonal temperature variations
(variations < ∼ 6 °C) provided optimal conditions for soil
methanotrophy and soil–atmosphere gas exchange. In contrast to previous model
analyses, but in agreement with recent observational data, MeMo predicted low
fluxes in wet tropical regions because of refinements in formulation of the
influence of excess soil moisture on methanotrophy. Tundra and mixed forest
had the lowest simulated CH4 uptake rates of 176 and
182 mg CH4 m−2 yr−1, respectively, due to their marked
seasonality driven by temperature. Global soil uptake of atmospheric CH4
was decreased by 4 % by the effect of nitrogen inputs to the system;
however, the direct addition of fertilizers attenuated the flux by 72 % in
regions with high agricultural intensity (i.e. China, India and Europe) and
by 4–10 % in agriculture areas receiving low rates of N input (e.g.
South America). Globally, nitrogen inputs reduced soil uptake of atmospheric
CH4 by 1.38 Tg yr−1, which is 2–5 times smaller than
reported previously. In addition to improved characterization of the
contemporary soil sink for atmospheric CH4, MeMo provides an opportunity
to quantify more accurately the relative importance of soil methanotrophy in
the global CH4 cycle in the past and its capacity to contribute to
reduction of atmospheric CH4 levels under future global change
scenarios
The global methane budget 2000-2017
Understanding and quantifying the global methane (CH4) budget is important for assessing realistic pathways to mitigate climate change. Atmospheric emissions and concentrations of CH4 continue to increase, making CH4 the second most important human-influenced greenhouse gas in terms of climate forcing, after carbon dioxide (CO2). The relative importance of CH4 compared to CO2 depends on its shorter atmospheric lifetime, stronger warming potential, and variations in atmospheric growth rate over the past decade, the causes of which are still debated. Two major challenges in reducing uncertainties in the atmospheric growth rate arise from the variety of geographically overlapping CH4 sources and from the destruction of CH4 by short-lived hydroxyl radicals (OH). To address these challenges, we have established a consortium of multidisciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate new research aimed at improving and regularly updating the global methane budget. Following Saunois et al. (2016), we present here the second version of the living review paper dedicated to the decadal methane budget, integrating results of top-down studies (atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up estimates (including process-based models for estimating land surface emissions and atmospheric chemistry, inventories of anthropogenic emissions, and data-driven extrapolations
The global methane budget 2000-2017
Understanding and quantifying the global methane (CH4) budget is important for assessing realistic pathways to mitigate climate change. Atmospheric emissions and concentrations of CH4 continue to increase, making CH4 the second most important human-influenced greenhouse gas in terms of climate forcing, after carbon dioxide (CO2). The relative importance of CH4 compared to CO2 depends on its shorter atmospheric lifetime, stronger warming potential, and variations in atmospheric growth rate over the past decade, the causes of which are still debated. Two major challenges in reducing uncertainties in the atmospheric growth rate arise from the variety of geographically overlapping CH4 sources and from the destruction of CH4 by short-lived hydroxyl radicals (OH). To address these challenges, we have established a consortium of multidisciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate new research aimed at improving and regularly updating the global methane budget. Following Saunois et al. (2016), we present here the second version of the living review paper dedicated to the decadal methane budget, integrating results of top-down studies (atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up estimates (including process-based models for estimating land surface emissions and atmospheric chemistry, inventories of anthropogenic emissions, and data-driven extrapolations). For the 2008-2017 decade, global methane emissions are estimated by atmospheric inversions (a top-down approach) to be 576 Tg CH4 yr-1 (range 550-594, corresponding to the minimum and maximum estimates of the model ensemble). Of this total, 359 Tg CH4 yr-1 or ĝ1/4 60 % is attributed to anthropogenic sources, that is emissions caused by direct human activity (i.e. anthropogenic emissions; range 336-376 Tg CH4 yr-1 or 50 %-65 %). The mean annual total emission for the new decade (2008-2017) is 29 Tg CH4 yr-1 larger than our estimate for the previous decade (2000-2009), and 24 Tg CH4 yr-1 larger than the one reported in the previous budget for 2003-2012 (Saunois et al., 2016). Since 2012, global CH4 emissions have been tracking the warmest scenarios assessed by the Intergovernmental Panel on Climate Change. Bottom-up methods suggest almost 30 % larger global emissions (737 Tg CH4 yr-1, range 594-881) than top-down inversion methods. Indeed, bottom-up estimates for natural sources such as natural wetlands, other inland water systems, and geological sources are higher than top-down estimates. The atmospheric constraints on the top-down budget suggest that at least some of these bottom-up emissions are overestimated. The latitudinal distribution of atmospheric observation-based emissions indicates a predominance of tropical emissions (ĝ1/4 65 % of the global budget, < 30ĝ  N) compared to mid-latitudes (ĝ1/4 30 %, 30-60ĝ  N) and high northern latitudes (ĝ1/4 4 %, 60-90ĝ  N). The most important source of uncertainty in the methane budget is attributable to natural emissions, especially those from wetlands and other inland waters. Some of our global source estimates are smaller than those in previously published budgets (Saunois et al., 2016; Kirschke et al., 2013). In particular wetland emissions are about 35 Tg CH4 yr-1 lower due to improved partition wetlands and other inland waters. Emissions from geological sources and wild animals are also found to be smaller by 7 Tg CH4 yr-1 by 8 Tg CH4 yr-1, respectively. However, the overall discrepancy between bottom-up and top-down estimates has been reduced by only 5 % compared to Saunois et al. (2016), due to a higher estimate of emissions from inland waters, highlighting the need for more detailed research on emissions factors. Priorities for improving the methane budget include (i) a global, high-resolution map of water-saturated soils and inundated areas emitting methane based on a robust classification of different types of emitting habitats; (ii) further development of process-based models for inland-water emissions; (iii) intensification of methane observations at local scales (e.g., FLUXNET-CH4 measurements) and urban-scale monitoring to constrain bottom-up land surface models, and at regional scales (surface networks and satellites) to constrain atmospheric inversions; (iv) improvements of transport models and the representation of photochemical sinks in top-down inversions; and (v) development of a 3D variational inversion system using isotopic and/or co-emitted species such as ethane to improve source partitioning. The data presented here can be downloaded from https://doi.org/10.18160/GCP-CH4-2019 (Saunois et al., 2020) and from the Global Carbon Project. © 2020 Copernicus GmbH. All rights reserved