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Highlights in carbon science

Selection of recent new findings and data synthesis that are contributing to the advancement in carbon sciences and the analysis of the carbon-climate-human feedback.

Articles and data

Net-zero approaches must consider Earth system impacts to achieve climate goals
Commitments to net-zero targets now cover 88% of countries' emissions. Underlying the accounting behind net-zero frameworks is the assumption that emissions can be balanced with removals such that their net climate effect is zero. However, there are reasons to expect that the two are not equivalent.
Empirical estimates of regional carbon budgets imply reduced global soil heterotrophic respiration
Resolving regional carbon budgets is critical for informing land-based mitigation policy. For nine regions covering nearly the whole globe, we collected inventory estimates of carbon-stock changes complemented by satellite estimates of biomass changes where inventory data are missing.
Opportunities and challenges in using remaining carbon budgets to guide climate policy
The remaining carbon budget represents the total amount of CO2 that can still be emitted in the future while limiting global warming to a given temperature target. Carbon budget estimates range widely however, and this uncertainty can be used to either characterize the most ambitious mitigation targets as impossible, or to argue that there is ample time to transition to a low-carbon economy.
Temporary reduction in daily global CO2 emissions during the COVID-19 forced confinement
Government policies during the COVID-19 pandemic have drastically altered patterns of energy demand around the world. Many international borders were closed and populations were confined to their homes, which reduced transport and consumption patterns. Here we compile government policies and activity data to estimate the decrease in CO2 emissions during forced confinements.
Methane removal and atmospheric restoration
Zeolites and other technologies should be evaluated and pursued for reducing methane concentrations in the atmosphere from 1,860 ppb to preindustrial levels of ~750 ppb. Such a goal of atmospheric restoration provides a positive framework for change at a time when climate action is desperately needed.
Cape Grim research station Focus on Negative Emissions Scenarios and Technologies
The latest IPCC Assessment Report (AR5) concludes that achieving climate stabilization at safe levels (i.e., below 2°C) will require sustained emission reductions, leading to near-zero or negative emissions (NE) towards the end of this century. During the past decade, however, emissions from fossil fuel combustion and cement production have continued to rise. Emissions in 2013 reached 10 Pg C year-1, a 61% increase compared to the 1990 value.
Cape Grim research station Historical greenhouse gas concentrations for climate modelling (CMIP6)
Atmospheric greenhouse gas (GHG) concentrations are at unprecedented, record-high levels compared to the last 800000 years. An accurate representation of GHG concentrations is hence important to understand and model recent climate change. Here, we provide consolidated datasets of historical atmospheric concentrations (mole fractions) of 43 GHGs to be used in the Climate Model Intercomparison Project – Phase 6 (CMIP6) experiments.
plot of projected carbon intensity of energy Key indicators to track current progress and future ambition of the Paris Agreement
Details are missing on how to track progress towards the 'Paris goal', inform the five-yearly 'global stocktake', and increase the ambition of Nationally Determined Contributions (NDCs). We develop a nested structure of key indicators to track progress through time.
thumnail of plan view photo of a suburban area taken at altitude showing houses, roads and waterways symmetrically oriented in a four pointed diagonal cross like arrangement with the waterways forming the cross arms, intersecting in the middle at a pool Urban infrastructure choices structure climate solutions
Cities are becoming increasingly important in combatting climate change, but their overall role in global solution pathways remains unclear. Here we suggest structuring urban climate solutions along the use of existing and newly built infrastructures, providing estimates of the mitigation potential.
thumnail of cemet bags stacked on a pallet Substantial global carbon uptake by cement carbonation
Considerable attention has been paid to quantifying CO2 emissions from cement production, but the natural reversal of the processócarbonationóhas received little attention in carbon cycle studies. It is estimated that a cumulative amount of 4.5 GtC has been sequestered in carbonating cement materials from 1930 to 2013, offsetting 43% of the CO2 emissions from production of cement over the same period, not including emissions associated with fossil use during cement production
thumnail of optimization framework to reduce uncertainties in decadal variability of the global carbon budget with multiple datasets Reducing uncertainties in decadal variability of the global carbon budget with multiple datasets
Conventional calculations of the global carbon budget infer the land sink as a residual between emissions, atmospheric accumulation, and the ocean sink. Here, we present a Bayesian fusion approach that combines multiple observations in different carbon reservoirs to optimize the land and ocean carbon sinks, land use change emissions, and indirectly fossil fuel emissions.
gum forest with fern understory Simulating the Earth system response to negative emissions
An important issue in developing carbon budgets to achieve climate stabilisation targets is the behaviour of natural carbon sinks, particularly under low emissions mitigation scenarios as required to meet the goals of the Paris Agreement. A key requirement for low carbon pathways is to quantify the effectiveness of negative emissions technologies which carbon cycle feedbacks will affect strongly.
part of earth showing change in leaf area Greening of the Earth and its drivers
Global environmental change is rapidly altering the dynamics of terrestrial vegetation, with consequences for the functioning of the Earth system and provision of ecosystem services. Yet how global vegetation is responding to the changing environment is not well established. Here we use three long-term satellite leaf area index (LAI) records and ten global ecosystem models to investigate four key drivers of LAI trends during 1982–2009.
Land greenhous gas source Land is a greenhouse gas source
The net biogenic greenhouse gas balance resulting from anthropogenic activities and its effect on the climate system remains uncertain. Here we use bottom-up and top-down approaches to quantify the global net biogenic greenhouse gas balance between 1981 and 2010 resulting from anthropogenic activities and its effect on the climate system.
Asia Carbon Budget Asia Carbon Budget
Asia is an important region for the global carbon budget, with 4 of the world's 10
largest national emitters of CO2. Using an ensemble of seven atmospheric inverse systems, we estimated land biosphere fluxes based on atmospheric observations of CO2 concentration.
Weaker Greening Arid regions & CO2
While sink strength is dominated by highly productive lands (mainly tropical forests), the trend and interannual variability of the sink are dominated by semi-arid ecosystems.
Weaker Greening C sink trends
The land and ocean absorb on average just over half of the anthropogenic emissions of carbon dioxide (CO2) every year. These CO2 "sinks" are modulated by climate change and variability. Here we use a suite of nine dynamic global vegetation models (DGVMs) and four ocean biogeochemical general circulation models (OBGCMs) to estimate trends driven by global and regional climate and atmospheric CO2 in land and oceanic CO2 exchanges with the atmosphere over the period 1990–2009, to attribute these trends to underlying processes in the models, and to quantify the uncertainty and level of inter-model agreement.
Weaker Greening Weaker Greening
Above 30°N, the strength of the relationship between the interannual variability of growing season NDVI and temperature declined substantially between 1982 and 2011. This decrease is mainly observed in temperate and arctic ecosystems; drought being the cause in temperate regions.
Carbon and other biogeochemical cycles Carbon and other biogeochemical cycles
Chapter 6 of Working Group I "The Physical Science Basis" of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.
Carbon and other biogeochemical cycles Carbon turnover times in terrestrial ecosystems
Whole-ecosystem carbon turnover times that combines new estimates of vegetation and soil organic carbon stocks and fluxes. Mean global carbon turnover time is 23 years.
Semi arid ecosystem Semi-arid ecosystems emerging role in global carbon cycle dynamics
tree silhouette on blue and ornge background Asymmetric effects of daytime and night-time warming on Northern Hemisphere vegetation

Enhanced Seasonal Exchange of CO2 by Northern Ecosystems Since 1960

First Signs of Carbon Sink Saturation in European Forest Biomass
Climate Extremes and the Carbon Cycle
tropical forest
Variations in Atmospheric CO2 Growth Rates Coupled with Tropical Temperature
There is strong and persistent coupling between interannual variations of the CO2  growth rate and tropical land–surface air temperature during 1959 to 2011, with a 1 °C tropical temperature anomaly leading to a 3.5 ± 0.6 Petagrams of carbon per year (PgC/y) CO2 growth-rate anomaly on average.
graph Attributing the Increase of Atmospheric CO2 to Emitters and Absorbers
Climate change policies need to consider the contribution of each emitting region to the increase in atmospheric carbon dioxide (CO2), which includes both their CO2 emissions and sinks. The study unambiguously attribute the largest share of the historical increase of CO2 between pre-industrial times to developed countries. However, the excess CO2 attributed to developing countries is greater than their share of cumulative CO2 emissions, because a greater fraction of their emissions occurred more recently.
river flowing to the ocean Anthropogenic Perturbation of the Carbon Fluxes from Land to Ocean
A substantial amount of the atmospheric carbon taken up on land through photosynthesis and chemical weathering is transported laterally along the aquatic continuum from upland terrestrial ecosystems to the ocean. We show that anthropogenic perturbation may have increased the flux of carbon to inland waters by as much as 1.0 Pg C yr-1 since pre-industrial times, mainly owing to enhanced carbon export from soils.
permafrost zone Expert Assessment of Vulnerability of Permafrost Carbon
to Climate Change

The overall amount, rate, and form of C released to the atmosphere in a warmer world will influence the strength of the permafrost C feedback to climate change. We used a survey to quantify variability in the perception of the vulnerability of permafrost C to climate change. Experts were asked to provide quantitative estimates of permafrost change in response to four scenarios of warming.
graph Carbon Sink Increases
It is predicted that the Earth has a limited capacity to take up atmospheric CO2 and that when this capacity is reached more CO2 emissions will remain in the atmosphere thus accelerating human-induced warming. Although numerous studies suggest the so-called C sinks on land and in the ocean may becoming limited, we see no evidence of this based on global measurements of atmospheric CO2 and estimates of CO2 emissions.
SOCAT plot The Surface Ocean CO2 Atlas (SOCAT)
SOCAT brings together, in a common format, all publicly available surface water data from the global oceans, including the Arctic, and the coastal seas. All data are evaluated for data quality using methods that are transparent and fully documented on SOCAT website.
forest A Large and Persistent Carbon Sink in the World's Forests
The terrestrial carbon sink is large but its size and location remain uncertain. Using forest inventory data and long-term ecosystem carbon studies, a new study estimates a total forest sink of 2.4±0.4 Pg C yr-1 globally for 1990-2007, - equivalent to one third of current annual fossil fuel emissions.

Current and Future CO2 Emissions from Drained Peatlands in Southeast Asia
Tropical peatlands are a large storage of carbon and provide significant sink capacity. Under past and current peat management, drainage is a common practice that has led to enhanced emissions from decomposition of 355- 855 Mt CO2 in 2006, as a reference year.

Methane Hydrates Gas Hydrates: Entrance to a Methane Age or Climate Threat?
Methane hydrates are a potentially vast fossil fuel energy source that could provide up to 10% to 15% of global natural gas production within the next two decades. At the same time, hydrates extraction for energy use and potential hydrate destabilization due to global warming could lead to the release of large emissions further providing an acceleration of climate change.
China Carbon Balance Soil Organic Carbon Pools in the Northern Circumpolar Permafrost Region
The vast amount of carbon stored in the Arctic and boreal regions of the world is more than double that previously estimated, according to a study published this week. The new estimate is over 1.5 trillion tons of frozen carbon, about twice as much carbon as contained in the atmosphere.
China Carbon Balance The Carbon Balance of Terrestrial Ecosystems in China
During the 1980s and 1990s, China showed a net carbon sink of 0.19–0.26 Pg carbon (PgC), which is smaller than that in the conterminous United States but comparable to that in geographic Europe. Northeast China is a net source of CO2 to the atmosphere owing to overharvesting and degradation of forests. By contrast, southern China accounts for more than 65 per cent of the carbon sink, which can be attributed to regional climate change, large-scale plantation programmes and shrub recovery.
Contact authors: ShiLong Piao, Philippe Ciais
Press Release (pdf, 38Kb); Presentation (ppt, 5Mb); Download paper
IBUXI GOSAT Satellite "Ibuki" - Greenhouse Gases Observing Satellite (GOSAT)
The Japan Aerospace Exploration Agency(JAXA) confirmed on 24-1-09 that the Greenhouse Gases Observing Satellite "IBUKI" (GOSAT) is now ready for the initial functional verification operation after shifting its attitude control system to the regular mode. The IBUKI was launched at 12:54 p.m. on January 23, 2009 (JST.)
see also http://www.jaxa.jp/projects/sat/gosat/index_e.html
Carboscope inversion map CARBOSCOPE - Global Sources/Sinks
CarboScope is an exploring tool for CO2 and CH4 developed within the framework of the ICOS project. It provides general information on these two greenhouse gases and the scientific methods used to estimate CO2 and CH4 surface fluxes (atmospheric inversion). Carboscope provides a user friendly interface to compare CO2 and CH4 fluxes from different european contributors.
Frozen Sediments in Eastern Siberia

Vulnerability of Permafrost to Climate Change
Thawing permafrost and the resulting microbial decomposition of previously frozen organic carbon is one of the most significant potential feedbacks from terrestrial ecosystems to the atmosphere in a changing climate. Accounting for carbon stored deep in the permafrost more than doubles previous high-latitude inventory estimates.

Plantations Australia

Managing Forests for Climate Change Mitigation
Forests currently absorb billions of tons of CO2 globally every year, an economic subsidy worth nearly half a trillion dollars if an equivalent sink had to be created in other ways. Concerns about the permanency of forest carbon stocks, difficulties in quantifying stock changes, and the threat of environmental and socioeconomic impacts of large-scale reforestation programs have limited the uptake of forestry activities in climate policies.

Autumn Warming

Carbon Sink Capacity in Northern Forests Reduced
The duration of the net carbon uptake period (CUP) in northern ecosystems has on average decreased due to warmer autumn temperatures. Simulations and observations indicate that northern terrestrial ecosystems may currently lose carbon dioxide in response to autumn warming, with a sensitivity of about
0.2 PgC °C-1, offsetting 90% of the increased carbon dioxide uptake during spring.

Coal Dredge CSIRO Accelerating Atmospheric CO2 Growth
This study finds that the recent swift increase in atmospheric CO2 is due to faster economic growth coupled with a halt in carbon intensity reductions, in addition to natural sinks removing a smaller proportion of emissions from the air. Efficiency of natural sinks to remove emissions from human activities has been declining for 50 years.
Industrial Sunset

Drivers of Accelerating CO2 Emissions
A new analysis shows that carbon intensity in the world economy is increasing. While emissions of carbon dioxide (CO2) are accelerating worldwide, we are gaining fewer economic benefits from each tonne of fossil fuel burned.

Ocean Wave, British Antarctic Survey

Saturation of the Southern Ocean CO2 Sink
A four-year study by scientists from the University of East Anglia (UEA), British Antarctic Survey (BAS) and the Max-Planck Institute for Biogeochemistry reveals that an increase in winds over the Southern Ocean, caused by greenhouse gases and ozone depletion, has led to a release of stored CO2 into the atmosphere and is preventing further absorption of the greenhouse gas.

Forest Burn Scar Tropical Forests and Climate Policy
A tropical forests and climate policy study in the journal Science highlights the importance of slowing deforestation in tropical countries in the global effort to avert dangerous climate change.