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What Do You Know — Really — About The Global Carbon Budget?

How have anthropogenic activities influenced our climate system? Is there hope for the Earth’s decarbonization?

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If you had to guess, what would you say is the global carbon cycle over the historical period from pre-Industrial time to the recent period? To be specific, how would 1750+ differ from 1958, the onset of atmospheric CO2 measurements? How would you estimate that the last decade (2012–2021), the last year (2021), and the current year (2022) differ in their global carbon cycle?

The Global Carbon Budget will help you to determine how close your approximations are. It’s produced with the support of more than 100 people from 70 organizations in 18 countries. Since 2006, as part of the Global Carbon Project, the Global Carbon Budget has provided a wealth of information on carbon emissions and the ramifications for reaching the global climate goals. The estimation of global CO2 emissions and sinks is a major effort by the carbon cycle research community that requires a careful compilation and synthesis of measurements, statistical estimates, and model results.

Since the Budget is described in a 25,000-word paper, allow us at CleanTechnica to provide you with the highlights. Afterward, if you’re craving a deeper dig into the math and methodology, go for it.

What is the Global Carbon Project? The Global Carbon Project (GCP) integrates knowledge of greenhouse gases for human activities and the Earth system. Their projects include global budgets for 3 dominant greenhouse gases — carbon dioxide, methane, and nitrous oxide — and complementary efforts in urban, regional, cumulative, and negative emissions.

Why should we care about CO2 emissions and their distribution within the Earth’s biosphere? Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change.

What is the purpose of an annual carbon budget? The delivery of an annual carbon budget serves two purposes.

  1. There is a large demand for up-to-date information on the state of the anthropogenic perturbation of the climate system and its underpinning causes. A broad stakeholder community relies on the data sets associated with the annual carbon budget including scientists, policy makers, businesses, journalists, and non-governmental organizations engaged in adapting to and mitigating human-driven climate change.
  2. Over the last decades we have seen unprecedented changes in the human and biophysical environments (e.g. changes in the growth of fossil fuel emissions, impacts of the COVID-19 pandemic, Earth’s warming, and strength of the carbon sinks), which call for frequent assessments of the state of the planet, a better quantification of the causes of changes in the contemporary global carbon cycle, and an improved capacity to anticipate its evolution in the future. Building this scientific understanding to meet the extraordinary climate mitigation challenge requires frequent, robust, transparent, and traceable data sets and methods that can be scrutinized and replicated. The budget, via “living data”, helps to keep track of new budget updates.

What are the major components of the Global Carbon Budget? Fossil CO2 emissions are based on energy statistics and cement production data, while emissions from land-use change, mainly deforestation, are based on land use and land-use change data and bookkeeping models. Atmospheric CO2 concentration is measured directly, and its growth rate is computed from the annual changes in concentration. The ocean CO2 sink is estimated with global ocean biogeochemistry models and observation-based data products. The terrestrial CO2 sink is estimated with dynamic global vegetation models. The resulting carbon budget imbalance, the difference between the estimated total emissions, and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle.

Is the GCB recognized by governmental authorities? The global CO2 budget has been assessed by the Intergovernmental Panel on Climate Change (IPCC) in all assessment reports and by others. The Global Carbon Project has coordinated this cooperative community effort for the annual publication of global carbon budgets for the several years. Multiple organizations and research groups around the world generated the original measurements and data used to complete the global carbon budget.

How Do Fossil CO2 Emissions Differ among Time Periods?

Pre-industrial carbon emissions: The concentration of carbon dioxide (CO2) in the atmosphere has increased from approximately 278 parts per million (ppm) in 1750, the beginning of the Industrial Era, to 414.7 ± 0.1 ppm in 2021. The atmospheric CO2 increase above pre-industrial levels was, initially, primarily caused by the release of carbon to the atmosphere from deforestation and other land-use change activities. Then, in 1850, 46% of fossil CO2 emissions came from coal, 35% from oil, 15% from natural gas, 3% from decomposition of carbonates, and 1% from flaring.

Fossil fuel emissions post-1958: While emissions from fossil fuels started before the Industrial Era, they became the dominant source of anthropogenic emissions to the atmosphere from around 1950, and their relative share has continued to increase until present. Anthropogenic emissions occur on top of an active natural carbon cycle that circulates carbon between the reservoirs of the atmosphere, ocean, and terrestrial biosphere on timescales from sub-daily to millennia, while exchanges with geologic reservoirs occur at longer timescales. Over the period 1960 to present the increase in the global terrestrial CO2 sink is largely attributed to the CO2 fertilization effect, directly stimulating plant photosynthesis and increased plant water use in water-limited systems, with a small negative contribution of climate change.

In the recent period 1960–2021, global fossil CO2 emissions have increased every decade. The growth rate in these emissions decreased between the 1960s and the 1990s, from 4.3% per year in the 1960s (1960–1969), 3.2% per year in the 1970s (1970–1979), 1.6% per year in the 1980s (1980–1989), and 0.9% per year in the 1990s (1990–1999).  In contrast to growing fossil emissions, CO2 emissions from land use, land-use change, and forestry have remained relatively constant over the 1960–1999 period but show a slight decrease since the 1990s.

Fossil fuel emissions 2012-2021: During 2010–2016, the ocean CO2 sink appears to have intensified in line with the expected increase from atmospheric CO2. Over the historical period, the sink increased in pace with the exponential anthropogenic emissions increase. After this period, the growth rate began increasing again in the 2000s at an average growth rate of 3.0% per year, decreasing to 0.5% per year for the last decade (2012–2021). Fossil CO2 emissions decreased in 24 countries during the decade 2012–2021.

The global carbon budget averaged over the last decade (2012–2021) indicates that 89% of the total emissions were from fossil CO2 emissions and 11% were from land-use change. The total emissions were partitioned among the atmosphere (48%), ocean (26%), and land (29%).

Fossil fuel emissions 2021: In 2021, global fossil CO2 emissions were 5.1% higher than in 2020 because of the global rebound from the worst of the COVID-19 pandemic, distributed among coal (41 %), oil (32 %), natural gas (22 %), cement (5 %), and others (1 %). Compared to the previous year, 2021 emissions from coal, oil, and gas increased by 5.7 %, 5.8 %, and 4.8 %, respectively, while emissions from cement increased by 2.1%. Effects of the pandemic on trends in fire activity or forest cover changes are hard to separate from those of general political developments and environmental changes, and the long-term consequences of disruptions in agricultural and forestry economic activities.

Fossil fuel emissions 2022: The 2022 projection estimates that global fossil CO2 emissions (including cement carbonation) will grow by 1.0% in 2022, exceeding their 2019 emission levels. Global increase in 2022 emissions per fuel types are projected to be +1% for coal, +2.2% for oil, −0.2% for natural gas, and −1.6% for cement.

Data available suggest fossil CO2 emissions continued to increase by 1.0 % in 2022 relative to 2021, bringing emissions slightly above the 2019 level. Emissions from coal, oil, and gas in 2022 are expected to be above their 2021 levels (by 1.0 %, 2.2 % and −0.2 % respectively). While emissions in 2022 are expected to have decreased by 0.9 % in China and 0.8 % in the European Union, they’ve increased by 1.5 % in the US, 6% in India, and 1.7 % in the rest of the world.

How was the 2022 projection calculated? The 2022 assessment of growth was based on the monthly calculated global atmospheric CO2 concentration through August. Additional analysis suggests that the first half of the year (the boreal winter–spring–summer transition) shows more interannual variability than the second half of the year (the boreal summer–autumn–winter transition). The ocean CO2 sink forecast for the year 2022 is based on the annual historical and estimated 2022 atmospheric CO2 concentration, the historical and estimated 2022 annual global fossil fuel emissions from this year’s carbon budget, and the spring  Oceanic Niño Index.

What’s the summary of emissions from pre-Industrial to present? During the historical period 1850–2021, 30% of historical emissions were from land-use change and 70% from fossil emissions. However, fossil emissions have grown significantly since 1960 while land-use changes have not, and, consequently, the contributions of land-use change to total anthropogenic emissions were smaller during recent periods (18% during the period 1960–2021 and 11% during 2012–2021).

Calculating the Global Carbon Budget

Where are emissions data gathered? Since 1980, monthly data are from NOAA/GML and are based on an average of direct atmospheric CO2 measurements from multiple stations in the marine boundary layer. The 1958–1979 monthly data are from the Scripps Institution of Oceanography, based on an average of direct atmospheric CO2 measurements from the Mauna Loa and South Pole stations.

How is the input of CO2 to the atmosphere quantified by emissions from human activities? It is quantified by the growth rate of atmospheric CO2 concentration and the resulting changes in the storage of carbon in the land and ocean reservoirs in response to increasing atmospheric CO2 levels, climate change and variability, and other anthropogenic and natural changes. Inherent within this quantification is an understanding of this perturbation budget over time and the underlying variability and trends of the natural carbon cycle. These factors, in turn, generate natural sinks to changes in climate, CO2, and land-use change drivers and to quantify emissions compatible with a given climate stabilization target.

How does land use and land use change figure into these equations? The net CO2 flux from land use, land-use change, and forestry includes CO2 fluxes from deforestation, afforestation, logging, and forest degradation (including harvest activity), shifting cultivation (cycle of cutting forest for agriculture, then abandoning), and regrowth of forests (following wood harvest or agriculture abandonment). Emissions from peat burning and drainage are also added.

How are sinks defined with the GCB? The CO2 sinks conceptually include the response of the land (including inland waters and estuaries) and ocean (including coastal and marginal seas) to elevated CO2 and changes in climate and other environmental conditions. Global emissions and their partitioning among the atmosphere, ocean, and land are in balance in the real world.

Why is there uncertainty around the atmospheric growth rate? The uncertainty around the atmospheric growth rate is due to 4 main factors.

  1. The long-term reproducibility of reference gas standards
  2. Small unexplained systematic analytical errors that may have a duration of several months to 2 years come and go
  3. The network composition of the marine boundary layer with some sites coming or going, gaps in the time series at each site, and so on
  4. The uncertainty associated with using the average CO2 concentration from a surface network to approximate the true atmospheric average CO2 concentration (mass-weighted, in three dimensions) as needed to assess the total atmospheric CO2 burden

Is there hope for decarbonization? Globally, fossil CO2 emissions growth is slowing, and this is due to the emergence of climate policy and technological change, which is leading to a shift from coal to gas, growth in renewable energies, and reduced expansion of coal capacity. At the aggregated global level, decarbonization shows a strong and growing signal in the last decade, with smaller contributions from lower economic growth and declines in energy per GDP. Despite the slowing growth in global fossil CO2 emissions, emissions are still growing, but these are far from the reductions needed to meet the ambitious climate goals of the UNFCCC Paris Agreement.

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Carolyn Fortuna (they, them), Ph.D., is a writer, researcher, and educator with a lifelong dedication to ecojustice. Carolyn has won awards from the Anti-Defamation League, The International Literacy Association, and The Leavy Foundation. Carolyn is a small-time investor in Tesla and an owner of a Model Y as well as a Chevy Bolt. Please follow Carolyn on Twitter and Facebook.


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