What is the Global Carbon Budget (GCB)?

Since 2006, the Global Carbon Budget has summed up all anthropogenic emissions of carbon dioxide (CO₂) to the atmosphere, and all the carbon removed from the atmosphere by land and ocean, to account for the rise in atmospheric CO₂, as this drives climate warming. It brings together many independent sources of data, including systematic observations and state-of-the-art model ensembles, to provide a robust, independent scientific assessment of CO₂ sources and sinks each year and their associated uncertainties. It tracks changes over time in CO₂ emissions from burning and other uses of fossil fuels and from land use change. It also assesses how the Earth’s carbon sinks on the land and oceans are changing in response to human activities and climate change. These data are integrated at global, regional, and national levels, providing a benchmark against which UNFCCC negotiations can take place. The Paris Agreement goal of limiting global warming well below 2°C sets the budget for the additional CO₂ that can be added to the atmosphere for this temperature target. The remaining carbon budget diminishes each year, and has direct ramifications for UNFCCC negotiators working to achieve the Paris Agreement goals. The GCB is the most comprehensive carbon budget assessment available, and contributes to assessments or reports by the IPCC and the World Meteorological Organization.

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What are the latest results of the GCB?

The GCB is updated annually; results for 2023 show:

• Global carbon emissions from fossil fuels have risen again in 2023 – reaching record levels. The GCB projects fossil carbon dioxide (CO₂) emissions of 36.8 billion tonnes in 2023, up 1.1% from 2022.
• Fossil CO₂ emissions are falling in some regions, including Europe and the USA, but rising overall. Global action to cut fossil fuels is not happening fast enough to prevent dangerous impacts of climate change.
• Emissions from land-use change (such as deforestation) are projected to decrease slightly but are still too high to be offset by reforestation and afforestation (new forests). You can explore the data here Global Carbon Budget Data
• Including land-use change emissions, the report projects total global CO₂ emissions of 40.9 billion tonnes in 2023. This is about the same as last year, and part of a 10-year “plateau” – far from the steep reduction that is urgently needed to meet the Paris Agreement commitment to limit warming well below 2°C.

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What is the remaining carbon budget?

The remaining carbon budget is the amount of carbon dioxide that can still be emitted while keeping global warming within a certain temperature limit, such as 1.5°C above pre-industrial levels. The budget for 1.5°C is rapidly diminishing as human emissions from fossil fuels and land-use change continue to far outpace the rate at which carbon is removed from the atmosphere.

 

How long until we pass 1.5°C of global warming?

While many temperature records have been broken in 2023, the GCB study focuses on the remaining carbon budget before 1.5°C is consistently breached over multiple years. At the current rate of emissions, the team estimates a one-in-two chance that global warming will consistently pass 1.5°C in seven years. All such projections have a degree of uncertainty, but it’s clear that the remaining carbon budget – and therefore, the time left to keep to the 1.5°C limit – is running out fast. Seven years are clearly insufficient to decarbonize the world’s energy system, and therefore it is now inevitable that the 1.5°C target of the Paris agreement will be breached. In addition to reaching net zero emissions, large efforts to remove atmospheric CO₂ could bring the global mean temperature back down to 1.5°C later in the century.

So far, there is little evidence of the credible policies required to cut global emissions enough to prevent the world from staying with the temperature targets of the Paris Agreement. However, trends in emissions in some regions are beginning to decline, showing climate policies can be effective. COP28 is a vital opportunity to accelerate global action.

What is new for 2023?

The GCB assessment evolves year to year as improvements are made in scientific understanding of the carbon cycle and climate system. New data and analyses for 2023 include the impact of wildfires, CO₂ uptake from Carbon Dioxide Removal (CDR), both from terrestrial vegetation methods and others not using vegetation (e.g., Direct Air Carbon Capture and Storage), additional budget component estimates from changes in atmospheric oxygen levels, and additional budget component estimates using Earth system models. The budget components have also been broken down by regions to investigate agreement with data from the RECCAP-2 project. For the greenhouse gases methane and nitrous oxide, the budgets for their emissions and sinks are analysed and published separately.

Why are wildfires included in the GCB?

Wildfires in forests, grasslands, and other ecosystems can be caused by humans or natural processes such as lightning. Wildfires are part of the carbon cycle, and are affected by and affecting Earth’s climate through several mechanisms:

• Release of CO₂ to the atmosphere from the loss of carbon stored in vegetation: since wildfire damages vegetation, it reduces the amount of carbon stored in an ecosystem, taking from a few years to a century or more (depending on where the fire occurs) to recover and reabsorb carbon from the atmosphere. If wildfire returns before the ecosystem has recovered, or if wildfires become more severe, the ecosystem may lose some of its capacity to absorb and store carbon. There is also potential for the release of methane (CH₄) if there is incomplete combustion of the organic matter.
• Black carbon (soot) emissions: as fine particulate matter, soot can be carried by the wind over long distances. If deposited on snow or ice, soot can accelerate climate warming by reducing the reflectivity of the ice surface leading to increased absorption of sunlight and accelerated ice melt. It is also a pollutant detriment to human health.
• Nutrient recycling acts to restore carbon sinks: wildfire releases nutrients into the soil from vegetation and animals more quickly than if they had slowly decayed over time. This increases soil fertility and enhances vegetation growth, helping to re-establish the carbon sink. Smoke from wildfires also contains iron and phosphorus, which, when deposited into the ocean, can boost the growth of algae, sequestering large amounts of carbon that could wholly offset the carbon released by the fire in some cases.
• Climate-carbon feedbacks: Climate change is affecting the role of wildfire in the carbon cycle. Rising temperatures, changes in trends and patterns of precipitation and lightning, and faster growth of vegetation due to higher levels of carbon dioxide in the atmosphere are some of the changes that are contributing to an increased likelihood and severity of wildfires. Climate-related changes can also impede post-fire ecosystem recovery and carbon sequestration.
• Wildfire may be reducing the remaining carbon budget overall, and therefore contributing to global warming. However it is not currently possible to fully account for the wildfire-related components in the GCB due to the difficulty of differentiating between fires caused by humans and those of natural cause.

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What is Carbon Dioxide Removal (CDR)? What contribution does CDR make to tackling Climate change? 

Anthropogenic carbon dioxide removal (CDR) aims to remove CO₂ from the atmosphere and store it in durable form, such as in forest biomass and soils through afforestation or reforestation. These vegetation-related methods account for over 99% of CDR removals. The GCB quantifies this type of CDR in its analysis, looking at CO₂ sources and sinks from land use changes. The Global Carbon Budget 2023 has also included other CDR methods, such as direct air capture and storage, or enhanced weathering methods.

New analysis shows that current non-vegetation related CDR offset 0.00003% of fossil CO₂ emissions in 2022. That’s just 0.01 MtCO2 taken out of the atmosphere. This is more than a million times smaller than current fossil CO₂ emissions. Whilst vegetation-based CDR makes a significant contribution to removing CO₂ from the atmosphere, other CDR methods are still small-scale and do not yet provide a viable climate solution. CDR may have a role in mitigating climate change but it should not be a substitute for reducing CO₂ emissions at source.

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What are natural sinks, and why are they changing? 

Natural sinks refer to forests, soils, and oceans that absorb and store CO₂ from the atmosphere. These carbon sinks have increased over time as atmospheric CO₂ levels have increased. However, these natural sinks are also changing due to rising land or ocean temperatures, altered rainfall patterns on land, or changes in large-scale ocean circulation. There is modelling evidence that climate change already reduces the land and ocean sinks by about 20% and 7%, respectively already, making their future contribution to mitigating climate change more uncertain.  Taken together, the land and ocean sinks continued to take up around half (53% over the past decade) of anthropogenic CO₂ emitted to the atmosphere, despite the negative impact of climate change.

The ocean CO₂ sink was 10.4 GtCO₂ per year during the decade 2013-2022 (26% of total CO₂ emissions), 1.5 GtCO₂ larger than during the previous decade (2003-2012), with a preliminary estimate of 10.8 GtCO₂ for 2023. The ocean CO₂ sink has not grown between 2019 and 2022 due to a triple La Niña event during these years.

The land CO₂ sink was 12.3 GtCO₂ per year during the 2013-2022 decade (31% of total CO₂ emissions), 0.9 GtCO₂ larger than during the previous decade (2003-2012), with a preliminary 2023 estimate of around 10.4 GtCO₂, significantly lower than previous years, as expected from the emerging El Niño event.

 

What is the Global stocktake?

The GST is a process for countries and stakeholders to see where they’re collectively making progress toward meeting the goals of the Paris Agreement and where they are not. The GST is like taking an inventory. It means looking at everything related to where the world stands on climate action and support, identifying gaps, and working together to chart a better course forward to accelerate climate action. The stocktake takes place every five years, with the first-ever stocktake set to conclude at COP 28.

It is intended to inform the next round of climate action plans under the Paris Agreement (Nationally determined contributions or NDCs) to be put forward by 2025. By evaluating where the world stands when it comes to meeting the goals of the Paris Agreement and using its inputs, the stocktake can help policymakers and stakeholders strengthen their climate policies and commitments in their next round of NDCs (Ref: UNFCCC website).

 

How do the GCB and the GST compare?

The GCB provides a robust and independent view of CO₂ emissions sources and carbon sinks on land and in the oceans, from national and regional-scale to the full global-scale carbon budget. It can be used as a complementary source of information to the GST, to compare to national greenhouse gas inventories and Nationally Determined Contributions (NDCs), as well as indicate the scale of mitigation action required to prevent dangerous climate warming as part of GST efforts.

The GCB takes a comprehensive and Earth system-level assessment of all carbon sources and sinks which are important for the ultimate stabilization of the climate. In this way, it differs from GST, e.g., in their consideration of non-managed lands – such as natural tropical or boreal forests. GCB includes them but they are excluded in GST reporting. These natural carbon sinks play a fundamental role in the carbon cycle, removing significant proportions of anthropogenic CO₂ emissions from the atmosphere, and therefore important to track. It is important to understand their potential contributions in a warmer climate.

The GST aims to look at the world’s collective progress towards the Paris Agreement goals – which include reducing carbon emissions, but also adaptation, implementation, and support for developing countries. The 1st GST will conclude at COP28, with data for this cycle assessed from 2021 onwards. The GCB is instead concerned with the physical impact of human-induced climate change, using data back to 1750 for historical context.

GCB @COP 28

The GCB 2023 will be presented at a number of events at COP 28:

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