29 June 2021
With rising atmospheric carbon dioxide (CO2) concentrations driving human-induced climate change in Australia and around the world, it is critically important to track the sources and sinks of CO2. The tracking of atmospheric CO2 sources and sinks and the net balance between all sources and sinks is called the ‘carbon budget’.
Why do we need carbon budgets?
Stabilising the climate at +1.5° C above pre-industrial levels and ‘well below’ +2° C to meet the targets of the Paris Agreement requires CO2 emissions to reach ‘net zero’. Net zero can only be reached when the amount of CO2 that is added to the atmosphere is no more than the amount that is taken away.
Crunching the numbers on the amount of greenhouse gases that are emitted and removed by all countries year-on-year is an incredibly complex task, but one that has been undertaken annually since 2016 by the Global Carbon Project (GCP), supported in part through the NESP Earth Systems and Climate Change Hub.
Perturbation of the carbon cycle caused by anthropogenic activities. Anthropogenic fluxes of CO2 measured in GtCO2 per year, averaged globally for the decade 2010-2019. The ‘budget imbalance’ is the difference between the estimated emissions and sinks, which forms the basis of further research. Source: CDIAC; NOAA-ESRL; Friedlingstein et al. 2020; Ciasis et al. 2013; Global Carbon Budget 2020.
What can carbon budgets tell us?
The GCP provides an annual assessment of global human-caused CO2 sources and sinks. In addition to CO2, other greenhouse gas budgets are tracked, including methane and nitrous oxide. These budgets provide a transparent and traceable method of assessing global greenhouse gas emissions. Estimation of the sources and sinks, and methodologies, are made publicly available in science journals every year.
Other than enabling us to estimate the ‘remaining carbon budget’, carbon budgets also help us better understand land and ocean carbon sinks, which draw down atmospheric CO2. They are called ‘sinks’ because they store CO2 and thereby slow the accumulation of human-cased CO2 emissions, playing an important service in mitigating climate change.
Since CO2 has continued to accumulate in the atmosphere over decades (even despite some slowdown as a result of COVID-19), it’s critically important to quantify the extent to which the sinks are uptaking CO2. An active area of research in the science community is understanding the ability of the sinks to continue to sequester CO2 under a warming and variable climate.
Global fossil fuel emissions in billion tonnes of CO2 (GtCO2). The Global Carbon Budget tracks global fossil fuel emissions every year. Source: Global Carbon Project.
Who uses carbon budgets?
Providing a holistic view of the land– and ocean–atmosphere exchange alongside human-induced carbon emissions and sinks puts human-related emissions into perspective for the UN Framework Convention on Climate Change, and government and non-government policy actors.
For example, the Intergovernmental Panel on Climate Change (IPCC) now relies on the annual Global Carbon Budget reports to provide the carbon budgets for its assessment reports.
Hub researcher Pep Canadell (Project 5.6) is a Coordinating Lead Author on Chapter 5: Global carbon and other biogeochemical cycles and feedbacks in the upcoming IPCC report through Working Group I.
Have we accounted for everything? Read more on carbon budgets at our new (June 2021) brochure Global and regional carbon budgets.
Image credit: Josh Withers/Unsplash