Climate Change: What Are Net-Zero Emissions? (CRS Report for Congress)
| Release Date |
Sept. 4, 2024 |
| Report Number |
IF12753 |
| Report Type |
In Focus |
| Authors |
Jonathan D. Haskett |
| Source Agency |
Congressional Research Service |
Summary:
“Net-zero emissions” refers to a situation in which humancaused greenhouse gas (GHG) emissions from sources such
as fossil fuel combustion and deforestation are fully
balanced by carbon dioxide removal (CDR) from the
atmosphere. Methods of removal include natural absorption
and storage in forests and other ecosystems as well as
technological removal and storage.
When emissions of carbon dioxide (CO2) are balanced by
and equal to the removal of CO2, the net addition of CO2 to
the atmosphere is equal to zero. This balance is referred to
as net-zero CO2. CO2 is not the only GHG. Human-caused
emissions of other GHGs—including methane (CH4),
nitrous oxide (N2O), and hydrofluorocarbons (HFCs)—also
increase global temperatures. The influence of GHGs on
global temperatures is the combined effect of CO2 and the
other non-CO2 GHGs. The combined influence of all GHGs
may be determined by normalizing the global warming
potentials of the GHGs to the global warming potential of
carbon dioxide (CO2). This results in a metric of carbon
dioxide equivalent (CO2e) to compare across GHGs.
Net-zero GHG means that the combined net emissions of all
GHGs must be zero, accounting for the different warming
effects of the various GHGs. For example, methane is a 27-
30 times stronger GHG than CO2, over a 100-year time
horizon.
No commercially available method for removing non-CO2
GHGs from the atmosphere exists. This means that to
balance emissions of non-CO2 GHGs that cannot be abated,
additional removals of CO2, by the use of CDR, would be
needed. These removals are sometimes known as negative
emissions. Net-zero GHG is achieved when CO2e emissions
of all GHGs are equal to CO2e removals from the
atmosphere through removals of CO2.
