New Zealand ratified the Paris Agreement in 2016, and committed to a target of reducing greenhouse gas emissions to 30 per cent below 2005 levels by 2030. The Government is now working to enact a Zero Carbon Bill, which will define a climate target for 2050 and establish a process for setting emission budgets that put the economy on a trajectory to meet that target.
The Government intends its 2050 target to be consistent with the goals of the Paris Agreement. These goals were broadly framed. Countries committed to a long-term global goal of ‘holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C …’. Countries also agreed to aim globally to ‘achieve a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century’.
The three main greenhouse gases are carbon dioxide, methane and nitrous oxide. While most countries are focused on reducing emissions of carbon dioxide, New Zealand is forced to think harder about the contribution of methane and nitrous oxide from agriculture, which together make up a particularly high proportion of our total emissions.
This reflects the large role that agriculture plays in our economy today, and is the legacy of more than a century of pastoral farming. Agriculture’s contribution to biological emissions started with the mass release of carbon dioxide from large scale deforestation, as forests were cleared to make way for farming. In the decades that followed, large amounts of methane began to be emitted by a growing livestock industry. In more recent years New Zealand’s pastoral agriculture has intensified, relying on more nitrogen-rich feed and fertiliser, which has allowed more animals to be reared and also led to increasing amounts of nitrous oxide being emitted.
There is no easy blueprint to follow for reducing biological emissions from agriculture. For that reason, I decided to provide parliamentarians and their officials with a full report on how biological sources and sinks (e.g. afforestation) might be treated in the context of target setting and policy implementation. The full report is scheduled to be finalised later this year and, in common with all my reports, will rely on a mixture of in-house and commissioned research and analysis.
As part of that research I commissioned some modelling to provide a better understanding of how much warming a given level of methane emissions from livestock causes, and over what timeframe. The results of that modelling are relevant to further defining one of the target options in the Government’s Zero Carbon Bill discussion document – namely, ‘net zero long-lived gases and stabilised short-lived gases’ by 2050.
The Government has provided no indication of the level at which methane emissions might be stabilised under this option, or the amount of warming that might follow from stabilisation. Indeed, the rationale behind such a ‘split gas’ target was missing.
I have decided to release the results of the modelling prior to the release of my full report, to inform the current debate over how methane should be treated in the context of the proposed Zero Carbon Bill. I hope that providing this modelling will result in a debate that is better grounded in the underlying science. The modelling report is annexed to this note.
I must stress, however, that these results alone cannot answer policy questions about the treatment of methane in target setting or policy implementation. For that reason, I am providing this note to explain the key findings from the modelling, and the limitations of such modelling for policy decisions.