The document has been described by world leaders as a "code red" for humanity and states that unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting warming to close to 1.5°C or even 2°C will be beyond reach.
The report shows that emissions of greenhouse gases from human activities are responsible for approximately 1.1°C of warming since 1850-1900, and finds that averaged over the next 20 years, global temperature is expected to reach or exceed 1.5°C of warming.The methane debate
The assessment is authored by 234 scientists from 66 countries and includes insights from 514 additional contributors. The extensive 3,164-page report highlights the challenges warmer conditions will bring for global agriculture, including altered seasonality which has the potential to impact the range and metabolism of some pollinators, pests, diseases and weeds.However, it also considers the debate over how methane gas is measured and has reduced the global warming potentials (GWP) for both methane and nitrous oxide due to their shorter lifespan.
The measurement of methane has become of a topic of hot debate among the scientific community. Currently, studies commonly measure greenhouse gases in terms of their CO2 equivalence (CO2e). However, while methane is a more damaging gas, with around 28 times the warming effect of CO2, its lifespan is only a fraction of that of CO2. While CO2 is thought to accumulate in the atmosphere taking more than 1,000 years to break down, methane takes just 12 years. This means that even if CO2 emissions were to cease, the warming it causes would remain relatively fixed for centuries. Meanwhile, ‘short-lived’ climate pollutants such as methane – which is predominantly produced by livestock through enteric fermentation – do not accumulate thanks to their relatively rapid natural removal from the atmosphere.IPCC conclusions on methane
The IPCC report makes its own conclusions on how methane should be accounted for. It states: "...Expressing methane emissions as CO2 equivalent emissions using GWP21 100 overstates the effect of constant methane emissions on global surface temperature by a factor of three to four over a 20-year time horizon while understating the effect of any new methane emission source by a factor of four to five over the 20 years following the introduction of the new source." The report also highlights the effects of different types of methane emissions and stated that it had "high confidence" that methane emitted from fossil fuel sources has "slightly higher emission metric values than those from biogenic sources" (or animals in layman's terms), "since it leads to additional fossil CO2 in the atmosphere". As a result, the IPCC report states that the new emission metric approaches, such as Combined Global Temperature Change Potential (CGTP) and Global Warming Potential* (GWP*), give a better account for the different physical behaviours of short and long-lived gases.'A game-changer'
Irish Farmers' Association (IFA) Environment chairman Paul O’Brien said the development was a "game-changer" for agriculture. “This is hugely significant and must be factored into the upcoming climate budgets and sectoral targets,” he said.It would be a total nonsense to make decisions based on a metric that is about to be changed fundamentally."“The clear acknowledgement of this by the IPCC is a game-changer and it must be reflected in policy formulation and how we account for methane emissions in Ireland,” he said.
