IPCC Annual Report 6: Physical Science Basis

By: Dr. Logan Thompson and Dr. Kim Stackhouse-Lawson

In August 2021, the Intergovernmental Panel on Climate Change (IPCC) 6^th annual report released its draft on the physical science behind climate change. This draft report, developed by a global team of scientists from IPCC: working group 1, is set to be finalized and published in September of 2021. The report shows that global average temperatures have rose approximately 1.1°C since 1850-1900 and is on pace to surpass 1.5°C in the next couple of decades. This has been primarily driven by carbon dioxide (CO₂) emissions over this time, followed by methane (CH₄) emissions. Atmospheric GHG emissions of well-mixed greenhouse gas (GHG) concentrations have increased considerably since 1750 and are unequivocally caused by human activities. To limit this human-induced global warming, this report highlighted the need to cumulative CO₂ emissions and reach net-negative emissions (removal of more CO₂ than we emit) as soon as possible, in conjunction with strong reductions in other greenhouse gas emissions. Perhaps most concerning, it was reported that with virtual certainty irreversible change is already underway due to present and past emissions.

How has/will this impacted weather patterns?

These rising GHG concentrations and changes in global temperature have already led to changing weather patterns, which are predicted to become more severe as emissions continue. Heat extremes and agricultural droughts have become more frequent and intense across most regions since 1950 and cold extremes have become less frequent and less severe. Additionally, heavy precipitation events have increased over this time as well as have fire weather across many regions. It was estimated that with each additional 0.5°C rise in temperature, these events increase in intensity and frequency. This will lead to increased challenges for the agricultural sector as systems will have to change to increase resiliency in the face of such weather extremes.

New accounting metrics that impact ruminant livestock

Included in this report were two new GHG accounting metrics that we not included in the previous annual report- Combined Global Temperature Potential and GWP*. These metrics were developed to account for the short-lived nature of certain greenhouse gases, with methane being one. Methane is an important GHG for ruminant systems and is the predominate contributor to the carbon footprint of livestock. Using GWP* rather than global warming over a set time horizon includes a time step component to calculate warming relative to its emission rate to determine impact on temperature. What we see is that methane emissions needs to gradually decrease for stable warming to occur. This reduction rate was estimated to be 0.3% by Cain et al. (2019). This improves of the global warming potential accounting metric as that metric shows that impact on temperature would continue to rise even as emissions are reduced by treating it as a stock (or long-lived gas) like CO₂. This is important as companies and countries continue to set net zero goals as net-zero emissions from short-lived gases such as CO₂ is not necessary to achieve stable warming but rather reduction in emission rate is. Therefore, ruminant livestock industries need continued focus on enteric methane reduction technologies to help achieve positive climate outcomes.