PLEA Network

22 May 2018, Carbon Brief, Guest post: Don’t shift the goalposts of Paris Agreement’s temperature limits. The adoption of the Paris Agreement started a lively debate among scientists about the interpretation of several of its elements. Of particular interest has been the long-term temperature goal of limiting warming to “well below” 2C or 1.5C above pre-industrial levels and the question of how progress against the goal should be tracked. As there are a number of different observed datasets for global temperature – as well as methods that use climate models – it means different studies can arrive at different assessments. But therein lies a problem. If studies use a different dataset or method from the one that underpins the Paris limits – established in the IPCC’s fifth assessment report (AR5) – they are potentially tracking something different from 1.5C or 2C. To provide consistent information for policymakers – and not inadvertently shift goal posts – new research needs to be linked to the science underlying the Paris Agreement. A blind spot in the scientific debate The Paris Agreement represented a step-change not only for climate policy, but also forclimate science. It provides an important new signpost for climate scientists who want to link their research to policy. The renewed focus on 1.5C, in particular, has seen a flurry of studies attempt to quantify how achievable the limit is. Many of these studies use the concept of carbon budgets – the amount of CO2 emissions we can emit while still holding warming to no more than 1.5C. A 2017 study by Dr Richard Millar and colleagues triggered a scientific debate about how using different metrics to assess global temperature will affect the remaining carbon budget to achieve 1.5C. The research quantified the amount of global warming to date and used this as a basis for calculating the remaining 1.5C budget. The findings suggested a carbon budget of more than 15 years of current emissions for a 66% chance of holding temperature rise to 1.5C. This is larger than most other estimates. Their surprising conclusion was partly a result of their choice of temperature record, as well as a well-known difference between observed and model-based global average temperature estimates. This was explained in more detail in a Carbon Brief article at the time. Recent literature has also explored other factors that affect the size of the carbon budget. But the debate revealed a worrying blind spot when it comes to the linkage to the Paris Agreement. Global temperature limits are political targets based on risk assessments. Policymakers did not adopt the 1.5C and 2C limits for the sake of it, but because they intend to avoid the impacts of climate change that come with reaching or exceeding these warming levels. Read more here