A redistricting plan proposed by Republican legislators in Wisconsin in 2011 was overturned by a lower court based in part on the magnitude of the efficiency gap, although this ruling was overturned in 2018 by the US Supreme Court in Gill v. Whitford. In oral arguments, Chief Justice John Roberts dismissed this metric as “sociological gobbledygook.” Roberts’ critique is unfair in substance because the efficiency gap is a mathematical formula, not nonsense. But it is not entirely wrong in spirit. Some mathematicians have argued that these metrics do not accurately reflect “common-sense understanding of political unfairness.”

How can we identify gerrymandered maps if not by sight? Numerical metrics such as the Polsby–Popper test attempt to measure the “compactness” of an electoral district (the ratio of its area to the square of its perimeter), while the efficiency gap calculates the number of “wasted” votes by computing the proportion of votes that are not used to elect a winner.

The potential for cuts in 2030 is 31 gigatons of CO2 equivalent – which isaround 52 per cent of global greenhouse gas emissions in 2023 – and 41gigatons in 2035.· Increased deployment of solar photovoltaic technologies and wind energy coulddeliver 27 per cent of this total emission reduction potential in 2030 and 38 percent in 2035.· Action on forests could deliver around 20 per cent of the potential in both years.• Other strong options include efficiency measures, electrification and fuelswitching in the buildings, transport and industry sectors.