Correction to: Nature Astronomy https://doi.org/10.1038/s41550-019-0843-7, published online 5 August 2019.

In the version of this Letter originally published, in the PDF version the natural logarithm symbol was mistakenly omitted from equation 1; the equation should have read σ(T) = σ0 + σ1ln(T/1 K). This has now been corrected.