In 2011, when Minutes to Midnight was first published, the Doomsday Clock was set at five minutes before the fatal hour; the atomic scientists were confident enough to assert, ‘We are poised to bend the arc of history.’ In 2020, in a state of alarm, they broke the two-minute barrier to set the clock at 100 seconds before global disaster and to declare:

This warning was published before the outbreak of the coronavirus pandemic, which has compounded the major threats to humanity.

Meanwhile, also since 2011, the Anthropocene Epoch has been more widely recognised as marking the confluence of two kinds of time, the historical and the geological. ‘Era’, a geological term used in this instance by a minority of specialists, has seemed to me rightly or wrongly more appropriate for a book mainly concerned with history.

‘Anthropocene’ (human recent time) was introduced in 2000 by the Nobel Prize winner Paul J. Crutzen and his colleague Eugene Stoermer. The two chemists dated the beginning of the epoch from 1784, when James Watt perfected the modern steam engine, choosing this date because ‘during the past two centuries, the global effects of human activities including an increase in carbon dioxide and other “greenhouse gases” have become clearly noticeable’. However, they also suggested that their choice might seem ‘somewhat arbitrary’ and that ‘alternative proposals can be made (some may even want to include the entire “holocene” [wholly recent time]’, or ‘Before Present’ beginning in 11,650 BC, with present defined as 1 January 1950).

In 2009, the International Committee on Stratigraphy set up the Anthropocene Working Group (AWG). On 21 May 2019, the AWG published the results of a binding vote by its members. They expressed their commitment to the search for a new unit of geological time scale via a Global boundary Stratotype Section and Point (GSSP) commonly known as a Golden Spike.