Fine particulate pollution shortens lives at every level yet measured, with no threshold found, and the global estimates of deaths attributable to it run into the millions a year. In Europe and North America concentrations have fallen for decades, and the attributed deaths with them. In much of Asia they have not. The estimates are modelled from exposure and a concentration–response curve, so they move when either is revised. Revisions have been large.
Multi-country studies of daily deaths find that cold kills far more people than heat in temperate countries, of the order of ten times more, because moderate cold on many days outweighs extreme heat on a few. Temperature is the newer question, and the two are moving in opposite directions. Europe's summers of 2022 and 2023 produced tens of thousands of heat-attributable deaths by the standard method, the highest on record, and the series of heat deaths is rising. Cold-attributable deaths are falling as winters warm and housing improves. Whether the net effect of a warming climate on mortality in a given country is positive or negative over the coming decades is contested. It depends on adaptation. It is exactly the kind of question in which the method chooses the answer.
Three things make the evidence uneven. Attribution methods differ between agencies, so heat-death counts for the same summer vary severalfold. Exposure is measured well where the harm is smallest. And the people most affected — the old, the poor, those in bad housing — are those least well represented in the cohorts that have been set up to investigate.
Whether new technology can change what people do at the scale of a population: apps, wearables, automated messages, digital programmes and platforms, and how far their effects last and reach.
