We can all get irritable, lethargic, and less focused when too hot. This is particularly problematic in the workplace. Not only do people work less effectively when in a hot and stuffy environment, they are also more likely to take time off due to work-related illness, and have more accidents when at work — facts that have been recognized by the IPCC. But what are the actual economic costs?

Kerstin Zander and colleagues (page 647) have examined this issue by analysing patterns of work absenteeism and reductions in labour performance in Australia, which has experienced an increasing number of heat waves over recent decades. This upward trend is expected to continue into the future as a result of climate change. To work out the potential economic impact of such changes, the researchers analysed self-reported estimates of work absenteeism and performance reduction caused by heat during 2013–2014, based on a representative sample of nearly 2,000 working adults who had completed an online questionnaire.

A substantial proportion of respondents — around three-quarters — said they been affected by heat in the workplace. Many also reported having taken at least some time off work, or having been at least less productive on occasion over the last year as a consequence of heat. Zander and colleagues then went further by estimating average annual costs at around US$655 per person. By extrapolation, this suggests a cost to the Australian economy of around US$6.2 billion. This may seem a modest sum when compared with Australia's government debt of around AUD 686 billion (US$524 billion) but it is nevertheless a substantial amount of money. No wonder then that Zander and colleagues highlight the need for adaptation measures to reduce the impact of future heat waves on labour productivity.

Of course Australia is not alone, even among developed countries, in facing the prospect of more frequent heat waves. In a separate study presented in this issue, Bryan Jones and colleagues (page 652) provide a model-based projection of population exposure to extreme heat for the continental United States. They find that heat exposure will increase four- to sixfold into the latter half of the present century compared with the late twentieth century. Their analysis also shows that changes in the size and distribution of the population, as well as climatic changes, affect levels of exposure, and that the relative importance of these factors varies across regions of the country.

Both of these studies underscore the need to foresee and (through adaptation and mitigation efforts) forestall the impacts of future heat waves on human health and welfare.