The study is of high quality. It uses a very robust dataset and employs the most modern and accurate statistical methodology to analyse this data. Furthermore, it is carried out by a team of recognised prestige and extensive experience in this field. Finally, it has passed all the review filters of a top scientific journal. 

The study indicates that high temperatures are directly related to an increase in hospital mortality due to respiratory causes. It seems a contradictory result, since we know (and the study also shows) that there are many more admissions in winter, but, on the other hand, the proportion of those admitted who die is higher in summer. Moreover, after ruling out other possible influences on mortality, it shows that high temperatures play a decisive role.

These results should alert us to the importance of protecting people with chronic respiratory pathology from heat waves and also alert hospital organisations to the need for adequate air-conditioning of their facilities, as failures or breakdowns in air-conditioning systems are not uncommon (there were also energy-saving measures that limited the air-conditioning of some buildings or services). 

In terms of limitations, the study is still observational and there are factors that cannot be fully controlled. For example, although an attempt has been made to analyse in the study, it is not possible to completely rule out that organisational changes due to staff summer holidays may result in lower quality of care. It is also possible that, due to the holidays of the population (especially in large cities such as Madrid and Barcelona), the patients admitted in August in these cities are citizens with more serious illnesses and/or of a lower socio-economic level who cannot go on holiday and remain in the city, so that the profile of patients admitted may be more serious/complex than the profile of patients admitted in winter. Finally, it is mentioned that the study was carried out in the provinces of Madrid and Barcelona, but there are very different microclimates within these provinces; it would be more accurate to limit the study to the cities of Madrid and Barcelona. 

High temperatures certainly play an important role, but there are other factors that may also contribute to this relative increase in mortality in summer.

I believe the study undoubtedly adds value, is of high methodological quality and covers a topical issue with an innovative approach. There was evidence of the impact of extreme cold or heat and temperature variability on the incidence of hospitalisations for respiratory diseases, but the impact of environmental temperature on in-hospital mortality after admission for respiratory reasons had not previously been assessed. Thus, this study does reveal an increased in-hospital mortality in summer, clearly related to high ambient temperature, which causes immediate effects 3 days after exposure, based on pneumonia, acute bronchitis, bronchiolitis, COPD or respiratory failure. This finding is in contrast to the incidence of hospitalisations for respiratory reasons, which are associated with the winter season.

Despite being an observational and retrospective study, it has a large sample size, a long evaluation period (14 years), reliable sources of morbidity and environmental data and high quality statistical analyses have been carried out with different perspectives, also taking into account confounding factors such as levels of major pollutants, relative humidity, age and variability in the quality of care due to the holiday period of health professionals. A limitation in the variables collected could be the absence of data on certain patient characteristics, such as other comorbidities; however, the available sample size and the epidemiological perspective can compensate for this lack.

We know that climate change causes adverse health consequences and this is one of them, which implies increased mortality in patients with pneumological diseases, which are very prevalent and a frequent reason for hospitalisation. In short, apart from preventive and corrective climate change policies, hospital facilities must be improved to reduce the thermal impact on hospitalised pneumological patients.