This is a valid question since death certificates don't necessarily mention the weather. The death certificate may say "blunt force trauma to the head" but anyone reading it might not know that the person died when a chunk of concrete jarred loose during an earthquake fell on their head. Or the cause of death might be "heart failure" but doesn't mention that the person had been enduring a heat wave. However, there are various methodological ways to try and estimate the numbers. It may not provide an exact number, but at least if the methods are applied fairly, the resulting numbers for the different phenomena are useful.

For example, the heat wave that hit Europe in 2003 can have widely varying numbers regarding the death toll due to the way causes of death are recorded and reported in the different European countries. One later attempt to sift through the records to find heat-related deaths indicated over 50,000 deaths attributed to that one long heat wave. Fifty thousand!