LONDON — Beer, barbecues and crumpets, three staples of life in Britain as it enjoys an unusually warm summer, may soon experience shortages as the country faces an unexpected shortfall — of carbon dioxide.

The gas is used in a wide range of ways, including to give beer and soft drinks their fizzy quality, and to stun animals before they are slaughtered. Food companies also use carbon dioxide to give their products a longer shelf life.

But the gas is increasingly in short supply.

Carbon dioxide has many sources, but it is a byproduct, among other things, of ammonia fertilizer. Several plants in Britain and elsewhere in Europe that produce fertilizer have had to shut down for maintenance, a renovation period that coincides with the region’s warmest months. Technical difficulties at other plants have squeezed supplies further.

Food safety requirements mean that companies cannot simply capture carbon dioxide present in the atmosphere. Companies that sell the gas acquire it from ammonia plants before cleaning and purifying it. That has left many companies (and customers) in Britain worried that summer cookouts may soon be off the menu.