What is one effect of cold water on diving efficiency?

Cold water has a significant impact on diving efficiency, particularly influencing a diver's air consumption. When divers enter cold water, their bodies tend to experience a drop in temperature, which can lead to increased physical exertion as the body works to maintain warmth. As the body struggles to stay warm, there may be a rise in metabolic rate and thus an increase in energy expenditure. This heightened level of physical activity leads to increased air consumption because divers will breathe more heavily and frequently to meet the body's demand for oxygen, resulting in a potentially shorter dive time.

In contrast, the other options do not accurately represent the effects of cold water on a diver's efficiency. Decreased buoyancy is generally not a direct effect of cold water; rather, water temperature has a minimal effect on buoyancy when considering the overall buoyancy of the diver. Reduced air consumption could be misleading, as cold water typically leads to increased air usage instead. While improved mental focus might be a potential benefit of cold water diving for some experienced divers, it is not a universally recognized effect of cold water on diving efficiency.