In the midst of a heat wave, with temperatures reaching 32 degrees Celsius (about 90 Fahrenheit) and higher, physical tasks can be difficult. What about mental tasks?
A hot environment has been shown to impact the brain, with uncomfortable heat diminishing cognitive abilities. One review of the literature in the oddly-specific International Journal of Hyperthermia concluded that complex tasks are impaired more than simple tasks. At around 30 degrees Celsius, any task that requires a lot of mental effort will start to be much harder to pull off.
The stakes can be high. Studies have found that increased temperatures contributes to reduced workplace safety. Nearly any job has a cognitive component, so workers that spend time outdoors, or in offices without air conditioning, will be hit with a splash of reduced productivity and danger along with any heat wave.
With the planet heating up, the problem will become more common as the years go on. The only solution for now is to get out of the heat—find shade, take a dip in some water, or move indoors. Drinking water will also help; obviously heat will dehydrate you quickly, and even aside from the stress of the temperature, not drinking enough water has its own detrimental effects on cognitive performance.