A mysterious and deadly kidney disease has been plaguing labourers in the sugar fields of Central America. In the past 20 years, some 20,000 workers have died of the disease, and the crisis has been growing worse.

At first the epidemic was thought to be caused by chemicals such as pesticides, but the disease only affected labourers in coastal areas – those working at higher altitude in hills were largely unaffected.

A recent study found that hard work in the hot climate of the lowlands left workers dehydrated, putting such a heavy strain on their kidneys that it fatally damaged them. “When it’s extremely hot, the risk for kidney damage really begins to become evident,” said Richard Johnson of the University of Colorado, Denver.

Similar epidemics of kidney disease were also found in farm workers in other hot climates, in Sri Lanka, Egypt and Andhra Pradesh in India. And as global temperatures rise and heat waves become more intense, so the new type of kidney disease is increasing, according to the study published in the Clinical Journal of the American Society of Nephrology.

Another impact of global warming is more cases of kidney stones. This painful condition results from salts crystallising in the kidneys, often caused by dehydration. In the US, around 50% more cases of kidney stones occur in the warm climate of southern regions than northern states.

And the number of cases has been rising since temperatures began to warm noticeably in the late 1970s, especially in the summer. As the climate warms further, the high-risk zone for kidney stones is expected to expand northwards, with many more new cases predicted.