Faster international action to control global warming could halt the spread of dengue fever in the Western Hemisphere and avoid more than 3 million new cases a year in Latin America and the Caribbean by the end of the century, scientists report.

The tropical disease, painful but not usually fatal, afflicts hundreds of millions of people around the world. There is no vaccine, so controlling its spread by reining in global warming would be a significant health benefit.

The study is one of several recently published that attempt to quantify the benefits of cutting pollution fast enough to keep warming below 1.5 degrees Celsius. It also projects infection patterns at 2 degrees of warming and 3.7 degrees, a business-as-usual case.

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Scientists have predicted that climate change could create the wetter, hotter conditions that favor diseases spread by various insects and parasites. This study focuses on one widespread disease and on one geographical region.

Half a Degree Can Make a Big Difference

Published May 29 in the Proceedings of the National Academy of Sciences, the study was conducted by researchers from the University of East Anglia in the United Kingdom and the Universidade do Estado de Mato Grosso in Brazil.

It is part of an urgent effort by scientists around the world to collect evidence on the difference between 2 degrees of warming and 1.5 degrees, under the auspices of the Intergovernmental Panel on Climate Change (IPCC), which is due to report on the latest science this fall.

Either target would require bringing net emissions of carbon dioxide to zero within the next several decades, the IPCC has projected, but to stay within 1.5 degrees would require achieving the cuts much more rapidly.

Avoiding 3.3 Million Cases a Year

Without greater ambition, the study projected an additional 12.1 million annual cases of dengue fever in the Caribbean and Latin America by the end of the century.

By comparison, if warming is held to 2 degrees Celsius from pre-industrial times—the longstanding international climate goal—the number of estimated additional cases in the region falls to 9.3 million.

Controlling emissions to keep the temperature trajectory at 1.5 degrees Celsius would lower that to an annual increase of 8.8 million new cases.

The increase in infection is driven in great part by how a warmer world extends the dengue season when mosquitoes are breeding and biting.

The study found that areas where the dengue season would last more than three months would be "considerably" smaller if warming is constrained to 1.5 degrees Celsius.

Which Countries in the Region are Most at Risk?

The areas most affected by the increase in dengue would be southern Mexico, the Caribbean, Ecuador, Colombia, Venezuela and the coastal regions of Brazil. In Brazil alone, global warming of no more than 1.5 degrees might prevent 1.4 million dengue cases a year.

The study found that under the 3.7 degree scenario, considered "business as usual," dengue fever could spread to regions that have historically seen few cases. Keeping to 1.5 degrees could limit such a geographical expansion.

People living in previously untouched areas would have less built-up immunity and would be more likely to get sick, while public health providers in some such places "are woefully unprepared for dealing with major dengue epidemics," the authors warned.