Last fall Politico ran a special feature on global health that featured a graphic presentation of increased incidence of insect-borne diseases in the United States from 2004 to 2013, blaming the increase on global warming.

“Warming global temperatures are changing the range and behavior of disease-carrying insects like mosquitos and ticks and extending the seasons in which they are active. As a result, incidence of the diseases they carry—including Lyme, spotted fever, West Nile and malaria—are all on the rise, despite yearly fluctuations.” One part of the graphic, reproduced below, showed lowest, highest, median, and 2013 incidence for each of six diseases between 2004 and 2013:

The large variances between high and low incidences, the fact that the median in most instances is far from the midpoint (suggesting large year-to-year fluctuations), and the short time covered (10 years) all suggest that one should be very cautious about any inferences from the data from which Politico author Christina Animashaun infers the claim that global warming is driving increased incidence of the diseases. But there are more fundamental problems.

Animashaun cited the U.S. Global Change Research Program’s Climate Health Assessment for her claims, but writing in May 17’s Just Facts Daily James D. Agresti and Rachel McCutcheon went to the source—and found that it didn’t support her claims.

“First, with regard to ticks, it states:

Though there are links between climate and tick distribution, studies that look for links between weather and geographical differences in human infection rates do not show a clear or consistent link between temperature and Lyme disease incidence.

“Similarly, the assessment states the following about West Nile Virus [WNV] and other mosquito-borne diseases:

WNV is an invasive pathogen that was first detected in the United States just over 15 years ago, which is long enough to observe responses of WNV to key weather variables, but not long enough to observe responses to climate change trends.

“Further contradicting Politico’s storyline, the assessment states:

Western equine encephalomyelitis virus (WEEV) and St. Louis encephalitis virus (SLEV) were first identified in the 1930s and have been circulating in the United States since that time. Like WNV, both viruses are transmitted primarily by Culex mosquitoes and are climate-sensitive. …

Despite climatic warming that would be expected to favor increased WEEV and SLEV transmission, both viruses have had sharply diminished incidence during the past 30 to 40 years. Several other mosquito-borne pathogens, such as chikungunya and dengue, have grown in importance as global health threats during recent decades; however, a link to climate change induced disease expansion in the United States has not yet been confirmed.

“The assessment says nothing about the causes of spotted fever or malaria, except that malaria is ‘primarily acquired outside of the United States and based on travel-related exposures.'”

Agesti and McCutcheon refute the case for blaming global warming for the spread of the diseases—and the insects that carry them. They point out that “Although disease-carrying insect populations have increased greatly over the past several decades, there is no reliable evidence that climate change is the reason. Instead, the surge of these insects corresponds to the banning of a highly effective insecticide”—DDT. Despite the fact that its own scientific assessments found it safe, and it had been widely used, especially throughout the South, in the 1950s and 1960s to eradicate the mosquitos that had made malaria common there for centuries, “The EPA banned DDT in 1972, but its effects sometimes continued for decades. In New York State, for example, ‘it took mosquito communities nearly 40 years to reach pre-DDT levels.'”

Agresti and McCutcheon’s full article reveals much more that’s wrong with blaming climate change for the spread of insect-borne diseases. Globally, growing populations and increasing mobility are more important contributors. And in the United States especially, the chief culprit is the banning of the most effective, and least expensive, insecticide that once controlled the insects.