Concentration of CO2 in the Atmosphere

Ticks, Diseases, and Climate Change

Perhaps this is the real cause of Lyme disease. Photo: downtowngal, Wikimedia Commons.

Perhaps this is the real cause of Lyme disease. Photo: downtowngal, Wikimedia Commons.

By George Harvey

I spent an appreciable part of my childhood at a house in the southwest corner of New Hampshire. In those days, sixty years ago, we had a lot of mosquitoes. In fact, we could not go out in good weather without having two or three buzzing about our heads. We often had bug repellent on us, though it did not seem all that effective.

We also had swallows, which made their living by eating the mosquitoes. Their flocks settled at certain times of day on the telephone wires in front of the house. We could easily see four telephone poles in front of the house, and the swallows covered the wires, about six inches apart, over the lengths of wire running from one to the next.

There were other things we did not have. They included ticks, Lyme disease, and mosquito-born illness.

By the time my children lived in that same house, we had noticeably fewer swallows. But we did have ticks in the area.

By the time I moved to Vermont, in 2004, there were nearly no swallows left at the old family home. But with the ticks, people were getting tick-borne illnesses. In addition to Lyme disease, there is babesiosis, which mimics malaria pretty well, among others. We also increasingly see mosquito-borne diseases, including eastern equine encephalitis and West Nile virus, which had not been here. Arguably, all of these are impelled by climate change.

These are anecdotal evidence of climate change. We have many others. But in 2003, compelling scientific evidence of climate change arrived with a new hardiness zone map.

Hardiness zone maps divide the country into zones according to the coldest normal winter temperatures. All locations with their coldest nights normally in the range of -20° F to -30° F are in zone 4; those whose coldest nights are normally in the range of -10° F to -20° F are in zone 5, and so on.

It happens that the coldest night of the year is the very time most sensitive to climate change. An increase of one degree in the average temperature through the year can be reflected by an increase of five degrees in the temperature of the coldest night.

In 2003, the American Horticultural Society produced a draft hardiness zone map for the United States Department of Agriculture (USDA). When the 2003 draft map was compared to the 1990 map then in use, it quickly became clear that the zones had all moved north. In fact, nearly half the country was in the next warmer zone than it had been. The change implied that the coldest nights of winters were generally nearly 5° F warmer than they had been only thirteen years earlier.

Nevertheless, the Department of Agriculture, which had commissioned the new map, decided to continue using the old one.

Now, in 2017, warming has continued. In some states, nearly all locations are in the next warmer zone than they had been in 1990. Almost all of Kentucky has changed, but Vermont is not far behind. Maps showing the changes up to 2015 can be found at

The maps are published for landscapers, gardeners, and farmers to help them decide what perennial plants to plant. But their data can also be used to tell us what pests will survive the winter and what diseases plants and animals, including human beings, are likely to get.

According to “Lyme On The Rise: A Look At The Numbers,” a story published in 2014 by VPR, there were a total of 94 confirmed cases of Lyme disease in Maine, New Hampshire, and Vermont in 1999. ( The number rose to 2,273 confirmed cases in 2012. Some public health experts believe only about 10% of the cases of Lyme disease are reported. That could be a major problem, because the disease can be a chronic challenge unless it is treated properly.

The list of diseases on the move is not limited to Lyme disease, babesiosis, West Nile virus, and eastern equine encephalitis. Other are moving north with warmer temperatures.

This year is expected to be one of the worst on record for Lyme disease in parts of New England. It would be wise to continue caution on Lyme disease even after cold weather arrives. While the rate of infection of many diseases declines, it is still possible to get Lyme disease in the winter. It is important with Lyme disease, and with the other diseases, to get proper treatment.

One thing that is often forgotten is that in this public health problem, an underlying cause is climate change. And this is caused by the over-use of fossil fuels. Do you want to slow the progress of Lyme disease and other health problems? You might start by looking at your consumption of fossil fuels.

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