As temperatures and humidity rise in the United States, conditions are becoming more favorable for disease-carrying deer ticks.
The U.S. Environmental Protection Agency (EPA) reports that climate change has expanded the geographical range of ticks. Deer ticks specifically are most active when temperatures are above 45 degrees Fahrenheit and humidity is at least 85 percent. As temperatures and humidity rise in many parts of North America, so too are tick populations. The EPA reports that the incidence of Lyme disease in the U.S. has doubled since 1991.
The Northeastern U.S. has experienced the sharpest increase Lyme disease transmission. This part of the country is becoming more humid, making conditions better for ticks to emerge from the ground and latch onto hosts. New Hampshire, Maine, and Vermont have seen the largest spike in Lyme disease incidence since 1991, followed closely by Delaware and Massachusetts. On average, the EPA reports, these states now see 50 to 100 more cases per 100,000 people than they did in 1991.
Iowa has experienced a serious increase in humidity since 1971, according to leading climate scientists in the state.
This increase of 8 percent to 23 percent, varying for different cities across the state, can be attributed to climate change.
“Absolute humidity, which is typically measured by dew point temperature, has increased statewide from 1971 to 2017. Measurements show Dubuque had the largest increase in humidity, a springtime increase of 23 percent,” said Gene Takle, director of the Climate Science Program at Iowa State University.
The 2017 Iowa Climate Statement, which was released by the Center for Global and Regional Environmental Research today, describes the impact this high humidity has on people, animals, crops, and infrastructure. The statement was signed by 190 science faculty and researchers from 39 Iowa colleges and universities.
These impacts are far greater than just discomfort. High humidity leads to hazardous health conditions for workers, worsened asthma conditions, higher costs of air conditioning, more waterlogged soil, and stress on crops, livestock, and pets.
The statement calls Iowans to recognize the damaging effects of increased humidity, and to understand more must be done to mitigate the effects of climate change.
The first of its kind, a recent study found that climate change is likely to decrease the number of “nice weather” days worldwide.
The authors of the study, scientists from the National Oceanic and Atmospheric Association and Princeton University, define “nice” or “mild” days as those days when temperatures are between 64 and 86 degrees Fahrenheit, dew points are below 68 degrees Fahrenheit and less than half of an inch of rain falls. Currently there are an average of 74 nice days globally per year, but that number is likely to drop to 70 in the next twenty years and to 64 by 2081.
Karin van der Wiel is a postdoctoral researcher at Princeton University and lead author of the study. She said,
“We used a climate model to simulate the current climate. In that simulation we counted the number of mild days. Then, we increased greenhouse gases in the climate model to simulate the future effects of climate change. This leads to increasing temperatures, changes in humidity, changes in precipitation over the whole world and with very specific patterns. In this new, future climate, we counted the number of mild days again. We could then calculate the change — increase or decrease — of mild weather days for each location globally.”
Not all corners of the Earth will be affected equally, however. Tropical regions are expected to lose the most nice days, with some areas losing up to 50 per year by the end of this century. Meanwhile, London is expected to gain 24 nice days each year.
Predictions for Cedar Rapids, Iowa mirror global averages. Eastern Iowa currently enjoys 76 nice days annually; researchers say that number is expected to drop to an average of 72 between 2016 and 2035 and to 66 each year between 2081 through 2100.
Frequent high humidity makes it tough for Iowa to meet the pleasant weather criteria outlined in the study. Absolute humidity has risen by 13 percent during the summer months in Des Moines since 1970, according to Iowa State climate scientist Gene Takle. Increased humidity also contributes to the extreme rain events that have plagued Iowa in recent years.
van der Wiel said, “Mild weather is something everyone knows, experiences, and has memories of,” she continued, “Our study shows that human-caused climate change is going to lead to changes in mild weather all over… The changes are happening now, and where people live.”