A new study found that the warming climate may be partially responsible for Boston's growing rat population.
The study, which was published Jan. 31 in the journal Science Advances, used data from 16 cities around the world to examine rat population trends.
Of these 16 cities, 11 saw significant increases in rat populations, the study said. Boston was one of these 11 cities, though that may not surprise most Bostonians.
It's no secret that Boston's rat problem has been a burden on its residents. Rats can damage infrastructure, contaminate food, and spread over 50 pathogens and parasites to people, according to the study.
Boston residents who are well aware of the city's ongoing rat problem will likely remember the announcement of the Boston Rodent Action Plan (BRAP) last summer. In a collaboration between multiple city agencies, the initiative aimed to decrease the city's rat population.
In the announcement, city officials cited poor trash mitigation and Boston's aging infrastructure as the main causes of the city's rat problem. The warming climate can now be added to the list of contributing factors, according to the study.
Though changing temperatures have not been explicitly confirmed to be the cause of increased rat activity, the study observed trends that are "in line with potential biological responses to changing urban environments."
Rats are typically less active in the winter months due to their need to maintain internal body homeostasis, the study said. However, the warmer temperatures brought by climate change have expanded "the seasonal window for aboveground foraging and active breeding period for rats, supporting population growth," according to the study.
The study also cited increasing human populations and the resulting food waste as supporting the growing rat population.
Though Boston's rat population has been steadily increasing, it had only the ninth biggest increase in rat sightings during the study period. Washington, D.C., San Francisco, and Toronto were among the cities with the largest increases in rat sightings.
Further analysis in the study showed that the cities which saw the greatest increases in temperature change over time also saw the greatest increases in rat populations.
Although the warming climate seems to be the main contributor to Boston's growing rat problem, other factors include the proportion of vegetation cover and population density within the city, according to the study.
In last year's BRAP announcement, city officials cited population density as a factor behind the rat population increases in Boston specifically.
"The densely populated neighborhoods with intertwining alleyways and old sewer systems, along with century-old cobble or brick streets and sidewalks, provide an environment for rodents to thrive," officials said in the announcement.
Despite the warming climate's global impact, a few cities showed decreases in their rat populations, including Tokyo, Louisville, Ky., and New Orleans, according to the study. In these cities, more aggressive rat control practices led to these decreases, the study said.
In New Orleans, rodent control programs upheld more proactive surveillance and increased efforts to engage other city departments and educate residents about controlling the rat populations. Similarly, Tokyo's high sanitation standards have been fostered by media platforms where residents can publicize and report unsanitary areas where rats may congregate, according to the study.
The study concluded that the most effective approach that cities with increasing rat populations can take is to create an urban environment that is less conducive for rats rather than removing the rats that already populate the area. Though these tactics likely will not eliminate these cities' rat populations altogether, they have proven to be effective in controlling the issue, the study said.
By focusing on these environmental changes rather than extermination, Boston and other cities may be able to similarly rein in their rodent populations.