If you thought last year's heat waves were bad, brace yourself because there's a good chance things are going to become even more intense, especially if you live in a major city. Economists from the UK, Mexico and the Netherlands report that thanks to the urban heat island effect, around a quarter of the 1,692 cities surveyed could become warmer by as much as 8°C (14.4°F) by 2100. As the mercury spikes, so will the economic costs of running an overheated city. On the bright side, there's a solution to this and it begins in your neighborhood.

The heat island effect is a phenomenon that causes urban areas to become warmer than the surrounding rural regions, as concrete buildings and roads replace open land and vegetation. Other factors contributing to this effect include the generation of waste heat via human activities, pollution and humidity. According to the US Environmental Protection Agency, pavement surface temperatures can be as much as 50-90°F (27-50°C) hotter than the surrounding air on a hot summer's day.

While the heat island effect is not a by-product of climate change, it does have a synergistic relationship with it. In the case of urban areas that are already experiencing the heat island effect, climate change could lead to a spike in temperatures and more frequent heatwaves. As it is, the latter is becoming increasingly commonplace across the globe, resulting in record-high temperatures, droughts, nuclear reactor shutdowns and an increase in heat-related hospitalizations and deaths. Last July, for instance, temperatures in Kuwait reached a record 54°C (129.2°F), the highest ever recorded in Asia and the Eastern hemisphere. According to the study, those living in the world's most populated cities can expect the heat island effect to add another two degrees to global warming estimates by 2050.

Apart from their impact on public health, higher-than-average temperatures could also cripple a city economically via civil unrest and reduced productivity due to heat stress and disrupted sleep. This would also be exacerbated by an increased demand for electricity, which would in turn put more stress on a city's power grid, resulting in more frequent or prolonged outages, or a need for a whole new system entirely. According to the study, the researchers found that the total economic costs of climate change increased 2.6 times when they took heat island effects into consideration. In particular, the worst-off city could stand to lose as much as 10.9 percent of their GDP by the end of the century, nearly double the global average of 5.6 per cent.

That said, the study is not all doom and gloom. These problems are not insurmountable, say the researchers. In fact, the simplest way to effect change is to engage in climate-friendly practices at a local level. These include building pavements that reflect more sunlight and absorb less heat; installing green roofs and simply growing more trees and plants.

"Any hard-won victories over climate change on a global scale could be wiped out by the effects of uncontrolled urban heat islands," says study author Richard Tol, a professor of economics at the University of Sussex. "We show that city-level adaptation strategies to limit local warming have important economic net benefits for almost all cities around the world."

What is also worth noting is that these solutions don't require an overhaul of a city's infrastructure to be effective. The researchers found that switching just 20 percent of a city's roofs and half of its pavements to 'cool' forms could save cities up to 12 times the cost of their installation and maintenance fees, and bring air temperatures down by about 0.8°C. When conducted in tandem with global initiatives, these local interventions could help amplify the former's positive effects.

"It is clear that we have until now underestimated the dramatic impact that local policies could make in reducing urban warming," says Tol. "In fact, the largest benefits for reducing the impacts of climate change are attained when both global and local measures are implemented together."

And even if these large-scale programs don't succeed, city dwellers will still be able to benefit from local efforts to curb the heat island effect.

"[Even] when global efforts fail, we show that local policies can still have a positive impact, making them at least a useful insurance for bad climate outcomes on the international stage," says Tol.

The study was published in Nature Climate Change.