While summer in the northern hemisphere is just a few days old, it is already proving to be a scorcher, with heat waves blanketing countries from China to the United States.
As the mercury soars, city dwellers in those places – and many more – are turning to air conditioners (ACs) to stay cool. The irony: the widespread use of ACs is actually driving up temperatures by feeding the climate crisis, which could leave up to three-quarters of humans exposed to periods of life-threatening heat and humidity by 2100.
That has begged the question: can cities adapt to rising temperatures without resorting to air conditioning?
We spoke to Mark Radka, Chief of the Energy and Climate Branch of the United Nations Environment Program (UNEP), about that quandary – and he says some of the solutions lie in nature.
How much hotter could climate change make cities?
Mark Radka (MR): By 2050, if we continue on the same trajectory, close to 1,000 cities will experience average summer highs of 35˚C – nearly triple the 350 cities that already do. The urban population exposed to these high temperatures will increase by 800 per cent, reaching 1.6 billion by mid-century.
Extreme heat can obviously be deadly. But can’t it also have a devastating effect on economies?
MR: Yes. In fact, a recent report found that in the Bangladeshi capital Dhaka, heat stress was responsible for an estimated loss of 8 per cent of the city’s GDP, a figure that will increase with warming temperatures.
How does cooling contribute to the climate crisis?
MR: Cooling is a big contributor to global warming. Much of the existing cooling equipment uses hydrofluorocarbon refrigerants, which are potent greenhouse gases, and use a lot of energy, making them a double burden for climate change. Even with the phasedown of hydrofluorocarbons required by the Kigali Amendment to the Montreal Protocol, business as usual means emissions from refrigeration and air conditioning are expected to double by 2030 and triple by 2050, rising from 7 per cent of global GHG emissions today. Right now, the more we cool, the more we heat the planet. If we are serious about reversing current trends, we cannot go about cooling our planet with a business-as-usual approach.
How much energy is ultimately devoted to keeping buildings cool?
MR: We now know space cooling demand accounts for nearly 20 per cent of electricity used in buildings and is the fastest growing use of energy in buildings globally, set to triple by 2050. But this consumption and growth varies wildly by country and within countries. Those intra-country differences are often tied to location, climate conditions and incomes.
How can municipalities reduce the environmental toll of cooling?
MR: Cities can deliver or incentivize many of the solutions needed to address cooling demand, whether through enforcing planning rules, bringing nature into cities, delivering social housing, or promoting approaches like district cooling. At UNEP, we have developed a handbook for cities to do just that: Beating the Heat: A Sustainable Cooling Handbook for Cities.
How can nature-based solutions help turn down the heat in cities?
MR: Nature-based solutions bring multiple benefits to cities and will be critical for cities to adapt to climate change. By keeping cities cool, they mitigate the urban heat island effect, lower cooling demand and improve citizens’ resilience to extreme heat.
What are some of those nature-based solutions?
MR: Planting and preserving large areas of trees and forests within cities can significantly cool the urban environment by shading streets and buildings, enhancing evaporative cooling, and reducing air temperatures through transpiration. On a normal sunny day, a single tree can transpire several hundred litres of water, which represents a cooling effect equivalent of two domestic air conditioners running for 24 hours. Research has found that globally, investing $100 million annually in street trees would give 77 million people a 1°C reduction in maximum temperatures on hot days.
Is there anything else cities can do?
Creating water bodies, such as lakes, canals, ponds and wetlands in urban areas, can have a significant cooling effect. UNEP and the government of the Lao People’s Democratic Republic are currently working on a major project to restore wetlands in four cities, which is expected to benefit 10 per cent of the entire population.
As well, the National Research Council of Canada found that green roofs – where a roof is fully or partially covered in vegetation – can reduce air conditioning costs in the summer by up to 75 percent.
When it comes to cooling, where does the world need to go from here?
The cooling benefits of nature-based solutions are well documented, but they need to be better understood and leveraged to increase implementation and bring about change at a global level.
UNEP is at the forefront of supporting the Paris Agreement goal of keeping global temperature rise well below 2°C, and aiming for 1.5°C, compared to pre-industrial levels. To do this, UNEP has developed a Six-Sector Solution, a roadmap to reducing emissions across sectors in line with the Paris Agreement commitments and in pursuit of climate stability. The six sectors identified are: Energy; Industry; Agriculture & Food; Forests & Land Use; Transport; and Buildings & Cities.