Science·What on Earth?

Small backyard homes could offer both housing and climate relief

In this week's issue of our environment newsletter, we examine the growth of 'garden suites' in urban areas and a trio of lethal lakes in central Africa.

Also: 3 lethal lakes in Africa present danger — and opportunity

(Sködt McNalty/CBC)

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This week:

  • Small backyard homes could offer both housing and climate relief
  • These lethal lakes in Africa present danger — and opportunity
  • Blood-sucking lampreys arrive in New Brunswick waterways to spawn

Small backyard homes could offer both housing and climate relief

A garden suite design created by Fabrication Studio.
(Fabrication Studio)

Change is taking root in the Toronto housing scene

In February, city council voted to allow homeowners to build a garden suite, or secondary residence, in their backyards. It's part of a housing strategy that aims to address Toronto's rental crunch.

Proponents say garden suites, along with laneway suites (which were approved in 2018), are a much-needed tool to gently add density to existing residential neighbourhoods — an alternative to highrises or car-dependent sprawl and part of the city's broader sustainability goals.

Other cities in Ontario (Barrie, Kitchener) and across the country (like Vancouver, Calgary and Edmonton) already allow garden suites. Toronto looked closely at some of those plans to see what worked best to address zoning issues.

Karen Chappele, director of the University of Toronto's School of Cities, has studied garden suites extensively and says 60,000 were built in California, mostly in Los Angeles, over the last three years alone. She says the concept "takes pressure off of the rest of the housing market." 

"Even if it's not an affordable unit for a low-income family, [a garden suite is] accommodating somebody who's not going to displace a low-income family in an affordable unit."

Proponents of garden suites say the benefits are many. Homeowners can use the rent to help pay off their mortgage, or as a residence for their adult children, who might not be able to afford to buy in the same area. Some want a residence for elderly parents or a caregiver for themselves. 

In terms of sustainability, the small size means less building material and the location allows it to tap into existing amenities in the main house, like electrical or plumbing infrastructure. 

François Abbott, an architect and owner of Toronto's Fabrication Studio, says that in general, garden suites promote a more climate-friendly lifestyle. "There's less consumerism because you're in a small space. You've got to just pick and choose your objects carefully," he said.

Craig Race, architect and co-founder of Toronto firm Lanescape, agrees.

"They can be as sustainable as you want them to be. Passive house, off grid, you name it — those opportunities are there."

Race says garden suites alone won't fix everything, but adds that "Toronto has a huge 'tall and sprawl' problem — highrises and single-family homes and not much else."

Abbott set up Fabrication Studio to focus solely on building garden and laneway suites, after seeing what he calls "the garden movement" taking shape in Toronto. He sees possibilities to design spaces that seamlessly blend into their gardens using green roofs, green walls and other plantings.

"It's a garden, after all — let's use that," he said. "It's a beautiful way to live. You know, it's compact architecture, but it's beautiful and it can be a nice life, even though it's smaller."

To clients concerned about cost, he points out it's still less expensive than buying or building a new home in the city.

"It's the cheapest possible option to make a new dwelling in the city. And then it adds value right away to your home, and so you have either income or enjoyment from your own use of the garden suite," he said.

David Driedger, a senior planner with the City of Toronto, says garden suites "can take up 40 per cent of the rear backyard area, up to a maximum footprint of 60 square metres [or 646 square feet]."

There are also height limitations. The unit must be smaller than the main house, and provide access to emergency services, while trees and green space must be protected. 

Several neighbourhood associations in Toronto appealed the bylaws, citing concerns about adequate tree protection and whether multiplexes should qualify. Driedger says that once the appeals are resolved, homeowners could potentially start building before the end of the year.

In two years — or after the first 200 garden suites are built — the city will evaluate the bylaws for any issues that might arise.

Race points out that garden suites are a way for homeowners to benefit from new housing construction, rather than just developers.

"I wouldn't be surprised if Toronto was building 500 laneway and garden suites every year in the not-too-distant future. That's like two highrises just being invisibly placed into our lowrise neighbourhoods, built entirely by everyday homeowners."

— Alice Hopton

Reader feedback

After we published Nicole Mortillaro's story about the Keeling Curve and the measurement of atmospheric carbon, a number of readers took issue with the use of the term "manometer" to describe the infrared analyzer, the instrument that determines the level of CO2 in a given air sample.

Jeff Schering wrote, "An infrared analyzer is not called a manometer. A manometer is used for measuring pressure."

Indeed, this is true, and we fixed the wording in the original story. Thanks to those who wrote in. 

We also went back to Ralph Keeling, Charles David Keeling's son and a professor of geochemistry at the Scripps Institution in California, for further clarification. Here's what he wrote in an email:

"The [CO2] measurements ultimately rely on BOTH a manometer and an infrared analyzer. The air samples are directly measured in an infrared analyzer. We have such an analyzer at Mauna Loa [Hawaii] as well as at our lab at Scripps. The infrared analyzer yields very precise numbers for the CO2 concentration in air, but needs to be calibrated. The calibration relies on the manometer. The manometer measures CO2 very accurately, but it's a slow process to get one number. The manometer is used to determine the CO2 concentration of air that has been pumped into high-pressure tanks. This 'known' air is introduced periodically into the infrared analyzer to perform the calibration."

Write us at whatonearth@cbc.ca.

Old issues of What on Earth? are right here.

CBC News recently launched a dedicated climate page, which can be found here.

Also, check out our radio show and podcast. It started out as a way to connect during the pandemic, but now Dianne Cerqua and her siblings talk about climate change every month. As she told What On Earth host Laura Lynch, not only has Cerqua learned more about the topic, she's found the courage to broach it with others. What On Earth now airs on Sundays at 11 a.m. ET, 11:30 a.m. in Newfoundland and Labrador. Subscribe on your favourite podcast app or hear it on demand at CBC Listen.


The Big Picture: Lethal lakes in Africa

Most lakes around the world pose predictable risks — drowning or maybe a run-in with a testy marine animal. But three lakes in central Africa have something unique stirring in their depths: dangerous concentrations of methane and carbon dioxide. 

These accumulations of dissolved gas are the result of thousands of years of volcanic activity, and the pressure building in these waters can lead to catastrophic harm. In 1986, Lake Nyos in Cameroon experienced what's known as a limnic eruption, which spewed a toxic cloud of carbon dioxide into nearby villages, killing countless animals — as well as 1,746 people while they slept. A similar gas release occurred at Lake Monoun (which is about 230 kilometres south of Nyos) in 1984, killing 37 people.

How did the gas get into these bodies of water? Researchers say it likely seeped in through cracks in the lake bed. These lakes are quite deep, and the cold water at the bottom can hold significant amounts of carbon for long periods of time. 

At Lake Kivu in Rwanda (see photo below), they have found a way to harness this strange gas buildup. In a feat of engineering derring-do, workers with the KivuWatt power plant pump the gas-rich water to the surface, where they are able to separate out the methane and carbon dioxide, sending the former along a pipeline to the natural gas plant and pumping the latter back into the depths in order to maintain the delicate balance below. The slow, careful removal of the methane reduces the pressure in the lake, ultimately decreasing the risk of a deadly eruption.

A gas platform on Lake Kivu in Rwanda, where workers with the KivuWatt power plant harness the gas dissolved in the water.
(Simon Maina/Getty Images)

Hot and bothered: Provocative ideas from around the web


Blood-sucking lampreys arrive in New Brunswick waterways to spawn

The sea lamprey is a fish with a powerful suction cup of a mouth filled with multiple circular rows of horn-shaped teeth and a tongue that burrows into the body of the host.
(T. Lawrence GLFC)

It's spawning season for the parasitic sea lamprey, meaning they're moving upriver in New Brunswick in droves. But the good news is that they're so focused on reproduction that their digestive systems shut down, making them less of a risk to other creatures in waterways. 

"They couldn't feed if they wanted to," said Marc Gaden, communications director for the Great Lakes Fishery Commission. "They have only one thing in mind once they reach that spawning phase, and that's to find a mate and to spawn successfully."

Sometimes mistakenly called an eel, the sea lamprey is a fish with a powerful suction cup of a mouth filled with multiple circular rows of horn-shaped teeth and a tongue that burrows into the body of the host.

Sea lampreys are native to Atlantic Canada. They are part of the ecosystem, and other species have learned to evolve with them. But elsewhere, they are an invasive species that has altered the ecosystem and decimated fish populations. 

The Great Lakes were particularly hard hit after canals opened new habitat for sea lampreys in the mid-1900s.

These lamprey spend a good part of their life at sea attached to — and feeding off the blood of — other fish. But at this time of year, adults return to inland brooks and rivers to spawn. 

Oana Birceanu, an assistant professor at Western University in Ontario, has been studying sea lamprey for years, but said "I've never seen them build their nests in the wild."

That's why she was fascinated by underwater footage taken recently by Mike Sherwood near his home in the area of Belleisle, N.B., and posted to social media of several lamprey building nests in a brook. At one point, the footage even captures two fish spawning in one of the crescent-shaped nests they were working on.

Birceanu said the males typically leave the Atlantic Ocean first and lead the way to the spawning grounds. She said they are guided by pheromones given off by the larvae from previous seasons that are still in the area. The females then follow those pheromones and the ones given off by the males, which begin working on the nests before the females arrive. 

Sea lampreys seek out rocky areas to spawn, she said, because the rocks help protect the newly laid eggs. Ideally, they look for rocky terrain upstream and a silty bottom downstream. 

The eggs develop into worm-like creatures that make their way to where they can burrow into the sandy bottom. They usually remain in this state, feeding off algae and decomposing matter, for three to seven years — and as long as 14 years in some cases, said Birceanu. 

Once they reach about 12 centimetres in length, they stop feeding and go through a metamorphosis, where they assume their adult bodies. Once the transformation is complete, these juveniles head to the sea, where they attach to host fish. 

After they latch onto fish, their tongue drills through the scales and skin of their host and they feed on blood and tissue. 

"Very often in their native range in the Atlantic, the sea lamprey will be a true parasite. That is, it might be able to feed off of the fish and not kill the host and then maybe move on to another species." 

But in the Great Lakes, the native species aren't large enough to survive their parasitic hitchhikers, and millions of fish have been killed in the process. Gaden said a single sea lamprey can feed and kill off about 40 pounds (about 18 kilograms) of fish in about two years. 

For decades, the Great Lakes Fishery Commission has been working to get control over the lamprey population. Each year, they spread lampricide in waterways to kill the larvae by the millions.

Since their numbers peaked in the mid-1900s, Gaden said the eradication efforts have reduced sea lamprey by 95 per cent, "and that saves well over 110 million pounds [50 million kilograms] of Great Lakes fish a year."

Without such sustained efforts, Gaden said it wouldn't take long for sea lampreys to flourish again. After all, each female is capable of laying between 50,000 and 120,000 eggs. And without any natural predators, the comeback would be swift. 

"Sea lamprey are very opportunistic. If you ease up control even briefly, they'll bounce back in [a] matter of a couple of years."

Mia Urquhart

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Editor: Andre Mayer | Logo design: Sködt McNalty

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