4 March, 2025

Martha Henriques This week, we take a look at some of the valuable resources we throw away simply because they are, well, a bit gross. Take pee, for example: it's full of nutrients that can be used to help crops grow, cutting down on the need for synthetic fertilisers. In Vermont, farmers have been experimenting with using urine to safely boost harvests. Meanwhile in Canada, entire sewer systems have been tapped for heat, which can be cleanly harnessed to keep buildings warm. What else have we been funnelling straight into the drain that we can use to help tackle climate change? Also this week: the urgent search for a new home for two orcas.

THE BIG PICTURE Saving the world's strongest current The Antarctic coast is kept cold by a fast-moving band of current around the continent. Credit: Getty Images It's not as well known as the Gulf Stream, but the fast-flowing water that encircles Antarctica is the strongest ocean current in the world. The Antarctic Circumpolar Current acts like a moat around the continent, keeping warmer waters away and protecting the sea ice from melting. But new research suggests this extremely strong current may be more vulnerable than we thought. If we act now, it may not be too late to save it. Read the story here.

CLIMATE CONVERSATION  Why do we waste so much waste? Using urine on crops can boost growth without the use of synthetic fertilisers. Credit: Rich Earth Institute For centuries, getting rid of our own waste has been a matter of public health. Sewers to take away human waste, and incinerators to burn hazardous materials, have played a role in keeping harmful material away from where we eat, sleep, work and play. ‌ When a sewer is rolled out across a city – such as in Paris in the late 19th and early 20th centuries – you can track how life expectancy increases by years as each neighbourhood joins the system. ‌ It's infrastructure that saves countless lives, but what if we could safely harness the resources that our waste still holds before releasing it? Here's a whistle-stop tour from Vermont to Malawi to see how the things we usually throw away can be salvaged to help the climate.

The nutrients in urine often end up polluting waterways if flushed down the toilet. Credit: Rich Earth Institute In Windham County, Vermont, a group of around 250 people are taking part in the Urine Nutrient Reclamation Program, donating a total of around 12,000 gallons (45,400 litres) of urine each year to be "peecycled". The nitrogen and phosphorus in urine help plants grow – as much as doubling crop yields compared with using no fertiliser. ‌ "Our bodies create a lot of nutrients, and right now those nutrients are not only wasted, but they're actually causing a lot of problems and harm downstream," Jamina Shupack, executive director of the Rich Earth Institute, which runs the peecycling programme, tells Becca Warner. Read the full story here. ‌ It's not just about pee though – what about the rest of our waste? In Malawi, a prison's kitchens have been fuelled with methane thanks to a biodigester for human waste. A biodigester can even turn potentially harmful medical waste, such as placentas, into a source of methane for cooking, as this hospital did in Nepal. ‌ Elsewhere, even if you leave the waste itself, you can get valuable heat from the sewage system that can keep buildings warm without using fossil fuels. In one Vancouver district, 6,210 apartments get their heating from renewable sources, and sewage heat is the biggest contributor. ‌ "There's enough heat in the sewerage system to literally heat up neighbourhoods," says Derek Pope, manager of neighbourhood energy for the city of Vancouver. "That's what we've been doing here in False Creek since 2010." Read Anna Turns' story here. ‌ And failing all else, several start-ups have become adept at using the waste that clogs sewers to reduce the need for fossil fuels – to power batteries with urine or "faecal sludge", or turn the fatbergs from our sewers into fuel. Read Richard Gray's story here.