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Under a new French scheme cars are labelled according to the pollution that they emit. This allows the worst offenders to be banned when necessary

Last week Paris suffered its fourth smog of the winter and tried a new idea to protect its residents from the worst effects. Like many European cities, the Paris region has a well-established system of emergency actions that escalate if smog persists. Initial steps include health warnings, reduced speed limits and restrictions on lorries in the city centre. Final steps include cheaper public (€3.80 for a day pass), and bans on half of cars, using an odd/even number plate system.

Related: The UK’s deadly air pollution can be cured: here's how

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RETs are the only policy tool left to shift Australia’s electricity sector away from fossil fuels, RepuTex modelling shows

State-based renewable energy targets are becoming essential drivers of Australia’s carbon reduction framework and, based on current policy settings, will be vital for Australia to meet its 2030 emissions targets, according to a report by the energy consultancy RepuTex.

The finding comes amid attacks on state-based renewable energy targets by the prime minister, Malcolm Turnbull, and his ministers, who have called for them to be scrapped.

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Cities are facing more heatwaves, but not all strategies to keep us cool are equal. Sydney image from www.shuttrstock.com

The recent spate of heatwaves through eastern Australia has reminded us we’re in an Australian summer. On top of another record hot year globally, and as heatwaves become more frequent and intense, our cities are making us even hotter.

This is the urban heat island, where city temperatures can be significantly warmer than the surrounding rural regions.

The question, then, is what we can do to keep our cities cooler.

Why are cities hotter?

The temperature difference is caused by a range of factors, including dense building materials absorbing more of the sun’s energy, fewer trees to provide shade, and less soil to cool by evaporation.

Buildings can also act like the hairs on a husky, reducing wind speeds and blocking thermal radiation up to the night sky. On top of that, waste heat from car engines, air-conditioners and other energy use adds to overall air temperatures.

Why does this matter? Even a small increase in air temperature pushes up overall energy demand, and about 25% of our energy bills are for only 40 hours per year when the grid is most heavily used.

The most extreme heat events can buckle train lines, cause rolling blackouts and cost billions in lost productivity. And it’s not just bad for our wallets.

Heat stress can cause organ failure or exascerbate heart or breathing problems. Since 1900, extreme heat events have killed more Australians than bushfires, cyclones, earthquakes, floods and severe storms combined.

So, what can we do?

There are a number of things individuals can do to reduce the impact of heat in their homes, such as installing light coloured roofing material, insulation or an air-conditioner.

But it gets more complicated when considering the city as a whole, and how these small actions interact with each other and with the climate.

Air-conditioners

In heatwaves, air-conditioners save lives, allowing stressed bodies time to cool. But our homes can only be made cooler by blowing heat outside, along with the extra energy to run the system.

As well as increasing outside air temperatures in the short term, the fossil fuels burned add to global warming. A world cooled by air-conditioning probably isn’t the answer.

Trees and parks

Trees provide shade, but also cool the air, because evaporating water from leaves takes energy, reducing peak temperatures by 1-5° C.

Most city planners agree on the broad benefits of urban vegetation, with some metropolitan councils developing urban greening strategies.

However, urban trees can be a vexed issue for some councils; they use water, can be costly to maintain, can damage utilities and property, and can worsen air quality instead of improving it. Larger cities are often made up of dozens of councils; getting them to agree is a major challenge.

White roofs

We know that black surfaces get hotter in the sun, but demand for dark roof tiles still far outweighs demand for light colours. More reflective roofs can reduce a household’s energy bill, as well as the overall temperature of a city.

White roofs are most effective in warmer climates, because in cold climates, the cost savings in summer must be balanced with additional heating costs in winter.

Green roofs and walls

Green roofs and walls are building structures with integrated vegetation. They provide cooling benefits by shading buildings and through evaporation from leaves. They generally show less cooling benefit than white roofs, cost more to install and maintain, and use additional water and energy.

But they do look nice, improve biodiversity and make people happier.

Pavement watering

Prior to an extreme heatwave, it may be possible to reduce temperatures by wetting down building and road surfaces. It’s a traditional practice in Japan, and is now being considered in major cities like Paris.

But temperature and humidity are important factors in heat stress, so pavement watering should only be undertaken if the extra humidity does not increase heat stress.

Large scale rooftop solar

Solar panels convert energy from the sun into electricity, so less energy is required from the network overall. If enough roofs were covered with solar panels, could that lower air temperatures?

Probably a little. Other benefits include a reduction in the energy required for cooling (because the roofs are shaded by panels), and a stable, lower cost, decentralised renewable energy system.

Building density

A building with lots of thermal mass (think sturdy, double-brick home) can be an effective way to keep inside temperatures more stable. Heat is absorbed during the day and released at night. The same idea can work for an entire city.

An urban cool island can form in high-density cities like Hong Kong because tall buildings provide extra heat capacity and shade.

For similar reasons, the tight street layout of traditional Arabian and Mediterranean cities keep those streets cooler.

Shading structures

Installing light shading structures over streets, pavements and roofs can reduce the surface temperature of materials, and reduce the heat absorbed and radiated back into streets. Shading structures need to be designed so that they do not limit airflow, trapping heat and air pollution in streets.

Which is best?

To figure out what works best, we need to be able to model the physics of different strategies, in different types of cities and in different climates. We can then assess the economic and health impacts and decide on appropriate and plans that give us the biggest bang for our buck.

Here we have focused on heat in cities, but there are other important concerns like air quality or flooding.

In colder cities, an urban heat island could actually be a good thing. Each city is different; each requires a tailored and integrated plan developed over the entire metropolitan region, and then implemented locally by councils, businesses and households.

Mathew Lipson receives funding through an Australian Government Research Training Program (RTP) Scholarship, UNSW Sydney and the ARC Centre of Excellence for Climate System Science.

Melissa Hart receives funding from the ARC Centre of Excellence for Climate System Science, the NSW Environmental Trust and the NSW Office of Environment and Heritage.

Huge coral system reef where the Amazon River meets the Atlantic Ocean was discovered last year.

A project aims to investigate the social case for gardens and what impact they have on well-being.

As London pollution hits a five-year high, will we see a return to the carpets of fog?

Last Sunday evening, the air over London achieved a remarkable quality. As winds died and a freezing stillness gripped the city, levels of nitrogen oxides and particles of soot slowly built up in the air until they reached maximum measurable levels at 24 different locations across the capital. It was a degree of pollution that had never been recorded in London since the government introduced its current methods and scales for recording air quality, the Daily Air Quality Index, in 2012.

“What we recorded was a very intense pollution event over London – in common with several other areas of western Europe,” said air pollution expert Gary Fuller, of King’s College London. “We had not seen anything like it here for the past five years.”

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A few intrepid tour operators are determined to reduce the harm we do to the planet with our holidays

I love an untapped resource (as opposed to a very overstressed one). The responsible travel movement is perfect. It takes the huge global travel industry (1.2 billion people holidaying abroad in 2015) and shapes it into a force for good, rather than one that trashes local host communities, siphoning profits to rich countries.

It’s untapped partly because we’re encouraged to think like travel consumers (obsessed with injustices such as single-person supplements) and not as citizens of the world. But a few tour operators are determined to change us.

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Writers and artists were inspired by the pea-soupers but smog cost thousands of lives

Londoners are being warned not to breathe too deeply when they go outside. A toxic fog is hanging over the streets, threatening the health and wellbeing of the capital. It is small consolation to know that this has been the state of the city’s air for more than 200 years.

London is in a natural basin surrounded by hills and its air generally holds moisture because of the river running through it, so it has always had a natural fog problem.

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Consumers could be exposed to American farming practices banned by the EU

Those of us who want to eat safe, healthy food awoke to a nightmare on Tuesday, a chilling interview on Radio 4’s Today programme. Bob Young, chief economist at the American Farm Bureau Federation, made it crystal clear that any US trade deal struck by Theresa May would be contingent on the UK public stomaching imports of US foods that it has previously rejected: beef from cattle implanted with growth hormones, chlorine-washed chicken, and unlabelled genetically modified (GM) foods.

Wiping the sleep from our eyes, we hoped it was just a bad dream, but the grim reality worsened. Martin Haworth, director of strategy at the National Farmers Union (NFU), was up next. Surely our own farmers, who have worked for decades to stricter EU standards shaped by consumers’ demand for safe, natural food, would reiterate their commitment to keeping them? Not a bit of it. Haworth’s only concern was that if such controversial American products were allowed into the country, British farmers should be able to use the same production techniques to ensure “an even playing field”. Do you find it credible that British farmers could beat the US’s vast industrial feedlots, hi-tech poultry plants and vast GM prairies at their own game? No matter, the NFU does.

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A tiny town in southern Greenland is fighting for its future. Behind it sits one of the world’s largest deposits of uranium. Should a controversial mine get the green light?

It is a beautiful morning on the southern tip of Greenland; the sun is high in a cloudless sky, but there is a tang of cold in the air. A crowd of Spanish tourists in red parkas has gathered at the small jetty in Narsaq, to watch boatmen who have just returned from hunting a minke whale in the open sea. From the shoreline, the Spaniards watch the men below busy themselves, slicing the whale meat into slippery rectangular chunks. They work swiftly, as if cleaning up the scene of an emergency, deferring to one young man in orange overalls. As word spreads that a catch has landed, local people arrive with carrier bags and choose from the cuts laid out on the bloodstained floor of the little boats bobbing in the water. The bags are slung on handheld scales; today, whale meat costs 80 Danish kroner a kilo, about £9. A woman pushes a wheelbarrow down the jetty, loaded with what looks like a ribcage.

The whale hunter is a symbolic figure in Greenland but the flurry the Spaniards are observing is humdrum, devoid of ceremony. Sebu Kaspersen, the hunter in orange overalls, explains that there was a calm sea and they could see a lot of whales; they shot one with a rifle and then fired a harpoon to finish it off. It is, he says, the second minke whale he has killed this year, the limit of his quota. His living largely comes from fishing halibut, and hunting seals for their skin; mostly, he works alone, without a crew.

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Rising temperatures could boost mercury levels in fish by up to seven times the current rates, say Swedish researchers.

Strathnairn, Highlands Looking at siskins so close is a delight. I can never decide if their plumage is yellow-green or lime-green

My study is separate from the house, in the 0.4 hectare garden, and I find there are three main distractions when I try to write there during daylight. (Though not the Toad’s Hole engraving by the door, which so intrigues visitors – it’s a family joke, dating back to a time when I used to work away a lot and write home signing myself “Toad”).

The first is the large pond just below the window. We had the pond dug out 30 years ago, for the wildlife, and it has been a great success – you can even see it on the latest Ordnance Survey map.

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The seeds of domesticated plants could offer clues as to why cultivated crops are larger than their wild cousins, a study suggests.

In New Zealand genetic diversity is proving a barrier for conservation measures aimed at boosting numbers of endangered birds.

Australia's rufous fantails have managed to avoid extinction by snake, unlike their unfortunate cousins on the island of Guam. Lindsey Nietmann is trying to find out how these 'mad fans' do it.

Crocs and cattle don't mix on a Northern Territory station; meet a specialist alpaca shearer; and a fish restocking program pays big dividends in the Kimberley.

In trial aimed at cutting air pollution, diesel motorists parking in Marylebone will pay an additional 50%, or £2.45 extra an hour

Westminster will become the first council in the UK to charge drivers of diesel cars extra money to park as town halls across London battle air pollution.

The charge will be introduced for a trial period from April. Drivers of diesel-powered cars and vans will pay an additional 50%, which at current rates would be an extra £2.45 an hour to park on the street in Marylebone, one of the most polluted areas of the borough.

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A tiny possum, an emblem of the state of Victoria in Australia, is rapidly heading towards extinction, say scientists.

The week’s top environment news stories and green events. If you are not already receiving this roundup, sign up here to get the briefing delivered to your inbox

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A baboon squaring up to a leopard, white-tailed eagles, and a cauliflower jellyfish are among this week’s pick of animals from the natural world

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