Welcome back: Two stories highlighted in the newsletter today focus on the challenges sustainability executives face in the current climate, and we close with one to lift the spirits. First: more companies are recalibrating environmental efforts they rushed to embrace in recent years.

Oil giant BP recently said it would slash spending on renewable energy and pivot back to fossil fuels. Porsche has similarly scaled back its all-electric ambitions and is investing in new combustion-engine cars, citing lower-than-expected demand from consumers.

Now, France's Airbus is rethinking its plans for a zero-emissions, hydrogen-powered aircraft, in what is being seen as a blow for the dream of clean aviation, which governments, investors and customers alike have pushed the industry to tackle. See below for more details.  

In the U.S. this week, the Trump administration imposed tariffs of up to 3,521% on imports of solar cells from Southeast Asia, making the products effectively unmarketable to American consumers. The levies come at a challenging time for the broader solar industry. Since regaining office, President Trump has begun implementing an energy policy that could jolt demand for solar panels, including by lifting certain barriers to mining coal that some analysts think will slow the closure of coal-fired power plants.

Lastly, electricity generators that use temperature differences to produce power have been around for a while. They are deployed on space missions, among other things. But previous iterations weighed a lot and often relied on coolant or water, making them cumbersome for everyday vehicles.

Now, a prototype eliminates the need for coolant and can be fitted into tailpipes of cars, helicopters and unmanned aerial vehicles to generate electricity without changing how they operate.

Read on for more on these stories and other news linked to below.

Five years ago, Airbus made a bold bet: The plane maker would launch a zero-emissions, hydrogen-powered aircraft within 15 years that, if successful, would mark the biggest revolution in aviation technology since the jet engine, the WSJ's Benjamin Katz reports.

The plan raised eyebrows, not least because the technical challenges were huge. Engines would need to be reconfigured to run on a different fuel. Jets would need to store the hydrogen in liquid form at minus 423 degrees. The heavier fuel load and equipment would weigh on seat capacity and range.

And then there were the safety concerns exemplified by the 1937 Hindenburg disaster.

The company settled on hydrogen-fuel cells, which use a chemical reaction to generate energy for an electric motor, producing only water vapor. But the plan required a radical redesign of the airframe and propulsion system. The plane would carry only 100 passengers about 1,000 nautical miles.

Now, Airbus is pulling the brakes. The company has spent more than $1.7 billion on the project, according to people familiar with the matter, but over the past year concluded that technical challenges and a slow uptake of hydrogen in the wider economy meant the jet wouldn’t be ready by 2035.

The U.S. this week imposed steep tariffs on solar imports from four Southeast Asian countries where mainland manufacturers have set up factories in recent years, the WSJ's Kimberley Kao reports.

Tariffs of more than 3,500% on imports of solar cells from Cambodia, Thailand, Vietnam and Malaysia would effectively make the products unmarketable to U.S. consumers. The move follows a yearlong investigation by the U.S. Department of Commerce into claims by American producers that Chinese companies in those countries were dumping solar cells and panels in the U.S. at artificially low prices.

China has become the biggest target in a trade war that the U.S. launched this year over what it sees as unfair trade practices used by most trading partners, including many of Washington’s allies. Tit-for-tat tariff responses by the White House and Beijing are threatening to make much of the trade between the world’s two biggest economies grind to a halt.

The solar tariffs announced Monday illustrate concern in the U.S. that China could avoid paying punitive tariffs by raising exports from a global network of factories that it has expanded in recent years.

Since then the Trump administration has said it is considering lowering tariffs on some Chinese imports. Beijing has also signaled that it is open to trade talks with the U.S. 

About three-quarters of the energy produced by a typical combustion engine is lost through heat and released through a car’s exhaust system. But what if some of that heat could be captured and turned into electricity?

In a recent study, researchers created a prototype of a device, called a thermoelectric generator, designed to do just that. When inserted into an exhaust pipe, the device can turn waste heat into a continuous source of electricity for vehicles such as cars, helicopters and unmanned aerial vehicles, making them more efficient, the researchers say.

Converting even a fraction of the waste heat produced by such vehicles into electricity could reduce fuel consumption and battery usage, they say, leading to lower carbon-dioxide emissions, Lisa Ward writes for WSJ.

The study was partly funded by the U.S. Army with unmanned aerial vehicles in mind, but the researchers believe the device has the potential to be used much more broadly. That’s because the thermoelectric generator can be installed into tailpipes of different vehicles without changing how they operate, says Bed Poudel, a research professor at Penn State’s College of Earth and Material Sciences and one of the study’s authors.

The Army says the next step is to independently evaluate the prototype in its own lab, which it plans to do.

Tell me what you think: Send me your feedback and suggestions at perry.cleveland-peck@wsj.com or reply to any newsletter. If you were forwarded this newsletter, you can sign up here.

• Dyson’s new HQ is a reversible building within a building. (WSJ)
   
• Google signs offshore wind deal in Asia Pacific with CIP. (ESG Today)
   
• Brewery installs giant heat pump to clean up its emissions. (Bloomberg)
   
• Equinor must explain climate discrepancy, shareholders say. (Reuters)
   
• New York pension funds put asset managers on notice. (FT)
   
• Microsoft is mining hard drives for rare earths. (Trellis)
   
• Eastern Shoshone tribe classify buffalo as wildlife. Here is why. (AP)
   
• How Pope Francis helped inspire the climate-change movement. (NYT)

WSJ Pro Sustainable Business gives you an inside look at how companies are tackling sustainability. Send comments to bureau chief Perry Cleveland-Peck at perry.cleveland-peck@wsj.com and reporter Yusuf Khan at yusuf.khan@wsj.com. Follow us on LinkedIn at wsjperry and yusuf_khan.