Industrial pollution is making life difficult in Iran, adding to a long list of economic and political grievances, according to Hamid Arabzadeh, an Iranian-born environmental health expert who teaches at UCLA. Pollution is among the reasons for the protests in Iran in December and January, Arabzadeh said.

The pollution “started with water resources,” he noted. “It led to air pollution, and now in some of the very large cities in Iran, people literally don’t have the air to breathe.”

Arabzadeh said one of the largest salt lakes in the world, Lake Urmia in northwestern Iran, is drying up because of dams diverting water and the pumping of groundwater.

“The government has been promising for many years that they are going to reverse some of the ill-conceived policies,” he said. "And it never happened."

Pollution has led to decades of protests in China and officials have responded, making environmental protection a priority, said Alex Wang, who teaches environmental law at UCLA. He has worked in the Beijing office of the environmental advocacy group Natural Resources Defense Council.

“There’s a new concept that the (Chinese) state is calling ecological civilization,” he said, “and it’s been all over the official propaganda and the state leadership messaging.” Wang explained that the approach has been “top-down,” with the officials taking the lead and sometimes limiting the flow of information on environmental problems through media censorship.

Thanks to citizen-activists, however, the process has also been bottom-up. Chinese farmers in a village in Heilongjiang province won the first round of a lawsuit against the Qihua Group, arguing that its chemical plant was contaminating their land. The lawsuit was spearheaded by Wang Enlin, a farmer with just three years of formal schooling who spent 16 years studying law on his own. The farmers won compensation in early 2017, but an appeals courts reversed the verdict, and the case continues.

Chinese officials are moving too slowly for many. A 2015 internet documentary called "Under the Dome," by former Central China Television journalist Chai Jing, shows the devastating impact of pollution. The documentary was widely circulated online, but pushed the limits for government censors who monitor the web for signs of unrest and challenges to state authority.

“That video within three days of being posted garnered by some estimates up to 300 million viewers, and within three or four days had also been blocked,” Wang said.

The stakes are higher in countries where corruption and the scramble for resources can lead to violence against the people, but the repression hasn’t stopped the activists who demand a voice, said Billy Kyte of the London-based organization Global Witness.

“Mining industries, agribusiness, logging, hydrodams are being built and imposed on people without their consent,” says Kyte. “This leads to them campaigning or protesting.”

Global Witness counted 200 killings in 24 countries in 2016 alone. The numbers recently released for 2017 were nearly as bad, with 197 killings. Kyte noted that the problem is worse in areas where corruption is common, with Latin America seeing the largest number of killings both years.

“Murder is just the sharp end of a whole range of attacks and tools used by industries and states to try and silence environmental activism,” he said, adding that threats and intimidation are also tools against activists.

Yet from Pakistan to Indonesia, activists are pressing their demands and are sometimes prompting action, often finding more success in societies that are open, said Arabzadeh.

“It has a lot to do in an organic and dynamic relationship with democratic institutions, with women’s rights, and with citizen’s empowerment,” he argued.

In the United States, activists have found a new target in President Donald Trump, who is withdrawing the U.S. from the Paris climate agreement that limits the release of so-called greenhouse gases, unless he can secure better terms. Trump is a global warming skeptic and calls the agreement unfair.

The U.S. is the world’s second-largest emitter of greenhouse gases such as carbon dioxide, which most scientists say lead to climate change. China is the worst emitter.

Chinese protests usually focus on the regional impacts of industrial pollution, and environmental law professor Alex Wang is worried about limitations on activists and controls on the flow of information in China.

“While it’s good that the state, by all accounts, seems to be investing tremendous amounts of resources on pollution reduction, in order to keep it going, you need that public attention and public support, he said.”

Kyte of Global Witness said the activists his group calls Defenders of the Earth brave threats and violence in corrupt regimes, and harassment in others, where their activism is “criminalized.” And yet, they continue to speak out.