Beijing’s air on Tuesday morning had 20 times more the level of tiny cancer-causing pollutants than is considered healthy by the World Health Organization. Even chain-smoking taxi drivers complained about the toxic air. “Very serious,” said one. A smog cloud the size of California that blanketed much of northern China since Sunday was expected to linger for a couple days.

The smog is the latest evidence that despite China’s government’s calls for radical solutions—last year Premier Li Keqiang said the country would “declare war” on smog—the scale of the problem suggests there will be no quick fix.

The problem is that China’s economy is overly reliant on producing steel, which takes large amounts of coal to produce, and coal-fired electricity, which supplies about two-thirds of China’s energy use compared to 40% in the U.S.. The government has said that the country’s greenhouse gas emissions will only peak in another 15 years, in 2030.

The irony is that Beijing is actually meeting the government’s recent pollution goals. On Sunday, China’s environment minister announced that the country had achieved its targets for reducing major pollutants outlined in the last five-year plan ending this year ahead of schedule. Discharges of sulfur dioxide fell by 13% from 2010 levels, and a measure of water pollutants was down by 10% from 2010 levels. Stories appeared just last month of Beijing’s improving air in 2015. But this week’s dangerous smog levels prove that a patient’s improving blood pressure readings doesn’t mean much if he still suffers a heart attack.

The area surrounding Beijing, in Hebei province, is a window into the larger problem China faces. Hebei produces 11% of the world’s steel, more than the U.S., Germany, and Italy combined. A reduction in industrial emissions would have the biggest improvement on air quality, says the Paulson Institute, the think tank founded by former Treasury Secretary Hank Paulson. But the cheap fuel is unlikely to be replaced, as China has 13% of the world’s coal reserves.

Greenhouse emissions from burning coal and other sources contribute to dangerous levels of air pollutants categorized as PM 2.5 (particulates smaller than 2.5 micrometers) that cause smog and enter the bloodstream as known carcinogens.

In Hebei, and the rest of China’s north, there’s another problem: coal-fired power plants. Ninety-five percent of public heating in Hebei comes from coal, according to Tsinghua University. A 30% reduction in emissions associated with heating would have the biggest impact on air quality out of any change, the Paulson Institute projects.

Recent research has linked air pollution to dramatically shorter lifespans. A study by Yuyu Chen, associate professor at Peking University’s Guanghua School of Management, shows that smog reduces life expectancy in northern China by five years. Air pollution from coal consumption caused almost 700,000 deaths last year, according to a study by Tsinghua and Peking Universities.

At a U.N. summit on climate change in Paris on Tuesday, President Obama met with China’s President Xi Jinping about the importance of the countries’ role in reducing global warming. China passed the U.S. as the world’s biggest polluter in 2007.

But Xi pressed for leniency in a speech at the summit, where he emphasized that developing countries needed leeway in climate talks so they could continue the type of infrastructure building and development that boosts their economies.

Residents of China’s smog-choked cities were probably hoping for a stronger message from their Beijing-based leader.