I am an optimist, both by temperament and observation. But I maintain my hopeful outlook partly because I know that we can confront challenges, ones that people — perhaps less optimistic than I — will sound the alarms on. Pope Francis has issued just such a warning with his encyclical on the environment.

The document is eloquent and intelligent, especially in its handling of science. “Most global warming in recent decades is due to the great concentration of greenhouse gases (carbon dioxide, methane, nitrogen oxides and others) released mainly as a result of human activity,” it says. “Concentrated in the atmosphere, these gases do not allow the warmth of the sun’s rays reflected by the earth to be dispersed in space.” That is as lucid a two-sentence description of the mechanism of global warming as I have read.

The encyclical is gloomy. But in fact, remarkable changes are taking place that could put the planet on a much more sustainable path. You get a sense of them if you read another important report that was issued this week, to much less fanfare than the pope’s missive — the International Energy Agency’s special report on energy and climate change.

The report points out that last year the global economy grew at 3 percent but that energy-related carbon dioxide emissions stayed flat, the first time this has happened in 40 years. Renewables accounted for nearly half of all new power generation last year, and the energy intensity of the global economy dropped by twice as much as it has on average annually over the past decade. With concerted action, we could actually push global emissions downward in the next few years.

How? Well, an ongoing revolution is taking place in energy technology. Natural gas has replaced coal in many places. The cost of solar cells has plummeted, leading to their widespread use. Cars, buildings and machines are becoming much more energy efficient. And over the horizon, one can see progress in batteries, nuclear power and biofuels, which could collectively produce a new energy ecosystem.

But innovation alone isn’t what is spurring progress, and it won’t be enough. We need a revolution in public policy as well. Fred Krupp, head of the Environmental Defense Fund, points out that most of the improvements that have been made in technology and efficiency would not have happened without rules and laws. And a series of smart policies — which are not very costly or disruptive — could dramatically accelerate the shift to a cleaner economy.

First, stop doing harm. Even Bjorn Lomborg, a skeptic about many efforts to tackle global warming, argues for a reduction in the massive, market-distorting subsidies for fossil fuels. The IEA estimates that last year these subsidies globally amounted to $510 billion, about four times those provided to renewable energy.

“We still have a long way to go on energy efficiency,” Krupp notes. “Buildings waste 30 percent of their energy. And a dollar spent in this area usually yields two to three dollars in energy savings in return.” He argues that solar power could become far more widespread if governments were not as beholden to utility companies and their phalanx of lobbyists. “There are lots of nonmarket barriers to renewables, placed at the behest of the established players,” he said.

Natural gas is better than coal, but its production, transport and use release significant amounts of methane, which has much worse effects on the climate than carbon dioxide. The good news is that serious studies have found that these emissions could be reduced relatively cheaply with new regulations. President Obama has called for nearly halving oil and gas methane emissions from 2012 levels by 2025. Krupp points out that if the same is done globally, that would have the same impact on the climate over the next 20 years as would shutting down 1,000 coal-fired power plants.

The smartest new policy would be the simplest, and one supported by many diehard free marketeers, such as Reaganite Republican and former treasury secretary George Shultz: a carbon tax — effectively putting a price on greenhouse gas emissions to encourage companies to adopt cleaner technologies. This seems impossible to imagine — yet this month, several major oil companies in Europe came out in favor of a price on carbon, whether through a tax or an emissions trading system like those used in California and Europe.

Technology and policy innovations are happening, just not on the scale that they need to be. That’s why the pope’s warnings are so useful and important — even to an optimist like me.

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