The big picture: Natural gas was the fastest-growing energy source last year —accounting for 45% of all such growth — with most regions and many industries turning to the fuel as a cleaner alternative to coal and oil, according to anInternational Energy Agency report released Friday. It’s set to keep growing in the coming years.

The intrigue: Environmentalists and some politicians are increasingly opposed to natural gas because they worry it’s locking in far too much global warming. Looking purely at the math and science of climate change, they’re right.

• Ramping up natural gas would make it impossible to cut emissions to a level scientists say would avert the worst impacts of a warmer world. That assumes there won’t be a massive buildout of emissions-capturing technology, which is still in its infancy and expensive.

But, but, but: Science and math don’t operate in a vacuum. And the reality is, natural gas is providing a cheap, plentiful, cleaner-burning option for countries to get off the world’s dirtiest — and historically dominant — power source: coal.

• Natural gas emits very little particulate pollution, which is a big draw for developing nations whose populations are choking on smog from coal and oil.
• To think countries wouldn’t make this transition because of what the science says reflects a lack of appreciation for how the real world embraces science: imperfectly and unevenly.

Let’s go back to that personal analogy I opened with:

• Doctors say we should eat several servings of vegetables daily and exercise at least 30 minutes a day. Yet most of us fail to live up to those recommendations for numerous reasons: We’re unmotivated, busy, can’t afford healthy food, really like unhealthy foods, etc.
• While we don’t do perfectly what the doctor recommends, most of us also at least try to fit in exercise and opt for the salad over the fries because we want to prevent health conditions today and as we age.

Similarly, it’d be ideal if we could immediately begin rapidly transitioning to using only zero-emitting energy resources to avert the worst impacts of a warmer world today and into the future because that’s what the science recommends.

• But we’re not doing that for a whole host of reasons, including: Natural gas is plentifully available, often times the cheapest electricity option and a source for things not easily created with renewables (like chemicals). Political influence and jobs from these industries are other big factors.
• To be clear, variable wind and solar costs are plummeting, and they’re booming alongside natural gas around the world. In some places they’re even cheaper.
• But zero-emitting options like batteries to back them up when needed aren’t similarly cheap yet. Natural gas offers cleaner-burning backup compared to coal.

Where it stands: Natural gas has been and is projected to be a big driver of emission reductions around the world, even accounting for uncertainty around methane emissions, per the IEA. Methane is the primary component of gas, but also a greenhouse gas whose impact on warming the planet is far greater on a shorter time frame than CO2.

• In developed countries, like the United States and the United Kingdom, natural gas displacing coal is a big reason emissions in these countries have dropped. Other drivers include renewable energy, stagnant power demand and energy efficiency.
• In some rapidly growing regions of the world like Southeast Asia, electricity demand is so great that nearly all energy sources, but especially natural gas and renewables, are likely to be needed for decades.
• Europe is increasingly importing American liquefied natural gas, even as the fuel’s long-term future there is limited by competition from renewables, per the IEA report.

“Gas of course has a much lower carbon content than any other fossil fuel. Therefore, we think gas is very important as an intermediate balancing fuel,” Maroš Šefčovič, European Commission vice president, said in an interview in May.

• Longer term, he said, natural-gas infrastructure should eventually be repurposed for zero-emitting sources, such as hydrogen from renewable energy.

What we’re watching: Whether technology and policy will develop in a way that helps or hinders natural gas. For the next decade or two, the fuel is poised to be the dominant energy source — even with moderate prices on carbon dioxide emissions, because that actually hastens the shift away from coal to gas.

The bottom line: Whether gas remains king depends on how aggressively world leaders act on climate change.