The uphill climb to a successful United Nations climate summit

The G20 just offered an extended preview of why spurring on-the-ground emissions cuts — not just airy pledges — will be so tough at the critical U.N. climate summit that's less than 100 days away.

Driving the news: The formal communique from the G20 energy ministers' meeting in Naples, Italy late last week finally arrived just yesterday, a reflection of the difficult and protracted talks.

Why it matters: What's most striking is what's not in the 14-page document — any agreement on phasing out coal consumption or overseas coal plant finance by the member countries.

• That's important because coal is the most carbon-intensive fuel, and steep reductions are needed to keep the Paris climate agreement's goals within reach. We dug into that impasse here.

Where it stands: The outcome fails to expand the recent G7 agreement on coal to the wider G20 that includes major coal consumers China and India, among others.

• A statement from G20 president Italy notes they were unable to reach agreement on coal phaseout timing, finance and a date for phasing out "inefficient" fossil fuel subsidies "despite a prolonged and tireless discussion."

The intrigue: This morning also brings yet another sign of climate tensions among G20 members.

"China said on Monday the European Union's plan to impose the world's first carbon border tax will expand climate issues into trade in violation of international principles and hurt prospects for economic growth," Reuters reports.

The big picture: OK, onto what the communique does say...it calls the 2020s a "critical decade" to act, "recognizing that the impacts of climate change at 1.5°C are much lower than at 2°C."

• It also commits countries to submit updated pledges under the Paris Agreement "well ahead" of the U.N. summit that begins in October.

• Key nations including China — the world's largest emitter — and India have yet to unveil revised commitments.

What's next: The limited outcome underscores the careful and high-stakes maneuvering looming ahead of the U.N. meeting known as COP26 — and all eyes will especially be on how coal and fossil fuel subsidies are addressed at the G20 heads of state meeting just beforehand.

Charted: Putting the G20 coal deadlock in context

That chart above, via BP's annual energy stats report, offers a look at global coal demand.

Why it matters: Coal's been on a generally downward trend for years in the U.S. and Europe, but on a global basis remains near peak consumption.

The International Energy Agency estimates that coal-fired power generation could reach an all-time high next year.