A just-published Brookings Institution analysis of U.S. cities' pledges to cut carbon emissions reveals very mixed results.

Why it matters: The potential — and limits — of city and state initiatives have gotten more attention amid President Trump's scuttling of Obama-era national policies.

The big picture: It finds "laudable aspirations, notable GHG reductions in some cases, and less auspicious outcomes in most other cities."

The state of play: The authors undertook the difficult task of comparing cities' emissions-cutting vows and progress toward meeting them.

• Plans have varying baseline years, targets and so forth, and the analysis also has to grapple with what might happen in the absence of the plans.
• There's also a time-lag in getting information, but that map above is close to the current state of play, Brookings analyst Mark Muro said.

Where it stands: Among the 100 most populous U.S. cities, only 45 have both emissions-cutting targets and a detailed emissions tally — or "inventory" — to gauge them against.

• Seventeen of those 45 have rolled out new or upgraded plans since Trump took office.
• These cities' pledges often align with the goal of cutting emissions by 80% by 2050.
• That's aggressive but falls short of what's needed globally to hold warming to 1.5°C above preindustrial levels, the study notes.
• Another 22 of these 100 cities have vowed emissions cuts but lack specific targets or completed inventories.

By the numbers: If the 45 cities with plans and baseline data successfully follow through, it would cut emissions by an estimated 365 million metric tons of CO2-equivalent annually by 2050.

• That's the equivalent of taking 79 million passenger vehicles off the roads, the report states.
• Viewed another way, that "translates to roughly 6% of total U.S. GHG emissions in 2017," it finds.
• That's "not insignificant," but also far from the net-zero by 2050 levels consistent with the very ambitious 1.5°C goal.

Threat level: Lots of cities are falling behind on their pledges.

• Of 32 cities that conducted new inventories since 2010, 26 have cut emissions compared to baseline levels, led by L.A.'s 47% cut below 1990 levels. Six have seen increases, led by Tucson, Arizona's growth.
• "Overall, about two-thirds of cities are currently lagging their targeted emission levels." On average, cities analyzed would need to cut emissions by 64% by 2050 to meet their goals.

What's next: The report offers ways to bolster and expand city initiatives.Two examples: More philanthropic help for small and midsized cities; and more big-city efforts to decarbonize power generated outside their borders by working with surrounding communities, regional governments and other stakeholders.