From a climate perspective, these two moves together could have a sizable impact if they’re finalized. Weaker vehicle rules could add an extra 28 million to 83 million metric tons of carbon dioxide to the atmosphere in 2030 alone, according to a Rhodium Group analysis. The proposal to relax rules for coal plants would add another 47 million to 61 million tons of CO₂ that same year, according to the E.P.A.’s own numbers.

To put that in context: At the high end, that’s the climate equivalent of putting an extra 31 million cars on the road. It’s more carbon dioxide than many midsize nations like Belgium or Greece put out in an entire year. And it comes at a time when global emissions are still rising, while scientists say they need to be falling rapidly to avoid the worst impacts of global warming.

That said, it’s not yet certain that this higher emissions scenario will come to pass, and there are a few things we’ll be watching closely in the months ahead.

First, it’s worth noting that the Trump administration’s proposals are far from finalized and, like all regulations, are certain to lead to fierce court battles. (Note that the Obama-era Clean Power Plan never actually took effect because it is still tied up in court .)

Lately, federal courts have been striking down a number of the administration’s regulatory moves. California plans to sue over the vehicle rollbacks, arguing that the proposal constrains the state’s longstanding authority to set its own car standards. And environmentalists are likely to challenge a section of the coal rule that would exempt plants from certain pollution controls if they invest in upgrades.

We’ll also be watching what’s happening in the fast-changing electricity sector, which accounts for one-third of the nation’s carbon emissions. The Trump administration’s power plant proposal could plausibly give a second life to some coal plants and slow the transition toward cleaner energy. But how this plays out will depend on a complex mix of factors, like state-level policies, energy prices and the growth of wind and solar power. (Much will also depend on whether the Energy Department decides to pursue a separate, highly contentious bailout of struggling coal plants.)

Which is all to say that this story is still in flux and even the most careful predictions about what different policies mean for global warming could change over time. Stay tuned.