Colorado lawmakers are on the brink of introducing legislation that would set the state on course to cut planet-warming greenhouse gas emissions drastically over the next 30 years.

For weeks, there has been chatter in the Capitol about the legislation. But differences between Gov. Jared Polis and House Speaker KC Becker over how to hold greenhouse gas emitters accountable have slowed progress.

The legislation, expected to be introduced as soon as this week, would put Colorado on track to meet greenhouse gas reductions goals similar to those set out in the 2015 Paris climate agreement, lawmakers say, slashing emissions from an array of sources, such as transportation, electricity generation and oil and gas drilling.

Becker, who calls the legislation her “No. 1 priority” this session, said she wants to direct the Air Quality Control Commission to adopt new rules mandating that the state meet the emission-reduction targets. It’s unclear whether the mandates will be in the legislation when it’s introduced.

How strictly to hold everyone accountable has been a key point of contention between Polis and Becker, who nonetheless share the same broader climate-action goal. An environmental attorney by trade, Becker wants enforceable mandates. Polis, whose libertarian streak is well documented, pushed for an approach that prods rather than demands.

“The governor’s office, he’s generally saying, ‘Oh, let’s just see if this happens on its own,’” Becker told The Colorado Independent during an interview Tuesday. She added, “Typically none of this happens voluntarily.”

Sources with knowledge of the legislation’s drafting characterized the negotiations as tense at times. The two have met several times to hash out details and reached an agreement “in principle” in recent days, though the finishing touches are still being written ahead of the legislation’s introduction.

Becker said the legislation is about addressing climate change. While Colorado’s emissions are a mere blip on the map of global greenhouse gas emissions, supporters of state action say it can set a model for other states. “Climate change is real. It’s happening. And we have a moral and economic imperative to act now,” Becker wrote in an op-ed for The Daily Camera earlier this month.

A key part of the legislation calls for reducing greenhouse gas emissions 90 percent, as compared to 2005 levels, by the year 2050. In 2017, former Gov. John Hickenlooper signed an executive order that set the goal of slashing emissions 26 percent, as compared to 2005 levels, by 2025.

This new goal is still short of what scientists say is needed to avoid irreversible climate change, which in Colorado is expected to result in more intense heat waves, droughts and wildfires.

According to the United Nations’ Intergovernmental Panel on Climate Change (IPCC), the only way to ensure global temperatures don’t rise above 1.5 degrees Celsius (3.6 degrees Fahrenheit) — the point at which climate change becomes irreversible — is to have net zero emissions by 2050.

Achieving zero emissions by mid-century would be drastic, but not impossible, scientists say. It would mean more renewable energy production from wind and solar as well as efforts to capture carbon dioxide from the atmosphere with new technology or land-use measures, such as reforestation.

“At the end of the day these emissions have got to get to zero,” said Brad Udall, a water and climate researcher at Colorado State University (also a former Colorado Independent board member).

Udall said such a transformation will require the fossil fuel industry, which includes oil and gas, to find a new business model or go out of business.

“The hardest part of this whole problem is the social upheaval and change revolving around finding a new way for our fossil fuel industry to move forward,” he said. “Because they can’t operate as they do now. What do you do about Craig, Colorado? What do you do about oil and gas workers?”

On the campaign trail, Polis promised that, if elected, he would put forward a plan to ensure all electricity is generated with renewables by 2040. He is also supporting a bill — SB 181 — that seeks to create more stringent oil and gas regulations across the state.

But, according to sources familiar with the negotiations over the emissions reduction legislation, Polis’s general opposition to mandates has delayed the measure. (Notably, however, in mid-January, when he signed his first executive order as governor to promote electric vehicles, he called for the state to follow the example of a mandate first adopted in California.)

The governor’s office declined several requests for an interview on the proposal. A spokeswoman provided the following statement: “Governor Polis is committed to tackling climate change and increasing renewable energy across Colorado. We will carefully review any legislation that comes forward.”

Though the governor has resisted mandates in this case, Becker said she’s found some industry representatives actually comfortable with them. They’d prefer to know what to expect, she said, and not move forward with lingering uncertainty as to what the state will, or may, require of them.

“Having that kind of certainty does drive those markets,” said Whitney Painter, owner of Buglet Solar Electric Installation in Golden, a business she launched in 2006, two years after Amendment 37 passed. That measure said 3 percent of retail electricity sales had to come from renewable sources by 2007, increasing to 10 percent by 2015.

The environmental advocacy group 350.org calls on Polis in a recent video to take a stronger position on climate change policy, including greenhouse gas reductions.

“We’re really looking to him to lead,” said Micah Parkin, executive director and cofounder of 350.org Colorado, “and for Colorado to be a national leader on this issue.”