With Democrats poised to take control of Congress, the prospects for President-elect Joe Biden to pursue more aggressive policies to tackle climate change and other major environmental problems have expanded overnight.

Even the thinnest Democratic majorities will enable Biden to press for much more generous federal support for renewable energy, environmentally friendly infrastructure, expanded tax breaks for electric vehicles and stricter energy-efficiency standards.

Democratic control of Congress will make it easier for Biden to reverse some of President Trump’s rollbacks of environmental protections and to win confirmation for political appointees across the U.S. government who can shift policy toward a greener future.

But with razor-thin margins in both chambers of Congress, the incoming administration will still have to navigate the demands of climate activists who expect Biden to live up to his bold environmental promises and the reality of a Senate split 50-50, with ties broken by a Democratic vice president.

“The change in Senate leadership and committee leadership will place climate change and clean energy legislation and oversight much higher on the agenda,” Scott Segal, a lobbyist at the law firm Bracewell, which represents an array of energy-related companies. But he added, “Given the narrow margin of leadership in both the House and Senate, there still isn’t much in the way of open-field running for comprehensive climate change legislation.”

The pressure Biden is likely to face — even within his own party — to move quickly and forcefully was already on display earlier this week.

On Tuesday night, before either of the two Georgia Senate races had been called for Democrats, the Sunrise Movement’s New York chapter threatened to target Sen. Charles E. Schumer (D-N.Y.) — now poised to become majority leader — if he didn’t pass clean energy legislation right away.

“Hey heyy @SenSchumer, 15 days until you get to pass legislation for 100% renewable electricity by 2035! Either that or we picket your building allll the time,” read a tweet by the group, which represents young climate activists.

Jamal Raad, co-founder of the liberal climate group Evergreen Action, agreed that activists will be pushing the Biden administration and Democratic lawmakers to follow through on their campaign promises.

“We’ll give them some time, but we do expect them to pursue an aggressive climate agenda,” Raad said in an interview Wednesday. “A lot of people voted for this, and we have a moral responsibility to meet what the science demands on this issue.”

But overall, he added, the fact that the Senate is now blue is “a good problem to have.” Biden will have a better shot at getting the $2 trillion in climate-focused investments he proposed during the campaign, as well as more quickly staffing key positions at the Environmental Protection Agency, Interior Department, Treasury and other posts, Raad said.

“Those folks can more quickly get to the job of pursuing the all-of-government approach to climate that Biden has laid out,” he said. “We have window here to act. This could be a historic presidency in that respect.”

Business groups, however, plan to rely on conservative Democrats and Republicans’ use of the legislative maneuver known as the filibuster to block climate legislation they oppose. The filibuster requires 60 votes to cut off debate and pass a bill. There is some debate among Democrats about whether to end the filibuster, which would mean legislation could pass by a simple majority. But Sen. Joe Manchin III (D-W.Va.), a key swing vote, recently said in a television interview that he wants to maintain the filibuster.

With 50 Democratic votes in the Senate, the Biden administration could use a procedure known as reconciliation to squeeze through climate measures that are connected to the tax code or mandatory spending, though Biden isn’t likely to seek tax increases for some time given the ailing economy.

Mike Sommers, president of the American Petroleum Institute, said he was “confident we’ll be able to continue to work on both sides of the aisle.” The oil and gas industry is most concerned about any effort by a Biden administration to halt drilling leases on federal lands and waters, as well as other issues such as tax credits for electric vehicles, he said.

Even as they are likely to focus immediately on a coronavirus relief package, Democrats could soon seek to pass Biden’s massive “Build Back Better” plan aimed at eliminating carbon pollution from the electric sector by 2035, boosting renewables and creating incentives for more energy-efficient cars, homes and commercial buildings.

Gene Karpinski, president of the League of Conservation Voters, said in an interview that he expected Democrats will go further than the Obama administration on climate and the environment.

“The beauty of the Build Back Better plan,” he said, is that Biden has advocated for 40 percent of the funding to go to disadvantaged communities and areas likely to lose jobs in a clean energy transition, such as West Virginia and states in the Rust Belt.

“There’s no reason for the Biden administration to scale back an ambitious plan. It makes sense, and it’s wildly popular,” he said.

The stock market got a bounce Wednesday from the Georgia election results and optimism about further climate policies. Shares of First Solar, a solar panel manufacturer, and of Vestas Wind Systems, a Danish wind turbine manufacturer, each jumped more than 8 percent on news of the Democratic victories.

One major legislative priority for Schumer will be tackling the country’s biggest source of carbon emissions — transportation. On Wednesday, the EPA reported that for the first time in five years, the overall fuel efficiency of the U.S. auto fleet fell and pollution increased. Under President Barack Obama, U.S. automakers had pledged to increase their average gas mileage by 5 percent each year.

For years, Schumer has pushed for passage of a massive tax credit for the purchase of electric cars to discourage motorists from using gasoline-powered cars by 2040. Biden included Schumer’s proposal for a juiced-up electric vehicle rebate in his sweeping climate plan.

Rich Powell, who heads the conservative-leaning energy group ClearPath, said broad bipartisan support exists for energy innovations such as better batteries or techniques for capturing carbon dioxide from the air. “We need to build stuff faster, cheaper and cleaner,” he said.

It remains unclear whether Democrats will aggressively use another tool at their disposal — the Congressional Review Act, which allows lawmakers to nullify a rule within 60 legislative days of its adoption. Republicans used this to wipe out several environmental safeguards adopted at the end of the Obama administration. But the law then blocks Congress from adopting a regulation that is “substantially the same” in the future.

Despite the legislative hurdles, there is little question the new administration will now have willing allies in positions of power on Capitol Hill.

“I see climate change for the existential threat it poses to my state, our nation and the world,” Sen. Thomas R. Carper (D-Del.), who is poised to take over the Environment and Public Works Committee, said in a statement. “The climate crisis is a challenge too big and too great to be met with small thinking and short-term solutions.”

Meanwhile, Carper said there has already been one change resulting from the runoff. “I woke up in bed this morning, the first words my wife said to me [were] ‘Good morning, Mr. Chairman.’ ”

Dino Grandoni contributed to this report.