While many of them acknowledge that climate change is real, they largely downplay the issue and reject policies that would slow rising temperatures.As wildfires in Canada have sent masses of smoke over the United States this week, engulfing much of the Northeast in a yellow haze of hazardous air pollution, scientists are clear that we are seeing the effects of climate change. But the Republicans campaigning for the presidency have largely downplayed the issue and rejected policies that would slow rising temperatures.On Wednesday, even as the country experienced one of its worst days on record for air quality, with New York City especially hard-hit, former Vice President Mike Pence said in a town-hall event on CNN that “radical environmentalists” were exaggerating the threat of climate change.His response reflected what has become a pattern among Republican officials. Many of the candidates acknowledge that climate change is real, in contrast to party members’ years of outright denial. But they have not acknowledged how serious it is, and have almost universally rejected the scientific consensus that the United States, like all countries, must transition rapidly to renewable energy in order to limit the most catastrophic impacts.Here is a look at where some of the major Republican candidates stand.Donald J. TrumpAs president, Donald J. Trump mocked climate science and championed the production of the fossil fuels chiefly responsible for warming the planet.He rolled back more than 100 environmental regulations, mostly aimed at reducing planet-warming emissions and protecting clean air and water; appointed cabinet members who were openly dismissive of the threat of climate change, including Scott Pruitt as head of the Environmental Protection Agency; and withdrew the United States from the Paris Agreement, under which almost every country had committed to try to limit warming to 2 degrees Celsius above preindustrial levels.President Biden rejoined the Paris Agreement and undid many of Mr. Trump’s policies, but the damage may not be fully reversible. A report last year from researchers at Yale and Columbia found that the United States’ environmental performance had plummeted in relation to other countries as a result of the Trump administration’s actions.Mr. Trump has given no indication that his approach would be different in a second term. He has repeatedly minimized the severity of climate change, including claiming falsely that sea levels are projected to rise only ⅛ of an inch over 200 to 300 years. But according to the National Oceanic and Atmospheric Administration, sea levels are rising by that amount every year.Ron DeSantisGov. Ron DeSantis leads a state, Florida, that is on the front lines of climate change: It has been hit hard by hurricanes, which are becoming more frequent and more severe as the Atlantic Ocean gets warmer.But Mr. DeSantis has dismissed concern about climate change as a pretext for “left-wing stuff” and said on Fox News last month, “I’ve always rejected the politicization of the weather.”He has, however, taken significant steps to fortify the state against stronger storms and rising waters. Among other things, he appointed the state’s first “chief resilience officer” and backed the Resilient Florida Program, which has sent hundreds of millions of dollars to vulnerable communities to fund projects like building sea walls and improving drainage systems.Scientists support these sorts of adaptation efforts, because the climate has already changed enough that even aggressive emission reductions will not avert all the effects. But they are also clear that such measures are not enough on their own.Nikki HaleyNikki Haley, a former governor of South Carolina, has acknowledged that climate change is real and caused by humans, but she has generally rejected governmental efforts to reduce emissions. Her advocacy group Stand for America said that “liberal ideas would cost trillions and destroy our economy.”As ambassador to the United Nations during the Trump administration, Ms. Haley was closely involved in withdrawing the United States from the Paris Agreement. At the time, she said, “Just because we pulled out of the Paris accord doesn’t mean we don’t believe in climate protection.” Over the next three years, the Trump administration systematically reversed climate protections.But Ms. Haley has supported greater use of carbon capture technology to remove carbon from the air. She and some other Republicans — including another presidential candidate, Gov. Doug Burgum of North Dakota — have presented this as a way to limit climate change while continuing to use fossil fuels. Many experts agree that carbon capture could be a powerful tool, but it is unlikely to be sufficient on its own, in part because of its high cost.Mike PenceMr. Pence has acknowledged that climate change is real. He said during the 2016 campaign, “There’s no question that the activities that take place in this country and in countries around the world have some impact on the environment and some impact on climate.”But that assertion falls short of the scientific consensus that human activity is the primary driver of climate change. He has also downplayed the severity, like in his comments this week that “radical environmentalists” were exaggerating climate change’s effects. And as vice president, Mr. Pence had a hand in Mr. Trump’s defiantly anti-climate agenda, including defending the decision to withdraw from the Paris accord by saying Mr. Trump had stood up for “America first.”Mr. Pence’s political organization, Advancing American Freedom, has denounced “the left’s climate radicalism” and called for a rejection of “climate mandates.” It has also called for expediting oil and gas leases and taking other steps to “unleash the full potential” of fossil fuel production in the United States.Tim ScottSenator Tim Scott of South Carolina has also acknowledged that climate change is occurring, once telling The Post and Courier, his home-state newspaper: “There is no doubt that man is having an impact on our environment. There is no doubt about that. I am not living under a rock.”At the same time, he has opposed most policies that would curb carbon dioxide emissions. During the Obama administration, Mr. Scott challenged a regulation that would have required utilities to move away from coal and adopt wind, solar and other renewable power. During the Trump administration, he argued for dumping the Paris Agreement. And last year, he voted against President Biden’s expansive climate and health legislation that will invest about $370 billion in spending and tax credits over 10 years into clean energy technologiesChris ChristieChris Christie acknowledged the reality of climate change before many of his fellow Republicans did. “When you have over 90 percent of the world’s scientists who have studied this stating that climate change is occurring and that humans play a contributing role, it’s time to defer to the experts,” he said in 2011.As governor of New Jersey, he announced a moratorium on new coal-plant permits, filed a successful petition with the E.P.A. to demand reduced pollution from a coal plant along the Pennsylvania border and signed offshore wind power legislation. But state regulators in his administration didn’t approve any wind projects — and at the same time, Mr. Christie withdrew New Jersey from the Regional Greenhouse Gas Initiative, a multistate cap-and-trade partnership, and vetoed state legislators’ efforts to rejoin it.He also said in 2015 that climate change, while real, was “not a crisis.” Last year, he called for increases to domestic oil production.Asa HutchinsonAsa Hutchinson, the former governor of Arkansas, has not spoken much about climate change. But when he has, he has generally stuck to the Republican Party line, rejecting government efforts to reduce emissions.He criticized President Barack Obama’s power plant regulations and, in 2019, praised the Trump administration for its environmental deregulation. Shortly after Mr. Biden was elected president in 2020, Mr. Hutchinson joined several other Republican governors in pledging to sue if the federal government mandated emission reductions.“Our power companies have voluntarily embraced sources of alternative energy without heavy-handed regulation from government,” he said at the time.Vivek RamaswamyVivek Ramaswamy began his presidential campaign by claiming that “faith, patriotism and hard work” had been replaced by “secular religions like Covidism, climatism and gender ideology.” In an interview with The New York Times, he defined “climatism” as “prioritizing the goal of containing climate change at all costs.”He is also an outspoken opponent of environmental, social and governance investing, or E.S.G., in which financial companies consider the long-term societal effects — including climate-related effects — of their investment decisions.Mr. Ramaswamy supports using more nuclear power and has painted a conspiracy theory for why many environmentalists oppose it. “The problem with nuclear energy is it’s too good,” he claimed on Twitter this April. “And if you solve the ‘clean energy problem’ activists lose their favorite Trojan Horse for advancing ‘global equity’ by penalizing the West.”But many environmental activists cite concerns about the safe storage of nuclear materials and the potential for accidents as the reason for their opposition — though they are by no means united in their stance, and many support nuclear power as a carbon-free source of energy.Doug BurgumGov. Doug Burgum of North Dakota has pushed harder to address climate change than most Republicans by actively identifying carbon neutrality as a goal: In 2021, he announced that he wanted North Dakota to reach it by 2030.He wants to do so through carbon-capture programs alone, without transitioning away from fossil fuels. (Climate scientists are skeptical that this is possible, even as they agree the technology holds promise.)Mr. Burgum, who created a tax incentive for one form of carbon capture, argued in an interview with Future Farmer magazine in 2021 that his policies showed “North Dakota can reach the end goal faster with innovation and free markets and without the heavy hand of government mandates and regulation.” More