A glacier in Antarctica in 2007. Melting ice is likely to raise sea levels and affect ocean currents, rainfall patterns and weather systems. (Rodrigo Arangua/AFP/Getty Images)

Environmentalists are not happy with the Trump administration. There are rumors that Trump may withdraw from the landmark Paris agreement on climate change. And Secretary of State Rex Tillerson, the former CEO of ExxonMobil, is probably unlikely to champion U.S. environmental priorities in his diplomatic agenda.

Trump’s Environmental Protection Agency pick, Scott Pruitt, is not a fan of environmental regulation and is unlikely to support the Clean Power Plan, Obama’s signature climate policy.

U.S. cities are leading the way on climate change policy

Here’s the good news: States, cities and many companies in the United States realize that sensible climate policy is, well, sensible. Having rational policies in place provides important health benefits, such as reducing smog, and helps authorities prepare for climate-induced changes, such as floods and droughts. For companies, planning for the future is just good business.

A number of cities around the world have been at the vanguard of climate action. The C40 Cities initiative is a network of more than 80 cities, including 13 in the United States, and represents 600 million people around the globe. Their governments are collaborating on climate efforts, and they have committed to mandatory measurement and reporting of emissions and other policy measures. C40’s nifty interactive dashboard provides data on participants’ emissions.

Eight U.S. cities also joined the ambitious Carbon Neutral Cities Alliance, where cities pledge to cut emissions by at least 80 percent by 2050.

U.S. cities are also preparing for a changed climate. In the wake of Hurricane Sandy, New York created the Office of Recovery and Resiliency and a plan to minimize impacts of similar storms. Miami just announced a $100 million plan to combat persistent flooding and sea level rise.

Cities’ vulnerability helps explain why urban residents are more likely to support policies to regulate carbon dioxide as a pollutant and require that utilities source a set percentage of energy from renewable sources.

States are generating demand for clean energy

States also have the autonomy to take action on climate change, with or without a federal mandate. California is continuing its long-standing role as a climate leader. The state’s landmark climate legislation, AB 32, aims to reduce greenhouse gas emissions to 1990 levels by 2020, and then 80 percent below 1990 levels by 2050.

AB 32 includes aggressive policies to promote renewable energy, enhance fuel efficiency and increase both the use of low-carbon fuels and the number of zero-emission vehicles. Since 2015, California has linked its cap-and-trade scheme to Quebec, creating the first international carbon market between state governments rather than federal ones.

The California legislature passed the measure, so there is no obvious federal action that could undo this market. And California and other large states may also spur broader action.

Here’s an example of the “California effect”: In the 1980s, California’s fuel-efficiency standards exceeded those set by the federal Clean Air Act. Congress eventually responded by bringing federal rules up to California standards. Because cars sold in California — a large market — had to meet more stringent standards, car manufacturers boosted the efficiency of new vehicles nationwide.

Other states, regardless of their political leanings, are also moving ahead on renewable energy. Texas and 28 others have renewable portfolio standards, which require utilities to sell a certain amount of renewable energy. Another eight have voluntary renewable energy standards.

State laws have helped drive the growth in renewables, which now account for roughly 10 percent of total U.S. energy consumption. Employment in the solar industry is soaring — and accounted for 1 in 50 new jobs in 2016.

Companies also lead by example on environmental policy

Politicians may wonder whether climate change is happening; CEOs do not. They see climate change as bad for business; droughts, floods and extreme weather events can interrupt supply chains. And regulation can raise production costs. Many firms agree that being prepared for climatic and regulatory changes can help lessen negative impacts.

Others are voluntarily “greening” themselves, and improving the bottom line as a bonus. The campaign RE100, for example, has 90 member firms, including 32 U.S. companies, that have pledged to move to 100 percent renewable energy.

In 2014, the global coalition We Mean Business launched an initiative to promote the transition to a low-carbon economy. Almost 700 companies and investors, representing $8 trillion in revenue, have committed to policies like putting a price on carbon, committing to 100 percent renewable power, removing commodity-driven deforestation from supply chains, and reporting climate change information as a fiduciary duty.

In an increasingly global economy, moreover, companies need to adapt to climate regulations and plan for carbon restrictions coming into place in other countries. Just like car manufacturers adjusted to accommodate California’s strict standards, U.S. and other multinational firms are greening their practices to meet environmental laws in other nations.

The fate of the Clean Power Plan

Although pro-climate policies are likely to continue, thanks to efforts at the state, national and corporate levels, the fate of Obama’s Clean Power Plan (CPP) is unclear. The CPP is the centerpiece of the U.S. pledge to the Paris agreement, and it aims to reduce emissions from power plants 30 percent below 2005 levels by 2030.

Trump seems keen to repeal the CPP, but regulations are not easily undone. The Supreme Court issued a stay of the CPP in 2015, but if it is upheld, then a rollback will take longer.

The Trump administration could then go back to court to allow the EPA to revisit the rule, or it could rescind the rule. As Jody Freeman of Harvard Law School spells out, rescinding the rule would require both a notice and comment period and an explanation of why such a move is necessary. Further litigation would be likely, which would slow efforts to undo the CPP.

More important, many U.S. utilities are moving forward assuming CPP or other regulations will be in place — eventually. Utilities are retiring coal plants and not planning to build new ones. Indeed, the country’s seventh-largest emitter announced that it will probably close this year, because of competition from natural gas.

Coal now supplies only about one-third of the total energy used in U.S. electricity generation, down from about 50 percent in the 1990s. With the majority of U.S. coal plants built before the 1980s, more shutdowns are probable.

The federal government is necessary, but not sufficient

In short, a Trump administration can’t entirely reverse progress on climate change. It may slow things, but the CPP won’t be repealed overnight. And many of the changes underway are simply not subject to federal authority.

The rate of climate change is alarming, and we need to move as quickly as possible to de-carbonize. States and cities continue to take action on climate change. Corporations are also leading the way and increasingly urging governments to follow. All of these moves suggest there’s reason to be hopeful that U.S. progress on climate change will continue.

Jessica F. Green (@greenprofgreen) is assistant professor of environmental studies at New York University. She is the author of “Rethinking Private Authority,” published by Princeton University Press.