Exxon is lobbying for a carbon tax. There is, obviously, a catch.

ExxonMobil, the largest investor-owned oil company in the world, announced last week that it will spend $1 million over two years to lobby for a US carbon tax.

The announcement came just after the Intergovernmental Panel on Climate Change reported that the world may have as little as 12 years to act to limit global warming to 1.5 degrees Celsius, and Exxon’s news got somewhat buried.

But it’s a significant move from a company with a decades-long history of studying climate change, misleading the public about it, and funding organizations that deny climate change even exists.

Exxon has actually endorsed a carbon tax before, but now the company is putting some money behind the policy: a $1 million donation to Americans for Carbon Dividends, a Republican-led lobbying effort for a carbon tax. (Exxon did not respond to a request for comment.)

There’s some debate about whether this is a cynical delay tactic, a show of genuine concern for the environment, or an act of rational self-interest in a changing energy landscape. (Or as the Onion put it, “ExxonMobil CEO Depressed After Realizing Earth Could End Before They Finish Extracting All The Oil.”)

But what’s gone largely unnoticed is that Exxon’s proposal comes with a massive catch: In exchange for a tax, the company wants immunity from all climate lawsuits in the future.

Cities across the United States are currently suing oil companies to make them pay for damages wrought by climate change, which could put companies like Exxon on the hook for billions of dollars in payouts.

The proposal Exxon wants to enact is one that would shield the company from lawsuits while also preventing further climate change regulations. All in all, it would grant oil companies the kind of immunity from litigation the gun industry currently enjoys.

Let’s take a closer look.

Policy wonks and the IPCC are generally in agreement that pricing greenhouse gas emissions is a critical measure in fighting climate change. The idea behind a carbon tax is to make companies pay for greenhouse gas emissions that they ordinarily pump into the atmosphere for free. That would then raise the price of more polluting sources and make cleaner alternatives more viable.

Exxon’s proposal is the model outlined by the Climate Leadership Council, led by former Republican Secretaries of State James A. Baker III and George P. Shultz. The price would start at $40 per ton of carbon dioxide emissions and then rise. The money would then be sent back to citizens in the form of rebates, starting at $2,000 per year for a family of four.

A tax like this is one way a company like Exxon, valued at $340 billion, copes with a world likely to face more greenhouse gas emissions restrictions. Rather than fighting climate change legislation, the company is working to establish a climate policy on its own terms.

“It prevents other things that they think would be worse for their business model,” said Joseph Majkut, director of climate policy at the Niskanen Center. Things like the United Kingdom’s proposed ban on internal combustion engines, most of which run on oil products, for example. A carbon tax would favor building cleaner and more efficient cars rather than getting rid of them altogether.

A carbon tax could also work in favor of Exxon because the heaviest burdens of a tax would fall on the dirtiest fuels, namely coal. A price on carbon would force coal-fired generation off the market and leave a vacuum for alternatives, even higher-priced oil and gas.

Exxon itself has observed that cleaner fuels like natural gas and renewables are the largest growth sectors in energy.

So it makes sense that a powerful oil company wants to get ahead of any energy transitions.

“Any company or organization that is serious about advocating for a carbon price is a good thing,” said Ben Pendergrass, senior director of government affairs for Citizens’ Climate Lobby, another group lobbying for a carbon price, in an email. “Having heavy hitters like Exxon at the plate, pushing for similar solutions, just adds more momentum in the right direction.”

Oil companies have been trying to rebrand themselves as “energy” companies for decades, dating back to the oil embargo in the 1970s. Many invested in renewables and hydrogen fuels before. BP once branded itself “Beyond Petroleum” and was at one point one of the largest solar panel manufacturers in the world.

At the same time, fossil fuel companies have campaigned for decades against environmental regulations of any sort, particularly those around climate. That’s why some observers are cynical about Exxon’s sincerity in curbing greenhouse gas emissions.

The $40 per ton price on carbon might not move the needle much on fighting climate change or dealing with its consequences. “You really need a much stronger response to meet global goals,” said Paul Griffin, a distinguished professor of management at the University of California Davis, who studies greenhouse gas accounting.

Researchers calculated last month that the environmental damages of greenhouse gas emissions for the United States, the country’s social cost of carbon, is about $48 per ton. The global median social cost of carbon is $417 per ton. A meaningful carbon tax has to be high enough to compensate for this harm as well as drive further reductions in greenhouse gases if the goal is to actually curb warming.

Griffin also noted that publicly disclosing greenhouse gas emissions and the risks of climate change to business operations is another critical step companies can take to aid policies around global warming. However, Exxon has long fought climate disclosure efforts, even from their own shareholders.

And as Vox’s David Roberts noted, the Climate Leadership Council’s carbon tax proposal comes with several strings attached, namely that the tax would generate no new revenue for the government, allow no new spending, and would rollback other climate regulations like the Clean Power Plan.

But perhaps the biggest tradeoff Exxon wants in exchange for supporting a carbon tax is immunity from climate change lawsuits.

“Robust carbon taxes would also make possible an end to federal and state tort liability for emitters,” according to the Climate Leadership Council’s carbon dividend proposal.

Currently, Exxon is named as a defendant in suits from 10 cities and counties seeking damages from oil companies for rising sea levels and changes to the climate stemming from burning fossil fuels.

Getting the Climate Leadership Council’s carbon tax legislation through Congress would close the door to expensive payouts from Exxon. For comparison, the four largest US tobacco companies are paying a $206 billion settlement stemming from lawsuits over illnesses from smoking.

So granting Exxon immunity to climate change lawsuits is a huge, huge concession.

“It’s incredibly naïve to think that Exxon for $500,000 a year has suddenly gotten religion on climate change,” said Richard Wiles, executive director of the Center for Climate Integrity. “Climate liability lawsuits present a major threat to their bottom line.”

Congress and the courts have historically been reluctant to grant this kind of blanket immunity, though gun manufacturers do have some legal protections against lawsuits that few other industries receive. The Supreme Court this week declined to block a $400 million judgment against lead paint manufacturers despite efforts from the industry to limit their liability.

However, a federal judge has dismissed lawsuits filed by San Francisco and Oakland against Exxon and other oil companies for causing climate change. The cities are currently appealing the ruling, but more cities are filing their own suits on grounds that the greenhouse gas emissions lead to climate change which poses a public nuisance. In July, the state of Rhode Island filed a climate lawsuit against oil companies.

There’s nothing inherent in a carbon tax that requires legal immunity for polluters. The Citizens’ Climate Lobby, the other group lobbying for a carbon price, has a fee and dividend model that doesn’t absolve oil companies of liability.

The outcomes of all these climate suits is still unclear, and resolving this uncertainty is another upside for Exxon in pushing for a carbon tax.

Right now, there are some efforts underway to price carbon dioxide in Congress. Rep. Carlos Curbelo (R-FL), has proposed his own a carbon tax, which starts at $24 per ton and includes some limitations to greenhouse gas regulations.

The fate of any legislation to price carbon is tied to the outcome of the November midterm election, which could change the balance of power in Congress. But even if Democrats take over the House and Senate, a carbon pricing bill would still need the signature of President Donald Trump, who has his own thoughts about how climate change will affect the economy.