In Bush family lore, Jeb was always supposed to be the smarter, more level-headed one.

As with many media constructs, of course, that’s just not true. When it comes to climate change, Jeb Bush is a lot more radical than his brother.

Jeb doesn’t just want to keep burning fossil fuels while the planet burns. He’s an out-and-out flat-earther – just like the other Republicans seen as leading contenders in the 2016 presidential race – and he’s been on the record denying climate science for years.

“I think global warming may be real,” Jeb Bush said in 2011, in what seemed like a promising start to the subject in a Fox interview. But he followed it up with the false statement that there is some kind of dispute among scientists about the causes of climate change – which there is not:

It is not unanimous among scientists that it is disproportionately manmade. What I get a little tired of on the left is this idea that somehow science has decided all this so you can’t have a view.

Those comments put Jeb Bush in lock-step with the other climate deniers in the Republican party – and now that he has become the party’s first (almost) declared candidate, they should help set early battle lines for climate change as a major campaign issue.

Democrats say they are convinced climate change can be a winning issue – or at least a convenient form of political shorthand for defining even the least conservative GOP candidates as extreme, anti-science or just plain old.

Now we’ll get a first look at how the other other Bush chooses to define himself. But there are clear signs Jeb Bush feels most comfortable in the dubious territory between denial and doubt.

In 2009, Jeb was even an early adopter of the “I am not a scientist” line – which gained traction among some Republicans this year as a way of ducking the denier label. It’s hard to see how those extreme views on climate will go down with corporations – and potential donors – that have been distancing themselves from outright denier positions, such as those promoted by the American Legislative Exchange Council.

Among Republican primary voters, however, climate denial still holds sway.

Reports do surface now and then of an underground cell among Republicans who do accept the science of climate change. But Jeb Bush, for now, clearly wants no part of that.

Brother George – or 43, as he is apparently known at family get-togthers – never went as far as outright climate denial, but he was certainly no friend of the environmental movement. As president, 43 had a Texas oil man’s approach to global warming. He pulled the US out of the Kyoto protocol, let oil companies dictate energy policy, and installed other oil men in environmental posts who censored government scientists’ warnings about climate change.

But George W Bush did make a half-hearted pitch for renewable energy – dropping a mention of switch grass into his 2006 State of the Union address – and he declared what was then the world’s largest marine reserve on his way out of the White House. And on climate change (as opposed to stem cell research and the morning after pill), 43 did not go out of his way to try to undermine science.

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That was certainly a kinder, gentler time for Republicans. Back in the day, even John McCain, Barack Obama’s opponent in the 2008 presidential race, supported curbs on greenhouse gas emissions.

But over the last five years, climate change has turned into a big floating iceberg of an issue for presidential politics – a defining line between Republicans and Democrats. The Democrats’ initial response to that was to duck and run. Obama barely mentioned climate change in his first term or in his 2012 re-election campaign.

Then the green billionaire mega-donor Tom Steyer began backing climate-friendly candidates, though he didn’t have a lot to show after spending $74m on pro-climate candidates in the midterm elections.

But 2016 promises to be different. By the time the primary campaigns heat up, Obama will be winding down his presidency – the greatest legacy of which may be his decision to defy Congress and use government agencies to regulate the greenhouse gas emissions that cause climate change.

Republicans, under the incoming majority leader Mitch McConnell, will have spent nearly two years trying to block those efforts. International negotiators from more than 190 countries will have gathered in Paris to try to put together a global climate deal. And Jeb Bush will be just another stumbling, mumbling Republican candidate for president who is not a scientist, doesn’t want to listen to scientists, and may spend as much time undoing years of progress on the environment as the GOP will have spent trying to undo Obama’s healthcare law.

At a League of Conservation Voters dinner in New York earlier this month, Hillary Clinton said she would defend climate rules. “The unprecedented action that President Obama has taken must be defended at all costs,” she said.

Now with Jeb Bush’s declaration, we know where the likely Republican frontrunner stands, too: on the wrong side. He’s on the wrong side of those climate rules, and on the wrong side of reality. If things go according to the Democratic plan, that could put him on the wrong side of history, too.