The godfather of climate denial has warned that a United Nations deal on global warming would spell “economic suicide” for America and a disaster to the world, according to a leaked fundraising letter.

In the rambling 13-page letter, Fred Singer, a retired rocket scientist who rejects the science underlining climate change, appeals for at least $425,000 (£270,212) to stop what he called the “radical, economy-wrecking and sovereignty-destroying UN climate pact”.

The letter, penned on behalf of the Committee for a Constructive Tomorrow (Cfact), an ultra-conservative group that denies the existence of climate change, suggests growing desperation about the prospects of a climate change deal emerging from the Paris meeting. Cfact did not dispute authenticity of the document.

A leaked copy of the letter which was sent to Cfact supporters was obtained by the Guardian.

Cfact letter on Paris climate summit

“This is a very dangerous treaty and it is something that we think should not be supported by the international community,” said Craig Rucker, the executive director of Cfact. “We wan’t to make sure it doesn’t happen.”

He went on: “It would be something that we would be very concerned about. Yes, it would not be a thing that we would relish.”

Other Cfact personalities, including Marc Morano, the group’s communications chief, have warned that climate deniers are on the verge of defeat in 2015.

Those anxieties about the prospect of a global warming deal in Paris have increased with the intervention of the Pope, who made a strong appeal to phase out fossil fuels to help the poor earlier this month. Rucker, in a blog post, called the pastoral letter “Rome’s greatest scientific blunder since Galileo”.

The 8 June fundraising appeal, describes 2015 as a “make or break year” for climate, and asked for $425,000 to send a delegation of “climate truth tellers” to monitor the talks in Paris.

It sought unspecified additional funds to finance a spoiler film by Morano.

Cfact has no formal relationship with Singer, according to Rucker. But he said Singer had written such fundraising appeals for the small Washington group in the past, and that they had tended to be lengthy letters.

Within the small fringe of climate denial, Singer, who is 90, enjoys special cachet for possessing genuine scientific credentials as a trained atmospheric scientist.

The Vienna-born Singer, who was forced to flee the Nazis in 1938, has long-argued that environmental regulation is a pretext for global domination. The letter re-hashes many of those arguments, saying: “President Obama is pandering to zealots on the Far Left fringe posing as environmentalists.”

Elsewhere he accuses Obama of embarking on an “anti-energy regulatory jihad”.

Cfact climate letter.

He refused to comment on the letter, saying in an email that he was in the middle of a move.

Cfact is little-known outside the fringe of climate denial. In 2012, the organisation was buoyed by an in infusion of $3.7m from a secretive funding network for corporations and ultra-conservative billionaires.

But that revenue stream – Cfact’s biggest source of cash – abruptly dried up the next year, when the thinktank got just $325,000 in dark money.

In a further blow to the world of climate denial, the Smithsonian said on Friday it was strengthening its policies on funding and conflict of interest following revelations that the researcher Willie Soon had refused to disclose grants from fossil fuel companies in published papers.

A spokesman said Soon would have to abide by the new policies. He remains the subject of a separate investigation.