The UK’s most influential conservative thinktank has published at least four books, as well as multiple articles and papers, over two decades suggesting manmade climate change may be uncertain or exaggerated.

The Institute of Economic Affairs (IEA) has issued publications arguing climate change is either not significantly driven by human activity or will be positive. The group is one of the most politically influential thinktanks in the UK, and boasts that 14 members of Boris Johnson’s cabinet, including the home secretary, foreign secretary and chancellor, have been associated with the group’s past and current initiatives.

Despite a longstanding international consensus among climatologists that human activity is accelerating climate change, the IEA’s publications throughout the 1990s and 2000s heavily suggested climate science was unreliable or exaggerated. In recent years the group has focused more on free-market solutions to reducing carbon emissions.

The IEA said it did not take a corporate position on any policy matter. It said the majority of the publications identified by the Guardian predated most of its current staff.

Q&A What is the polluters project? Show Hide The Guardian has collaborated with leading scientists and NGOs to expose, with exclusive data, investigations and analysis, the fossil fuel companies that are perpetuating the climate crisis – some of which have accelerated their extraction of coal, oil and gas even as the devastating impact on the planet and humanity was becoming clear.

The investigation has involved more than 20 Guardian journalists working across the world for the past six months. The project focuses on what the companies have extracted from the ground, and the subsequent emissions they are responsible for, since 1965. The analysis, undertaken by Richard Heede at the Climate Accountability Institute, calculates how much carbon is emitted throughout the supply chain, from extraction to use by consumers. Heede said: "The fact that consumers combust the fuels to carbon dioxide, water, heat and pollutants does not absolve the fossil fuel companies from responsibility for knowingly perpetuating the carbon era and accelerating the climate crisis toward the existential threat it has now become." One aim of the project is to move the focus of debate from individual responsibilities to power structures – so our reporters also examined the financial and lobbying structures that let fossil fuel firms keep growing, and discovered which elected politicians were voting for change. Another aim of the project is to press governments and corporations to close the gap between ambitious long-term promises and lacklustre short-term action. The UN says the coming decade is crucial if the world is to avoid the most catastrophic consequences of global heating. Reining in our dependence on fossil fuels and dramatically accelerating the transition to renewable energy has never been more urgent.

Its first book on climate science was published in 1994. Referring to a “so-called scientific ‘consensus’” on global heating, its foreword suggested the public had been “taken in” by media coverage of climate change and that investing resources in studying the subject was wasteful.

“An alternative course of action would be to expose the shoddiness of the apocalyptic predictions,” the foreword continued. “Unfortunately, governments cannot be expected to undertake this task. Hence it is left to private individuals and institutions to try to breach the barriers to the dissemination of good news … this IEA study is one such attempt.”

The book was also the first of several IEA publications to suggest that increased atmospheric CO2 would be beneficial, because it would result in “increased crop yields and reduced water requirements of plants”.

Three years later the group published a book of essays called Climate Change: Challenging the Conventional Wisdom that described climate scientists as having established a “false consensus”.

“Estimates by some of the world’s most respected climate scientists suggest that even if a warming of 2 degrees centigrade does occur the impact on humankind will not be catastrophic,” the group said. “Indeed agricultural productivity is likely to increase in many parts of the world, due to longer growing seasons and increases in uptake of CO 2 .”

The scientific consensus suggests the likely impacts of global heating will in fact be overwhelmingly detrimental to agriculture, largely because of the increased frequency of extreme weather events.

The group has also hosted a series of shorter papers, articles and blogs questioning climate science, including an article celebrating “20 years denouncing the eco-militants” in 2013, and blogposts recycling allegations of academic fraud against climate scientists at the University of East Anglia that were subsequently disproven.

Announcing its 2007 paper Global Warming False Alarms, the group said “the high salience of the climate change issue reflects the fact that many special interests have much to gain from policies designed to reduce emissions through increased government intervention and world energy planning”.

In recent years, however, the group’s publications have increasingly focused on free-market solutions to decarbonisation rather than disputing climate science. It told the Guardian it had recently published a paper discussing the pros and cons of a carbon tax.

As a registered educational charity, the IEA is entitled to various tax breaks. However the group has previously faced controversy over the political nature of its work, which principally involves campaigning for free-market policies.

Last year the Charity Commission issued the group with a formal warning over its failure to be balanced and neutral in a report on Brexit. The warning was later withdrawn and the report has since been edited and republished.

It has also been criticised for its policy of refusing to identify its donors, which it says would breach their privacy and expose them to harassment. However it is known to have previously received funding from the oil corporations BP and ExxonMobil.

After revealing to an undercover reporter from Unearthed that the group had regularly received money from BP, the IEA volunteered that it had accepted donations from the company every year since 1967.

Historical accounts state it also received £21,000 from ExxonMobil of the US to fund a grant for a researcher in 2005.

A spokesperson for the IEA said: “The Institute of Economic Affairs does not hold any corporate positions on policy. All views belong to the authors who publish with us, or speakers who take part in our events.

“The majority of the Guardian’s list of IEA publications on climate change predate almost all staff who currently work at the organisation, and has failed to include our most recent output on the topic, including a paper which discusses the merits of a carbon tax, and a panel discussion on achieving net-zero carbon emissions by 2050.”

The IEA declined to comment on what proportion of its funding was drawn from entities with an interest in fossil fuels, but said donors and their interests had no influence over its publications.

“The institute’s editorial and policy output – in both our reports and our educational material – is decided by its research team and academic advisory council only. Any funding we receive does not, under any circumstances, influence the focus or conclusions of our research,” it said.

The IEA complained the Guardian had been unfairly selective in its examination of its climate publications. However, when invited to identify any other publications presenting an alternative position, it referred to its original statement.