Hidden behind the save-the-world rhetoric of the global climate change negotiations lies the mucky realpolitik: money and threats buy political support; spying and cyberwarfare are used to seek out leverage.

The US diplomatic cables reveal how the US seeks dirt on nations opposed to its approach to tackling global warming; how financial and other aid is used by countries to gain political backing; how distrust, broken promises and creative accounting dog negotiations; and how the US mounted a secret global diplomatic offensive to overwhelm opposition to the controversial "Copenhagen accord", the unofficial document that emerged from the ruins of the Copenhagen climate change summit in 2009.

Negotiating a climate treaty is a high-stakes game, not just because of the danger warming poses to civilization but also because re-engineering the global economy to a low-carbon model will see the flow of billions of dollars redirected.

Seeking negotiating chips, the US state department sent a secret cable on 31 July 2009 seeking human intelligence from UN diplomats across a range of issues, including climate change. The request originated with the CIA. As well as countries' negotiating positions for Copenhagen, diplomats were asked to provide evidence of UN environmental "treaty circumvention" and deals between nations.

But intelligence gathering was not just one way. On 19 June 2009, the state department sent a cable detailing a "spear phishing" attack on the office of the US climate change envoy, Todd Stern, while talks with China on emissions took place in Beijing. Five people received emails, personalized to look as though they came from the National Journal. An attached file contained malicious code that would give complete control of the recipient's computer to a hacker. While the attack was unsuccessful, the department's cyber threat analysis division noted: "It is probable intrusion attempts such as this will persist."

The Beijing talks failed to lead to a global deal at Copenhagen. But the US, the world's biggest historical polluter and long isolated as a climate pariah, had something to cling to. The Copenhagen Accord, hammered out in the dying hours but not adopted into the UN process, offered to solve many of the US's problems.

The accord turns the UN's top-down, unanimous approach upside down, with each nation choosing palatable targets for greenhouse gas cuts. It presents a far easier way to bind in China and other rapidly growing countries than the UN process. But the accord cannot guarantee the global greenhouse gas cuts needed to avoid dangerous warming. Furthermore, it threatens to circumvent the UN's negotiations on extending the Kyoto protocol, in which rich nations have binding obligations. Those objections have led many countries – particularly the poorest and most vulnerable – to vehemently oppose the accord.

Getting as many countries as possible to associate themselves with the accord strongly served US interests, by boosting the likelihood it would be officially adopted. A diplomatic offensive was launched. Diplomatic cables flew thick and fast between the end of Copenhagen in December 2009 and late February 2010, when the leaked cables end.

Some countries needed little persuading. The accord promised $30bn (£19bn) in aid for the poorest nations hit by global warming they had not caused. Within two weeks of Copenhagen, the Maldives foreign minister, Ahmed Shaheed, wrote to the US secretary of state, Hillary Clinton, expressing eagerness to back it.

By 23 February 2010, the Maldives' ambassador-designate to the US, Abdul Ghafoor Mohamed, told the US deputy climate change envoy, Jonathan Pershing, his country wanted "tangible assistance", saying other nations would then realize "the advantages to be gained by compliance" with the accord.

A diplomatic dance ensued. "Ghafoor referred to several projects costing approximately $50m (£30m). Pershing encouraged him to provide concrete examples and costs in order to increase the likelihood of bilateral assistance."

The Maldives were unusual among developing countries in embracing the accord so wholeheartedly, but other small island nations were secretly seen as vulnerable to financial pressure. Any linking of the billions of dollars of aid to political support is extremely controversial – nations most threatened by climate change see the aid as a right, not a reward, and such a link as heretical. But on 11 February, Pershing met the EU climate action commissioner, Connie Hedegaard, in Brussels, where she told him, according to a cable, "the AOSIS [Alliance of Small Island States] countries 'could be our best allies' given their need for financing".

The pair were concerned at how the $30bn was to be raised and Hedegaard raised another toxic subject – whether the US aid would be all cash. She asked if the US would need to do any "creative accounting", noting some countries such as Japan and the UK wanted loan guarantees, not grants alone, included, a tactic she opposed. Pershing said "donors have to balance the political need to provide real financing with the practical constraints of tight budgets", reported the cable.