The Wisdom of Whores, Elizabeth Pisani's vivid and often eye-popping account of ten years as a scientist working across the globe in "the bloated Aids industry", takes us into government bureaucracies, police stations, rehab centres, brothels, strip clubs and massage parlours. But although it offers many poignant, shocking and plain weird glimpses of life "on the ground", it is equally interesting in its examination of how research is carried out, and how its findings get translated (or fail to get translated) into public policy.

In the early days, Pisani's colleagues were working with such limited data that they could make a few adjustments to their assumptions, re-run their computer models and exclaim cheerfully: "We've just saved about a million Nigerians." But even as the data became more reliable and what needed to be done grew ever clearer, finding the money and the political will needed to undertake the necessary action was a quite different challenge. Sometimes it is the statistics that have to be massaged.

The problem, as Pisani explains with disarming frankness, is often quite simple. Effective Aids-prevention programmes usually require governments "to do nice things for drug injectors, sex workers and gay men". This is not always popular with politicians, their voters or powerful American lobbies. So one of the best techniques in reporting research was playing "the innocent wives and babies" card. Religious charities that wouldn't give a penny while Aids was considered a disease of "promiscuous queens in rich countries" might be very generous for "loyal wives in dirt-poor countries" and "their helpless wide-eyed infants".

Professional scientists can't, of course, simply make up figures, but that still leaves plenty of room for "beating them up" or presenting them in a favourable light. In Indonesia, for example, Pisani and her colleagues came up with estimates of "eight million men buying sex". Why not imply to the Finance Ministry that "their philandering could have serious knock-on effects, potentially exposing millions of wives and children to HIV"? This might be nonsense - "16,000 women at risk" was a much more realistic figure - but who could object if a little economy with the truth led governments to adopt policies that saved countless lives?

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Pisani is a born maverick, but she raises ethical and professional issues that are equally relevant to academics studying topics such as climate change. The language of science, to put it mildly, often lacks urgency. Those who are used to its conventions learn to read between the lines of wording such as "The balance of evidence suggests that ... ", and can spot the key distinction between "likely" and "very likely" (the latter, translated into plain English, is often science-speak for "all but certain").

The historic 1950 report by the US Surgeon General, Pisani reminds us, "risked the wrath of the rich and powerful tobacco companies by saying that smoking is bad for you" - except that he didn't. He said it was "a health hazard of sufficient importance to warrant appropriate (but unspecified) remedial action". Would a phrase such as that in a 400-page report really make people change their lifestyle?

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It all comes down to how we deal with bad news. The media have an insatiable appetite for catastrophe. Presenting complex technical material to a non-specialist audience inevitably involves selection and simplification. Isn't there sometimes a temptation to sensationalise it as well, to make the news about global warming, for example, not just bad but apocalyptically (or headline-grabbingly) bad? For those who genuinely believe that climatic or other environmental disaster will soon be upon us, the crucial question is simple: what is most likely to spur people to action?

Consider the nature of the debate. The industries and corporations whose interests are threatened, it is safe to say, are unlikely to play by the Queensberry Rules. Now that there is broad agreement on global warming, "maverick" columnists and television producers get a lot of mileage from "fearlessly" claiming that climate change is just a myth or a conspiracy. Even the reports of the Intergovernmental Panel on Climate Change represent a consensus view based on conservative assumptions and out-of-date information, which inevitably makes them seem too cautious - or not sufficiently alarmist - to many individual researchers. So how can concerned scientists get their message across?

Roland Clift, distinguished professor of environmental technology at the University of Surrey, describes himself as an industrial ecologist who "looks at flows of material and energy through the economy rather than through pipes". While he still has a shrinking number of colleagues who just want to discover the precise scientific facts about climate change (and leave any practical implications to others), he is happy to call what he does "commitment research".

Although Clift has no doubt that "climate change is actually happening", not least because "the Matterhorn is melting", there are always elements of uncertainty and things that are intrinsically unpredictable, regardless of the state of our knowledge. Yet if we wait until the evidence is totally unambiguous, it will be too late. Hence the dilemmas for communicators, he says. "The media interpret caveats as expressing doubt ... There is a lot of denial about, so people are looking for uncertainty (so they don't have to change their lifestyles) ... Fair and balanced (coverage) doesn't spur people to action." The inevitable question, of course, is: what does?

Some seem to believe, or at least hope, that responsible presentation of the facts will eventually have the desired effect. Former academic Simon Gerrard is programme manager of CRed, a low-carbon innovation centre at the School of Environmental Sciences at the University of East Anglia. "I think it's fair to say that the majority of people are unlikely to change their behaviour in the face of uncertain evidence," Gerrard admits. "The greater the scientific uncertainty, the greater your own belief/faith needs to be to change."

Nonetheless, Gerrard believes that "science has to be transparent to be trustworthy. So accepting and reporting uncertainties is vital. That leaves a tough job for policymakers who will need to take tough decisions in the face of considerable uncertainty. Are our policymakers sufficiently brave to do this? It's a good question. However, I find some comfort in the fact that I make a whole host of everyday decisions under conditions of considerable uncertainty - even things like where best to cross the road."

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Gerrard's emphasis on honesty means that he believes carbon-reduction policies need to be accompanied by a new realism about what is and is not achievable. "Any strategy has to have both a mitigation and an adaptation side," he says. "We will need to think about handling the impact (of climate change)."

Mark Maslin, director of the Environment Institute at University College London, takes a rather different line. He argues that researchers are "walking a tightrope between doing excellent science, which is clearly defensible and has the support of peers, and communicating with the public. If you go too far towards communication (or stray out of your true specialist areas), you lose the credibility that makes you worth listening to in the first place." Nonetheless, there is also a real "desire to make a difference - it is strong because of the consequences of the science".

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Because they had "struggled so long to get attention", claims Maslin, climate scientists tend to be pretty politically astute. At one point, he suggests, there was a temptation to use scare tactics, but now he worries that too much doom and gloom can paralyse people into inaction - his friends in the art world sometimes complain to him about "climate porn". There are also differences between Britain and the United States, he says, with regard to the evolution of the debate. "Al Gore is still trying to wake people up. Sir David King (Britain's former Chief Scientific Adviser) is now working to find solutions."

Bitter experience underlies the views of Stephen Schneider, professor of biological sciences at Stanford University. Scientists, he said when interviewed by Discover magazine in 1989, "are ethically bound to the scientific method, in effect promising to tell the truth, the whole truth and nothing but - which means that we must include all the doubts, the caveats, the ifs, ands, and buts".

Yet, on the other hand, they are also human beings who generally would "like to see the world a better place". This inevitably requires them "to capture the public's imagination" through "loads of media coverage". And this in turn meant that they had "to offer up scary scenarios, make simplified, dramatic statements, and make little mention of any doubts we may have".

The result is often a "double ethical bind", Schneider told Discover. "Each of us has to decide what the right balance is between being effective and being honest. I hope that means being both." It is perhaps inevitable that those keen to discredit environmentalism should have seized on the interview and quoted the first but not the second of those sentences, implying that Schneider was promoting rather than just discussing opportunistic dishonesty. The result, he has written, was "fifteen years of subsequent distortions and attacks".

Schneider has reflected a good deal on effective science communication and remains "quite frustrated about the soundbite nature of the public debate" and by "the substantial element of hide-and-seek between a reporter looking for juicy quotes and a scientist trying to minimise damage to his reputation from oversimple public pronouncements or outright media distortion".

Some distortions of his words have been almost criminal. He remembers, for example, a headline in a local paper that read "Scientist predicts Ice Age". The article included lots of dramatic detail about how ghastly this would be but somehow managed to omit Schneider's important caveat that "we have 10,000 to 20,000 years before this happens".

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Nonetheless, he argues, there are ways of being "both effective and honest". One is to use "metaphors that simultaneously convey both urgency and uncertainty". Another is for those who engage in public debate to produce "a hierarchy of back-up products ranging from op-ed pieces to longer popular articles, which provide more depth, to full-length books, which meticulously distinguish the aspects of an issue that are well understood from those which are more speculative". All this may be admirable advice, but it makes huge demands on the time, energy and communications skills of scientists who want to "make a difference".