They say never judge a book by its cover, but chances are a lecture entitled "Real clothes for the emperor: facing the challenges of climate change" will be fairly down-to-earth. That proved to be the case when Kevin Anderson of the Tyndall Centre for Climate Change Research at the University of Manchester, UK, gave the Cabot Annual Lecture 2012 in Bristol, UK, in November 2012.

In response to an audience member who commented that most climate scientists were simply trying to pay their bills, Anderson said "I don't think it's OK to walk past a mugging on the way to pay the mortgage. Climate scientists need to be good citizens too. Our science tells us we are killing people in poor parts of the world by putting our lights on and we need to make people think about that. Scientists need to start standing up for what they believe in. By staying quiet we are legitimizing it."

Back in 2011, Anderson published a paper in the Philosophical Transactions of the Royal Society A on how he felt today's integrated assessment models, which combine climate data with economic data, are dangerously flawed. Why? Because they are based on "naive" assumptions for factors such as emission growth rates and the date of emission peaks, they limit annual energy-emission reduction rates to between 2 and 4%, and assume uptake of geoengineering as well as a high penetration of nuclear power alongside untested carbon-capture and storage technologies.

"Because integrated assessment models typically use similar and inappropriate sets of assumptions, they repeatedly come up with the same narrow and fundamentally flawed answers," Anderson told environmentalresearchweb at the time. In his November talk, on the topic of emission growth rates used in models that were lower than real-world growth rates, he said "We've always underplayed everything we possibly can – we've done exactly what the sceptics said but in reverse." In some cases, reports have been issued that assumed emissions peaked several years before the date of the report, leading to "policy recommendations premised on owning a tardis". Similarly, some scenarios assumed that emissions from developing countries would exceed those from developed countries well into the future, whereas in fact this happened in 2006.

"With few exceptions the scenarios out there hide or massage historical emissions and emission trends," said Anderson. "So they change the framing of where we are today. They underestimate short-term growth out to the peak of emissions. The peak choice is Machiavellian at best. No-one thinks that we're going to peak in 2016 and yet virtually every model will peak in 2016, which gives you a nice answer for your policymaker."

Anderson thinks it has been obvious for the last 10 years that we are pointing towards 4–6° "but it's interesting to see orthodox organizations coming out and saying this now". International Energy Agency (IEA) chief economist Fatih Birol emphasizes how current emission trends are "perfectly in line with a temperature rise of 6 °C", which he notes "would have devastating consequences for the planet", said Anderson. And consultancy PwC's Low Carbon Economy Index 2012 reports that even doubling our rate of carbon-emission reduction would still lead to emissions that are consistent with 6° of warming. "To give ourselves a more than 50% chance of avoiding 2° will require a six-fold improvement in our rate of decarbonization," states the report.

The Copenhagen Accord aims "to hold the increase in global temperature below 2° Celsius, and take action to meet this objective consistent with science and on the basis of equity". Anderson stressed that it is below, not a 50:50 chance of, 2°, and that the phrase "consistent with science" is quite radical and "on the basis of equity" even more so. "Most nations have signed up to this so I think we should hold our leaders to account," he said, adding that just this May, leaders of the G8 nations at a meeting in Camp David reiterated their commitment to do what was necessary to maintain "the increase in global temperature below 2 °C above pre-industrial levels, consistent with science". The UK government has adopted the Committee on Climate Change's budget for a 63% chance of exceeding 2°. "Can that 60-odd per-cent chance be reconciled with 'hold the temperature below 2 °C and take action on the basis of science'? Our job as scientists is to stand up and say 'hang on, that doesn't really fit'." But according to Anderson, scientists repeatedly stay quiet and silence is consent. "That process of consent is really quite invidious in the whole climate-change story."

Time for change

So what is the solution? Since infrastructure lasts a long time, Anderson believes it will take 20 to 25 years to get significant decarbonization of energy supply systems. "It's energy demand that really matters," he said. It's possible to change demand technologies in one to 10 years and to change behaviour immediately; most car journeys use vehicles that are less than eight years old, for example. "I'm not saying the supply side is not important but it cannot get you off the [emission] curve anywhere near fast enough," Anderson continued. "You'll have much higher temperatures if you just rely on engineers to come up with [supply] technologies that will solve the problem in 2025 or 2030."

Anderson thinks the group of climate scientists working at the interface between science and policy are massaging their assumptions to give a more palatable picture and make a 2016 emission peak sound doable. "Some people ask if James Hansen is too extreme," he said, "but extreme adjectives reflect the science." Scientists using words like "challenging" and "doable" make a 2° limit for temperature rise sound feasible, he added. But in the pub or at Chatham House Rules events, many scientists are saying "we cannot tell the public that" when it comes to reporting how low our chances are of staying within the 2° boundary. "I think we're on for 4–6 °C but we just can't be open about it," said Anderson.

In his talk, Anderson detailed how a respected political scientist has said "too much has been invested in 2 °C for us to say it is not possible – it would give a sense of hopelessness that we may as well just give in". Building on this, a government scientist told Anderson "We can't tell ministers and politicians that it [2 °C] is impossible; we can say it's a stretch, ambitious but that with political will 2 °C is still feasible."

Anderson's view, in contrast, is that "I'm paid by the state and I will say exactly what my findings are". He reckons 4° is challenging but achievable. But a 4° global-average future could mean temperature rises on land of 5–6°, along with large regional variations. Potentially, the hottest days of the year could see an additional 6–8° of warming. Roughly 20–30,000 people died in the 2003 heatwave in Europe as it was, without any additional warming on top. "There's a widespread view that a 4° future is incompatible with organized global community as we see it today," said Anderson. "It's likely beyond adaptation. I would go so far as to say that we should avoid 4° at all costs."

Cutting the future

There is a small amount of good news. An outside chance of exceeding 2° requires emission cuts of at least 10% per annum, said Anderson – basically about a 40% reduction in energy consumption in the next three years, 70% by 2020 and complete decarbonization by 2030 – at least for the wealthier nations. Anderson reckons about 40–60% of the world's energy emissions come from 1–5% of the population. This includes "climate scientists, every journalist, pontificator and sceptic, every other OECD academic, everyone who gets on a plane once a year" and anyone earning more than £30 k a year. "So we're the major emitters – we know who they are. Are we prepared to make changes to our lives now or have them forced upon us?" Anderson believes there is a lot we can do. "We don't require the whole world to do something, we require a small proportion of the world to change what they do today for the next 10 or 20 years while we put low-carbon supply in place."

Behaviour change can be instant, he said. Cutting energy use by, for example, turning off lights today can save more carbon than you might think because of the energy lost in electricity production, transmission and so on. Currently a typical vehicle in the UK emits around 175 g of carbon dioxide per kilometre but many diesel and petrol cars now achieve levels below 100 g and some manage as low as 75 g. Despite this, the EU target for average car emissions is an uninspiring 130 g of carbon dioxide per kilometre by 2015. Setting ambitious targets, along with a slight rise in the number of passengers per vehicle, could reduce emissions 60–70% by 2020, added Anderson.

That said, a maximum temperature rise of two degrees is looking more and more unlikely. "It's a wake-up call of where our rose-tinted spectacles have brought us," said Anderson. "Real hope if it's to arise at all will be from a bare assessment of the scale of the challenge that we now face and that's what I've tried to show [in this talk]." With clarity and imagination Anderson thinks we could.