Chinese scientist Lu Longhua is well acquainted with the cold; he has even been to the North Pole three times. But this winter, as a bitter cold snap blanketed Europe and Asia, and public interest in the Arctic soared, the veteran meteorologist of the Chinese Academy of Meteorological Sciences struggled to pinpoint a reason for the weather anomaly. A high-pressure system had built up in the Arctic, the northernmost part of the earth, pushing cold fronts further south and causing snows heavier than average, Lu said. It seemed like a common fluctuation of the Arctic climate. Scientists had no consensus on what caused the pressure build-up, though some said water vapour probably played a greater role than carbon dioxide. But pressed for an explanation for the heavy snow, Lu, in smog-choked Beijing, felt obliged to call it an extreme weather event linked to global warming. He proposed a significant cut in carbon dioxide emissions. 'Should I confess to the public our scientific ignorance or preach a politically correct answer?' he said. The question of whether politics and popular opinion is swaying scientific discourse troubles almost every mainland scientist studying climate change - and the battle lines have been drawn clearly. One camp, led by geologist Ding Zhongli, vice-president of the Chinese Academy of Sciences, believes politics should not influence science. The opposing side, led by meteorologist Ding Yihui, the central government's special adviser on climate change, argues that science can influence politics. Ding Zhongli cites climate change as an issue where many scientists, due to 'political correctness or other purposes', conform to the dominant view that human-triggered global warming causes problems and that carbon dioxide is to blame - even if serious climate change researchers have never denied glaring uncertainties about it. The biggest uncertainty is how acutely the climate responds to changing carbon dioxide levels. 'After accepting the precautionary principle, many people in the scientific community have, consciously or unconsciously, chosen an aggressive stand and made some extreme predictions popular,' Ding told the South China Morning Post in an e-mail interview. The precautionary principle states that if it is suspected an action risks harming the public or the environment but scientists are not fully agreed, the burden of proof is on those who say the contrary. For example, the geologist said, the United Nations-backed Intergovernmental Panel on Climate Change (IPCC) predicted that if we could limit the total amount of greenhouse gases equivalent to 450 parts per million (ppm) of carbon dioxide, we could hold global temperature rises to within 2 degrees Celsius in a century. But the global carbon dioxide level has already reached 390 ppm. Add in other gases such as methane, and we are very close to, or even breaching, the 450 ppm limit. Here lies a problem: world temperatures since the industrial revolution, which was an especially cold period at the end of the Little Ice Age, have risen by 0.74 degrees Celsius - way lower than the prediction of the IPCC's mathematical models. How do scientists account for the lower-than-expected temperature change despite accelerated emissions? 'Facing such reality, many scientists summon unreliable reasons such as the 'cooling effect of aerosols',' Ding said. 'That makes us suspect that they are choosing a side, the side serving political correctness and other purposes that I don't want to specify here.' The IPCC's predictions will not be verified for at least 50 to 100 years, and the scientists who made those forecasts may not live long enough to see the results. 'The mainstream scientists should make predictions for medium or even short term, but they obviously dare not' perhaps for fear of being wrong, Ding Zhongli said. He says scientists must be willing to admit that much remains unknown about how our climate works. 'The core of scientific spirit is to question. Even if scientists must consider political correctness, the voices of questions and suspicion must not be suppressed.' On the other side of the polarising debate, Ding Yihui says although climate change research has some gaps, scientists have found enough evidence for governments to act. For example, scientists are certain that the global temperature rose 0.74 degrees Celsius over the last century and that carbon dioxide levels are increasing more rapidly than ever. They are also sure that extreme weather patterns are occurring more frequently, that human activities can impact the climate system and that we can predict long-term climate changes more accurately than monthly weather forecasts. 'If we don't take some actions today we will be able to do nothing in the future,' Ding, the meteorologist, told the Post by phone. 'The theory of climate change is as important as Darwin's theory of evolution and Einstein's theory of relativity,' he said. 'It is therefore as easy to attract criticism as any major scientific breakthrough.' He also pointed out that the IPCC's findings were transparent and published in peer-reviewed journals. 'I don't think there is much conflict between scientific facts and political correctness,' Ding said. 'The 100-year prediction of IPCC has been proven correct in the first two decades. I am sure the more we study, the more confidence we will have on the theory.' The debate among Chinese experts is an echo of a larger controversy in the international scientific community: are we being too alarmist about climate change? Last month, 16 prominent scientists published a letter in The Wall Street Journal urging the public not to panic about global warming and warning that climate science had entered 'a frightening period'. They cited how Dr Chris de Freitas, Climate Research journal's editor, came under fire for daring to publish a peer-reviewed article in 2003 'with the politically incorrect (but factually correct) conclusion that the recent warming is not unusual in the context of climate changes over the past thousand years'. 'The international warming establishment,' the scientists wrote, 'quickly mounted a determined campaign to have Dr de Freitas removed from his editorial job.' They said alarmism over climate was 'of great benefit to many, providing government funding for academic research and a reason for government bureacracies to grow'. Nobel Prize-winning physicist Ivar Giaever resigned from the American Physical Society last year when the organisation stated: 'The evidence is incontrovertible: Global warming is occurring.' Giaever, in his resignation letter, said: 'In the APS it is OK to discuss whether the mass of the proton changes over time and how a multi-universe behaves, but the evidence of global warming is incontrovertible?' Given that the debate is as nebulous as the reason for the cold snap, it is perhaps understandable that Lu, the veteran scientist, offers a familiar answer. 'The public will get confused if they know too much about scientific uncertainties about global warming,' he said. There is one thing Lu says humanity can't compromise on. 'Environmental morality should be allowed to override scientific objectivity this time - or we will forever live under the spell of coal.'