Independent researchers have suggested that the use of incomplete data has led climate scientists to underestimate global temperature increases, resulting in the 'slowdown' in global temperature increases that attracted the attention of climate change deniers following the release of the latest climate report by the Intergovernmental Panel on Climate Change. 

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In September, ahead of its landmark report on Climate Change, which the Committee said provided "unequivocal evidence" that global warming is happening and that it is the result of human activity, the IPCC paid special attention to a perceived hiatus in global temperature increases. In briefing documents, scientists tried to explain the phenomenon to World leaders, and there was widespread concern that an apparent levelling off of temperature rises would be pounced upon by climate change deniers to fuel their arguments, but there was no scientific consensus on the cause of the hiatus.

Having increased steadily since the 1970s, global temperatures appear to have remained relatively constant since the 1990s, according to the data examined by the UN-convened IPCC's working group. However, new research from scientists at the Universities of York and Ottawa suggests that the IPCC's calculations may have been wrong, and that expanding the scope of analysis reveals temperature rises have continued throughout the controversial flatspot. 

Publishing their study in the Journal of the Royal Meteorological Society, the researchers – who are not climate scientists – concluded this week that oversights in collecting data have led to an "underestimation of recent temperature trends."

Despite the official data showing that surface temperature had remained relatively constant, according to WMO Secretary-General Michel Jarraud, "All of the warmest years have been since 1998 and this year once again continues the underlying, long-term trend. The coldest years now are warmer than the hottest years before 1998."

The UK-Canada partnership revealed earlier this week that, by failing to collect data from all over the world, previous figures have been biased (estimates had been based on data from 84 percent of the world, with the two polar regions and parts of Africa being consistently left out of temperature gathering efforts). A number of sources have shown that warming over the Arctic and Antarctic has been faster than over the rest of the world, though climate research centres had assumed that warming has been occurring in the Polar Regions at the same rate as elsewhere.

The scientists tested more complete datasets, using information from satellites to achieve near global coverage, and discovered that "Coverage bias causes a cool bias in recent temperatures relative to the late 1990s which increases from around 1998 to the present." They also found that El Nino activity in the late ‘90s contributed to the 'cool bias', making global temperatures appear cooler than they actually were. Once the missing datasets are included in temperature analyses, the trend in temperature rises changes greatly; increases over the past 16 years increase by 2.5 times that seen in previously published data, from 0.05°C to 0.12°C.

Although Met Office figures showed a pause in warming, experts at the UK's national weather service maintained that its indicators showed climate changes continued through the period, and that observed changes were "consistent with a globally warming world." The Met Office had stated that "Changes in the exchange of heat between the upper and deep ocean appear to have caused at least part of the pause in surface warming, and observations suggest that the Pacific Ocean may play a key role."

The two researchers said that, although their new data reveals only slight temperature changes year on year, cumulatively these amount to a significant, worrying and consistent change in average global surface temperature. Their findings have been welcomed by climate experts at a number of global institutes, though some warned that there may still be a slowdown in temperature rises, albeit not as pronounced as was first thought.