The temperature of Earth's surface has increased by only 0.06°C in the past 15 years - a fact that contradicts global warming climate models.

This so-called 'pause' has been used by some groups as evidence that climate change is not taking place.

Now a new study suggests that the discrepancy between the models and reality is all down to random fluctuations in the Earth's climate – and that the long-term trend still points to severe warming.

The solid black line is the global mean surface temperature. The dashed black line is the average for this data on surface temperatures. The blue and red lines are linear trends for each 15-year period from 1840. The researchers claim to have shown that these 15-year trends are dominated by natural variations in the climate

Researchers at Max Planck Institute for Meteorology in Hamburg and Leeds University in the UK say the models do not overestimate man-made climate change.

They claim global warming is 'highly likely' to reach critical proportions by the end of the century - if the global community does not finally get to grips with the problem.

'The claim that climate models systematically overestimate global warming caused by rising greenhouse gas concentrations is wrong,' says Jochem Marotzke from the Max Planck Institute.

The apparent mismatch between observed temperature increases and predictions from climate change models has led to some to claim that global warming has stalled, as seen by the black line in the graph above

WHAT IS THE 'GLOBAL WARMING PAUSE'? The global average temperature has risen only slightly since 1998 – which is surprising, considering scientific climate models predicted considerable warming due to rising greenhouse gas emissions. Some people used this apparent contradiction to question climate change per se – or at least the harm potential caused by greenhouse gases – as well as the validity of the climate models. Meanwhile, the majority of climate researchers continued to emphasise that the short-term ‘warming hiatus’ could largely be explained on the basis of current scientific understanding and did not contradict longer term warming. Recently, researchers have been looking into the possible causes of the warming hiatus over the past few years. In a separate study, ETH Zurich recently concluded that two important factors are equally responsible for the hiatus. One of the important reasons is natural climate fluctuations, of which the weather phenomena El Niño and La Niña in the Pacific are the most important, they claim. According to the study, the second important reason for the warming hiatus is that radiation from the sun has been weaker than predicted in the past few years. Advertisement

'Climate sceptics often make precisely this claim, citing the warming pause as evidence.

'Yet they cannot deny that nine of the ten warmest years since systematic climate observations began have occurred in the new millennium and that global warming has slowed at a very high level.

'The sceptics also ignore the fact that ocean temperatures continue to rise as rapidly as many models have predicted.

'On the whole, the simulated trends agreed well with the observations'

To explain the discrepancy between model simulations and observations, Professor Marotzke and Piers Forster compared simulated and observed temperature trends over all 15-year periods since the start of the 20th century.

For each year between 1900 and 2012 they looked at the temperature trend that each of the 114 available models predicted for the subsequent 15 years.

They then compared the results with measurements of how the temperature actually rose or fell.

By simulating the average global temperature and other climatic variables of the past and comparing the results with observations, they were able to check the reliability of their models.

The 114 model calculations withstood the comparison.

'On the whole, the simulated trends agree with the observations,' said Professor Marotzke.

'The most pessimistic and most optimistic predictions of warming in the 15 subsequent years for each given year usually differed by around 0.3 degrees Celsius.

Climate models, such as the one above, predict a significant increase in temperature by the end of this century, especially at the Earth's poles. No model, however, has predicted the global warming hiatus which climate researchers have observed since the turn of the millennium

GLOBAL WARMING HASN'T STOPPED - THE HEAT IS JUST HIDING Some scientists claim one of the causes of the ‘plateau’ in sea-surface temperature is a change in the exchange of ocean water. They believe this exchange is occurring between warm, surface waters and cold, deep waters below 2,300ft (700 metres) – as if the warming is ‘hiding’ underwater. Easterly trade winds of the Pacific Ocean have increased significantly over the past two decades and as a result are blowing higher volumes of warm surface sea water to deeper depths. Stronger trade winds blowing from South America to Australia have had the net effect of cooling surface temperatures by a global average of between 0.1°C and 0.2°C, This would be enough to account for the apparent hiatus in global average temperatures over the past 15 years. The warm water won’t hide below the surface forever: scientists believe that it may re-emerge later or affect other climate indicators, such as sea level or ocean circulation. Advertisement

'However, the majority of the models predicted a temperature rise roughly midway between the two extremes.

'The observed trends are sometimes at the upper limit, sometimes at the lower limit, and often in the middle, so that, taken together, the simulations appear plausible.

'In particular, the observed trends are not skewed in any discernible way compared to the simulations,' Professor Marotzke explains.

If that were the case, he said, it would suggest a systematic error in the models.

The scientists are now also analysing why the simulations arrived at disparate results by looking at how the models react to increases in atmospheric carbon dioxide.

Since 1998, the warmest year on record, the steep increase in global temperatures seen during the 1990s has levelled off, failing to match computer model predictions for climate change.

This pause, or hiatus, has been blamed on weak solar activity and increased uptake of heat by the world's oceans.

The UN's Intergovernmental Panel on Climate Change last year concluded that the deep oceans had been responsible for absorbing an increasing amount of heat, but warned that this could not continue indefinitely.

However, in a paper published in November last year, atmospheric scientists at the Massachusetts Institute of Technology found that small volcanic eruptions in the early 21st century, which had been largely overlooked, were responsible for up to a third of the hiatus in warming.