What they say: ‘The rate of warming over the past 15 years [at 0.05C per decade] is smaller than the trend since 1951.'
What this means: In their last hugely influential report in 2007, the IPCC claimed the world had warmed at a rate of 0.2C per decade 1990-2005, and that this would continue for the following 20 years.
The unexpected 'pause' means that at just 0.05C per decade, the rate 1998-2012 is less than half the long-term trend since 1951, 0.12C per decade, and just a quarter of the 2007-2027 prediction.
Some scientists - such as Oxford's Myles Allen - argue that it is misleading to focus on this 'linear trend', and that one should only compare averages taken from decade-long blocks.
What they say: ‘Surface temperature reconstructions show multi-decadal intervals during the Medieval Climate Anomaly (950-1250) that were in some regions as warm as in the late 20th Century.’
What this means: As recently as October 2012, in an earlier draft of this report, the IPCC was adamant that the world is warmer than at any time for at least 1,300 years. Their new inclusion of the ‘Medieval Warm Period’ – long before the Industrial Revolution and its associated fossil fuel burning – is a concession that its earlier statement is highly questionable.
What they say: ‘Models do not generally reproduce the observed reduction in surface warming trend over the last 10 – 15 years.’
What this means: The ‘models’ are computer forecasts, which the IPCC admits failed to ‘see... a reduction in the warming trend’. In fact, there has been no statistically significant warming at all for almost 17 years – as first reported by this newspaper last October, when the Met Office tried to deny this ‘pause’ existed.In its 2012 draft, the IPCC didn’t mention it either. Now it not only accepts it is real, it admits that its climate models totally failed to predict it.
What they say: ‘There is medium confidence that this difference between models and observations is to a substantial degree caused by unpredictable climate variability, with possible contributions from inadequacies in the solar, volcanic, and aerosol forcings used by the models and, in some models, from too strong a response to increasing greenhouse-gas forcing.’
What this means: The IPCC knows the pause is real, but has no idea what is causing it. It could be natural climate variability, the sun, volcanoes – and crucially, that the computers have been allowed to give too much weight to the effect carbon dioxide emissions (greenhouse gases) have on temperature change.
What they say: ‘Climate models now include more cloud and aerosol processes, but there remains low confidence in the representation and quantification of these processes in models.’
What this means: Its models don’t accurately forecast the impact of fundamental aspects of the atmosphere – clouds, smoke and dust.
What they say: ‘Most models simulate a small decreasing trend in Antarctic sea ice extent, in contrast to the small increasing trend in observations... There is low confidence in the scientific understanding of the small observed increase in Antarctic sea ice extent.’
What this means: The models said Antarctic ice would decrease. It’s actually increased, and the IPCC doesn’t know why.
What they say: ‘ECS is likely in the range 1.5C to 4.5C... The lower limit of the assessed likely range is thus less than the 2C in the [2007 report], reflecting the evidence from new studies.’
What this means: ECS – ‘equilibrium climate sensitivity’ – is an estimate of how much the world will warm every time carbon dioxide levels double. A high value means we’re heading for disaster. Many recent studies say that previous IPCC claims, derived from the computer models, have been way too high. It looks as if they’re starting to take notice, and so are scaling down their estimate for the first time.
