In 2001 and 2007 the Intergovernmental Panel on Climate Change (IPCC) (and here) estimated that the world would warm at a rate of 0.2 deg C per decade in the future due to greenhouse gas forcing. Since those predictions were made it has become clear that the world has not been warming at that rate. Some scientists retrospectively revised their forecasts saying that the 0.2 deg C figure is an average one. Larger or smaller rates of warming are possible as short-term variations.
Global warming simulations, some carried out by the UK Met Office (here, here and here), have been able to reproduce “standstills” in global warming of a decade or so while still maintaining the long-term 0.2 deg C per decade average. These decadal standstills occur about once every eight decades. However, such climate simulations have not been able to reproduce a 15-year standstill:
“Near-zero and even negative trends are common for intervals of a decade or less in the simulations, due to the model’s internal climate variability. The simulations rule out (at the 95% level) zero trends for intervals of 15 yr or more, suggesting that an observed absence of warming of this duration is needed to create a discrepancy with the expected present-day warming rate" (NOAA 2008).
We also note a comment in an email sent by Professor Phil Jones of the University of East Anglia Climatic Research Unit: “Bottom line – the no upward trend has to continue for a total of 15 years before we get worried.”
