The Financial Times reports:
The final draft of the summary for policy makers (which is still officially confidential) has a stab at explaining why this has happened, but it is not exactly an easy read – especially for a document that is supposed to be a simple and accessible explanation of climate change. It says:
“The observed reduction in warming trend over the period 1998–2012 as compared to the period 1951–2012, is due in roughly equal measure to a cooling contribution from internal variability and a reduced trend in radiative forcing (medium confidence). The reduced trend in radiative forcing is primarily due to volcanic eruptions and the downward phase of the current solar cycle. However, there is low confidence in quantifying the role of changes in radiative forcing in causing this reduced warming trend.”
Other parts of the summary are clearer, and its overwhelming message is that even though temperature rises may have stalled, there is plenty of other evidence of climate change: warming oceans, rising sea levels, melting Arctic sea ice and the diminishing Greenland ice sheet.
But CO2 is the dominant factor in global warming therefore CO2 levels must have declined. Other factors are minor and the only influence the sun can have is TSI variability – according to the IPCC in years gone by.
The IPCC have low confidence in solar activity (or as they call it the downward phase of the current solar cycle) in causing the near 24 year long pause (RSS, 95% confidence) as indeed they must. If this were not the case they must also have higher confidence that warming in the second half of the twentieth century was due to the Grand Maximum of solar activity.