As with WG II report, the fundamental messages  have not changed since the previous edition. See summary for policy makers which is readable at just 33 pages.

This time the report provides careful optimism on transitioning to clean energy. In 2013, renewables accounted for more than half the new electricity generation added around the world. Yet we will have to treble investment in renewables in the next 35 years.  Jim Skea (Imperial College London and a co-chair of the WG III) told the Guardian: “It is not a hair shirt change of lifestyle at all that is being envisaged and there is space for poorer countries to develop too.”
Thrust of this report is largey unchanged since previous analysis, with high levels of certainty and evidence of actual impacts on natural and human systems in recent decades. Investments in better preparation can pay dividends now and for the future. 

Many key risks constitute particular challenges for the least developed countries and vulnerable communities, given their limited ability to cope.

Link to Summary for Policy Makers