IPCC AR5 Working Group I ‘Summary for Policymakers’ (2013) — a plain summary

What this document is

This is the ‘Summary for Policymakers’ from Working Group I of the IPCC’s Fifth Assessment Report, approved on 27 September 2013. Working Group I is the strand of the IPCC devoted to the physical science of the climate: the observed changes, their causes, and what the models project for the future.

A Summary for Policymakers is a condensed, carefully worded distillation of a much longer technical report, agreed line by line by member governments so that it accurately reflects the science. This page is a general summary for readers who reached a broken link; the exact statements, figures and confidence levels should be read from the IPCC original.

What it covers

As the physical-science volume, the WGI summary concentrates on how the climate system is behaving and why. In broad terms it addresses the following.

• The warming of the atmosphere and oceans observed over the instrumental record;
• Changes in the water cycle, in snow and ice, and in global sea level;
• Rising concentrations of greenhouse gases and their role in driving warming;
• The assessment that human influence on the climate is clear;
• Projections of future change under a set of standardised emission scenarios.

This edition is also well known for framing climate stabilisation in terms of a cumulative carbon budget: the idea that total emissions over time, rather than the rate in any single year, largely determine how much warming ultimately occurs.

Why it matters

The WGI summary is the scientific foundation on which the rest of AR5 — and much subsequent climate policy — was built. When later documents discuss impacts or mitigation, they rest on the physical assessment set out here.

Its release drew wide international coverage as a clear statement of the evidence, and it was an important input to the negotiations leading to the 2015 Paris Agreement. Because so many articles once linked to the original PDF, a stable summary such as this one preserves the reference.

How it relates to UK energy

The physical science summarised here is the reason energy policy has moved towards decarbonisation. Because most greenhouse gas emissions come from producing and using energy, the findings connect directly to how electricity and heat are supplied in Britain. Our environment guides translate that global picture into practical UK context, from carbon to low-carbon heating.

You can read the original on the IPCC’s official AR5 Working Group I page.

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