In October, I trawled through the final draft of this report, which was released at that time:

• Intergovernmental Panel on Climate Change (IPCC), Climate Change 2013: The Physical Science Basis.

Here’s what I think are its key messages:

1. The warming is unequivocal.
2. Humans caused the majority of it.
3. The warming is largely irreversible.
4. Most of the heat is going into the oceans.
5. Current rates of ocean acidification are unprecedented.
6. We have to choose which future we want very soon.
7. To stay below 2°C of warming, the world must become carbon negative.
8. To stay below 2°C of warming, most fossil fuels must stay buried in the ground.

I’ll talk about the first of these here, and the rest in future parts—click to get to any part you want. But before I start, a little preamble.

The IPCC was set up in 1988 as a UN intergovernmental body to provide an overview of the science. Its job is to assess what the peer-reviewed science says, in order to inform policymaking, but it is not tasked with making specific policy recommendations. The IPCC and its workings seem to be widely misunderstood in the media. The dwindling group of people who are still in denial about climate change particularly like to indulge in IPCC-bashing, which seems like a classic case of ‘blame the messenger’. The IPCC itself has a very small staff (no more than a dozen or so people). However, the assessment reports are written and reviewed by a very large team of scientists (several thousands), all of whom volunteer their time to work on the reports. The scientists are are organised into three working groups: WG1 focuses on the physical science basis, WG2 focuses on impacts and climate adaptation, and WG3 focuses on how climate mitigation can be achieved.

In October, the WG1 report was released as a final draft, although it was accompanied by bigger media event around the approval of the final wording on the WG1 “Summary for Policymakers”. The final version of the full WG1 report, plus the WG2 and WG3 reports, have come out since then.

I wrote about the WG1 draft in October, but John has solicited this post for Azimuth only now. By now, the draft I’m talking about here has undergone some minor editing/correcting, and some of the figures might have ended up re-drawn. Even so, most of the text is unlikely to have changed, and the major findings can be considered final.

In this post and the parts to come I’ll give my take on the most important findings, along with a key figure to illustrate each.

(1) The warming is unequivocal

The text of the summary for policymakers says:

Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased.

(Fig SPM.1) Observed globally averaged combined land and ocean surface temperature anomaly 1850-2012. The top panel shows the annual values; the bottom panel shows decadal means. (Note: Anomalies are relative to the mean of 1961-1990).

Unfortunately, there has been much play in the press around a silly idea that the warming has “paused” in the last decade. If you squint at the last few years of the top graph, you might be able to convince yourself that the temperature has been nearly flat for a few years, but only if you cherry pick your starting date, and use a period that’s too short to count as climate. When you look at it in the context of an entire century and longer, such arguments are clearly just wishful thinking.

The other thing to point out here is that the rate of warming is unprecedented:

With very high confidence, the current rates of CO2, CH4 and N2O rise in atmospheric concentrations and the associated radiative forcing are unprecedented with respect to the highest resolution ice core records of the last 22,000 years

and there is

medium confidence that the rate of change of the observed greenhouse gas rise is also unprecedented compared with the lower resolution records of the past 800,000 years.

In other words, there is nothing in any of the ice core records that is comparable to what we have done to the atmosphere over the last century. The earth has warmed and cooled in the past due to natural cycles, but never anywhere near as fast as modern climate change.

You can download all of Climate Change 2013: The Physical Science Basis here. It’s also available chapter by chapter here: