Jack Bain assesses the change in language and tone on climate change

On Monday last week, we saw the release of the first instalment of the Intergovernmental Panel on Climate Change's (IPCC) sixth assessment report, AR6.

This report is the most up-to-date physical understanding of the climate system and of climate change.

With input from more than 200 authors from around the world and 8 years since the last report (AR5), much has changed, and this year's report has drawn the attention of both global media and policymakers alike.

As a full report AR6 is more than 3000 pages of highly technical analysis but released alongside this full report is the 'summary for Policymakers' (SPM) - which is a non-technical synopsis of the report's key findings.

At just over 40 pages, the SPM is a much more accessible and useful document for many - and on top of this, each line of the SPM is approved by government delegates representing the majority of nations around the world.

Let’s hope that this translates into tangible action in Glasgow this November

Jack Bain Jack Bain Member of the Sustainability Team

It’s now unequivocal

Even in the shortened synopsis provided by the SPM, there’s a lot to digest, and more than would fit into a Hub article.

However, of note is the evolution in the science, certainty and language being used by scientists and politicians alike. A good point of comparison would be to compare the statements in AR5 relating to global temperatures:

  • AR5: "It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century"
  • AR6: "It is unequivocal that human influence has warmed the atmosphere, ocean and land."

This shift from 'extremely likely' to 'unequivocal' is more than just semantics - the IPCC use a calibrated language to align their reports to scales of probability.

This means that when AR5 released, scientists were between 95% and 100% sure that humans were warming the planet, where in AR6, this has become an 'unequivocal' truth.

A stark picture

The report also highlights the fact that temperatures have been climbing much faster during this assessment cycle than previously, and even revises the previous AR5 estimate of the temperature change between 1850 – 1900 and 1986 – 2005 as being 0.08°C higher than previously thought. This revision is largely the result of ‘dataset innovations’ that have enabled a better way to assess historical changes in the way we measure sea temperature change to provide a clearer understanding of global temperature records.

Overall the report paints a stark picture, with reassessments of previous AR findings added to new data gathered since the last AR cycle (8 years) showing us a familiar, but worrying trend:

“Observed changes in the atmosphere, oceans, cryosphere and biosphere provide unequivocal evidence of a world that has warmed. Over the past several decades, key indicators of the climate system are increasingly at levels unseen in centuries to millennia, and are changing at rates unprecedented in at least the last 2,000 years.”

Measuring against the goals of the 2015 Paris Climate Agreement, to ‘limit global warming to well below 2, preferably to 1.5 degrees Celsius, compared to pre-industrial levels’ AR6 shows us a global mean surface temperature (GMST) increase of 1.09°C between the pre-industrial benchmark and the most recent decade 2011 – 2020. In context, if 1.5°C is the limit we wish to adhere to, we are already 72.6% of the way there!

This decade has also been given a confidence rating of “more likely than not” (>50% probability) for having been the warmest 10 year period in roughly 125,000 years – a hypothesis that is less surprising, given that each of the last four decades have been in turn warmer than any that preceded it since 1850.

Show your stripes

The Carbon Brief have provided a fantastic summary of AR6's SPM, looking at more comparisons to the last iteration of the report which I highly recommend looking at:

With COP26 fast approaching, and policymakers preparing to stand up and make public commitments to tackle climate change, this document is likely to inform many of the decisions that must be made - and soon - for us to reach goals such as Net Zero 2050 and live more sustainably as a species.

As Professor Ed Hawkins - author of the #ShowYourStripes graphic that many of you will be familiar with, and a contributor to this report - has said in a press briefing:

"So it is a statement of fact, we cannot be any more certain; it is unequivocal and indisputable that humans are warming the planet…And every government agreed to that [wording in the SPM]."

Let’s hope that this agreement translates into tangible action in Glasgow this November...

Jack Bain is a member of the Sustainability Team