“It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred.”

These are the opening words of the 6th Assessment Report from the Intergovernmental Panel on Climate Change – the authoritative summary of the current state of understanding of the science.  At just short of 4000 pages long, this is just the Working Party 1 report, dealing with the science of what has happened to the climate, what is happening to the climate, and what we can expect to happen under a series of different future scenarios.  Working Group 2, which reports in February 2022, assesses the impacts of climate change on ecosystems and biodiversity, and on humans and their diverse societies, cultures and settlements: it draws experts from the biological sciences and from the social sciences.  Working Group 3, which will publish in March 2022, addresses technical and economic options for mitigating climate change – so it’s quite interdisciplinary but with a strong input from economists.  Then finally a team with members from all three working groups will publish a synthesis report later in 2022.

These reports take a lot of work, so they are only published every 6 or 7 years – the 5th Assessment Report came out in 2013-2014, though the IPCC has published a number of important special reports on specific subjects in the intervening years.

Why should we pay attention?  Because this is the closest we get to a comprehensive state-of-the-art understanding of the climate crisis.  The IPCC – established in 1988 by the UN Environment Programme and the World Meteorological Organisation – exists to advise the world’s governments on the subject.  It is free from commercial or political bias – the bulk of the work is done by scientists and other experts volunteering massive amounts of their time to the task of analysing all of the relevant peer-reviewed literature.  So the 234 authors of the Working Party 1 report, coming from nearly 100 countries, cited more than 14000 scientific research publications.  This is the most detailed and balanced study that we could possibly have – though inevitably it misses some of the most recent research, and if it has a bias it will be towards caution in its claims.

And the language is very measured.  It notes the confidence of its claims with terms like “likely”, “very likely”, “extremely likely”, “virtually certain”, “medium confidence”, “high confidence”, etc – and each of these terms has a specific statistical definition.  So when they say that the human influence on the climate is “unequivocal” it is not a rhetorical flourish: they really mean it.

Nobody can read a 4000 page scientific report in one sitting.  So there is a 150 page Technical Summary, which covers all the main points.  And there is a 41-page Summary for Policymakers.  (I would be interested to know how many actual Saskatchewan policymakers have read this – MPs, MLAs, city councillors, party advisors, etc.  I suggest that anyone seeking political office who doesn’t read it is failing in their duty.)  I have read both of these summaries, plus I’ve dug into a few areas of interest in the main text.

For those who have been following the science, there are no particularly new revelations, but things are clearer and starker than in earlier reports – and there is a lot more detail.  I can’t do justice to the full report here, but I will explain a few of their findings.

The concentrations of greenhouse gases – carbon dioxide, methane, nitrous oxide and others – continue to rise in the atmosphere as a result of human activities.  It has been known since the 1830s that the result is that less heat escapes from the earth and so there is a differential between the energy arriving from the sun and the energy flowing out.  This is called radiative forcing, and its value has been steadily increasing as the emissions of greenhouse gases continue.  The result of radiative forcing is global warming – all that extra energy has to go somewhere.  91% of it is going into the oceans – water has a very high specific heat capacity, which means it can absorb a lot of energy.  5% goes to warming the land, 3% to melting ice, and 1% to the atmosphere.  But that 1% has resulted in an average global surface temperature rise of about 1.1°C since the late 19th century.  Since 1970, the oceans have absorbed over 400 extra zettajoules of energy – that’s about a hundred million billion billion billion billion billion kilowatt-hours.  The report’s best estimate is that our emissions of carbon dioxide have resulted in 0.8°C of that rise, with 0.5°C from methane and smaller contributions from other greenhouse gases – but that warming effect has been partially balanced by the cooling effect of some of our other emissions (sulphur dioxide, for example).

That 1.1°C rise puts the earth’s average temperature higher than it has been since about 125000 years ago.  That’s a time long before human civilisation, when our species was still coexisting with Neanderthals.  And that prehistoric high temperature happened gradually as a result of variations in the earth’s orbit.  Our present high temperature has happened much much more suddenly.

The serious impacts on the world’s climate systems and on the oceans have become much more apparent, and the science points to clear causal links.  Precipitation – rain and snow – has increased, but with less reliable timing.  Glaciers have retreated all over the world, and the rate of retreat is unprecedented at least in the last 2000 years.  The area of arctic sea ice has reduced dramatically over 30 years – by 10% at its maximum seasonal extent (in March) and by 40% at its minimum seasonal extent (in September).  The oceans have warmed, they have become more acidic, and their oxygen concentration has dropped.  Sea level has risen by about 20cm since 1901, and the rate of increase is speeding up.  Climate zones have shifted towards the poles.  Some of the changes are effectively permanent:  changes in the ocean, ice sheets and global sea level are irreversible for centuries to millennia.

The report states that “human-induced climate change is already affecting many weather and climate extremes in every region across the globe”.  Hot extremes, including life-threatening heat waves.  Heavy storms and floods, including stronger hurricanes and cyclones.  Agricultural and ecological droughts.  And a greater chance of compound extreme events – for example, concurrent heatwaves and droughts, and fire weather.  (And, as we have seen over this summer, no location can assume it is immune to this.)

“Many changes in the climate system”, the authors write, “become larger in direct relation to increasing global warming.  They include increases in the frequency and intensity of hot extremes, marine heatwaves, heavy precipitation, agricultural and ecological droughts in some regions, and proportion of intense tropical cyclones, as well as reduction in Arctic sea ice, snow cover and permafrost.”

None of this is particularly new information, but all of it is more certain, and the numbers are more precise.

Where the report goes into somewhat new territory is with its future scenarios.  It has 5 of them, which range from SSP5-8.5, in which governments take virtually no action, down to SSP1-1.9, in which serious emissions reductions keep average global temperature rise down to 1.6°C at mid-century and reduce it to 1.5°C by 2100.  We know from the special IPCC report that came out in the autumn of 2018 that going beyond 1.5°C for any length of time risks catastrophic events and processes on an unmanageable scale – so really only one of the authors’ scenarios would give us a chance to manage the crisis and, over a long period of time, fully emerge from it.

Even under this SSP1-1.9 scenario, things will get worse than they already are – but not as badly as in the other cases.  To take one example:  Hot temperature extremes over land which historically happened only once every 50 years are already happening every 10 to 11 years.  At 1.5°C of warming, that reduces to once every 6 years; at 2°C to once every 3 or 4 years, and at 4°C to almost every year.  And the extremes of heat also increase disproportionately as we move from 1.1 to 1.5 to 2 to 4.  On top of that, the greater the global warming, the greater the variability of the global water cycle and the greater the severity of wet and dry events.

The report adds that “under scenarios with increasing CO2 emissions, the ocean and land carbon sinks are projected to be less effective at slowing the accumulation of CO2 in the atmosphere.”  This means that we must not lean too much on agricultural policy to sequester carbon – we can expect it to yield declining results.  Of course we need to move towards an agriculture which can use soil carbon storage to the extent that it is no longer a net emitter – but that will only work if we are also rapidly shifting away from burning fossil fuels and leaking methane.

This report leaves no doubt that continuing on our current path can lead only to destruction and misery.  So what do we need to do to avoid that?  A physical science report can only indicate what speed of emissions reduction we need to achieve, not specifically how to achieve it.  That comes later.

But to explain it we need the concept of carbon budgets.  From a starting point in the late 19th century, there was a fixed amount of carbon that we could emit if we were to stay below 1.5°C average temperature rise.  Once we have emitted that amount, we have spent our budget and we are in carbon debt.  The report finds that figure to be 2800 billion tonnes, for the whole world, for all time.  We have already, as a global society, emitted 2400 billion tonnes.  It’s been a great ride, but it very soon has to come to an end, because we have only 400 billion tonnes left in our budget.  If that sounds like a lot, a simple calculation shows that if we carry on as we are we will have blown our budget early in the 2030s.

For Canada, it is morally worse than that.  If everyone on the planet had an equal right to emit carbon dioxide, Canada would, at its current rate, get through its fair share in a little over 3 years.

And for Saskatchewan, it’s even worse.  We get through our share in fourteen and a half months.

We have an enormous amount of work to do – but, as I will argue in the next blog posts, it is still not impossible, and there are great opportunities as well as challenges.

But let’s go back to that almost-1.5-compliant pathway, the SSP1-1.9.  It tells us the same message that the IPCC scientists told us in their 2018 special report: as a global community we need to at least nearly-halve our CO2 emissions by 2030 and reduce them to zero around mid-century.  And also at least halve emissions of methane by half and nitrous oxide by about a quarter by mid-century.

But we have to go further than that in Canada.  We are a wealthy country.  We need to make bigger and faster cuts in our emissions, partly because we are better placed to do so, and partly because it is just morally right as high emitters (both currently and historically).  We have privilege as a society, and with privileges come obligations.  Anything less than a national 60% emissions reduction by 2030 is inadequate.  My next blog post will talk about the broad measures we need to achieve that.