If you have some means of interacting with the outside world like a TV, computer or smartphone,
then there's a reasonable chance you'll have heard about a major new publication called the
Sixth Assessment Report or AR6, published this week by the Intergovernmental Panel on Climate
Change or IPCC.. They've been releasing these climate assessment reports every seven or eight
years or so since 1990. The last main report, unsurprisingly titled AR5, came out in 2013 and it
was used extensively to shape the policy set out in the Paris Agreement which was signed by more
than 190 countries in 2015. The lack of subsequent climate mitigation actions by the governments of
those countries was so lamentable that it prompted the IPCC to really lay it on the line in a special
2018 interim report called SR15, spelling out in graphic detail the existential consequences
that we and all the other species on the planet would face if we humans didn't collectively get
off our backsides and do something pretty urgently and radically to drastically reduce the amount of
carbon dioxide and other greenhouse gases that our daily activities were spewing into the atmosphere.
That caught the attention of our wise and most excellent world leaders,
who all agreed it was a jolly poor show and that they would definitely have a
very good look at thinking about discussing the possibility of considering some concrete actions.
The sum total of that response was a rise in carbon dioxide emissions of more than 2% in 2018
followed by another 0.6% rise in 2019. it took an unprecedented global lockdown in 2020 to actually
achieve a reduction in emissions of about seven percent, all of which we've already made up for
as we move towards the third quarter of 2021. If it was a school report card it'd have a very big
F minus written in red pen at the bottom of the page. And now millions of people all over the
planet, from California to Europe and Siberia, and from Australia to China and Southeast Asia, are
already suffering some of the consequences that the IPCC has been warning us about for decades.
So where do we go from here? Have we had our final swig of whiskey at the last chance saloon,
or is there a chance we can somehow find a way out of this self-inflicted catastrophe? Well that's
precisely what this new IPCC Sixth Assessment report attempts to spell out for us all. Again
Hello and welcome to Just Have a Think. I think I've thrown enough preamble at you so let's just
dive straight into the report and have a look at what it's telling us. We'll start with these
two charts. The first one shows global surface temperatures relative to the 1850 to 1900 levels
from 1AD to the present day, with the shaded area showing the range of variability in the
reconstructions from paleoclimatic archives. You can see that the overall temperature remained
remarkably stable all the way up to the start of the industrial revolution. Then it all went a bit
haywire and now we've hit surface temperatures that are warmer than the warmest multi-century
period in more than a hundred thousand years. The chart on the right starts with a plot of
simulated temperatures that would have occurred from 1850 to the present day if we only took
natural occurrences like solar and volcanic activity into account. Again there's a shaded
area showing the range of modelling variability. The next line shows the computer model predictions
of what the temperature should have been once you added in all human activity with
the naturally occurring stuff. And the final line represents the actual observed temperature change.
So, you know, it's us! And it's clearly carbon dioxide that's causing the majority of the
heating, or what the scientists call radiative forcing, followed fairly closely by methane.
These blue bars, by the way, that dip into the negative or cooling zone, represent aerosol
particulates like sulphur dioxide that get up into the atmosphere and reduce the amount of
sunlight reaching the earth's surface. They mostly come from transport and industrial
activity and ironically at the moment they're actually cancelling out some of the warming.
The IPCC found that 2019 CO2 concentration levels were higher than at any time in the last 2 million
years, with methane and nitrous oxide levels higher than any time in the last eight hundred
thousand years. Those changes have already resulted in some very unwelcome record numbers.
2011 to 2020 late summer arctic sea ice area was smaller than any time in the last thousand years.
Since 1950 almost all the world's glaciers have been retreating at rates unprecedented
in at least the last 2,000 years. Global sea levels
have risen faster since 1900 than they have in any other century in the last 3,000 years.
The global oceans have warmed faster in the last century than any time in the last 11,000 years.
Extreme heat waves have become more frequent and more intense across most land regions since the
middle of last century while cold extremes have become less frequent and less severe. Some of the
hot extremes of the past 10 years would, according to the IPCC, have been extremely unlikely to have
happened without human influence on the climate systems. It's also likely that our activities
have increased the chances of extreme wildfires and floods like the ones we've been witnessing
in the last few years. Climate change is already affecting every inhabited region across the globe,
with hot extremes on the increase just about everywhere, heavy precipitation becoming more
frequent across most of the northern hemisphere and agricultural and ecological droughts worsening
in the mid-latitudes and parts of the southern hemisphere, which by the way is where we grow
a lot of our food. So that's a very quick summary of the state of our planet right now,
and it's not looking great is it? But perhaps more importantly, what does the IPCC report
tell us about the possible future world? Well, based on the literally thousands of existing
research papers that the report authors poured over to compile this latest assessment they've
been able to produce five future scenarios that they call shared socioeconomic pathways or SSPs,
ranging from the whole world locking down like we did in 2020 but, you know, for about the next
three decades, all the way through to everyone carrying on business as usual resulting in global
atmospheric temperatures reaching somewhere between 3.3 and 5.7 degrees Celsius above
pre-industrial levels by the end of the century. The research data show that we're now so far down
the road of excessive greenhouse gas emissions that in every single one of these scenarios,
even the ridiculously unlikely one where almost all modern day activities suddenly cease,
global surface temperatures will continue to rise until at least the middle of this century.
A global warming of 1.5 and 2 degrees Celsius will be exceeded during this century unless
deep reductions in CO2 and other greenhouse gas emissions occur in the coming decade. Our
scientists can now say it's virtually certain that the land surface will continue to warm between 1.4
and 1.7 times faster than the oceans and that the arctic will continue to warm more than twice
as fast as the global average. Every 1 degree Celsius of warming will intensify extreme daily
precipitation events by 7 percent. The proportion of category four and five cyclones is projected to
increase, with higher peak wind speeds, and we'll see a further amplification in permafrost thawing
releasing mind-boggling amounts of previously locked up methane into the atmosphere. And even
under the lowest SSP projection the arctic will become ice-free in September at least
once before 2050, with the likelihood that it will be far more frequent in the higher SSP scenarios.
Extreme temperature events that might have happened once a decade between 1850 and 1900
are already now likely to happen every three years or so, and they'll become
annual occurrences in the highest SSP projection. A really mega extreme heat wave event, with mass
casualties and fatalities, that might have been expected to happen perhaps only once or twice
in the whole of the 19th century is already now likely to hit us once a decade and could
be happening every other year by the end of this century in the worst case scenario.
Similar thing with precipitation, with a once a decade event happening every two or three years,
and with agricultural and ecological droughts with catastrophic decadal events of the 19th century
projected to clubber us every other year if emissions continue to rise unchecked. And if that
lot wasn't enough for, you how about this one - under SSP scenarios with increasing CO2 emissions
the ocean and land carbon sinks are projected to become less effective at slowing the
accumulation of CO2 in the atmosphere. That means more atmospheric CO2, which means
more warming creating one of many feedback loops. The magnitude of feedbacks between climate change
and the carbon cycle becomes larger and more uncertain in high CO2 emission scenarios too,
and that doesn't include what the IPCC describe as "additional ecosystem responses to warming
not yet fully included in the climate models, such as CO2 and methane fluxes from wetlands,
permafrost thaw and wildfires." All of which will further increase concentrations of those
gases in the atmosphere at levels that we can't yet predict. How you doing so far?
We're not finished looking at our children's bleakly dystopian future just yet though,
because the report also finds that many changes due to past and future greenhouse gas emissions
will be irreversible for centuries or even millennia. Mountain and polar glaciers are
now committed to melting for decades or centuries to come. Permafrost thaw is irreversible for many
centuries. The Greenland ice sheet is virtually certain to continue melting throughout the
21st century, and even the previously presumed rock-solid Antarctic ice sheet
is likely to continue losing mass. It's virtually certain that we'll see as much as half a metre of
sea level rise even in the best case SSP scenario and possibly up to two metres by 2100 in the worst
case. According to this 2019 study two meters of sea level rise would leave 630 million people
living on land below projected annual flood levels, not to mention the catastrophic storm
surges that would regularly wreck infrastructure and endanger lives in many coastal cities,
including some of the biggest and richest like London, Miami, New York and Shanghai.
And because of our lack of knowledge about the stability of the ice sheets
and deep uncertainty about how quickly they may give way,
the IPCC cannot rule out five metres of sea level rise by 2150 under a very high greenhouse
gas emission scenario. They also can't completely rule out what they call "low likelihood outcomes",
like complete ice sheet collapse, abrupt ocean circulation changes, compound extreme events,
and warming that's substantially larger than the assessed very likely range.
All these things, say the IPCC, must be taken into account as part of policymakers risk assessments.
One of the most significant ocean circulations is the Atlantic Meridional Overturning Circulation
or AMOC, made famous in the film The Day After Tomorrow. The IPCC found that the AMOC is very
likely to weaken over the 21st century. It won't have the effect that the folks in Hollywood dreamt
up for the film, but it could cause significant disruptions to global weather patterns.
All sounds a bit apocalyptic doesn't it? So what does the IPCC conclude we need to do
to avoid the worst of these existential calamities? Well it won't surprise you to
learn that they tell us we need to reach a minimum of net zero CO2 emissions as fast as possible.
Between 1850 and 2019 we humans put about 2,400 billion tons of carbon dioxide into our
atmosphere, and we're still spewing out around 40 billion tons a year today. There's a near
linear relationship between cumulative emissions and global warming, as this chart illustrates.
Every tonne of CO2 counts, and every thousand billion tons is assessed as likely causing around
half a degree of extra warming. So, as this table shows, if we're to have an 83% chance
of limiting global warming to 1.5 degrees Celsius above 1850 to 1900 levels then we've only got 300
billion tons of CO2 left to play with. That's less than eight years worth at today's emission rates.
As in previous reports, the IPCC looked at carbon removal and storage technologies
as their only real solution for keeping CO2 levels below critical limits. That's things
like direct air carbon capture or DACCS, and carbon capture utilization storage or CCUS.
Those technologies don't yet exist at anything like the required scale though.
Not even close. Several orders of magnitude out, as the science bods would say. So as our
world leaders congregate at the COP 26 climate conference in Glasgow in November this year,
we need them to be making firm binding commitments to drastically reducing fossil fuels in transport,
industry and energy sectors and pushing as hard and as quickly as possible towards the rollout
of the now very cheap renewable technologies of wind and solar. So, have we had our final
swig of whiskey at the last chance saloon? On the basis of this report the answer is probably yes.
COP 26 could well be our last real opportunity to reach international consensus and cooperation
on a global strategy the like of which the world hasn't seen since the end of the second world war.
Let's hope they don't mess it up, eh? That's it for this week. A big thank you,
as always to the folks at Patreon who keep these videos completely independent
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