Hello and welcome to Just Have Another Think - our twice monthly look at some of the environmental,
ecological and social consequences of the 21st century climate emergency. Here's a nice 'sciency'
phrase for you, courtesy of the Intergovernmental Panel on Climate Change. They tell us that our
climate is a 'non-linear chaotic system'. It's a phrase that's often abused by folks who are, shall
we say, less than keen to accept the realities of climate change. Those folks argue that by
definition a chaotic system can't be predicted and so it's impossible to produce a model that
can accurately tell us what the future may hold. They sometimes go all the way back to 1963, when
chaos theory was first expounded in a landmark paper by Edward Lorenz. He's the guy that brought
us the famous butterfly effect. You know, the one that says if a butterfly flaps its wings in one
part of the world, then a few weeks later it could result in a tornado somewhere else on the planet.
Lorenz argued that the inherent chaotic nature of weather meant it was impossible to make
accurate long-term forecasts by any method. But that was 1963. We've got supercomputers now,
with processing capabilities that would have been pretty much inconceivable back then. Plus,
two other very important points... 'climate' is not the same as 'weather'. And climate modelling
is not the same as weather forecasting. There's a good analogy for climate and weather - a bit
cliched now, so forgive me if you've heard it before, but it still does do a very good job of
explaining the difference, so I'm going to use it anyway. Think of the climate as being like
your personality, and the weather as being like your mood. Your mood can change from day to day,
and even from minute to minute, depending on a very complex and often unpredictable
set of variables that you're confronted with in your daily life. Others around you see your mood
changes, but they accept that you are still fundamentally you. You might be having a good
day or a bad day, but your personality - the thing that makes you 'You' - remains the same.
In climate terms, human activity, particularly since the start of the industrial revolution,
has increased the level of greenhouse gases in our atmosphere. The result has been well over one
degree Celsius of warming as an average across the planet. And for every one degree Celsius of
warming the atmosphere is able to retain seven percent more water. That means our climate is
developing what you might call a personality disorder. The climate personality that our
species has come to know and love, and depend on, over the 12 000 years since the last ice age
is now changing in ways that are making it less recognizable, with much more energy and moisture
now available to drive the weather. And just like a doctor providing a patient with a prognosis of
how a personality disorder is likely to progress within upper and lower boundaries of probability,
so our climate modelers can predict a range of very likely long-term outcomes for our climate.
And of course, just as a doctor might warn family and friends to look out for
extreme and sometimes violent mood swings in the personality disorder patients,
so our changing climate is increasing the likelihood of more and more extreme weather events
occurring all over the world. They can be anything from sub-zero arctic temperatures in Texas,
to record heat waves in the arctic circle, or several months worth of rain falling in 48
hours in Europe. Those weather events would of course all have been perfectly possible
within the planet's climate system at any point in the last 12 000 years, but the
changing personality of our climate makes those weather mood swings much more likely to happen
once a decade, or even once a year, instead of perhaps once a century or so. And if, for example,
you live in a part of the world that was already pretty hot and humid for large parts of the year,
the one thing you do not want is extra energy and moisture in the atmosphere. That exact predicament
has been assessed in some detail in a new research paper published this month in Nature Geoscience.
The paper focuses on the tropical zone from 20 degrees north of the equator to 20 degrees south,
and it looks specifically at a phenomenon known as extreme wet bulb temperature. The
bulb in question is not a plant bulb or a light bulb. It's actually the little bit of glass at
the bottom of the thermometer. So what does a wet thermometer have to do with climate change? Well,
one of the most effective mechanisms we humans have for cooling down when we're overheating is to
sweat - unless of course you're Prince Andrew, who appears to be on a one-man mission to definitively
prove the lizard people conspiracy theory... "I have a peculiar medical condition, which is that
I don't sweat"... but for the rest of us the water that we excrete from our sweat glands evaporates
out into the surrounding atmosphere. And as it does so, it draws heat away from our bodies and
that cools us down. It's all to do with something called 'the latent heat of vaporization',
which I looked at in an earlier video that you can watch by clicking up there somewhere.
If the surrounding atmosphere already contains a lot of moisture - in other
words if it's very humid - then the water on your skin has less chance of evaporating.
And that's where the wet bulb comes in. You can work out how humid the atmosphere
is by purchasing two ridiculously oversized thermometers from your local hardware store.
Stick them side by side somewhere out of the sun and away from the wind and then wrap a
piece of damp material like muslin or something at ambient temperature around the glass bulb on
one of the thermometers. If the surrounding area is very dry then the moisture in the material can
easily evaporate and the temperature in that thermometer will go down. If the air is humid
then the moisture won't evaporate so easily and the temperature won't go down so much. And if
the air is already saturated with moisture, in other words if it's at 100% humidity, there'll
be no evaporation at all and the temperature in both thermometers will be exactly the same.
So, the closer the temperatures in the two thermometers are, the more humid the
ambient air must be. Obviously there are more sophisticated versions of that DIY operation,
that are very accurately calibrated to calculate humidity precisely, but you get the idea.
All of that matters because at a wet bulb temperature of just 35 degrees Celsius,
or 95 degrees Fahrenheit, the human body is unable to lose enough heat through sweating to survive.
And if that human body happened to be yours, then you'd be dead within about eight hours or so.
The authors of the new paper looked at climate modelling in four tropical locations - the Amazon
rainforest, the African Sahel, the Indian peninsula and the southeast Asian maritime
continent, which is Indonesia and the Philippines and the few others. What they wanted to know was
how the extremes of basic air temperature and the extremes of wet bulb temperature
are projected to change as a result of overall average warming across the entire tropical zone.
That analysis produced four charts, which in their fully finished state are a wonderful cacophony of
confusing lines and shaded areas, so I decided to dismantle them all and build them back up step by
step so that I could more easily understand them. First of all, you've got the horizontal axes,
which show a range of possible future increases in mean tropical warming measured in degrees Celsius.
The vertical axes show a range of the potential extreme temperatures relative to the tropical
mean. And these dotted black lines represent a one-to-one ratio between those two measurements.
So let's start with the basic air temperature, which is the one our weather forecasters use
on the TV. The red shaded areas show the range of projected extreme air temperature changes
as the tropical mean temperature increases, taken from various different climate models.
And you can see that there's quite a lot of variability between those models,
with the red line representing the average of all of them.
This blue shaded area is the range of modelling variability for extreme wet bulb temperatures,
and the blue line is the average of all of them. You can quite clearly see that there's much closer
agreement between the models for extreme wet bulb temperatures than there is for extreme air
temperature. In fact, the paper tells us that the modelling variation for extreme air temperature
is 3.7 times greater than the modelling variation for extreme wet bulb temperature.
You can also see that the extreme wet bulb temperatures increase in an almost exactly
one-to-one relationship with rising average regional temperature. So what can we conclude from
all of that? Well, the research paper points out that the annual maximum of average daily extreme
wet bulb temperatures across 99.98% of the land area in the tropical region over the past 40 years
was 33 degrees Celsius. So if by some miracle the world does actually manage to keep average
global atmospheric warming to below 2 degrees Celsius, then that potentially fatal 35 degree
wet bulb temperature might just be averted. But if we sail past the two degree threshold,
which is most certainly what we're on course to do at the moment, then temperature and humidity
will become a real existential threat for about three billion people living in the middle part
of the globe. And let's not forget that all the temperatures we've looked at so far in this video
were taken in the shade. Meteorologists apply a different term for heat stress in direct sunlight.
It's something they call Wet Bulb Globe Temperature, and unsurprisingly the effect
on the human body of direct exposure to sunlight is far more severe than heat stress in the shade.
Now you could argue that people will simply need to use a bit of common sense in the future, and
stay inside an air-conditioned building during those extreme temperature events. And that's fine
if you've got one of those buildings available to you, and if you've got nothing else to do.
But if you're one of the hundreds of millions of people in the tropical zone who rely on outdoor
work for a living then your options are either to stop working and lose a day's pay, or a week's pay
or maybe even a month's pay, or carry on working regardless and risk your own life in the process.
I don't know about you, but that's a kind of horrific 'Hobsons Choice'
that I wouldn't wish on anyone. Whether we reach that shocking milestone or not depends on the
actions of every corporation, every government, and every individual like you and me literally
from today onwards. So that's your midweek food for thought folks. As always, thanks very much
for watching, and I'll see you for our regular Just Have a Think program on Sunday. Bye for now.