rC3 preroll music
Herald: It is with much pleasure that I
can now introduce our next speaker, so
it's just started raining outside, but
this heavy rain is not at all probably the
extreme weather effects that we will hear
about right now. The weather, the talk
that we are being presented next will deal
with extreme weather effects and how they
are linked with climate change and how we
even know about that. Our speaker today
is Fredi Otto. She's associate director of
the Environmental Change Institute of the
University of Oxford, and she's also the
lead author of the upcoming IPCC
assessment report, AR6. And without with
no further ado, I give you the stage
Fredi, please.
Frederike Otto: OK, thank you. Yeah. Hi.
It's stopped raining here in Oxford, just
about, but it's definitely flooded, so
that might actually be something to come
back to and talk about with respect to
climate change. So. Whenever we hear or
whenever today an extreme weather event
happens, we hear about hurricanes,
wildfires, droughts, etc., the question
that is immediately asked is, was this,
what is the role of climate change? And to
answer that, for quite a long time,
scientists gave an answer that we cannot
attribute individual weather events to
climate change. But… Sorry, OK. But this…
Because the first, the one answer that
people were giving were that, well, you
can't attribute individual weather events
or they were saying in a world where
climate change happens, of course, every
extreme weather event is somewhat affected
by climate change. And the latter is
attributed too, but that does not
obviously provide much information,
because it doesn't say anything about
whether the event was made more likely or
less likely or what the role of climate
change was. And the first answer that you
can't attribute individual events is not
true any longer. And this is... why that has
changed and how that has changed. And what
we can say is what the content of this
talk will be. So ultimately, every weather
event, extreme or not, is if you
absolutely boil down to it is unique and
they all have many different causes. So
there is always the role of just the
natural chaotic variability of the climate
system and climate and weather system that
plays a role. There's always a causal
factor in where the event
happens, whether it's over land, over a
desert, over a city or a forest, but also
man-made climate change can have an
influence on the likelihood and intensity
of extreme weather events to occur. And so
what we can say now, and what we mean when
we talk about attribution of extreme
weather events to climate change is how
the magnitude and likelihood of an event
to occur has changed because of man-made
climate change. And in order to do that,
we first of all need to know, what is
possible weather in the world we live in
today? So say we have a flooding event in
Oxford and the question is, was this
climate change or not? So the first
question is we need to find out what type
or what kind of event is the heavy
rainfall event that leads to the flooding.
So is it a 1 in 10 year event? Is it a 1
in 100 year event? And in order to do
that, you can't just look at the observed
weather records because that will tell you
what the actual weather that occurred is.
But it doesn't tell you what the possible
weather under the same current climate
conditions are. And so we need to find out
what is possible weather. And to do that,
we use different climate models. So we
simulate under the same climate conditions
that we have today, possible rainfall
events in December in Oxford. And we might
find out that the event that we have
observed today is a one in 10 year event.
And so if you do this, look at all the
possible weather events, you get a
distribution of possible weather under
certain conditions, which is shown in the
schematic on the slide here in the red
curve. And then you know that when it
rains above, say, 30 millimeters a day in
Oxford, then you have a real problem with
flooding. So you define that this is your
threshold from when you speak about an
extreme event. And so you have a
probability of this event to occur in the
world we live in today. Of course, that
does not tell you the role of climate
change, because in order to know that, you
would also you will also need to know what
would the likelihood of this event to
occur have been without man-made climate
change, and so. But because we know very
well how many greenhouse gases have been
introduced into the atmosphere since the
beginning of the industrial revolution, we
can actually remove these additional
greenhouse gases from the climate models
atmospheres that we use and simulate a
world that would have been exactly as it
is today, but without the greenhouse gases
from the burning of fossil fuels. And in
that world, we can then also ask the
question, what are possible heavy rainfall
events in December in Oxford? And we might
find that the event that we are interested
in is in that world, not a one in 10 year
event, but a one in 20 year event. And
because everything else is held the same,
we can then attribute the difference
between these two likelihoods of
occurrence of the extreme event in
question to man-made climate change. And
so with this fake example that I've just
used, we would then say climate change has
doubled the likelihood of the event to
occur because one that was one in 20 year
event is now one in 10 years. So that is
basically the whole theoretical idea
behind attributing extreme events and this
method can be used. And so, for example,
with our initiative that's called World
Weather Attribution, we have looked this
year at the extreme heat in Siberia, the
beginning of this year that, among other
things, led to temperatures above 38
degrees in the city of Verkhoyansk, but
also let to permafrost thawing and large
wildfires. And that event was made so much
more likely because of climate change that
it's almost would have been impossible
without climate change. So when we did the
experiments that the models it's a one in
80 million year event in a world without
climate change. And it's still a
relatively extreme event in today's world,
but it is possible. So this is the type of
event where climate change really is a
game changer. Another event that we have
looked at is Hurricane Harvey that hit the
Houston and Texas in 2017 and caused huge
amounts of damage with the rainfall
amounts it brought. And several attribution
studies doing exactly what I've just
described found that this type of, so this
extreme rainfall associated with a
hurricane like Harvey has been made three
times more likely because of climate
change. And colleagues of mine, Dave Frame
and his team, have then used these studies
to figure out how much of the economic
costs this hurricane can be attributed to
climate change, and found that of the 90
billion US dollars that were associated,
that were associated with the flood damage
from Harvey, 67 billion can be attributed
to climate change, which is in particular
interesting when you compare that to the
state of the art economic cost estimations
of climate change in general, which had
estimated only 20 billion US dollars for
2017 in the US from climate change. And of
course, not every year is an event like
Harvey, but it shows that when you look at
the impact of climate change in a more
bottom up approach, so looking at the
extreme events, which are how climate
change manifests and affect people, you get
very different numbers, as if you just
look at large scale changes in temperature
and precipitation. But of course, not
every extreme event that occurs today has
been made worse because of climate change.
So this is an example of a drought in
southeast Brazil that happened in 2014,
2015, where we found that Climate change
did not change the likelihood of this
drought to occur, so it was a one in 10
year event in 2014, 2015, and also without
climate change, it has a very similar
likelihood of occurrence. However, what we
did find when we looked at, OK, what else
has changed? Why has this drought that has
occurred in a very similar way earlier in
the 2000s and also in the 1970s with much
less impacts. We looked at other factors
and found that the population has
increased a lot over the last or over the
beginning of the 21st century, but in
particular, the water consumption in in
the area and the water usage has increased
almost exponentially. And that explains
why the impacts were so large. So this is
what I've just said is sort of basically
the the very basic idea and and how in
theory these studies work and how and some
results that we find. In practice, it is
usually not quite as straightforward,
because while the idea is still the
same, we need to use climate models and
statistical models for observational data
to simulate possible weather in the world
we live in and possible weather in the
world that might have been. That is, in
theory, straight forward, in practice,
it's often relatively difficult, and what
you see here is how the results of these
studies look when you don't use schematic
and if you're not a hydrologist, this
might be a bit of an unfriendly plot. But
it's it's basically the same as the
schematic that I've showed at the
beginning, but just plotted in a way that
you can see the tails of the distribution
particularly well, so where the extreme
events are. So on the X-axis, we have the
return time of the event in years on a
logarithmic scale and on the Y-axis, you
see the magnitude of the event and that
defines what our extreme event is. And
this is actually a real example from heavy
rainfall in the south of the U.K. And you
can see here in red, each of these red
dots that that you see on the red curve is
a simulation of one possible rainfall
event in the South of the U.K. in the year
2015 in the world we live in today with
climate change and the dashed line
indicates the threshold that led to to
flooding in in that year. And on the
X-axis, when you go down from the dashed
line, you can then see that this is
roughly a one in 20 year event in the
world we live in today. And all the blue
dots on the blue curve are simulations of
possible heavy rainfall in the South of
the U.K. in 2015, in a world without man-
made climate change. And you can see that
these two curves are different and
significantly different, but they are
still relatively close together. And so
the event in the world without climate
change would have been a bit less likely,
so we have roughly a 40 percent increase
in the likelihood. But still other factors
like, yeah, just the chaotic variability
of the weather and also, of course, than
other factors on the ground where houses
build in floodplains and so on play an
important role. So this is the
actual attribution step. So when we find
out what the role of climate change is,
but of course, in order to do that, there
are a few steps before that are crucially
important and absolutely determine the
outcome. And the first step, the first
thing to find out is what has actually
happened, because usually when we read
about extreme weather events or when we
hear about extreme weather events, you see
pictures in newspapers of flooded parts of
the world. And so you don't usually have
observed weather recordings reported in
the media. And the same actually is
true for us. So when we are, so we work a
lot with the Red Cross and they ask us:
OK, we have this large flooding event, can
you do an attribution study? Can you tell
us what the role of climate change is?
Then we also just know: OK, there is
flooding. And so the first step is we need
to find out what is the weather event that
actually caused that flooding. And that is
not always that straightforward. And this
is what you see here on this map, on this
slide is a relatively stark example, but
not an untypical. So it's of an extreme
rainfall event on the 10th of November
2018 in Kenya. And on the left hand side
is one data product of observational data,
of observational rainfall data that is
available and on the right hand side is
another showing the same event. And the
scale which I failed to to say on the
slide in millimeters per day. And so on
the left hand side, you have extreme
rainfall of above 50 millimeters per day,
which is considering that, for example, in
in my home town of Kiel in Schleswig-
Holstein, there is about 700 millimeters
of rainfall per year. You can see that 50
millimeters in a single day is very heavy
rainfall, whereas in the other data
product, you don't see as much rain. You
still see large rain, but it's not in
the same magnitude, and it's also not
exactly in the same place. And so given
that most countries in the world do not
have an open data policy, so you can't
actually get access to the observed
station data, but you have to use
available, publicly available products
like the two have shown here, you have to
know and you have to work with experts in
the region to actually know who hopefully
has access to the data to actually find
out what has happened in the first place.
But of course, if you don't know that or
there is not always a perfect answer, then
if you don't know what event that is. It's
very difficult to do an attribution study.
Assuming though you have found a data
product that you trust, the next question
then is what is actually the right
threshold to use for the event? So if you
have flooding that was pretty obviously
caused by one day extreme rainfall event,
then that would be your definition of the
event. But it could also be that the
flooding has been caused by a very soggy,
rainy season. So actually, the really the
real event you would want to look at is
over a much longer time scale or if the
flooding occurred mainly because of some
water management in the rivers and has
actually flooded further upstream, your
spatial definition of the event would be
very different. And so and what you see
here on this plot is an example of a heat
wave in Europe in 2019. And there, what
usually makes the headlines is the maximum
daily temperature. So if records are
broken, so you could use that as a
definition of the event that you're
interested in. But of course, what really
causes the losses and damages from extreme
events is not necessarily the one day
maximum temperature, but it is when heat
waves last for longer, and especially when
the night temperatures are also high and
not just the daytime temperatures. So you
might want to look at an event over five
day period instead of just the maximum
daily temperatures. Or, and this is sort
of why I have shown the pressure plot on
the right hand side, which is really just
an illustration, it's not terribly
important what's on there. But there are,
of course, different weather systems that
can cause heat waves, especially in the
area here in the south of France. It could
be a relatively short lived high
pressure system bringing hot air from the
Mediterranean. Or it could be something
that is caused from a long time stationary
high pressure system over all of Europe.
If you want to take that into account,
obviously also your event is different.
And there is no right or wrong way to
define the event because there are
legitimate interests in the maximum
daily temperatures, legitimate interest in
just a specific type of pressure system
and interest in what actually causes more
excess mortality on people, what would be
the three day or longer type of heat
waves. But whichever definition you
choose, it will determine the outcome of
the study. And here are some typical
results of attribution studies when you
look at them in a slightly more scientific
way and slightly less just the headline
way as the ones that I've shown earlier.
Because, of course, what also is important
is not only how you define the event,
depending on the impacts and depending on
what you're interested in. The extreme
event and what observational data you have
available. But of course, there's also
then the question of what models, what
climate models do we have available? And
there's always some tradeoff between what
exactly caused the event and what we can
meaningfully simulate in a climate model.
And then all climate models are good for
something and bad for other things. So
there always need to be a model evaluation
stage. So where you test if the models
that you have available are actually able
to simulate in a reliable way the event
that you're interested in. But even if you
have done all this, it can sometimes be
that the models and the observations that
you have show very different things. And
so the heat wave in Germany in 2019, which
was also on the slide before,
is an example of that. When we
look at the long term observations of
extreme, of high temperatures and see how
they have changed over time, we find that,
because of the change in climate, we have
observed, the likelihood of this type of
heat wave has increased more, yeah, about
300 times. So you see this
in the black bar, the black bar in the
middle of the blue bar, on the left hand
side, at the very top where it says DWD
obs, that's the Deutscher Wetterdienst
observations and we see that where this
black bar is about, again, a logarithmic
scale, about 300 hundred times more
likely. But of course, because we have
only 100 years worth of
observations and summer temperatures
are extremely variable, there is a large
uncertainty around this change. And so we
cannot, from the observations alone, we
cannot exclude 100.000 times change in the
likelihood of this heat wave. But
similarly, also not a 20 times heat wave.
But what the main point is, that in all
the climate models and all the red bars
that you see on there are the same
results, but for climate models where we
have compared today's likelihood of the
event to occur with the likelihood in the
world without climate change, and you see
that the change is much lower. And of
course, climate change is not the only
thing that has changed and that has
affected observed temperatures. But other
factors like land use change and things
like that are much smaller in the size
than the climate signal. So they cannot
explain this discrepancy. So this means
that the climate models we have available
for this type of study have obviously a
problem with the extreme temperatures in a
small scale. And there are effects that we
don't yet understand. And so we can't say:
OK, this heat wave was made 10 times more
likely. But we can only say, that with our
current knowledge and understanding, we
can say that climate change was an
absolute game changer for this type of
heat wave, but we can't really quantify
it. On the right hand side is a much nicer
result on the top one, which is for
extreme rainfall, in Texas 2019 and nicer
result I mean now for a scientist and
in a scientific way. So we have in blue
two different types of observations from
the heavy rainfall event, and they both
show pretty much exactly the same result.
And also the two climate models that we
had available that passed the model
evaluation tests show an increase in the
likelihood of this event to occur. That is
very similar to that in the observations
in terms of order of magnitude. And so in
that case, we can just synthesize the
results and give an overarching answer,
which is that the likelihood of this event
to occur has about doubled because of man-
made climate change. And the last example
that I, that is here is for drought
in Somalia in 2010, where not only the
observations are extremely uncertain. So
from the observations, you could say we
could have both an increase in likelihood
or a decrease in likelihood by a factor of
10. But also the climate models show a
very, very mixed picture where you can't
even see a sign that that is conclusive.
So in that case, you can say, we can
exclude that climate change made this
event more or less than 10 times, more
than 10 times or less than 10 times more
likely. But we can't say anything more. So
we can exclude that it's a complete game-
changer like we have for heat waves, for
example. But that's about the only
thing that you can say for a result
like this. So this was sort of the
most detailed scientific stuff that I
would like to show, because I think it's
important to get some background behind
the headline results that would just
be climate change doubled the likelihood
of this event. So there are always four
possible outcomes of an attribution study
a priori. And that is because
climate change affects extreme weather in
two ways basically. One way is what we
would call the thermodynamic way, which
means that because we have more greenhouse
gases in the atmosphere, the atmosphere
overall gets warmer. So you have, on
average, an increase in the likelihood of
heat waves decrease in the likelihood of
cold waves. A warmer atmosphere can also
hold more water vapor that needs
to get out of the atmosphere as rainfall.
So on average, from the warming alone, we
would also have more extreme rainfall. But
then there's the second effect, which I
call the dynamic effect, and that is
because we've changed the composition of the
atmosphere, that affects the atmospheric
circulation. So where weather systems
develop, how they develop and and how they
move. And this effect can either be in the
same direction as the warming effect. So it
can be that we expect more extreme rainfall,
but we also get more low pressure systems
bring rain to get even more extreme
rainfall. But these two effects can also
counteract each other. And so you
can expect more rainfall on
average. But if you don't get the weather
systems that bring rain, you either have
no change in likelihood and intensity or,
if the dynamics win, you have actually
decrease in the likelihood of extreme
rainfall in a particular season or region.
And so this is why a priori, that can
always be four outcomes: It can be that
the event was made more likely. It can be
that it was made less likely. It can be
there's no change. Or it can be that with
our current understanding and tools, we
can't actually answer the question. And so
this has been possible to do now for
about a decade, but only in the last five
years really have many, many people or
many scientists started to do these
studies. And so there is actually a
relatively large, there are
lots of attribution studies on different
kinds of extreme events. And what you can
see on this map here is what the news and
energy outlet CarbonBrief has put all
these studies together. And you can see in
red where climate change played an
important role, and blue where climate
change did not play a role. And in gray,
that was an inconclusive result. This is
very important, though, that this is not
representative of the extreme events that
have happened. This is just represents the
studies that have been done by scientists
and they are, of course biased towards
where scientists live
and also towards extreme events that are
relatively easy to simulate with climate
models. So there are lots of heat waves in
Europe, Australia and North America
because that is where people live. And on
this next map, I have tried to
show the discrepancy between the extreme
events that have happened and those for
which we actually do know the role of
climate change. So here in red are deaths
associated with extreme events since 2003.
So since the first event attribution
study. And it's death from heat waves,
storms, heavy rainfall events and droughts
primarily in different parts of the world,
the bubble is always on the capital of the
country. And the larger the bubble, the
more deaths due to extreme events in those
years. And in black overlaying that are
those deaths for which we know the role of
climate change. So that doesn't mean that
the deaths are attributed to
climate change, but it means that there
we do know whether or not to what
extent climate change played a role. And
you can see that most of the European
countries, the black circle is almost as
large as the red one. So for most of the
extremes or most of the deaths associated
with extreme events, we do know the role
of climate change. But for many
other parts of the world,
there are no or very small black circles.
So for most of the events and the deaths
associated with them, we don't know what
the role of climate change is. And I've
used death here not because I'm
particularly morbid, but because it's
an indicator of the impacts of
extreme weather that is relatively good
comparable between countries. So this
means that with event attribution methods
that we have developed over the last
decade, we now have the tools available to
do, to provide an inventory of the impacts
of climate change on our livelihoods. But
we are very far from having such an
inventory at the moment because most of
the events that have happened, we actually
don't know what the role of climate change
is. And so we don't know in detail on
country scale and on the scale where
people live and make decisions, what the
role of climate change is today. There's
another slightly related issue with that
is, that the extreme events that I've used
to create the map are shown before with
the death of climate change, with the
death of extreme weather events. They are
from a database called EM-DAT, which is a
publicly available database where losses
and damages associated with disasters
technological disasters, but also
disasters associated with weather are
recorded. But, of course, they only can
record losses and damages if these losses
and damages are recorded in the first
place. And so what you see on this map is
in grey and then overlayed with different
with different circles are heat waves that
have occurred, they have occurred between
1986 and 2015 on this map. But you could
draw a map from 1900 to today, and it
would look very similar. And that shows
lots and lots of heat waves reported in
Europe and in the US, India, but there are
no heat waves reported in most of sub-
Saharan Africa. However, when you look at
observations, and also we see that extreme
heat has increased quite dramatically in
most parts of the world and a particular
hotspot is sub-Saharan Africa. So, we know
from when we look at the weather that heat
waves are happening, but it's not
registered and it's not recorded. So we
have no idea how many people are actually
affected by these heat waves. And so we
then, of course, don't do attribution
studies and don't find out what the role
of climate change in these heat waves is.
So in order to really understand the
whole picture, we would also need to start
recording these type of events in other
parts of the world. And so my very last
point, before, I hope that you have
questions for me, is: Of course,
everything I've said so far was talking
about the hazards, so talking about the
weather event and how climate change
affects the hazard. But of course that is
not the same or translates immediately
into losses and damages, because whether
or not a weather event actually has any
impact at all is completely driven by
exposure and vulnerability. So who and
what is in harm's way. And I've already
shown, I've already mentioned the example
early on with the drought in Brazil, where
the huge losses and damages were to a
large degree attributable to the increase
in water consumption. And thus,
therefore, in order to really find out how
climate change is affecting us today, we
not only need to define the extreme events
so that it connects to the impacts, but
also look into vulnerability and exposure:
What is changing, what's there and what
are the important factors. But we can
do that. And so we have really made a lot
of progress in understanding of how
climate change not only affects global
mean temperature, which we have known for
centuries, and how it affects large
scale changes in temperature and
precipitation, which we have also known
for a very long time. But we now have
actually all the puzzle pieces together to
really understand what climate change
means on the scale where people live and
where decisions are made. We just need to
put them together. And one lens or one way
of where they are currently put together
is, for example, in courts. And so because
it's obviously people who experience
losses and damages from climate change.
And so one way to address that is going
through national governments, local
governments, hoping for adaptation
measures to be put in place. But if that's
not forthcoming quickly enough, there is
the option to sue. And so this is one
example which is currently happening in
Germany where a peruvian farmer is suing
RWE to basically pay their share of a
adaptation because of largely increased
flood risk from glacier melt in the area.
And they want RWE to pay from their
contribution to climate change, where
their emissions and then have some funding
for the adaptation measures from them. And
that is one example of where these kind of
attribution studies can be used in a very
direct way to hopefully change
something in the real world. And with
this, I would like to end and yeah, leave
you with some references, and hope you
have some questions for me.
Herald: Sind wir durch? So, ja. Herzlichen
Dank für den Vortrag. Ich hab, bevor wir
zum Q&A kommen muss ich einmal mich im
Namen der Produktion bei den Zuschauern
entschuldigen, ich glaube ihr hattet etwas
Produktionssound auf den Ohren, das sollte
natürlich nicht so sein. Gut, wir haben
jetzt keine Fragen aus dem Chat bisher.
Aber vielleicht eine Frage von mir, das
letzte Beispiel war ja ein Fall
einer Klage über Ländergrenzen hinaus
quasi, ist das ein Ansatz, den man, den
wir in Zukunft öfter sehen würden, das
heißt, dass über Ländergrenzen hinweg
Menschen oder Organisationen sich
gegenseitig versuchen quasi über den
Klageweg auf den richtigen Weg zu bringen.
FO: Also es ist tatsächlich ein, eine
Ausnahme, dass das im Fall RWE und Lliuya
funktioniert, denn das deutsche Recht
sieht vor, dass Firmen, die in Deutschland
ansässig sind auch verschieden
verantworlich sind, die nicht in
Deutschland stattfinden.
H: So sorry to interrupt. I just realized
that we are still in English talk. Sorry
for that.
FO: OK. No worries. So your question was
if we're going to see more
international court cases where across
countries, across nation states we have
climate litigation. And this type of
litigation that I've just shown as
the example is in so far an
exception, as in German law, a company is
also responsible for the damages caused
outside of Germany. Which is not the case,
for example, for companies in the US
or so. So, and this is why Lliuya sued RWE
and not, for example, ExxonMobil. But
these type of cases, where this
Lliuya case is an example. We see a lot of
a lot of them, an increasing number of
them each year. And they are difficult to
do across nations because this, the German
law is exceptional on that case. But there
are other ways, like, for example, why are
human rights courts that can be done
across nation states and that is also
happening. So it's at the moment, it is
still legally not super straightforward to
to actually win these cases, but
increasingly a lot of lawyers working on
that so that we will see a lot of
change in that in the coming years.
H: OK, thank you. In the meantime, there
appeared some questions from the chat and
from the Internet. I will go through them.
First question is: are the results of the
individual attribution studies published
as open data in a machine readable format?
FO: laughter So all the studies that
we do that that I've done with my
team, with world weather attribution. So
there all the data is
available, and it's available on a
platform that's called Climate Explorer.
So that should be machine readable. So and
this is deliberately because yeah, because
we want to make it as transparent as
possible so everyone can go away, use our
data, and redo our studies, and find out
if we made any mistakes. But this is not
the case for all the studies that exist,
because most of them or many of them are
published in peer reviewed journals and
not all peer reviewed journals have
open data and open access policies.
But increasingly, journals have.
So if you, for example, go to the
CarbonBrief website and look at the map of
studies, there you have links to all
the studies. And a lot of them have the
data available.
H: OK, maybe a follow up to this one. The
next question is, are the models somehow
available or usable for a wider interest
public or is APC required? I'm not quite
sure what APC means.
FO: So the model data is publicly
available from–and this is one reason why
we have been able to do these studies
because until relatively recently, model
data was not publicly available and only
scientist working in a specific country
could use the model developed in that
country–but now all the model data is
shared publicly and people can use it. So
it's definitely there and usable. It just
requires some expertise to make sense of
it. But it's, yeah, people can use it.
H: OK, the next question is: to what
certainty can you set up counterfactual
models, which are an important reference
to your percentage value, and what
data are the basis for these models?
FO: So the counterfactual simulations are-
the climate models we use are basically the
same models that are used also for the
weather forecast. They are just run in
lower resolution. So, which I guess most
of this audience knows what that means. So
the data points for the part, so that it's
not so computing intensive. And these
models, they are tested against observed
data. And so that is how we do the model
evaluation. So that is some simulations of
the present day. And for the
counterfactual, we know extremely well how
many greenhouse gases have been included
into the atmosphere since the beginning of
the Industrial Revolution, so that there
is some very large certainty with that
number and we remove that from the models'
atmospheres. So the models have exactly
the same set up, but the lower
greenhouse gases, lower amount of
greenhouse gases in the atmosphere, and
then are spun up and run in exactly the
same way. So, they, but of course, we
can't test the counterfactual. And so that
means that we assume that the sort of the
the weather was still the same, physics
will still hold in the counterfactual. And
that the models that are developed
using present day represent the
counterfactual. Which is, which is an
assumption.
But it is not a completely
unreasonable assumption, because of
course, we have now decades of model
development and have seen that, in fact,
that indeed climate model projections that
have been made 30 years ago have actually
come… come to… have been realized, and
pretty much the same way on a large scale
that they have, as they had been predicted
30 years ago. And so that assumption
is not, yeah, it's not a big assumption.
So the counterfactual itself is not a
problem. But of course, also the present
day model simulations, they are
not… they are very far from perfect. And
there are some types of events which state
of the art climate models just can't
simulate. And so, where we can- what
we can say very little. So well, for
example, for hurricanes, we can say
with high certainty about the
rainfall associated with hurricanes, the
hurricane strength itself and the
frequency of hurricanes is something
which is very difficult to simulate with
state of the art models. So our
uncertainty there is much higher.
H: OK. And then, well, some, one question
that emerges from all of this is,
of course, if we know this much and way
more than in the past, how are
politicians still ignoring that
information? And how can we
convey that into their minds?
FO: Well, if I knew the answer to that, I
would probably not be standing here,
but actually doing politics. But I
think it takes a frustratingly long time
for things to change and things should
change much faster. But we actually- the
last two years have shown huge progress, I
think, in terms of also putting climate
change on the agenda of every politician.
Because, and that's largely due to the
Fridays For Future movement, but also to a
degree, I think, due to the fact that we
now actually know that the weather that
people experience in their backyard–and
pretty much independent of where their
backyard is–is not the same as it used to
be. And so people do experience today
climate change. And I think that
does help to bring a bit more urgency.
And, of course, I would have said everyone
has climate change on their agenda, which
was very different even two years ago,
where there were lots of people who
would never talk about climate change and
their political agendas has played no
role. It doesn't mean that it
has the right priority on that agenda,
but it's still a huge step forward that
has been made. And so I think we do know
some things that do work, but we just have
to just keep doing that. Yeah, I don't
think I can say more. I don't have a magic
wand to change it otherwise.
H: Maybe some other point of impact.
One of the question is, is it possible to
turn the results of attribution studies
into recommendations for farmers and
people who are affected in a financial way
by extreme weather and how to change
agriculture to reduce losses from extreme
weather effects?
FO: Yes, absolutely. So that is
one of the most useful things of these
studies is well, on the one hand, to raise
awareness. But on the other hand, if you
know that a drought that you have
experienced that has led to losses is a
harbinger of what is to come, then that is
incredibly helpful to know how
agricultural practices might need to be
changed. Or that insurance for losses from
agriculture might need to be changed. And
so this is exactly why we do these
attribution studies. Because not
every extreme event has always
shows the fingerprints of
climate change. And if you know
which of the events are the ones where
climate change is a real game changer, you
also do know where to put your efforts and
resources to be more resilient in the
future. And for financial losses, it
is on the one hand, yeah, you can use
these studies to find out what your
physical risks are for your assets. And
how they, and of course, everything that
I've said, comparing the counterfactual
with the present we can do, and we do this
also with the future. So you can also see
how in a two degree world, the events,
the likelihood and intensities are
changing. And of course, you can then
also, in a less direct way, use this kind
of information to see, to assess what
might be other risks from- where might be
stranded assets, what are other risks
for the financial sector,
for the financial planning.
Where could liability risks be and how
could they look like. So there is, because
extreme weather events and their changes
in intensity and magnitude is how climate
change is manifesting, it really connects
all these aspects of where the
impacts of climate change are.
H: OK, last question for today. I hope I
can get that right. I think the question
is if there are study, if there are
studies on how we cultivates fields
and agriculture. How does this impact the
overall climate in that area? The example
here is that only an increase in water
consumption was directed to São Paulo. Or
might there also be a warm world created
by monoculture in central Brazil?
FO: So, yeah, I don't know details, but
there are, but land use changes and land
use does play a role. On the one hand, it
affects the climate. So if you have, if
you have a rainforest, you have a very
different climate in that location as if
there is a savanna or plantation. And
also, of course, if you have monocultures,
you are much more, your losses are
larger usually as if you have different
types of agriculture. Because
in a monoculture everything is in
exactly the same way vulnerable and
so that, yeah. So that does,
land use change plays a hugely important
role with respect to the impacts of
extreme weather. And that is one thing to
look at. When I was saying, talking about
looking at vulnerability and exposure, and
of course also changes in the hazard are
not just because of climate change, but
also because of land use change. And you
can use exactly the same methods, but
instead of changing the CO2 or the
greenhouse gases in the atmosphere of your
model, you can change the land use and
then disentangle these different drivers
in and hazards.
H: OK, Fredi Otto thank you very much for
your presentation and for the Q&A. It was
a pleasure to have you with us. And yeah,
if you have any questions, any more
questions, I guess there are ways to
contact you.
FO: laughter
H: I think your email address and contact
details are in the Fahrplan for all the
viewers that have way more questions. And,
I don't know, do you have access to the 2D
world and do you explore that?
FO: Given that I don't know what you mean,
probably not, but…
laughter
H: OK.
FO: That can also be changed.
H: Yeah, it's the the replacement for
the congress place itself. But anyway,
if you viewers and you people out there
have any more questions, contact Fredi
Otto. And thank you again very much for
your talk. And, yeah. Have a
nice congress, all of you.
rc3 postroll music
Subtitles created by c3subtitles.de
in the year 2020. Join, and help us!