past can help us understand something
about the future of climate change and
my story begins 2,000 years ago
when China’s Yellow River swollen with
late summer monsoon rain and choked with
sediment from centuries of environmental
neglect broke its banks and flooded the
flat fertile North China playing like an
out-of-control firehose the Yellow River
sprayed water and sediment across some
of the richest agricultural land in
China and home then to more than 23
million people without warning entire
villages were obliterated as the land
became like an ocean and there was no
running from these floods those trying
to escape found themselves calf deep in
the ewes and ox carts mired up to their
axles can you imagine the horror people
felt when they realized they couldn’t
escape the flood as the floodwaters
slowly and inexorably rose townspeople
and farmers alike perished by the
hundreds of thousands a contemporary
poem plaintively asked of the Yellow
River why are you so cruel and note that
the floods were so bad that even the
fish lament and those that had survived
had abandoned all their property and
found themselves now without hose to
farm houses and hope starvation stalked
the land like a wild beast devouring the
young and the old the all aged and the
hungry alike and the government the
government that had always been there in
the past in times of crisis they were
broke and broken
not long after the survivors banded
together to fight for food and safety
soon a ragged peasant army prodded by
gnawing hunger and fed with anger
marched on the imperial capital of Chong
Chong and their armed only with wooden
pitchforks and ancient metal tools they
improbable defeated the Imperial Army
storming the city and in an orgy of
violence they slaughtered thousands upon
thousands of affluent town dwellers
turning their anger on the Imperial
Palace they captured the Emperor
butchered his body and fed it to the
dogs one piece at a time thus ended the
Western Han Dynasty contemporary of Rome
in one of the world’s great
civilizations but what happened mind you
the homme were the most powerful
technologically sophisticated and
culturally advanced society in all of
Asia and how did one flood in a land
known for catastrophic flooding caused
such damage well the answers are complex
but at its heart the fall of the Western
Han was a human-made environmental
tragedy made worse by climate change and
because you and I are facing a period of
intense climate and environmental change
it begs the question what can the past
tell us about the future of climate
change I was struck by the urgency of
this question when not long ago I was
excavating a Han Dynasty archaeological
site called songyang’s Rong where we
found these roof tiles these tiles are
placed above doorways as a sign of good
luck and the inscription you read here
would translate as longevity the irony
of this fine is not long after this
house was
it was obliterated by that flood I’ve
just described a lesson from history
then is that longevity is fleeting even
for the greatest of Empires and there is
a context though for understanding this
tragedy that befell the Han during Han
times which is shown here in the yellow
box in climates were changing rapidly
but entirely naturally but as you can
see the trend is clear it was getting
drier and drier
in addition han populations were
expanding and resource consumption was
growing within the boundaries of the Han
it was a time of peace and prosperity
but the hon were avidly expanding their
empire in an attempt to capture more
resources and as a consequence they
embarked on a series of ceaseless Wars
that drain the Treasury and that
consumed people and resources the hyung
at the same time we’re trying to prevail
over nature so they were cutting down
forests clearing fields draining marshes
and especially building levees to
control the river and finally
conservative minded Han emperors and
bureaucrats alike thought that the past
was better than the present and they
turned increasingly to the past for
solutions to the present-day problems
and it didn’t work out well as a
consequence by the beginning of the
Common Era the Han Dynasty was a shadow
of its former self the coffins were
empty and the government was paralyzed
in one place we can see this process
playing out is in the Yellow River
itself the Yellow River is one of the
world’s great rivers and it’s the heart
of Chinese civilization but the Yellow
River is actually a funny River because
it’s very water poor but sediment rich
and some of this is because it flows
through a dry part of China
and also because it passes through the
lost plateau which is an area of thick
rich but very easily eroded sediment
now when I say sediment rich let me give
you an example the way we measure
sediment content in a river is to take a
cubic metre of water out of the river
sort of extract it from the river take
the water away and you weigh the
remaining sediment so if I do this for
instance in the Mississippi River
I might get four to six pounds of
sediment if I take a cubic meter of
water out of the Amazon River
I might get 20 to 40 pounds of sediment
but if I take a cubic meter of water out
of the Yellow River at flood I get
almost 800 pounds of sediment at
sediment concentrations like this it’s
no longer a river it’s simply a flowing
landslide and the reason for this is
because as it’s getting drier there’s
less vegetation to hold the soil in
place and as there are more mouths to
feed the hon have to intensify
agriculture particularly on the lost
plateau and as drought is increasing in
agriculture is becoming more intensive
more and more sediment is flowing into
the Yellow River and because DeHaan were
trying to prevail over nature they had
built up big levees so the sediment had
nowhere to go so the bed of the river
started to rise which meant the homme
had to build their levees higher which
meant the bed of the river rose in an
endless cycle but as the bed of the
river is going up and the levees were
keeping pace the land behind the levees
was effectively sinking and becoming
lower than the bed of the river for
example at song Young’s wrong at the
time of that flawed the site was 10 feet
below the bed of the river this meant it
was not a matter of if there was going
to be a catastrophic flood it was simply
a matter of when and how bad it would be
and for the harm the end came quickly
here we see the last pathetic events in
the life of
village of Sonia is wrong as a farmer up
to his ankles in the mud scrambles
desperately to gather the last of the
harvest before the site was inundated
but for the farmer for the village and
for the Empire it was too little too
late
now what does this have to do with the
present or the future for that matter of
fact well one important point of
comparison is that like the hon we are
facing a period of unprecedented climate
change although for us these changes are
caused entirely by humans but the
long-term trend is entirely clear it’s
getting warmer and warmer as you can see
here we’re adding greenhouse gases
especially co2 to the atmosphere at an
alarming rate
greenhouse gases trap heat and warm the
planet the more greenhouse gases we add
the warmer the planet will become we
just passed 400 parts per million of co2
in the atmosphere as an annual average
that’s a level of co2 not seen on earth
for at least the last four to five
million years and a level of co2 never
experienced by members of our species
you and I and our children and our
children’s children will never see co2
below 400 parts per million we’re
entering new territory here and not in a
good way and as a result of changing the
atmosphere we’re changing the climate
and we’re feeling the effects what we’re
seeing is is that it’s getting wetter
and hotter through time and like the Han
we have invested a great deal of money
in an infrastructure that isn’t designed
to handle the kinds of climate change
we’re seeing our infrastructure our
electrical grid
our roads our bridges our sewers our
water treatment plants they were not
designed to handle five hundred year
floods that are now happening every 20
years or hundred year floods that happen
every five years hurricane sandy is a
good or maybe a bad example of this
sandy which happened in 2012 was
actually a pretty minor storm there have
been a lot worse that have hit the
Northeast but hurricane sandy
overwhelmed the infrastructure of the
Metro New York area and caused extensive
damage both locally and because of New
York significance even nationally how
could one small storm caused such damage
well the main reason is because people
didn’t believe it could happen so they
didn’t prepare but of course we know
sandy happened and the scary thing is we
know that hurricane frequency is going
to end intensity is going to increase
under new climate conditions like the
Yellow River in HoN times it’s not a
matter of if there will be another
hurricane sandy simply a matter of when
and how bad it’s going to be jumping
back to China for a moment during Han
times there was a vigorous debate about
how to manage the Yellow River and it
came down to whether we would work with
nature or work against nature some
engineers believed in building low
levees set far apart to let the river
flow in its floodplain and they believed
that it was acceptable to have some
flooding today to prevent catastrophe
tomorrow but as we’ve seen the Han
government wanted to prevail over nature
so they built big levees and tried to
control the river but we can see the
same philosophical debate playing out
today in attempts to cope with climate
change so for example following
Hurricane sandy there was a set of
proposals to build a wall across the
mouth of New York City Harbor
for a mere eight to ten billion dollars
we can protect New York City from a
sandy like storm but even if we can
afford to do this do we want to do this
because one thing I can tell you is that
building that wall isn’t going to make
the storm go away and it’s not going to
make the storm surge go away all we’re
going to do is take that water and move
it somewhere else along the coast and
make it somebody else’s problem now I
don’t think that hurricanes or droughts
or floods are going to destroy America
or at least I sure hope not but the fact
of the matter is is that climate change
is real and it’s here mitigation alone
all the Paris Accords we want to sign
are not going to stop the notable
effects of climate change all we can do
now is slow down the rate of that kind
of climate change we will see indeed we
are seeing severe climate events that
are as bad or worse than sandy and it’s
what can the past then tell us about
climate change the Chyna case study
tells us that the homme never
anticipated their own downfall 2,000
years ago the hon government didn’t plan
or prepare in the face of changing
climates instead they look backwards and
as a result hundreds of thousands of
people needlessly died sadly failure is
an option over and over in my research
I’ve seen humans try to prevail over
nature and it doesn’t work out well
but whether it’s the harm or Hurricane
sandy the real issue is human arrogance
people don’t believe that climate change
can cause these problems so we don’t
adapt to it
but I think we can learn from the Han
example for instance we must resist
calls to build our levies higher we need
to let our streams and rivers flow in
their floodplain and not try to
constrain them and we need to accept
some laws today to prevent catastrophe
tomorrow but more than anything else we
need to plan and prepare because in
today’s world of rapid human shape made
climate change it’s not a matter of if
there will be another climate
catastrophe it’s simply a matter of when
and how bad it will be we must plan we
must prepare we must adapt to climate
change especially we need to live in the
present because if we don’t if we don’t
we’ll be like that farmer from 2,000
years ago
stuck in the mud unable to stop the
rising water and scrambling desperately
to save our friends our family and ourselves