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19 of the hottest years on record
occurred in the last 20 years compared
to global average temperatures from 1950
to 1980 the world today is about 0.85
degrees celsius or 1.5 degrees
fahrenheit higher and based on climate
model projections in another 40 years
these temperatures will increase by
another one and a half degrees celsius
or 2.7 degrees fahrenheit
now you might ask how can one degree of
warming matter so much
after all when you crank up the
temperature in your house by a degree
you might barely feel it but think about
the size of the entire earth and imagine
how much of an increase in energy
retention this mere one degree means it
is literally an astronomical number a
one degree increase means that just the
atmosphere contains about five times 10
to the 18 kilojoules more energy but if
you also include the fact that at least
a couple of meters of the ocean probably
reaches an equilibrium with the
atmosphere this energy retention number
doubles to give you an idea this is more
than all the energy contained in the
entire world's known oil reserves in
very simple terms this increase in
energy retained on earth has to go
somewhere and this is what causes the
havoc
more water evaporates from the oceans
causing more severe rainfalls in certain
parts of the world it increases the
energy contained in hurricanes causing
more damage to coastal areas sea levels
rise because warmer water expands in
volume and more polar ice melts
very few people in the world think the
climate is not changing at all as
illustrated on this chart the cause of
this change is where the controversy
lies because earth has gone through many
temperature cycles in the past why
should this be any different
so is this change natural what exactly
is causing it
can we do anything about it or are we on
an inexorable path to climate
catastrophe the answers might surprise
you that's coming up
right now
in order to discuss climate we should
agree on what we mean by climate just
because this winter was warmer than last
winter
doesn't mean the climate's getting
warmer the difference between talking
about climate versus weather is in the
duration of the changes when we talk
about a change in weather it could be in
minutes hours days or even a few years
the short period weather doesn't tell us
much about the general trends in climate
on earth if we have more rain two days
or even two years in a row it doesn't
mean the climate's changing climate is
something measured over decades usually
more than 30 years it describes a
general trend over a long period of time
in particular places when i talk about
an increase in global average
temperatures it's just that an average
there are parts of the world that will
warm less and some will warm a lot more
but some
rare areas might also cool
parts of southern africa for example are
warming about 2 degrees celsius and the
arctic appears to be warming 4 degrees
celsius while the southern tip of
greenland is actually cooling
temperature trends across the globe are
not uniform because of the diverse
geography of the earth but when
scientists calculate the overall average
temperature and how it has changed over
multiple years and decades they conclude
that the climate is indeed changing
a higher overall temperature results in
more extreme weather how does this
happen it can be understood based on a
simple principle when i say the extreme
weather causes havoc it means that it
imparts energy or does work in physics
we can write work simply as a change in
kinetic energy in other words you need
energy in order to do any kind of
weather damage so for example for the
wind to act on earth and cause storms or
tornadoes it needs energy where does
this energy come from the short answer
is the sun actually almost all energy on
earth comes from the sun in one way or
another
when the sun heats up earth the heating
is unequal over land the air is drier
and heats up faster than over the sea
this is because the specific heat
capacity of water is much higher than
that of land meaning that it takes more
energy to heat the sea than the land and
so it will generally remain cooler than
land this means that the air is much
warmer over land than at sea and as with
hot air balloons hot air rises up
because it has a lower density than cold
air but as the air from land goes up to
form clouds colder air from the sea
comes in to fill the gap and we get a
breeze or wind
because hot air has low density we get a
low pressure zone compared to the cool
air over the sea which has a higher
pressure zone air flows from high
pressure to low pressure and this
creates wind and if the pressure
difference is very high it can be a very
strong wind to complete the cycle the
hot air that rises up in the atmosphere
eventually gets pushed to the sea where
it cools down again and the cycle
continues with global warming the sun
heats up the earth more
causing a bigger pressure difference
between the sea and the land and thus
winds can be more severe causing more
extreme weather we also get more extreme
rainfall because the water cycle also
depends on the sun when the sun heats
the sea water evaporates to form clouds
eventually these clouds become bigger
and the water precipitates and falls as
rain or hail or snow global warming
accelerates the cycle of evaporating
more water resulting in more rain in
places where the rain falls in places
where much rain doesn't fall but where
temperatures are rising droughts result
because the little water that's present
there evaporates and not much rain falls
to compensate for it this means that
certain parts of the world can not only
experience more rain but also more snow
more hail
more drought higher winds and so on so
global warming is not just about hotter
weather but also more extreme weather
and that can be dangerous for us humans
let alone all the other species in
nature but what is to blame for all of
this i said earlier that the sun is the
main driving force for the climate as
well as life on earth without it earth
would be very cold and lifeless the
sun's energy output goes through cycles
about once every decade so could the
higher temperatures today be due to the
sun getting hotter
fortunately computer modeling technology
is advanced enough today to answer this
question and the answer is almost
certainly not because the total
irradiance
varies by only about
0.15 percent over 11 years this is not
nearly enough to explain the increase in
global temperatures one fact to keep in
mind is that the temperature on earth
has changed many times in earth's
history going back millions of years
earth's rotation around the sun slowly
changes over tens of thousands of years
causing cycles of ice ages and warm
periods the last ice age ended about 11
000 years ago but has earth ever been
this hot the answer is yes
it's actually been much hotter in fact
56 million years ago earth warmed by
five to eight degrees celsius you could
have had a tropical vacation in the
north pole because it was so warm and
lush at that time earth was in the midst
of extreme warming called the
pileocene-eocene thermal maximum or
p-e-t-m
now you might ask what's so bad about
warm weather i enjoy warm weather well
the problem is
that extreme warming cycles like the
petm
was a complete disaster for life on
earth deep sea organisms went extinct
oceans acidified much of the land mass
either went under water or was
uninhabitable by our mammalian ancestors
due to excessive heat or humidity why am
i talking about an event that occurred
tens of millions of years ago how is it
relevant
well scientists have determined that it
is the most analogous event to what we
are in the midst of experiencing today
it's being studied extensively to inform
us what we might be facing in the near
future there are many similarities but
also differences to the current warming
the petm was also initiated by huge
increases in carbon dioxide in the
atmosphere why does carbon dioxide cause
warming but not oxygen or nitrogen which
the earth's atmosphere is mostly made of
well greenhouse gases including carbon
dioxide water vapor and methane each
have at least three atoms in their
molecules the atoms in these molecules
are loosely held and can absorb more
vibrational energy
they're efficient at absorbing light in
the long wave range which is also called
heat which bounces up from the earth's
surface
these greenhouse gases then re-emit this
long wave radiation back towards earth's
surface resulting in warming
other non-greenhouse gases like oxygen
and nitrogen don't absorb the long wave
radiation and so the heat passes through
them and into space instead of being
reflected back to earth now you might
say but there were no humans back then
burning fossil fuels couldn't have
caused this how did so much co2 get into
the atmosphere the answer is that it was
probably caused by volcanic eruptions
many series of eruptions over thousands
of years are thought to have caused it
how do we know the evidence for this can
be found in the fossil record as well as
carbon dated rocks that show a
significant increase in carbon 13 which
is the isotope of carbon most prevalent
in volcanic eruptions
it's estimated that on average about a
net
0.24 gigatons of carbon was emitted into
the atmosphere during a 50 000 year
period to cause this severe warming that
is known as petm by contrast humans
today are emitting 10 gigatons or about
50 times that amount of carbon yearly
into the atmosphere in addition the
current one degree warming has occurred
not over thousands of years but in less
than a hundred years so is there
anything to support the claim that human
carbon emissions are a direct cause of
global warming couldn't it also be
natural show me the data
the most compelling evidence is in the
study of isotopes of carbon in the
atmosphere fossil fuels come from old
plants which contain a higher ratio of
carbon-12 to carbon-13 that the
atmosphere does as fossil fuels are
burned the percentage of c12 goes up in
other words the ratio of c12 to c13
would be expected to go up and that's
precisely what we see in the data
volcanic eruptions on the other hand
increase carbon 13 or c13 in the
atmosphere not c12 in fact volcanoes
only emit about one percent as much co2
as we do so they're not to blame
the sun is not to blame either because
if the sun was the culprit then it would
heat both the upper and the lower
atmosphere of earth but what we see is
only warming in the lower atmosphere
where greenhouse gases accumulate in
addition for the past 50 years solar
activity has been such that on its own
it would have lowered earth's
temperature
earth's natural climate cycles is likely
not to blame either because based on ice
core evidence we know that during the
end of the last ice age earth warms at
an average rate of about
0.06 degrees every 100 years but what we
are seeing today is at least 10 times
that increase or about 0.6 degrees per
100 years when simulations are run
using just natural causes of climate
change they predict no change in
temperature or even a slight cooling in
the 20th century but this is not what's
happening when we add in the unnatural
effects created by emissions from
man-made sources it more closely aligns
with observed results and if we plot it
all together combining the natural
effects with the man-made effects the
simulation fits the measured data almost
exactly
and it's not like scientists disagree on
the fact that earth's temperature is
changing the agreement can be seen here
between several notable institutions
including nasa in addition 97
of the world's climate scientists agree
that man is the cause of this change
sure you can find scientists in the
minority three percent to make fancy
youtube videos trying to prove everyone
else wrong but when was the last time 97
percent of scientists agreed on anything
this consensus should not be dismissed
carbon dioxide emissions are not the
only cause of global warming it is
exacerbated by other greenhouse gases
such as methane from farm animals and
natural gas processing not to mention
nitrous oxide from fertilizers and when
you add this to the fact that we've been
eliminating natural carbon absorbing
sinks like forests for the past 100
years the effects become even more
pronounced in the last hundred years
about twenty percent of the world's
forests have been lost so if humans are
really to blame what can we do about
this
each of us can help by reducing our
individual carbon footprint and
encouraging others to do the same
we only have one lifeboat there is no
spare what's more harmful than denial is
apathy climate change is not likely to
wipe out the human race what we are
really working towards is trying to
reduce human suffering because these
changes will cause more and more havoc
life will get even more difficult the
earth will survive
it is a passive canvas it does not give
a damn
what or who survives or who suffers to
paraphrase carl sagan no cavalry is
coming to help there's nothing that will
save us from ourselves except for our
collective determination
and if you want to do something about
this starting today you can start by
getting more informed in fact i was
prompted to make this video after seeing
an exceptionally informative series on
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[Music]
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