Welcome to the lecture number 4, in the module of on energy and environment under the ecology
and environment course.
My name is Sreenivas Jayanthi, I'm professor in Chemical Engineering Department.
We had already 3 lectures in this series, in the first lecture we looked at the connection
access between energy and environment, in the second lecture we looked at in detail
about what, where the energy is coming from and what kind of demand is expected from energy
in the coming years.
In the third lecture we looked at the pollutants that emerge from energy harvesting from nature.
In this lecture we are going to continue further and look at the present problem of global
warming which is attributed to anthropogenic causes especially to the harnessing of energy
from fossil fuels and other sources, other human related activities.
In the first lecture we looked at how the energy demand has been increasing year by
year, right from 1970's and how it is expected to increase for the coming several years and
also how most of the energy has been coming and is expected to continue to come from fossil
fuels, coal, natural gas and oil, and we also saw that when we draw energy from a coal power
plant, we have a number of emissions in terms of sulphur-dioxide,
nitric-oxide, carbon-monoxide, carbon-dioxide, particulates and aerosols of trace elements,
all of which can give us to a number of immediate health and environmental problems.
And we also saw that despite this fear about carbon-dioxide emissions we have a large increase
in, continued increase in carbon-dioxide emissions which came up to 49 Giga tons of carbon-dioxide
equivalent in the year 2010, and that these emissions are coming from all sectors of
human activity from transport, industry, energy, and buildings and agricultural activities,
industrial activities, all these things are contributing to carbon-dioxide emission, so
carbon-dioxide emission has permitted into the human life in a very involved way, but
the fact remains that in the modern era, in the past 50 years we see increasing rate of
emissions and large increases in carbon-dioxide concentration and methane and nitric-oxide
concentrations in the atmosphere, these concentrations are still very low, carbon-dioxide concentration
is only 0.04% by volume, and these concentrations are so low that they don't pose a direct danger
to us in terms of their toxicity, but we've been accumulating carbon-dioxide emissions
into the atmosphere at such a high rate that it is believed by a number of experts, a scientific
experts in the scientific community that this is actually caused a net
radiative forcing of the order of 2 to 3 watt per meter square compared to about 340 watt
per meter square of incidents of solar energy on to the upper reaches of the atmosphere,
so it's only about 1% or less, but still this has given rise to an increasing in the atmospheric
temperature of the order of 0.5 to 1 degree centigrade.
And this has led to huge accumulation of thermal energy in earth climate system in the upper
oceans, deeper oceans, in the ice, land, and also atmosphere.
And as a result of this it's expected to have serious consequences, these small temperature
changes are expected to have a serious consequences on the physical systems that are there on
the earth like the glaciers, snow, ice, permafrost, rivers, coastal areas, sea level
rises, erosion of coastal areas, and also biological systems, terrestrial ecosystems,
wildfire, marine ecosystems, and also human and managed systems like food production,
livelihoods, health and economics, all these factors are influenced by these sort of changes
that have been happening, which are attributed to our continued emissions of carbon-dioxide
and other greenhouse gases in the process of energy harvesting which is needed for our
economic prosperity.
So their lays conflict between and energy environment, in order to find possible midway
path between and energy environment we would like to take a close look at what is this,
what this global warming is about, and we'd like to understand the scales, the orders
of magnitude of the problem and see what kind of solution is possible, so in this lecture
we're going to look specifically at the global warming problem and what is behind it, and
what kind of message it has for us, okay.
So this issue of global warming has been under worldwide study of scientist across the world
under the form of IPCC intergovernmental panel on climate change which is celebrating his
30th year, this year and so it's been on the study, continuous study with improvements
and improvements and revisions over the past 3 decades and even more and these have produced
report, I think in 2014, latest report which has a very detailed analysis as of climate
change 2014, and it has a lot of analysis on observe changes and the causes in the atmosphere
climate, future climate changes risk and impacts and also it suggest that in pathways for adaptation,
mitigation and sustainability development, so all this aspects are important when we
deal with global warming, and we'd like to look at some of the contents of this report
for us to understand the science behind it and the causes behind it and the timescales
involved the magnitudes of effort that is required, that is involved all this things
we can get, we'd like to get an understanding of these issues by looking at some of the
evidence that is presented here, and some of the reasoning that is presented in this.
So we are going to look at a series of pictures extracted from this report, and I'd really
suggest this 1500 page report as a reading material for anybody interested in climate
science and it's multifarious effects on the global warming problem, it's a very detailed
report contains lots of analysis and lots of observations, lots of data using many,
many substituted techniques and it's a great compilation of current understanding of the
global warming problem, okay.
So I would really recommended to all of you and I hope some of you will be able to go
through it in bits and pieces, it's fairly downloadable from www.ipcc.ch if you go through
many of those options you'll be able to get, download the full report completely freely,
okay.
So let's comeback to this first picture here where we are talking about the global mean
energy budget and here the energy is what we are getting from solar source and more
than 99.8% of the total energy that we get is coming from the sun, and a small amount
is coming from the heat released by the core, in a core of the earth and even smaller, smaller
amount is coming from other radiation than solar energy, so sun is the main provider
and probably the only provider of energy for us in large quantities that as required by
us, so the sun energy can be considered in terms of watts per meter square, 300 watts
per meter square of surface area of the earth is varies in a number of waste but on the
average this is what it is, and it's been fairly constant over the several decades at
least, and 340 watts per meter square incident at the upper reaches of the atmosphere, and
then as it goes through atmosphere it gets modulated in a number of ways by our atmosphere,
by what's happening on the earth surface, and what's happening, what has happened before
also as we'll see, so out of the 340, 79 watts per meter square is absorbed in the atmosphere,
and a net of 100 watts per meter square so that's about 30% is reflected back into the
outer space, and 185 so slightly more than half is reaching the ground, and 24 of that
is reflected back as short wave radiation, reflected from the Antarctic guys, architect
guys and a number of, from the land, from the ocean, all this things, this known as
the albedo, so all of this contribute to reflection of the incident light without any modulation,
and so we have only less than half 161 watts per meter square coming on to the surface,
where it gets transformed in a number of waves it gets absorbed into the surface, it leads
to evaporation from the land, from the sea, and then it also contributes to sensible heating
of the atmosphere, and then it is also, it maintains a certain temperature of the earth
surface because of its temperature, it emits radiation to the extinct of 398 watt per meter
square, and this is reflected back into the atmosphere and a significant portion is emitted
back 342 is emitted back into the earth surface, and a net amount of 239 is what is lost into
this space.
So what is lost into the space as thermal radiation, as long wave radiation plus what
is reflected a short wave radiation is almost balanced by what is coming here 340, there
is a small difference that is 0.6 watt per meter square is supposed to be the imbalance
which is going into the earth surface, this has been the way for centuries, but it's not
always been like that, there were times of course when the oxygen concentration was minuscule
and carbon-dioxide concentration was as much as 10%, so this 10,000 PPM so it's not that
life things have been the same way as there are number of causes for this climate change,
natural and also human related anthropogenic, so there
are natural fluctuations in the solar output, and the aerosols, the minuet particles that
are present in the atmosphere contribute a significant amount in terms of capturing the
solar short wave radiation and also reflecting it and then also in the long wave range, these
aerosols can be generated by us by human activities they can also be generated by natural activities
like volcanic corruptions and then winds, storms, and number of fires, natural fires,
all this things can generate aerosols and then you can also have clouds, we know clouds
are found in many different ways, and then you can have ozone which is a substantial
gas which interferes with this process, and we've heard of ozone fluctuations caused by
number of factors, and then you have that culprits that we are interested in, the greenhouse
gases and large aerosols, some of which, many of which are contributed to by our human activities.
And then you also have vegetation changes on the earth surface, and ice and snow cover
during winter time, during summer time, as it changes as the cover changes then you can
have changes.
Ocean color wave height are also causes for the surface albedo, that is amount of wave
that's reflected, and I'd like to point out here that we are looking at 340 watt per meter
square as the amount that's coming into the upper reaches, and example what is reflected
by the earth surface is 24 watt per meter square, and what is attributed to anthropogenic
causes, the radiative forcing which can be compared with this is only of the order of
2 to 3 watt per meter square, so it's only about tenth of what is reflected by natural
causes on the earth surface, so in that sense we are looking at small changes in terms of
this, but it's not very simple as it's being too small and
things like that, there are other reasons for it, but let's postponed that description
short time, and complication arising is from a number of physical phenomena that happened,
for example you can have snow, ice, albedo effect, long wave radiation, and the lapse
rate so that is the rate at which the temperature decreases, clouds, water vapor, emission of
non CO2 greenhouse gas and aerosols, air-sea carbon-dioxide exchange, air-land carbon-dioxide
exchange in the process of vegetation growth and all that, bio geo physical process, and
peat and permafrost decomposition as temperature of changes, of the atmosphere changes, then
these kind of vegetal matter can decomposed giving rise to emissions of this GHG gases,
so there are all this factors which contribute to, which are affecting the way the temperature
evolves as a result of increase or decrease in concentrations of this GHG gases.
And also as a result of minuet changes in the temperature of the atmosphere, temperature
of the upper layers of the oceans, and the land and so on, so out of this we can see
there are some positives which mean that as a result of this we will have increase in
temperature, and then there are also negatives which can decreased, which can lead to decrease
in air temperature, so as a result of all these things there has been continual change
in the atmospheric concentration over millions of years, well, well before man was
born, and this is one such part of the data coming from number of sources other than direct
evidence, direct measurement, obviously it's so far back into the years, we are looking
at 60 million years and you can see that there was a time at which carbon-dioxide concentration
was in excess of 50 to 500 to 1000 PPM, there are a red bars but there is, there is been
a much higher concentration and over the past 40 million years, there has been a steady
decrease in this, and fairly constant variation over the last 10 to 20 million years ago,
and here we have, this is where we are really interested in, and this particular reduction
is attributed to a natural cause which leads to where we are, which is the collision of
India, the Indian subcontinent leading to the foundation of the Himalaya mountain range
is supposed to have, led to a large absorption of carbon-dioxide in the natural weathering
process, so as to decrease the atmospheric concentration of carbon-dioxide as a result
of which we had cooling here, and this cooling is supposed to be related to the formation
of what we now call as India, and of course other neighboring countries.
And so they've been natural causes which have led to large scale changes in carbon-dioxide
concentration, coming back to a closer range of 0 to 3 million years ago, okay, so we can
see sea level changes atmospheric concentration changes and you'll see variations here of
the order of between 200 to 400 PPM they have been like this, but variations and you can
see global sea level variation is giving by this compare to present level of 0, they've
been significant decreases of the order of -100 meters, so sea level has been rising
and falling, rising and falling by tens of meters, naturally, well before man has had
its footprint or he will hand into this, and we also see large scale changes of much larger
amplitude almost of the order of 100 meters happening in the last 500 to 1000 years like
this here, and we also see large scale fluctuations here of the sea surface temperature, okay.
And then other dust accumulation which is actually leading to this kind of observations
here, so there have been changes of the things that we have been looking at, and this is
more of the recent past where there is more of direct evidence in the form of ice course
that have been kept in various places, and from these things you can find variation of
sea-level, variation of Antarctic temperature with respect to the present and then sea surface
temperature in the tropical thing carbon-dioxide concentrations and also what is expected to
be one of the causes of this climate changes in the present times which is precession of
earth around the sun is supposed to cause a small change in terms of the radiation that
is received, and there is been some evidence to say that this have had that corresponding
changes in this, and these also seem to show that present day climate of this last million
years ago is far most susceptible to this kind of changes, which have led to changes,
systematic changes in the carbon-dioxide concentration and temperature changes of the order of several
degrees, a few degrees at least, sea-level changes of the order of 100 meters have happened
in the recent.
In the previous 800 to 1000 years, 8 lakh years, 0.8 million years, okay, so this is
an evidence that has stood scrutiny of number of scientist and so this is something that
is both a cause for worry, and also an assurance that things will not go, so much out of hand,
okay, so there is that kind of thing and if you look at one of the headline figures in
terms of the sea-level changes in recent past and what we are looking at is
a rate of sea-level changes, so about 20,000 years ago there is a rate of sea-level change
of the order of about 12 millimeters per year, okay, and around 15,000 years ago there is
a specific climatic event during which the rate of sea level changes as high as 40 millimeters
per year.
And over the last 2000 years it's minuscule you can see that it's 0.2 millimeters per
year and in the 20th century we have 1.7 millimeters per year, so this is very small compared to
the changes that have taken place about 15,000 years ago, and of course man was there but
man was not there leading to such a large footprint in terms of carbon-dioxide emissions
to an 15,000 years ago, so that's why we can say that these are assurances that much largest
scale changes have happened in the recent past and man himself has face them, of course
there is a lot of consequences on the human population and at one time during one of these
events it is said that there has been almost a decimation of the human population of that
time, so that is 90, decimation is coming down to a level of 10% of that, okay, but
large scale almost extension type of event, consequences have happened and so the consequences
of this can be very large for small changes in this, in the atmospheric temperature, and
when we say small changes in this we are talking about changes of the order of 4 degrees in
the sea surface temperature, so these kind of things possible and is that creditability.
If you look at the changes that are happened in the last 150 years in terms of temperature
change it has gone up from -0.6 to about 0.2, so it's about 0.8 degree centigrade over the
last 100 years, over the last 150 years, but worrying trend is that over the last 50 years
it's been rising at a fairly large rate, and sea level change in the last century has been
from -0.15 to about 0.05 so that's about 20 centimeters it has used in, so on the face
of it okay when you look at these figures whether it is carbon-dioxide concentration
or sea-level change, temperature changes, 1, 2 degrees what's the big deal because there
are seasonal changes which are much more rapid and much much higher, and we have sea level
change of 0.2 meters, 20 centimeters in 100 years, it's hardly anything for us to worry
about, this is something that on the face of it, it looks like this but consequences
of this on the whole are supposed to be much more harmful, and some of these are predicted
by the global climate models because of the complexities that are involved in the
agents that contribute to change of climate and the number of different factors that come
into picture, there has been a consorted attempt going back to 40, 50 years towards developing
global climate models, and early studies have linked only the atmosphere land and ocean
surface, but gradually we have other factors like aerosols coming into picture, the carbon
cycle, vegetation, the dynamic vegetation and some atmospheric chemistry, land ice,
all these factors have been gradually included into this.
For example when we look at carbon-dioxide concentration we really have to understand
how much carbon-dioxide there is, how much carbon-dioxide how it changes when you look
at this carbon cycle we have here stock of carbon in, so that is amount of carbon stored
in different state of the upper parts of the earth surface and the atmosphere, and then
we also have fluxes, because amount that is there in any particular reservoir is not constant,
it's being continuously exchanged with other reservoirs, so that there is a carbon cycle,
so you have atmosphere, and atmosphere and the ocean surface are in constant exchange
of carbon-dioxide because carbon-dioxide can dissolve in the sea water and then go into
bicarbonate form, or bicarbonate is getting converted into carbonate forms, and carbon-dioxide
can also be taken by vegetation on the surface, and when vegetal matter or aluminum matter,
decomposes or when you have a wild fire, you can have carbon-dioxide generation, and then
you can have volcano, volcanic eruptions giving rise to both direct evolution of carbon-dioxide,
that also more importantly some other minerals which come out on to the surface and lead
to carbon-dioxide absorption, there is a possibility.
And these volcanic eruptions also caused distribution of very fine scale aerosols into the atmosphere
which interact with incoming solar radius from the sun and also outgoing solar radiation
from the earth, and then lead to accumulation or release of this, and then you have vegetal
matter becoming deposits and then forming the earth surface, earth crust, and then all
these things, these are all and fossil fuel reserves that are there may be a kilometer,
2 kilometers inside the, from the earth surface, these are all carbon reserves, so carbon is
found on the earth crust and in the atmosphere in many, many
different forms, in gaseous form, in dissolve form in water, in transform solids in the
form of vegetation, and also in terms of fossils, in terms of carbonates and rocks, so there
are all these kind of things and each of these has a time scale, of
interaction so that if you were to release an amount of carbon-dioxide into the atmosphere
now, then it gets slowly, slowly evacuated by this natural processes, for example you
have 5000, 10 to the power 15 grams of carbon that is released into this, into the atmosphere
and a substantial portion about 30% is slowly absorbed into land, into the atmosphere, into
the ocean over 200 years, and then over 2000 years some more of that will go and you still
have about 30, 40% of the original carbon-dioxide still left in the atmosphere here, and some
amount has gone into the land and more amount has gone to the ocean, and after slow reaction
with calcium oxide to form calcium carbonates it becomes solidified, so after 10,000 years
you still have about 15% of carbon-dioxide still left here, and then you have some land
and the rest in this.
So you have slow evacuation of carbon-dioxide, so this causes in our time scales an accumulation,
so if our rate of release of carbon-dioxide is significant is large then there can be
accumulation and that's what we are seeing here, and this is what is actually the cause
of concern for us as shown by climate models, and this
climate models show that there is going to be a continued increase in the carbon-dioxide
concentration, for example here carbon-dioxide concentration from 2000 is of the order of
close to 400 PPM, 380 but if a current rate of emission
of carbon-dioxide continues for the next 100 years then it may go up to 1000, it may trouble,
that is if you don't take any action now, it can go up to 3 times what it is, and more
concern showing concern and taking some measures may take it up to double, okay, so if we retain
it at our current levels and not go through the increases that we have seen, then it may
lead up to doubling of carbon-dioxide concentration, okay.
So there are other scenarios which say that okay you can, they'll continue to grow up,
but if you take very strong action in terms of reducing carbon-dioxide emissions and going
towards near carbon zero emissions then over the next 50 years they continue to grow but
gradually decrease like this, so back into this and bringing it back towards is to 300
to 400 PPM level is a humongous task for which you have to go into almost carbon zero type
of emissions.
And we know that, that is a very big challenge and that's a challenge that we are face with,
that is if we continue our conventional 20th century way of life and where we are continuing
to extract and consume more and more energy and continue to extract more and more energy
from fossil fuels and if you continue to gated to our economic prosperity goals and needs
in the conventional way then by the end of this century we are going to see 3 times a
level of carbon-dioxide that is there, and that is expected to increase a temperature
by almost 5 degrees, 5 to 6 degrees centigrade over the past 1000 year average and that's
a huge decrease change because we've seen in some of the past cases that the sea-level
changes have been like several tons of meters, okay, so it's not sea-level is not going to
change so rapidly in our current thing, it's a big question mark, but there are other causes
like increased heat waves and increased cyclones, distractions and title waves and all this
kind of things are expected to happen, the climate, the immediate climate and the way
the rainfall patterns, precipitation patterns and the way that we are fed with water for
agriculture needs, drinking water needs, and these are going to be effected by small changes,
fractional degree changes, one or two degree changes in the ocean temperature, so that
is where we have a problem not in terms of absolute concentration of carbon-dioxide or
absolute level of the sea-level or the amount of small degrees of 1 or 2 degrees increase
in temperature, it's not the direct impact on the human beings, that is of concern to
us, but indirect impact on natural process on which we depend for our daily life, so
that is the biggest concern.
So in the next lecture we're going to see what we can do about it, how we can live with
it and how we can try to mitigate the consequences and what we can do to make to, not make them
more worse then what they can be, okay.
Thank you.