We have been hearing it for years. Climate change is happening. What I am about to present to you is fact. These are reliable measurements with multiple
peer reviewed papers confirming the information. Atmospheric carbon dioxide levels are the
highest they have been in over 400 thousand years, confirmed by our analysis of hundreds
of samples of arctic ice core, tree cores and isotope ratios in fossils. [1] Average global temperatures have risen
by 0.8 degrees celsius since the industrial revolution began, with two third of that change
occurring since 1975. [2] The evidence is overwhelming. This is fact. You are wrong if you deny it. If these trends continue, and I really shouldn’t
say if because they will continue, we are going to continue seeing stronger storms,
more heat waves and droughts, sea levels will continue to rise even after the ice caps have
vanished in the summer months in about 30 years, and to really make you motivated to
care about this, the world’s economy will suffer. We have been making strides in the technology
required to reduce our emissions of carbon dioxide, but the change over is happening
too slowly. The most effective thing our world has done
in the past 10 years in battling carbon emissions was going through a global financial crisis. Countries, like my own, are continually missing
carbon targets. We are going face up to 600 million euro in
fines every year after 2020 until we fulfil our promise of reducing our carbon emissions
by 20%. That money is going to come out of our pockets
through carbon taxes. Maybe then we will start to take climate change
seriously. We aren’t making significant decreases in
carbon dioxide emissions, we have only really leveled out [3] which is not good enough. So, if we aren’t making a difference by
reducing emissions, maybe we can reverse climate change. Maybe we can engineer our climate, and there
has been multiple suggested methods of doing that. In this new video series I’m going to explain
how several geoengineering methods intend to work, and their potential impact on the
world’s climate. The first plan we will examine is Afforestation. Afforestation is pretty much self explanatory. Plant forests, allow them to grow and store
carbon in their wood. The problem we run into is finding large enough
spaces to plant forests, that would have a significant impact on the climate and that
would not negatively affect the economies of countries employing the method. Taking land that could be used for agriculture
just isn’t a realistic solution, no-one is going to agree to it. Our options are limited, but we happen to
have huge expanses of land on earth that are not being used for anything productive, deserts. Now I know what you are thinking, deserts
are not the best place for growing anything, but with water desalination technology rapidly
advancing this isn’t as far fetched as it may seem. We are going to examine the feasibility and
effect of afforestation in the two largest subtropical deserts in the world, the Sahara
and the Australian outback. These are the perfect candidates for afforestation,
neither have large competing human populations, agricultural activity, or large natural animal
and plant populations. Conveniently, they are also in the sub-tropical
zones where a 12 month growth cycle is possible, maximising our carbon capture potential. To maximise our potential further, we need
to pick a suitable tree. The tree we chose will need to be suited to
this climate, be ever-green, grow rapidly, and be useful as a commercial resource. The Australian Eucalyptus grandis will be
candidate for this study. [4] Which also comes with the added benefit
of being a habitat for these cute little shits. Before even bothering to worry about how this
would be done, let’s first see if it’s worth being done. Let’s first look at the Sahara as an example. Ultimately we are trying to sequester atmospheric
carbon dioxide by storing it in wood. Every 10,000 square metres could hold about
1 thousand trees, and taking this patch of the Sahara between the 16 degree and 50 degree
longitudes we have about 9800 billion square metres of land, ignoring land needed for infrastructure,
that’s about 980 billion trees. Planting a forest of this size would increase
the world population of trees by about 33%. That’s a lot of trees. Estimates show [4 ] that this would capture
between 6 and 12 gigatonnes of carbon per year for about a century, before it would
meet a steady state where growth would slow and carbon dioxide in would equal carbon dioxide
out. 6 to 12 gigatonnes would capture between 16.3%
to 32.6% of our emissions per year, with humans generating a total of 36.8 gigatonnes of carbon
dioxide in 2017 [3]. Ideally we wouldn’t just let the trees grow
and forget about them, we would systematically cut them down and use them for construction,
synthetic feed-stock or convert them to liquid biomass fuel to replace our dwindling fossil
fuel supplies and burn that fuel in a power plant with its own carbon capture technology,
which would reduce emissions further, and produce new economies for these desert regions. Australia’s desert is about 60% the size
of the Sahara and so we could add an additional 60% to that figure, to bring our best case
scenario to just over 50% capture of our emissions per year. Bringing our emission levels per year down
to levels equivalent to the 70s. On the surface this seems great, but what
effect would this actually have on our environment. There are multiple things we need to consider,
first of all is the irrigation itself. A managed forest of this nature would need
about 500 mm per year of water, which equates to 4900 billion (4.9 x 10^12) metres cubed
of water per year for this number of trees. [4] Where is all this water going to come
from and at what cost? Fresh water supplies are obviously rare in
the Sahara, but surprisingly not as rare as the Australian outback. The world’s largest groundwater aquifer
actually resides beneath the Sahara, and is shared by four countries Egypt, Libya, Sudan
and Chad. [5] And it is not alone, new studies show
the Sahara is sitting on vast reservoirs of groundwater. This groundwater supply is vital for many
African countries, with it often being the primary source of freshwater for their populations. Draining at an industrial scale like this
comes with ethical concerns, as it is a non-renewable resource. Even these vast reservoirs of water would
run dry within a few years when pumped on this scale. However, the cost of desalination of sea water
has dropped dramatically in recent years [6], thanks in large part to countries like Israel,
The United Arab Emirates and Saudi Arabia who have invested in the technology and all
get over 50% of their drinking water from desalination plants. This technology still requires energy and
energy comes with a cost, both monetarily and as a source of carbon dioxide. It requires approximately 1.5 kiloWatt hours
of energy to desalinate a metre cubed of water. We then need to pump the water to a height
for distribution. With the average elevation of the Sahara at
450 metres, this would require a further 2.5 kilowatt hours per metre cubed, bringing our
total energy consumption to 4 kilowatt hours per metre cubed of water supplied. [4] The cost of this in terms of carbon footprint
and actual cost will vary with the energy source used, but considering the location
and nature of the project a mix of solar power and biomass energy with carbon capture technology
attached to it’s exhaust should be used. Let’s focus on a purely solar powered process
for now, as biomass is more expensive and has a larger carbon footprint without carbon
capture technology, though it would become cheaper as the project matures thanks to the
cheap source of fuel on its doorstep. Solar energy costs about 10 cent per kilowatt
hour with a median carbon footprint of 72 grams per kWh. [7] Putting all this together, the total energy
needed to irrigate this forest with 4900 billion metres cubed of water will be 19600 terawatt
hours a year, at a cost of 1.96 billion dollars a year and a carbon footprint of 1.4 gigatonnes
of carbon a year. Ignoring infrastructure costs, which would
likely push the initial costs into the trillions. This puts our total carbon capture for the
Sahara at a best case scenario of 10.6 gigatonnes a year at a cost of 184 dollars per tonne
of carbon dioxide captured. Expecting poor African nations to fund this
alone is unrealistic, so it would be reasonable to expect countries to pay for this project
through carbon taxes, like those that will be placed on Ireland in 2020, and thus allowing
them to offset their own carbon emissions with funding to the project. A litre of petrol when burned emits approximately
2.6 kilograms of carbon dioxide. Thus placing a carbon tax of about 48 cent
per litre of petrol could pay for the project, if we sell 4 billion litres of petrol with
the added carbon tax, which is about the total petrol and diesel consumption of a small country
like Ireland. [8] So it’s possible at a high cost, but if
the project can stop climate change, maybe it’s worth it. That’s the next problem we need to address. What effect will the forest actually have
on the world’s environment. With the help of climate models we can start
to get a clearer picture of what all this money and effort would give us. Temperature being the top of our list of concerns. Local temperatures would be affected most
due to the evaporative cooling caused by the increase in soil moisture, this would seed
clouds and increase local precipitation substantially, allowing us to reduce our ongoing costs, with
heavier irrigation only needed in drier months from May to October. [8] Local evaporative cooling does not decrease
overall global temperatures, as it just transports the heat within earth’s atmosphere. Critically we want reduce the amount of heat
retained in earth’s atmosphere by reducing greenhouse gases, allowing heat to escape
the system entirely. One of the biggest concerns with a project
like this is the modification of Earth’s albedo. Albedo is a measure how reflective a planet
is. A higher albedo means we reflect more sunlight
back into space rather than absorbing the solar radiation, and thus increasing the temperature. Forests have a very low albedo, they are literally
designed to absorb solar radiation. Where as snow and ice have a very high albedo,
they reflect quite a lot of light, as does sand. Placing forests over regions where sand once
resided will reduce the world’s albedo, alone it will actually negate the heat lost
due through reduction in greenhouse gases. [9] In this climate model however the clouds seeded
from the forest helps to counteract that decrease in albedo. The study shows an overall decrease in surface
temperatures, but a significant increase in ocean temperatures surrounding the forests. The conclusion of the primary paper used for
research in this video is fairly ambiguous with no definite answer to whether the project
would have a net negative or net positive effect on global temperatures. while other papers that did not factor the
increase in cloud cover affecting albedo suggesting that afforestation in the Sahara and Australian
outback would increase global temperatures by 0.12 degrees celsius by 2100, compared
a control model where no afforestation occured. [7] We also need to worry about the decrease in
fertilization that would occur due to Sahara dust no longer being transported to the Amazon
and the Atlantic ocean, which would likely decrease plant and plankton growth, and thus
negate much of the carbon sequestration that this forest would provide. The desalination plants would also need to
carefully manage their output of highly concentrated salt water, as dumping undiluted salt water
into the ocean would wreak havoc on the local aquatic environment. Overall, I think the idea is an interesting
thought experiment, but practically shows little evidence of benefit for the labour
and cost needed, and could potentially open a pandora’s box of unforeseen consequence. Ultimately our best tool for combating climate
change will be to decrease our carbon emissions, and that solution is staring us in the face
through the cheap solar and wind energy. We need more people acting on this issue,
we need more people funding and researching alternative energy sources. You can become one of those people today by
taking this course on solar energy on Brilliant. In this course you will discover the principal
methods of harvesting energy from sunlight, from both concentrated solar power and photovoltaic
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in servicing utility scale electric grids The best way to understand is by applying
concepts yourself, which is exactly what Brilliant allows you to achieve. These may initially sound complicated and
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that underlie everything in our lives. Feeling inspired? Then go to brilliant.org/RealEngineering and
sign up for free. And the first 73 people that go to that link
will get 20% off the annual Premium subscription. As always thanks for watching and thank you
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