For thousands of years now we humans have been chopping down trees to burn as fuel to keep
us warm and to cook our food, and for making all sorts of useful things from tools and furniture to
vehicles and buildings. Millions of people still choose to construct their homes using timber
today. You may well live in a timber-framed house yourself, especially if you're over in the States.
And I make all these videos in a cabin studio constructed entirely from timber. But of course
as societies became more urbanized over time brick and cement construction became more popular
in many parts of the world, and once we worked out how to use steel in the construction of very large
buildings in the early part of the 20th century we never really looked back did we? The slight
wrinkle is that steel and cement account for about 15 percent of total global CO2 emissions,
and that number is set to rocket up as humans continue migrating towards urban environments.
By 2050 about two-thirds of us will live in cities, and by the end of the century that's
projected to jump to about 80 percent. So now there's a growing movement among architects and
developers to use a modern engineered version of timber that has structural properties that
are comparable to steel and that'll also lock away the carbon that trees suck in as they grow.
But hang on, I hear you say, if we start chopping down hundreds of millions of more trees all
over the world to use in construction of urban buildings won't we be jeopardizing the ecosystems
and biodiversity of our forests and simply moving our emissions problem from one place to another?
Well now a new study has just been published that crunches all the numbers
to find out the answer to exactly that question. So let's dive in and take a look.
Hello and welcome to Just Have a Think. In August 2022 three separate planning
applications were submitted for timber buildings in Perth and Sydney in Australia. Nothing unusual
about that of course. Timber buildings are pretty common in many parts of the world.
What sets these planning applications apart though, is the fact that the buildings in question
will be between 180 and 220 metres tall. That's more than double the height of the current world's
tallest timber building which is an 87 metre tall apartment block in Milwaukee in the United States.
It's just not possible to build that height using solid timber from a felled tree that's simply been
run through a sawmill and plane to size. It doesn't have anything like the strength
required to cope with the various forces that very large buildings have to withstand.
Engineered timber is a completely different animal though. You may have heard it described
as mass timber or cross laminated timber or perhaps as laminated veneer lumber or glulam.
It's a very carefully constructed panel system made up of multiple layers of soft wood boards.
Each subsequent layer is turned through 90 degrees and bonded with glue and dowels or nails
to maximize strength. It was first developed in Europe in the 1990s but it's now becoming adopted
in other parts of the world as well, most notably in Australia and the United States. According
to an organization called The Mass Timber Code Coalition, recent mass timber buildings are only
about a fifth the weight of comparable concrete and steel buildings. That means foundation sizes
can be significantly reduced, which in turn means less concrete in the construction.
It also has a very high strength to weight ratio, which means it matches or even exceeds steel and
concrete on durability and stability, even against earthquakes. The fact that they're prefabricated
means engineered timber panels bring significant cost savings to construction projects,
not least through a 90% reduction in construction traffic and a 25% reduction in construction time.
They're also less sensitive to temperature changes, which can make building structures more
energy efficient. And the material even has fire resistance that beats steel and exceeds current
building codes. Now that last one might seem a bit counter-intuitive, but it has apparently been
rigorously tested. The International Code Council is the leading global body for codes and standards
in the building industry. A couple of years ago they set up a committee to update the 2021
International Building Code to include safe working parameters specifically for tall timber
buildings. The committee's work was informed by multiple fire performance tests on mass timber
structures conducted at the world's largest fire investigations lab at ATF in the United States.
During a resistance test of a five-ply cross-laminated timber panel wall the panel
was subjected to temperatures exceeding a thousand degrees Celsius and it lasted for three hours and
six minutes, which is far more than the two hour rating that building codes require. The reason
for that impressive performance is the fact that, during a fire, the outer surface of mass timber
gets charred and that forms an insulating layer that protects the internal material from damage.
And when it's clad with gypsum wall board the tests found that the mass timber can achieve
nearly damage-free performance during what the industry calls a 'contents fire burnout event'.
So in theory there's a lot to like about this construction material. And on top of all that,
many people would say it's a lot more aesthetically pleasing as well.
But here's where it all starts to get a bit contentious. This latest paper from
researchers at the Potsdam Institute in Germany compares the greenhouse gas emissions from raw
material production for conventional building materials and engineered wood
and accounts for long-term carbon storage in future wooden buildings. The analysis compares
three different construction scenarios compared to a business as usual case, which is essentially
continuing to make buildings using steel and concrete. Scenario one assumes 10% of all new
urban buildings would use an engineered timber construction. Scenario 2 is calculated based on
50% of new builds being timber, and scenario 3 is based on 90%. The result of the 90% scenario would
be a reduction in carbon dioxide emissions of 106 billion metric tons by the end of the century.
That sounds very positive indeed. 106 billion tons is more than 10 percent of the remaining carbon
budget to keep the planet below 2 degrees Celsius of warming compared to pre-industrial times.
But the researchers also found that in order to achieve the 90% scenario the world would
need to create an extra 143 million hectares of forest plantations dedicated to growing trees
specifically for the construction industry, which is where we start running into problems.
That's an area of land twice the size of Texas! So something would have to give. This second
chart shows how land use would change in each of the four scenarios. It's a bit of a busy graphic,
I must admit, but basically anything below the zero line represents a reduction in a particular
type of land use and anything above the zero line represents an increase. All four scenarios,
including business as usual, show reductions in primary and secondary forest land as well as
pastures, rangelands and what the report calls 'other lands' which is defined as non-forest
natural vegetation. But the scenario where 90% of new urban buildings use timber construction shows
a far greater loss of secondary forest to make way for a far greater increase in managed plantations.
And with most of Europe's forests heavily protected, and environmental concerns being
raised in the United States about huge plantations that already exist, mainly to supply wood pellets
for combustion in power stations, the report suggests it would be the tropics that would
have to lose vast areas of unprotected primary and secondary forest and non-forest vegetation
land to facilitate the changes. The problem with doing that, as the report itself points out,
is that you'd lose all the rich biodiversity in the existing well-established ecosystems in
those areas. That potentially means displacing or completely losing many species of plants
and animals living in those habitats. Natural forests tend to be better at resisting drought,
fires and disease as well, so they're are much safer carbon store than man-made plantations.
And by replacing a wide variety of vegetation with monoculture crops the soil is deprived of
the diverse nutrients and organic life deep underground that keep it healthy,
so over time the earth would become less fertile and the plantations will become more difficult to
maintain. And there's another little wrinkle as well. While reforestation of previously
depleted forestry areas is an absolutely crucial element of the climate mitigation challenge,
afforestation, which is the practice of converting non-forested land into forests,
increases the amount of solar radiation absorbed and reduces the amount of light and heat that
can be reflected into space. The report states "despite their carbon sequestration benefits,
land converted to forests via afforestation or otherwise
may exert a net warming influence via the albedo effect, especially in boreal regions.
We did not account for the impact of such an albedo effect in this study."
Something the report doesn't advocate is the use of existing agricultural land for new plantations.
In every one of the four scenarios cropland continues to grow throughout the rest of this
century, albeit by a smaller amount in the 90% scenario compared to the businesses usual model.
The research paper concludes that a doubling of land use intensification
driven by investments in what it describes as yield increasing technological change
will be needed in all scenarios to reach what it says will be the required
increase in the productivity of agricultural land to cope with the growing world population.
According to analysis by the number crunching website Our World in Data, 50% of all habitable
land on the planet is used for agriculture and 77% of that agricultural land is used for rearing
livestock. A large proportion of arable land is used to grow food specifically as feedstock for
all those animals. Analysis conducted on behalf of Greenpeace in 2019 calculated that 63% of all
arable land in the European Union was used for animal food crops rather than growing food for
human consumption. In this recent interview for the Guardian newspaper, Greenpeace European Food
and Forest Campaign Lead, Sine Etajaa, said "wood can play a bigger role in construction,
but to double the world's tree plantations at the expense of priceless nature is just bonkers, when
modest reductions in meat and dairy farming would free up the land needed." So, as is so often the
case with climate mitigation proposals, we're left with something of a conundrum aren't we? There's
no doubt that displacing a large proportion of steel and concrete with engineered timber would
significantly reduce direct carbon emissions in the construction industry. But what's your view on
the subject? Should we pursue this option, even if the price we have to pay is loss of biodiversity
and perhaps even a reduction in natural levels of carbon capture and surface reflectivity
elsewhere on the planet? Or maybe you think that we should be accelerating existing efforts to
decarbonize steel and cement making instead, which is something we've looked at in previous videos on
this channel. It's certainly a tricky one, so I'll be very interested to hear your thoughts
in the comments section below. And of course I'll leave a link to the full Potsdam research paper
in the description section below here too, so you can scrutinize their numbers for yourself.
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