Why are we doing this ?
In order to understand why climate change is such
a significant threat to society, it is necessary to grasp it
in a global context. Only from this perspective
can we begin to comprehend what is happening
and what consequences inaction will have.

Our planet has existed
for 4.5 billion years.

It has gone through changes difficult for us
to even imagine, including a vast cloud
of gas and dust, a global rainforest
with crocodiles in the current Arctic Ocean
and even a "Snowball" Earth nearly
entirely frozen.

Our planet can be imagined
as a large greenhouse.

In this greenhouse several gases are naturally
present, CO2, but also CH4 (methane)
and N2O (nitrous oxide). Theses gases capture
the energy and heat from the Sun. Without this
greenhouse effect, the mean temperature on the
surface of the Earth would be around -18°C, instead
of the current average of +15°C.
Our planet would be quite inhospitable.

The natural climate system
for the last couple of million
years has been controlled by :

  • the Earth's orbit around the Sun.
  • the natural greenhouse effect
  • the atmospheric and oceanic circulation

During these orbit-driven
cycles the changes in
atmospheric natural carbon
dioxide (C02) concentrations
varied between 175-280
parts per million (ppm) in the
atmosphere.

So what makes such changes
happen ? To understand this
complex topic, we might think
of the Earth as a "being",
just like you and I.

We are very sensitive to
temperature change ;
a couple of degrees make the difference
between healthy and hospitalized.

Similarly, the Earth is also
very sensitive to
temperature variations.

The average temperature
of the planet will change...

if the amount of energy coming from the Sun
varies, OR if the amount of greenhouse gases
(GHG) varies.

Most human activities
produce GHG. These
gases have
been accumulating in the
atmosphere since the
industrial revolution, for about
200 years now.

Fossil fuels combustion (oil, gas, coal) is the
main source (65%) of these human generated
GHG. Other human activites contribute to this
increasing concentration of GHG : mainly deforestation,
and the farmed meat industry.

CO2 is a long lived GHG,
and we are now releasing
40 billion tonnes a year.

It is now accumulating in
the atmosphere faster than
the land and oceans can
absorb it.

In 2015,
carbon dioxide
levels reached
400 ppm.

In the last 2 centuries the
average temperature on
Earth has increased due to
this GHG effect. This is what
we call "climate change".

IPCC

(Intergovernmental
Panel on Climate Change)

"Scientific evidence
for warming of the climate
system is unequivocal"

What might happen if we
remain on this path ? We
will likely see a global average
temperature increase of 4°C.


To put this in perspective,
during the last Ice Age
(which peaked 20,000 year ago) the
average global temperature
on Earth was only 5°C colder.

As a consequence, most
areas now occupied by
humans were uninhabitable.

With such a temperature rise,
the Polar Ice Sheets, including Greenland and the West Antarctic will lose significant mass.
Their complete loss would raise sea level by 10 meters or more.

This trend is already under-
way. The scientific debate is
currently mostly about the
timescale over which these
changes will occur.

The various ecosystems of the planet are our life
support systems, and that of all the other species.
We are totally dependent on these ecosystems for
our livelihoods. They are the hidden foundation of our global society.

If temperature rises :

  • The oceans will get more
    acidic as CO2 levels increase
  • Where we can get water will change
  • Where we can grow food will change
  • Many species will not be
    able to adapt and survive
  • Extreme weather events,
    such as droughts, hurricanes
    and floods, will be given
    a platform to intensify

There is now an international consensus that
recognises a 2°C increase in temperature is a
threshold which should not be passed.
It marks what is understood to be a tipping point
at which dangerous interference with the climate
system is initiated.

A 2°C commitment is what we
should get in Paris in December.

Paris is our chance to get
our politicians to effectively
respond in time.