Hello, now in this video we present the climate change topic.
In particular, we explain the climate module of MEDEAS which calculates the influence of
the rest of the modules on the climate, and also represents the feedback or consequences
of the climate impacts in the other modules.
In session 1), we will summarize how human activities affect the Climate System, and
describe the way the Climate System is modelled in MEDEAS.
In session 2), we will explain how the damages from climate change are implemented in the
MEDEAS model.
I will start by explaining human influence in the climate system.
The climate on Earth is a very complex system of rich, Physical, Chemical and Biological
feedbacks, within and between the components of the Earth’s Climate System.
Human interference in the climate system is by means of three main processes: first, by
Global emissions of the so-called “greenhouse” gases (affecting the atmospheric equilibrium);
second, by changes in the ecosystem and the land; and third, by indirect effects on all
the components (including the thinning of the cryosphere and circulation changes in
the hydrosphere).
The main greenhouse gas emissions are due to Fossil fuel combustion, of which carbon
dioxide and methane are the most important.
On the other hand, there are other emissions, like aerosols or other types of gases from
different sources, that also contribute to the greenhouse effect.
In particular, carbon dioxide is the gas which contributes most to this effect.
As can be seen in the image, the orange colours represent the carbon dioxide, showing that
it has the highest percentage contribution in comparison with the rest of the greenhouse
gases.
This is why it´s so important to understand the carbon cycle that includes carbon dioxide
sources and sinks.
In addition, there are some ecosystem changes, like for example land use changes, albedo
changes, cattle emissions or biodiversity loss, that also affect carbon dioxide, methane,
and other emissions.
Now, I am going to explain the way this part is modelled in MEDEAS
Climate models, such as General Circulation Models, are very complex and computationally
expensive to use in integrated assessment models.
On the other hand, Simple Climate models encapsulate the insights of the complex models, being
easy to use and understand and also computationally faster.
For all of these reasons, Integrated Assessment Models rely on this type of models, these
being the main reasons why we chose the Simple Climate Model C-ROADS to build this module.
But, the integration of C-ROADS in MEDEAS was not immediate, and we first had to adapt the climate model,
taking into account several aspects, such as the different start year of the simulation,
or including only those elements necessary for MEDEAS.
I will now describe the basic structure of the climate module in MEDEAS.
First, one of the inputs to the carbon cycle is the emissions of carbon dioxide due to
land use changes, whose estimated value can be modified by the user via the inputs excel
file.
The other input to this cycle is the carbon dioxide emissions due to fossil fuel use,
which are endogenously calculated in MEDEAS.
Additionally, in the case of Methane, the part of its emissions associated to the extraction,
distribution and combustion of natural gas is also calculated within MEDEAS.
On the other hand, the other greenhouse gases are included via their explicit cycles, and
the emission input to each cycle is exogenously set, taking as reference the Representative
Concentration Pathways scenarios.
The user can select one of these scenarios via the “INPUTS” EXCEL file.
This means that you can choose between high, moderate or low mitigation scenarios for these
gases.
Based on the gas concentrations in the atmosphere, which is an output to each gas cycle, the
total radiative forcing is obtained, exogenously adding the total Montreal Protocol gases radiative
forcing (on the one hand), and on the other, other forcings like aerosols or albedo effect,
taking the RCP scenario chosen by the user as reference.
The sum of all-radiative forcing determines the total radiative forcing on the system
which represents the thermal imbalance of the Earth.
In this way, increasing radiative forcing translates into temperature increase, and
this response depends on the climate sensitivity parameter, which is the equilibrium temperature
change in response to changes in the radiative forcing.
This parameter can be modified by the user via the INPUTS file.
In view of this, the climate module consists of different parts that are linked.
As an example, we will see, in more detail, one of the main parts of this module: the
carbon cycle.
As explained before, this is the gas which contributes most to the greenhouse effect.
The carbon cycle consists of stocks of carbon in the atmosphere, biosphere, mixed ocean
layer, and four deep ocean layers.
As the atmospheric concentration of carbon rises, its uptake by the ocean and biosphere
increases, and carbon is gradually stored.
In this model, the carbon storage in the biosphere is simplified into two stocks: biomass and
humus.
The atmospheric flux to the biomass consists of net primary production and this decreases
with rising temperatures.
On the other hand, the interaction between the atmosphere and the mixed ocean layer involves
a shift in the chemical equilibrium which shows that the ocean’s capacity to absorb
carbon dioxide decreases as the atmospheric concentration and the temperature rise too.
Finally, within the deep ocean, transport of carbon occurs.
This temperature feedback, which affects the biomass and ocean carbon uptake, can be activated
or deactivated by the user.
The same is true of the feedback that includes the sensitivity to temperature of methane
emissions from biological activity.
This is how the carbon cycle is modelled in MEDEAS, including all the variables involved
and the relationships between them: the Biosphere, the ocean and the temperature feedbacks.
But, how do all these climate changes impact on the rest of the modules?
In the next session, Iñigo Capellán will describe the way this damage is modelled in
MEDEAS.
You can find the cited bibliography and figure credits in this slide.
Thank you very much for your attention.