Samenvatting
Summary of Climate Change: Science & Policy
This is a summary of all the lectures of the course Climate Change
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Climate change: science & policyScience of climate change
Human activity is changing the climate?
1. The average global temperature has risen (and is still rising) since the
industrial era.
2. The greenhouse effect.
The earth traps heat because of the atmosphere.
UV radiation from the sun arrives at the earth’s surface, loses energy,
and is converted into infrared radiation.
GHGs absorb the infrared, this leads to heating.
3. [CO2] is rising steadily due to the use of fossil fuels.
When it is winter in the northern hemisphere, the [CO 2] go up because
there is less CO2 trapped in vegetation.
4. On geological timescales, temperature and [GHG] are strongly correlated.
5. We can only simulate our current climate with models if we include
anthropogenic GHG emissions.
The consequences of climate change are already visible: higher temperatures,
increase of precipitation, ocean warming and acidification, rising of sea level,
increase of wild fires etc.
The impacts are more severe in poor regions and for poor people as they are
more vulnerable and they have less capacity to adapt to climate change.
Global emissions are still rising.
Climate change: an international problem
Human-induced climate change is a global problem in terms of both causes and
impacts --> an international effort on climate change is needed.
Both causes and impacts are not uniformly distributed across the world.
Every country has its own story but most of them:
Rely heavily on fossil fuels for their energy.
Are not aware of their population’s vulnerability for climate change.
Climate change mitigation is often seen as a burden on the economy.
Politically unattractive: short-term cost for long-term gain.
Nonetheless, there are international efforts to take action.
The IPCC assesses objectively the scientific, technical and socio-economic
information relevant to understanding the scientific basis of risk of human-induced
climate change, its potential impacts and options for adaptation and mitigation -->
peer reviewed literature.
The IPCC is policy relevant so it writes about policy but it is not policy
prescriptive. Governments influence topic, outline, review, acceptance report and
approval SPM. Authors are nominated by countries.
,International climate agreements
The United Nations Convention on Climate Change (UNFCCC) was
established in 1992.
Target: stabilization of [GHG] in the atmosphere at a level that would
prevent dangerous anthropogenic interference with the climate
system. To ensure that food production is not threatened and to enable
economic development to proceed in a sustainable manner.
The first IPCC report was a scientific basis for the talks.
Kyoto agreement: the first climate treaty (1997).
Emission reduction targets for rich countries (by 2008-2012).
Emissions trading = cost-effective way of reducing GHG emissions.
Based on the principle that it does not matter where the emission
reduction takes place.
Treaty was not effective in achieving emission reductions.
The Protocol was in fact doomed from its birth in 1997 because
it did not encompass the world's largest and fastest growing
economies; it excluded developing countries (including the Peoples
Republic of China) from binding targets, and the USA failed to sign up.
Copenhagen: get a new climate treaty (2009).
Summit has failed --> there was no agreement reached.
2°C target was agreed.
Paris agreement: new climate treaty is urgently needed (2015).
Conference of Parties 21 in Paris
Top-down approach from previous COPs abandoned because it prevented
many countries of being able to disagree with the treaty text.
The negotiations were about long-term temperature goal, mitigation,
adaptation, finance, technology, capacity, legal status of the treaty, etc.
Every country decides for itself whether they agree to the treaty, but if you
miss a few key players in the accord, it can become somewhat meaningless.
(Intended) Nationally Determined Contributions were formulated by
countries before (or during) the Paris negotiations, for instance:
Absolute emission reduction targets compared to the past or compared
to a baseline.
Relative targets (CO2-emission per GDP).
The UNFCCC enables developing countries to achieve their NDCs.
The NDCs are reported and monitored to see if they are on track.
COP-decision:
“… much greater emission reduction efforts will be required than those
associated with the intended nationally determined contributions.”
“… by reducing GHG emissions to 40 gigatonnes in 2030.”
In the Paris agreement:
Well below 2°C, or even 1.5°C.
“to achieve a balance between anthropogenic emissions by sources
and removals by sinks of GHGs in the second half of this century.
Legally binding and five-year review: ratification needed by 55 parties
representing 55% of global GHG emissions.
, Actions on climate change
Overshoot = going over the 1.5°C mark but then gradually declining to below the
1.5°C mark. Overshoot is bad and should be prevented because:
1. If overshoot happens, there still will be negative irreversible impacts.
2. The negative emissions will be more difficult to manage in the second half of
the century in case of an overshoot, if this happens; the 1.5°C target cannot
be reached.
Preventing climate change means deep changes.
Mitigation = efforts to reduce or prevent emission of GHGs.
Adaptation = to prevent the effects of climate change or to lessen the damage
done by climate change.
Three categories of actions:
Mitigation Lowering [GHG] using less energy
CO2-free energy
less meat and dairy
CO2-capture and geological
storage
afforestation
Adaptation Adapt to climate water management: building
impacts dikes, room to rivers
change crops
disaster warning systems
Solar radiation Interfere in radiative stratospheric aerosol injection
management balance marine cloud brightening
GHGs & radiative forcing strength
Global mean surface temperature is increasing even with the large variability of
year-to-year temperatures. The mean temperature is the highest right now, than it
has been for thousands of years.
The warming has never been as fast as in the present.
Atoms in a gaseous state vibrate and move relative to each other.
GHGs: NO2, CO2, CH4, H2O, HFC can absorb electromagnetic radiation in the IR part
of the spectrum --> start vibrating faster --> they fall back in their previous
energetic state --> release their radiation --> contributing to greenhouse effect.
Radiative forcing = how effective a molecule is in trapping and releasing
the radiation.
CO2 is weak, CH4 is strong.
Atmospheric residence time = is the half-life of a molecule in the
atmosphere.
CO2 stays in the atmosphere for a long time.
CH4 and HFC are gone after only hundred years.
Global warming potential = radiative forcing + atmospheric residence
time.
It expresses the cumulative radiating forcing that a substance causes
over a given period of time.
Always put to a reference gas, usually CO 2 --> CO2-equivalent.
, Often the 100 year period is used.
Climate sensitivity = a measure of how much the temperature of the earth
increases when the amount of CO2 in the air is doubled. This is difficult to calculate,
as it is dependent on many factors.
Melting of permafrost causes the release of GHG CH 4 that was trapped in the frozen
soil.
Albedo effect = ratio of the amount of light reflected by a surface to the amount of
incident light. A greater reflectivity provides a cooling effect.
Surfaces with a higher albedo have a greater reflectivity.
Ice has a higher albedo (almost 1) than seawater (almost 0).
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