Resume

Samenvatting Global Change (006799)

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Global Change (006799)

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Vrije Universiteit Brussel (VUB)

Samenvatting van de hoorcolleges van het vak 'Global Change' gegeven door professor Huybrechts als titularis en andere gastdocenten aan de Vrije Universiteit Brussel.

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Publié le 27 septembre 2022
Nombre de pages 43
Écrit en 2021/2022
Type Resume

global change
2021 2022
006799
professor huybrechts
vub
vrije universiteit brussel

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Exam: 1 question per topic

1. Climate change: the physical science basis

a. Some basics of the climate system

Difference between weather and climate
- Weather: atmospheric condition at a given time and a given place
 Can be measured: air temperature, precipitation, clouds, air pressure, wind speed,
atmospheric humidity
 Has a chaotic component: ‘Lorenz butterfly’: if a butterfly flaps its wings somewhere in
the Amazon, this can be the cause of a thunderstorm in Australia 14 days later
o Cannot be predicted more than 10 to 14 days ahead
- Climate: mean and extreme conditions of the atmosphere, ocean, sea, ice, etc, over a longer
period of time (e.g. 30 years)
 Easier to model and project than the weather
- Climate is the statistic of the weather

Interactions are crucial
- Lithosphere = crust
- Cryosphere = frozen water in all its different forms
- Hydrosphere = water
- Atmosphere
- Biosphere = living organisms

The Earth’s climate system: is becoming easier to model

Climate system has to abide to the rules of physics
- Radiation balance of the earth: incoming radiation = outgoing radiation
 Q ( 1 – α) = εσT4
 The only true variable is the temperature T (earth’s mean global temperature)
o For current radiative fluxes: T = 14.8 °C
o Without greenhouse effect (epsilon = 1): T = -18.6 °C
▪ Most powerful way to effect climate change
▪ Greenhouse effect is important: life on earth is not possible without it
o Weaker sun (Q -1%): T = 14.1 °C
▪ Not a big effect: sun is not the cause of climate change
o Change albedo (alpha) effect (reflectivity of the earth): T = 6.3°C

1

,Exam: 1 question per topic

Greenhouse effect
- Smooth lines: Planck curves of radiation (theoretical)
- Jagged line: Actual radiation emitted by the Earth
- Contribution to natural greenhouse effect
 H2O vapor: 60%
o Is a feedback, not a forcing
 CO2: 26%
o Amount of CO2 is added by anthropogenic actions: is a forcing
o Effect of doubling the CO2 concentration
▪ Outgoing low wave radiation (L) lowers: 4 Wm² extra is trapped
▪ Temperature needs to rise: 1.2 °C to counter it
▪ Feedbacks kick in (water vapor): temperature rises around 2.5 °C

o
 O3: 8%
 CH4, NO2: 6%

b. Changes in human and natural drivers of climate

Changes of atmospheric concentrations of carbon dioxide, methane and nitrogen oxide
- First measurements of greenhouse gasses started in 1958 on Hawaii
 Carbon dioxide concentration increase = 50% since pre-industrial times (from 315 ppm in
1958 to 415 ppm in 2021): same effect as ppm between last glacial time (LGM) and the
1800s (180 ppm to 280 ppm): rise is exponential
 Increasing concentrations (CO2) is due to the combustion of fossil fuels: when CO2
concentration is rising, the O2 concentration is decreasing: burning consumes O2 and
releases CO2
o 2 lines: dark line is southern hemisphere: mean is lower: anthropogenic activity
that produces CO2 is mainly in the northern hemisphere
o Rigid line: due to summer/winter

2

,Exam: 1 question per topic

Fate of anthropogenic CO2 emissions:
- Sources: 86% fossil fuels, 14% deforestation
- Sinks: 46% in atmosphere, 31% in terrestrial biosphere, 23% in oceans
- Without the land and ocean sink: ppm would be around 600 ppm instead of 410 ppm

Role of aerosols: suspended particles in the air
- Direct effect by scattering and absorbing shortwave and longwave radiation
- Indirect effect by modifying the radiative properties, amount and lifetime of clouds
- Net cooling effect on climate change
- Lower life span than CO2: few years instead of centuries

Radiative forcing of the climate: positive radiating forcing due to human activities

Share of human activities to the enhanced greenhouse effect: fossil fuel combustion is the biggest
component (71%)

c. Observations of changes in climate: temperature

Rise of global mean surface temperature: has been measured (thermometers)
- Warmest years so far: 2016 and 2020
- 20 of the 21 warmest years since 1880 occurred in the 21st century
- Temperature has risen 1,1°C
- In the last 50 years observed temperature has increased unprecedented in at least 2000 years!
‘Hockeystick curve’

3

, Exam: 1 question per topic

- Belgium: Ukkel: total warming of 2.5°C
 Land is warming more than the ocean: larger temperature rise on the land than the global
mean average

d. Attribution of climate change

Human influence has warmed the climate: unequivocal
- Black line is observed: can only be reached when human drivers are involved

Observed warming to date has been driven by greenhouse gas emissions, roughly a third of which had
been masked by cooling of aerosol emissions

e. Impacts of climate change on the cryosphere and sea level

Components of the cryosphere
- Cryosphere = ‘early warning system’
- Located in remote places but its changes have global consequences (ice caps at the poles,
permafrost, glaciers, seasonal snow cover …)
 Changes in snow and ice affect the global radiation balance (decreases albedo: warms up)
and affect weather and climate elsewhere, including in Europe
 Melting of land ice raises global sea level

Decrease of seasonal snow cover
- Northern hemisphere snow cover extent decreased 1.1% per decade for April over the 1922 –
2018 period

4

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