Protecting Planet Earth:
Deforestation, Desertification and Heat Island Effect
Review of last lecture
• General circulation models: Grid size. 3
usages. Name of the basic set of equations.
• 4 components of the climate system model.
• Mesoscale models: grid size. 3 characteristics.
How do human activities change the
global climate?
Human beings are changing the global climate
system in three different ways:
• Change land cover (deforestation and
afforestation)
• Release or cleanse pollutants (aerosols)
• Release or cleanse greenhouse gases
Global map of vegetation
Global distribution of different
vegetation types
(From Bonon et al. 2002)
World map of tea production
Effects of vegetation
• Makes water/heat reservoir deeper (transport deep water
out of soil)
• Enhances evaporation (leafs increase evaporation area)
• Dependent on vegetation type
Effects of different surface types
Convective instability increases
Deeper heat reservoir (smaller T change)
Deeper water reservoir (Wetter surface)
Enhanced latent heat flux
Vegetation feedback
Vegetation in turn is affected by environmental
conditions (e.g. seasons, droughts, global warming)
Deforestation
• Deforestation is the permanent
destruction of forests where the
land is thereafter converted to a
non-forest use.
• Causes: agriculture (80%),
logging (14%), fuel wood (5%)
• An estimated 18 million acres
(7.3 million hectares) of forest,
which is roughly the size of the
country of Panama, are lost
each year, according to the
United Nations' Food and
Agriculture Organization (FAO).
Global map of deferestation
Desertification
• Caused mainly be
human activities and
climate change
• Is one of the most
significant global
environmental problems
• About a billion people
are under threat
Global desertification vulnerability
Change of PSDI in the last 100 years
Video: Urban heat island effect (by
Weather Channel)
• http://www.youtube.com/watch?v=tsXHl3l-rM
The heat island effect
• Nighttime: City warmer than surrounding rural area
• Daytime: City has same air temperature as rural area
Temperature distribution for Atlanta
(from
Dependence of heat island effect on
population
Causes of the heat island effect
• Increased SW absorption caused
by canyon geometry (increased
area and multiple reflection)
• Decreased LW loss caused by
canyon geometry
• Increased greenhouse effect
caused by air pollution
• Anthropogenic heat source
• Increased sensible heat storage
caused by construction materials
• Decreased latent heat flux caused
by change of surface type
• Decreased sensible and latent heat
fluxes caused by canyon geometry
(reduction of wind speed)
“Canyons” between buildings
Mitigation of heat island effect
• Greening the city
(streets and roof top)
• Change construction
materials
• Reduce anthropogenic
heat sources
Detection of Climate Change?
• We must contend with the problem of enhanced urban
heat islands influencing the data, which means that
records from large urban areas are not representative
of the surrounding region.
• Atmospheric scientists are well aware of this source of
bias in temperature records—which happens to be
relatively small— and routinely account for its effect,
either by discarding contaminated data or by adjusting
values downward for affected stations.
Summary
• Effects of vegetation: (1) makes heat/water reservoir
deeper, (2) enhance evaporation, (3) grows and dies in
response to environmental conditions
• Effects of different surface types: desert, city, grassland,
forest, sea. Deeper heat/water reservoir and enhanced
convective instability.
• Heat island effect. 7 causes