Complete samenvatting eindtentamen Quaternary Climate and Global Change
Samenvatting midterm: Quaternary Climate and Global Change
Samenvatting hoofdstukken Paleoclimatology
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Quaternary climate and global change (GEO34303)
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Chapter 1: Overview of Climate Science
Climate = broad composite of the average conditions of a region, measured by its temperature,
amount of rainfall/snowfall and other factors. Weather fluctuates in hours, days, weeks or a few
months.
There are three different temperature scales: Celsius, Kelvin (+273K) and
Fahrenheit (1.8Tc +32)
A slow warming between 300 and 100 million years ago was followed by a
gradual cooling during the last 100 Myr. This led to the appearance of Antarctic
ice sheet and later to the northern hemisphere ice sheets (which advanced and
retreated due to shorter isolations).
Earth system = many parts of the Earth’s climate system are interconnected
Climate system = air, water, ice, land and vegetation analysed by forcing and response.
Climate forcings:
- Tectonic processes: internal heat. Continents movement, uplift and basins. Millions of years.
- Change in Earth’s orbit around the Sun: alter amount of solar radiation received on Earth by
seas and latitude. Occur over tens to hundreds of thousands of years.
- Change in the strength of the Sun: also affect amount of solar radiation arriving on Earth. The
strength of the Sun has slowly increased throughout Earth’s existence.
- Anthropogenic forcing: unintended by-product of agriculture, industrial and other human
activities through additions of CO2 and other greenhouse gasses, sulphate particle and soot.
Climate responses: components of the Earth’s system respond to driving factors with a characteristic
response time (measure of time it takes to react fully to imposed change). There are fast responses
(atmosphere, land surface, ocean surface, vegetation and sea ice) and slow responses (mountain
glaciers, deep ocean and ice sheets).
- Forcing is very slow in comparison with the response: system
will passively track along with the forcing with a small lag. E.g.
long tectonic time scales.
- The forcing is fast in comparison with the response: little or no
response to the climate forcing occurs. E.g. solar eclipse.
- Time scales of forcing and climate response are similar: dynamic
response to the system.
Changes however commonly occur in smooth continuous cycles. The
faster responses will have earlier effect that slow responses.
There are feedbacks that alter the climate changes by amplifying them (positive feedback) or
suppressing them (negative feedback.
,Chapter 2: Earth’s Climate System Today
Energy travels through space in the form of waves:
electromagnetic radiation, which form the electromagnetic
spectrum. The incoming energy from the Sun is referred to as
shortwave radiation. 340 W/m^2 arrives at the top of the
atmosphere of which 70% enters the climate system. Of this
around 47% reaches the Earth’s surface. There is an equal
amount of heat back to space (back radiation/ longwave
radiation). There is a discrepancy because of the greenhouse
effect (trapped radiation). Water vapour, CO2 and CH4.
The Earth’s atmosphere is divided into four layers: the troposphere (8-18 km, weather), stratosphere
(to 50 km, ozone blocks UV), mesosphere (50-80km) and thermosphere (above 80 km).
Earth receives and absorbs more heat in the tropics than the poles and the climate system works to
compensate for this imbalance by transferring energy from low to high latitudes. A smaller fraction of
incoming radiation is absorbed at higher latitudes because there is a less direct angle and snow and
ice surfaces reflect more radiation (albedo).
Radiation and albedo vary seasonally. There is an albedo-
temperature feedback in which there is cooling, then
there is more snow and ice, so less solar radiation is
absorbed at the surface, so there is more cooling. Albedo
increases in NHS in winter because of increased snow
cover over land and more extensive sea ice and in the SHS
in winter because of more extensive sea ice.
Clouds also affect the regional receipt of heat at the Earth’s surface. Furthermore, the hydrological
cycle is also important in the heat transfer. Absorption and storage of solar heat are strongly affected
by the presence of liquid water because of its high heat capacity, a measure of the ability of a
material to absorb heat in calories. Heat capacity=density∗specific heat . Ocean surfaces heat
very slowly because temperature changes are mixed between the layers, and the land surface heat
and cool quicky and strongly because of their low capacity to conduct and store heat.
There is heat transformation because of: 1) sensible heat
(product of the temperature of the air and its specific heat)
leading to convection. Sensible heat at low latitude is largest
over land surfaces in summer. 2) Latent heat (heat carried by
the air is temporarily hidden in latent form as water vapor).
There is initial evaporating and storage of heat in water vapor
and later release of stored heat during condensation and
precipitation. Calories are released instead of stored. The latent
heat stored in evaporation of water is released when there is
condensation or precipitation, far from the site of evaporation.
There is also a water vapor feedback, where there is an initial change leading to climate warming,
this causes increased atmospheric water vapor, which causes an increased greenhouse trapping of
radiation which causes increased warming. This is thus a positive feedback loop.
, Atmospheric pressure increases towards the lower elevation. It is the pressure exerted by the weight
of the overlying column of air. Air flows from high pressure near Earth’s surface to lower pressures at
higher elevation. So, the compressed air at lower elevations has nowhere to go and pushes back
against the overlying layers. Over limited areas parcels of air will rise if they become less dense than
the surrounding air. The rising parcel begins to cool and increase in density and will eventually stop
rising at the level where its density matches out the surrounding. Air is also cooled by latent heating.
The rate at which Earth’s atmosphere cools with elevation is called the lapse rate.
Tropical heating drives a giant tropical circulation pattern called the Hadley cell. Condensation
produces ahigh rainfall in the rising part of the cell near the equator. The air is moved towards the
subtropics (from low to high latitudes) and there it sinks and warms by the increasing pressure of the
atmosphere at lower elevations and becomes drier. At the surface trade winds blow the subtropics
towards the tropics and replace the rising air. This warm dry air passes over the tropical ocean and
extracts water vapor, this contributes to the rising air motion and abundant rainfall along the ITCZ.
These movements of masses of air alter the pressure at the Earth’s surface. The pressure at the ITZC
is reduced and increased in the subtropics. The ITCZ move northward during summer in NHS and
southwards in summer SHS. There is also the Coriolis effect.
Important seasonal transfers of heat between the tropical ocean and land, called monsoons, arise
from the fact that water responds more slowly than land to these seasonal changes in solar heating
because of its larger heat capacity and high thermal inertia.
- Summer monsoon: in-and-up flow of moist air that produces precipitation. The land surface
heats up fast and the ocean absorbs the heat and warms up slowly. This causes initially a dry
process due to the rising of sensible heat and later a wet process linked to ocean moisture
and release of latent heat. Strongest monsoon is in India.
- Winter monsoon: reverse. In winter, the Sun’s radiation is weaker, and land surfaces cool by
back radiation. Because of differences in thermal inertia, land surfaces cool faster and more
intensely than the oceans. Air cooled over the land sinks toward the surface and creates a
region of high pressure where the extra mass of air piles up
The uppermost layer of the ocean is heated by solar radiation and
float on top of the colder, denser deep ocean. Most of the surface
circulation of the oceans is driven by winds, and one of the most
prominent results is huge gyres of water at subtropical latitudes
because of Coriolis. In the North Atlantic, the poleward transport
occurs in the Gulf Stream and its continuation, the North Atlantic
Drift.
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