Lecture 8: what is climate and palaeoclimates?

Question 1

CLIMATE FACTOR – LATITUDE

Answer 1

Variation of average incoming solar radiation at a given latitude.
Latitude is an important factor in determining the climate at a given location.

Question 2

GLOBAL PRESSURE DISTRIBUTION IN THE REAL WORLD

Answer 2

 The average surface wind and pressure distribution is largely determined by semi-permanent highs and lows.
 The pressure difference between the Icelandic Low and the Bermuda High is of great importance to the severity of the European winter.
 The zone where the trade winds converge is called the Inter-tropical convergence zone (ITCZ).
 Its seasonal variation is of great importance for tropical climates (e.g. monsoon climate in India and South- East Asia).

Question 3

MONSOON CLIMATE

Answer 3

• Monsoon refers to the reversal of mean surface wind direction from summer to winter
• Most regions between 350 N and 250 S and between 300 W and 1700 E experience monsoon climate (best known in South and South East Asia)
• Caused by the seasonal movement of the ITCZ

Question 4

INFLUENCE OF THE HIMALAYAS

Answer 4

The Himalaya Mountains cast an extensive rain shadow comprising the Tibetan Plateau and the Taklamakan desert

Question 5

WHAT FACTORS DETERMINE CLIMATE?

Answer 5

Latitude
determines how much average solar radiation a given location receives, impact on seasonality

Land and Water
determines continentality of a given location

Ocean currents
can provide e.g. an additional heat source for a region

Prevailing winds
determine e.g. how much moisture is advected and hence determine the potential for rainfall
Pressure cells
determine availability of cloud coverage and frontal systems

Mountain barriers
can deflect wind or result in rain shadow on the leeward side

Altitude- has an influence on temp

Question 6

CLIMATE VERSUS WEATHER – POSSIBLE DEFINITION- WEATHER

Answer 6

Weather is described through temperature, pressure, rainfall, visibility, cloud coverage. Weather is the current physical state of the atmosphere, i.e. the specific conditions of the atmosphere at a particular place and time, measured in terms of variables that include temperature, precipitation, cloudiness, humidity, air pressure, and wind.

Question 7

CLIMATE VERSUS WEATHER – POSSIBLE DEFINITION- CLIMATE

Answer 7

Climate is described through long-term averages of weather conditions (e.g., 30 year, 100 year, 150 year mean values) and the range of variability with respect to the mean value. It is the long-term average of conditions in the atmosphere, ocean, and ice sheets and sea ice described by statistics, such as means and extremes.

Question 8

CLIMATE CLASSIFICATION-Thornthwaite System

Answer 8

• After Charles W. Thornthwaite
• Classification based on moisture
• Used often by soil and water resource scientists
• Based on soil moisture content and evapotranspiration

Question 9

CLIMATE CLASSIFICATION- Koppen system

Answer 9

After Wladimir Köppen
• Also known as Köppen–Geiger
climate classification system
• Most widely used system
• Based on temperature and precipitation, linked to vegetation

Question 10

CLIMATE VARIABILITY

Answer 10

Climate Variability is caused by natural changes in climate that fall within the normal range of extremes for a particular region, as measured by temperature, precipitation, and frequency of events. Atmospheric oscillations are an important driver for natural climate variability.

Question 11

NORTH ATLANTIC OSCILLATION

Answer 11

• Defined as difference between sea level pressure between two stations during winter season (December to March)
• Two stations represent the centres of actions occurring over Iceland and the Azores
• Iceland is Stykkisholmur
• Azores is Ponta Delgada (Rogers, 1997), also Lisbon (Hurrel, 1995), and
Gibraltar (Jones, 1997)
• Positive phase: stronger than usual pressure difference
• Negative phase: weak pressure difference
• Positive phase: fast storm tracks bring wet warm winters in Western Europe, mild & wet winters on North American East coast.
• Negative phase: more cold air invasions on North American East coast and in Mediterranean Europe
• Of interest for long-term climatological analysis as phase changes often take decades

Question 12

THE CLIMATE SYSTEM AND ITS INTERACTIONS

Answer 12

The environmental spheres of the Earth/Climate System interact through feedbacks

o Positive feedback leads to instability: Changes in the system accelerate

o Negative feedback lead to stability: Changes in the system slow down

 Changes in one of the environmental spheres can result in changes in any other sphere

Question 13

FEEDBACKS IN THE CLIMATE SYSTEM

Answer 13

 Positive feedback leads to instability: Changes in the system accelerate
 Negative feedback lead to stability: Changes in the system slow down
 The strength of a feedback on temperature is called the feedback factor and is defined as

Question 14

Climate change

Answer 14

 “Climate change” refers to a statistically significant variation in either the mean state of the climate or in its variability, persisting for an extended period (typically decades or longer).

 Climate change may be due to natural internal processes or external forcings, or to persistent anthropogenic changes in the composition of the atmosphere or in land use.