Global Temperatures

Chapter 5

“Noah built an altar to the LORD and sacrificed on it the animals and birds that had been approved for that purpose. 

And the LORD was pleased with the sacrifice and said to himself, “I will never again curse the earth, destroying all living things, even though people’s thoughts and actions are bent toward evil from childhood.   As long as the earth remains, there will be springtime and harvest, cold and heat, winter and summer, day and night.”

 Genesis 8:20-22 (NLT)

There is an introductory video here:  http://youtu.be/PSOCymjgNRo

Temperature measures the average kinetic energy (motion) of particles.  We experience this as the sensible heat transferred from one object to another as the particles collide or move (by conduction, convection, or advection).

  • In the upper atmosphere, the temperature is actually very high (each particle is moving a lot, because it receives much insolation).
  • However there are so few particles – densities are so low – it does not feel warm.  This is because particles rarely collide, and thus no heat is transferred.  Temperature, measured in terms of how fast the particles are moving, is high.

Read the sections in your text about temperature scales (be aware of the different scales, particularly Celsius and Fahrenheit), and measuring temperature.  Being in Canada we will use Celsius.  In the US and UK Fahrenheit is more common.

I. Global temperatures are related to:

A. Latitude

Insolation is the most important variable in determining global temperatures.

The amount of insolation various parts of the Earth receive is directly related to latitude and seasons (what hemispheres are tilted toward/away from the sun).

  • Remember Figure 2.9, “Daily insolation received at the top of the atmosphere,” 4CE, p. 50 (2.10; 3CE, p. 48).
  • Look at Figure 5.5, “Latitude affects temperature”  4CE; p.123  (5.4; 3CE, p. 115).

The implications of this are straightforward:

  • Locations close to the poles receive less insolation than tropical and equatorial locations; therefore, on average, polar locations are colder!
  • Summers (when your hemisphere is tilted toward the sun) are warmer than winters.
B.  Altitude

In the troposphere (where we live), temperatures decrease with altitude, because the air becomes thinner (less dense).  Because sensible (felt) heat has to be conducted from molecule to molecule, the less dense the molecules are, the less heat is transferred.

The normal lapse rate is 6.4°C/1000 m.  This means that for every 1000 m of elevation you gain, the temperature drops, on average, 6.4°C.

At higher altitudes:

  •  the temperature is cooler,
  •  the temperature range – day to night and between sunny spots and shady spots – is greater,
  •  UV radiation is more intense (make sure you wear sunscreen in the mountains!).

Consider Figure 5.6, “Effects of latitude and altitude”  4CE; p. 124 (5.5; 3CE, p. 116).  .  Note the difference that high altitude (La Paz) makes, at the same latitude as a low altitude city (Concepción).

C.  Cloud cover

At any given time, about 50% of the earth’s surface is covered by cloud.  Clouds reduce insolation (moderate temperature), and act as insulation (keeping in longwave radiation).  Thus clouds tend to keep daytime temperatures lower (by blocking out insolation), and nighttime temperatures higher (by reducing the escape of long wave radiation).

In equatorial areas and subtropical areas, cloud patterns are somewhat predictable.  Equatorial areas have a typical pattern of afternoon cloud, reducing insolation and keeping temperatures warm, but not incredibly hot.  Subtropical areas rarely have any cloud cover – these are the hottest places on Earth.

In mid-latitude areas (us), cloud patterns are notoriously unpredictable!

D. Continentality (land-water heating differences)

As we noted in Chapter 4, coastal/maritime areas (near oceans/large lakes) tend to stay cooler during the day and in summer, and stay warmer at night and in winter, than inland areas …  why?

Water and land have different heating properties …

1. Evaporation:

In coastal areas, much insolation is used to evaporate water.  When insolation is used for evaporation, that energy is not available heat the surface as sensible (felt) heat.  The insolation used for evaporation is stored as latent heat, which can be released when the water vapor condenses.

NOTE:  The concept of sensible/latent heat is why people perspire and dogs pant!  When we release moisture to the atmosphere, energy from our bodies is used to evaporate it.  This reduces our body temperature, cooling us off on hot days.  We reduce our sensible heat, by using some our body’s energy to evaporate moisture as latent heat.

More insolation is used for evaporation in maritime areas than continental areas because there is more water available!  Thus less insolation is used for sensible heat – felt heating – in maritime regions.  Away from the ocean, less insolation used for evaporation; more insolation is used for sensible – felt – heat.

Because of coastal evaporation, there also tends to be more water vapor in the air and more clouds in maritime areas.

2. Transparency
  • See Figure 5.7, “Land-water heating differences” 4CE, p. 125 (3CE, p. 117).

a. Soil and rock are not transparent.  Therefore, insolation is absorbed right at the surface.  The surface of rock or of soil heats quickly (remember how hot asphalt can be in August!).  But the rock is not moving (usually!) so heat is not “mixed” by convection or advection.  Little heat is conducted down into the earth.  Earth absorbs heat quickly and heats quickly during the day – right at the uppermost surface – and it loses heat quickly and cools quickly at night.

Think about a sandy beach on a scorching summer day.  The surface of the sand will be cool at night. But it heats quickly to extremely hot temperatures during the day.  However if you dig your toes below the surface, it’s nice and cool.  The intense insolation is absorbed at the surface during the day, super-heating the surface.  But the warmth does not penetrate to any depth.  It is concentrated right at the top.  Once the sun sets the sand cools quickly.

b. Water is transparent.  Insolation penetrates an average depth of 60 m (in very clear water, up to 300 m).  Thus a given amount of insolation heats a great amount of water (not just the upper surface, like rock).  This water is also constantly being “mixed” by advection and convection currents.  The heat is dispersed over a vast depth and area.  Water heats slowly and cools slowly.

The net result is that maritime locations are more moderate than continental areas.  Over the course of a 24-hour period, there is less intense heating during daylight, and less intense cooling at night.  Over the course of a year, there is less intense heating during the summer, and less intense cooling during the winter.

Think about swimming in a large body of water (the ocean, a big lake).  While the temperature may change a bit between your noon-time dip and your midnight splash, it is not dramatically colder at night.  Annually, the ocean water temperature is not that much colder for the Polar Bear swim, January 1, than your Canada Day swim, July 1 – but the air temperature and land temperature is much, much colder in January!!!  Being in the water January 1 for the Polar Bear Swim isn’t normally the problem … it’s getting out that gets you!!

3. Specific heat or Heat capacity

More energy is required to heat one litre of water than one litre of rock.  The corollary of this is that one litre of water can hold more heat than one litre of rock.  This heat-holding capacity is called specific heat. Water has a specific heat about 4 times that of rock.

So … a given amount of insolation will heat rock much faster than the same amount of insolation will heat water.  But, the water will hold more heat than the soil.  This will also moderate temperatures around water – cooler during the day, warmer at night; cooler in summer, but warmer in winter.

4. Ocean currents

(we do this more in Chapter 16 in the other course)

Surface ocean currents tend to carry warmer equatorial and tropical waters toward the poles.

In the North Atlantic, the Gulf Stream carries warm water from the Gulf of Mexico, up the East Coast of North America to Europe.  See Figure 5.8, “The Gulf Stream” 4CE p. 126 (5.10; 3CE, p. 118).  For current movements in the Gulf Stream, click here.

Reykjavik, Iceland (almost on the Arctic Circle) averages temperature above 0°C all year – much warmer than most Canadian cities (certainly those inland, from central BC through to the Atlantic Coast, much further south  (from 45-54°N)!  This is the effect of continentality, related to water’s transparency, specific heat, and movement in currents.

In the North Pacific, the Japan Current, also called the Kuroshio, similarly brings warm water from the Sea of Japan along the East Coast of Asia to Alaska.

For current satellite imagery of sea-surface temperatures and currents, click here.

  • Figure 5.9, “Sea-surface temperatures,” 4CE; p. 127 (5.11; 3CE, p. 119)  shows that, although equatorial areas are warmest, heat is distributed north and south by currents.  This helps moderate polar winter temperatures, when polar regions receive no direct insolation.

Continentality is summarized well in your text, contrasting:

  •  Vancouver with Winnipeg (Figure 5.10, “Marine and continental cities – Canada,”  4CE; p. 128 (5.12; 3CE, p. 120)).
  • Norway and Siberia (Figure 5.11, “Marine and continental cities – Eurasia,” 4CE; p. 129 (5.15; 3CE, p. 124)).

Coastal cities  

  • are warmer in winter
  • are cooler in summer
  • have smaller annual temperature ranges
  • have small daily temperature ranges

because of the influence of oceans

Continental cities

  • are cooler in winter
  • are warmer in summer
  • have greater annual temperature ranges
  • have greater daily temperature ranges

because they lack the influence of oceans

II. Global temperature patterns

Study:

  • Figure 5.12, “Global mean temperatures for January,”  4CE; p.130 (5.13; 3CE, p. 121)
  • Figure 5.13, “Global man temperatures for July,” 4CE; p. 131 (5.16; 3CE, p. 124)
  • Figure 5.16, “Global annual temperature ranges,” 4CE; p.134 (5.18; 3CE, p. 128)

These figures in your text highlight how these factors influence global temperature patterns.  Study them!  The lines on the maps are isotherms, they join points of equal temperature.  (Those who are familiar with contour maps, contour lines join points of equal elevation – same principle).

The thermal equator (the heavy dotted red line on each figure) is the isotherm that connects all points with the highest mean (average) temperature at that time of the year.

A. On the January map (Figure 5.12; 4CE; p. 130/5.13, 3CE, p. 121):
  • the thermal equator is south of the Equator (0°).  Why?
    • Because the sun is over the Southern Hemisphere, near the Tropic of Capricorn (23 ½° S)!
  • in the southern hemisphere, the thermal equator dips furthest south over the continents (South America, Australia).  Why?
    • Because land heats more quickly than water.  The continents “super-heat”; the ocean stays cooler.
  • in the southern hemisphere the highest temperatures are over the continents.   Why?
    • Same reason – the land heats more intensely.
  • in the northern hemisphere, the coolest temperatures are over the continents (see Siberia and Greenland, -48°C!).  Note on the inset of North America that isotherms bend equator-ward (cooler air, further south)  Why?
    • Because land cools more quickly than water!
  • in the northern hemisphere, the warmest temperatures are in the oceans.   Why?
    • Because warm ocean currents bring warm water north (see the north Atlantic, toward Iceland and Norway), and water cools more slowly than land.
B. On the July map (Figure 5.13; 4CE ; p. 131/5.16; 3CE, p. 125):
  • the thermal equator is north of the Equator (0°).  Why?
    • Because the sun is over the Northern Hemisphere, near the Tropic of Cancer (23 ½° N)!
  • in the northern hemisphere, the thermal equator dips furthest north over the continents (North America, the Middle East).  Why?
    • Because land heats more quickly than water.  The continents “super-heat”; the ocean stays cooler.
  • in the northern hemisphere the highest temperatures are over the continents (Texas, Iran, China … even Siberia warms up!). Note on the inset of North America that isotherms bend poleward (warmer air, further north)  Why?
    • Same reason – the land heats more intensely.
  • in the southern hemisphere, the coolest temperatures are over the continents (see Peru, 0°C, Antarctica, -66°C!). Why?
    • Because land cools more quickly than water!
  • in the southern hemisphere, the warmest temperatures are in the oceans.   Why?
    • Because water cools more slowly than land.
C. On the annual temperature range map (5.16; 4CE, p. 134/5.18; 3CE, p. 128):
  • the greatest annual ranges are located in central Asia (Siberia) and central North America.  Why?
    • Because these areas are furthest from oceans.  They heat most intensely in the summer and cool most intensely in winter.  And, because there is a large seasonal difference in the amount of insolation received.
  • the greatest temperature ranges are in the northern hemisphere.  Why?
    • Because there are larger land masses in the northern hemisphere.  The Southern Hemisphere is almost all water (keeping temperature ranges moderate)
  • the least annual ranges are over equatorial waters.  Why?
    • Because the equator has little seasonal change in the amount of insolation received.  And, water cools and heats so slowly.

III.  Air Temperature and Us

  • Focus Study 5.1, “Heat Waves” 4CE, pp.136-7) (“Air temperature and the human body,” 3CE, pp. 126-127).

We “feel” different temperatures depending on water vapour content of air, wind speed, air temperature … and the sensitivity of our own bodies.

At the same “temperature”:

  • moist air “feels” colder than dry air
  • moving air (wind) “feels” colder than still air
  • The coldest is moist, moving cold air!

Our natural body temperature is 36.8°C.  When we are exposed to extremely low or extremely high temperatures, our bodies feel stress..

When exposed to low temperature we experience hypothermia.

When exposed to high temperature we experience hyperthermia.

Check out this article on the coldest and hottest temperatures recorded:  BBC News – Coldest spot on Earth identified by satellite

A. Wind Chill (4CE, p.118)

Anyone who has ever waited at a bus stop or taken a walk on a blustery winter day knows that you feel colder when the wind blows. We call the cooling sensation caused by the combined effect of temperature and wind the wind chill.

On a calm day, our bodies insulate us somewhat from the outside temperature by warming up a thin layer of air close to our skin, known as the boundary layer. When the wind blows, it takes this protective layer away-exposing our skin to the outside air. It takes energy for our bodies to warm up a new layer, and if each one keeps getting blown away, our skin temperature will drop, and we will feel colder.

Wind also makes you feel colder by evaporating any moisture on your skin-a process that draws more heat away from your body. Studies show that when your skin is wet, it loses heat much faster than when it is dry.

The wind-chill factor expresses the temperature that cold moving air really feels like – and the rate at which the body actually loses heat.

  • See 4CE Figure 5.2, p. 118 (Figure 1/5.1.1, “Wind Chill,” 3CE, p. 126).

Wind-chill can be cause by naturally created wind or by human-induced wind (i.e. skiing).  Beware!  Skiing at high speeds artificially produces very high wind chills!  Skiing at 30 km/h is as dangerous to exposed skin as a 30 km/h wind.

Canada has a new wind chill index (more scientific than the one presented in your text).

Just in case you were wondering, the equation to determine the new index is the following:

T_{\rm wc}=13.12 + 0.6215 T_{\rm a}-11.37 V^{+0.16} + 0.3965 T_{\rm a} V^{+0.16}\,\!
where T_{\rm wc}\,\! is the wind chill index, based on the Celsius temperature scale, T_{\rm a}\,\! is the air temperature in degrees Celsius (°C), and V\,\! is the wind speed at 10 metres (standard anemometer height), in kilometres per hour (km/h).

NO!   YOU DO NOT HAVE TO KNOW THIS FORMULA FOR AN EXAM!

Canada’s record Wind Chill was January 13, 1975: -91°C.  This occurred in Kugaruk (Pelly Bay), NWT when the temperature was -51°C and there was a 56 kmh wind.

Of course this is not the only measure of Canadian extreme temperatures!  Check out the just-in-fun Long John Index Service of Canada.  No, you don’t have to know this for an exam either!

B. Heat Index or Humidex (4CE pp. 136-138)

The heat index or humidex indicates how the human body reacts to high temperatures and high humidity (high water vapour content).  The higher the humidity, the more difficulty humans have “cooling down” by perspiration (the air is so saturated it cannot evaporate perspiration and we cannot cool by the loss of latent heat).

According to the Meteorological Service of Canada, a humidex of at least 30 causes “some discomfort”, at least 40 causes “great discomfort” and above 45 is “dangerous”. When the humidex hits 54, heat stroke is imminent.

The highest recorded humidex reading in Canada was 53, recorded at Carman, MB (July 25, 2007) and Castlegar, BC (July 14, 1961).

One curious (but true!) note:  hair length increases with humidity! The range between dry and saturated air can account for a difference in hair length of about three per cent.  In moist air, people with naturally curly hair experience the frizzies as their hair increases in length. Under the same conditions, people with long, straight hair find it going limp.

The official formula is this: (No, you don’t need to know it for the exam!)

\text{Humidex} = T_\text{air} + 0.5555 \left[6.11 e^{5417.7530 \left(\frac{1}{273.16} - \frac{1}{T_\text{dew}}\right)} - 10\right]

where

  • \scriptstyle T_\text{air} is the air temperature in °C
  • \scriptstyle T_\text{dew} is the dewpoint in K
Worth reflecting on …
  1. Sir John Polkinghorne, professor of physics at Cambridge University and an ordained Anglican minister, talks about the origins of his faith, how that faith stands alongside his scientific knowledge, and how he deals with doubt. The Faith of a Physicist – YouTube.  What are your thoughts?
  1. Reflecting on our Christian mission, Dayton and Pretiz write …

“What can we do in practical terms therefore to make sure that we are faithful witnesses to him in our life and work, regardless of where that life and work is lived out, and regardless of what its official business is?

“Firstly, just as it is now normal for some degree of anthropological or cultural study to be a regular part of cross-cultural training, along with the obvious demands of language study, so we should make it an essential part of our preparation to acquire an equal awareness and understanding of the physical setting in which we go to work. By definition those who merely visit a place are unfamiliar with all of its dynamics, ecological and otherwise. They tend to be acutely unaware of the constraints that must exist if their life is to be sustainable in an unfamiliar environment. They also have far less invested in its sustainability, because unlike those they have come to serve, they can always leave! If they are part of demonstrating or teaching a lifestyle that results from the gospel, as inevitably they are, cross-cultural workers need to be aware of the local context if they are not to endorse or even recommend disaster. Two actual examples, one negative and one positive serve to illustrate the point. In a semi-arid African country, missionaries began to feel acutely the difficulty in training church leaders who belonged to a nomadic group. The people were never in one place long enough for the teachers to complete any serious work. As the missionaries understood little of the interaction between the movement of the cattle, and the availability of food, they resolved to sink a borehole that would avoid the need for wandering, and provide constant water, keeping the people in place for long enough to be taught thoroughly. Needless to say, within four months the land for some thirty kilometres in every direction had become a dust bowl, trampled by the constant presence of the many animals who had now settled down in the area. Serious poverty was only averted by the resumption of the old nomadic lifestyle. More positively, in a South American country, a pastor was very concerned by the way his church people were destroying the last of a dryland forest in order to sell the wood for much – needed fence poles. Once the trees were cut, the land soon lost its topsoil, and families who had once lived in the area were forced to move. Furthermore the pastor was convinced by teaching Genesis that this kind of way of living by destruction didn’t reflect a proper human response to the Creator. So he gradually introduced a bee-keeping economy which ensured the protection of the woodlands that were habitat for the bees, but which served to safeguard the livelihood of his church members over future years. Properly understood, and obediently undertaken, the search to understand creation is part of a quest to understand God, just as the search to understand a culture is an act of compassion that reflects God’s love for the people he has made…

“Secondly, we can simply offer to our host country and church an awareness that our relationship to creation is relevant to our relationship with God and to our discipleship. For many Christian communities that will come as an entirely new idea, and will also conveniently serve to challenge the besetting dualism which does such damage in Christian living …  An affirmation of the fundamental goodness of Creation, and of the possibility of redemption in the midst of life, rather than by escaping life, is urgently needed. It will need great humility, and the awareness of our partial understanding of many issues, but it will do greater justice to the truth that any idea of what is “spiritual” must include all that is of the Spirit of God, rather than meaning “non-material” as is too often popularly assumed. A more biblical recognition of the role of the Holy Spirit in creation should protect us from that.

“Then thirdly, we must re-examine how our work in evangelism, which in one form or another makes up such a major part of normal missionary endeavour, is affected by a recovery of our understanding of God as Creator, and people as his creation. Once again this may seem to be of limited relevance, but in fact the reverse is true. If we begin from the understanding that in common with all people, both those who call themselves Christians and those who don’t, we are created human beings, we are immediately spared from a disastrous “us and them” posture. Whatever our good intentions, we need to accept that this has been widely misunderstood as elitism or arrogance. We share the gospel with those who hear it, it is for all of us, no matter what stage we may have reached in hearing or receiving it. There is a kind of created community here. Furthermore we understand that everything about all people is in some measure created – body, soul, spirit, person … God’s care is manifest to all his creation, and not merely a part of it. His care is for the created person, in need of redemption in all its fullness, and not merely for some non-material entity deemed to be eternal. Moreover, the understanding that all people, in every place and in every condition, share an equal status as created beings gives us a renewed motivation for crossing cultural barriers, and reaching out everywhere with the good news. No human community should be overlooked, or regarded as less important … Above all, we must be aware, because of the fact that the word was made flesh and lived among us, that whatever our preaching or talking, it will often be our embodiment of the message that speaks loudest. Once again our model is the ministry of Jesus, whose words served as explanation for the mighty works of God, and whose action in laying down his life and taking it up again brought our redemption. Tellingly we celebrate that now in a meal together, and not just in words. We cannot neglect the material reality that embodies our verbal evangelism. Who we are is as much our preaching as what we say.

“Finally the simple actions which involve us in exchanges with the Creation can be looked at and seen for what they are – either as grateful or exploitative, potentially worship, or thoughtless and indifferent. How do we use paper, or electricity, or transport, in our work? What is left for the future when our work is complete? Do we recognise any constraints and limits, and how are the other members of God’s creation affected by our projects? …

“Whatever our work or our life, it (mission) is inevitably something that we will all do, and the choice we face is merely whether we will do it well or badly, whether we will do justice to the gospel, or will distort it.”

Adapted from “Down-to-earth Christianity” edited by R W Dayton and P E Pretiz, 2000. ISBN 0-9678717-0-0 (http://en.arocha.org/bible/index2.html)

  • Do you agree with Dayton and Pretiz?  Why?  Why not?  Feel free to discuss this quote on the course discussion site …

3. Read about Pope Francis challenge to see care for the environment as a Christian imperative:  Pope calls for new work of mercy: Care for environment

To review …

Check out the resources at www.masteringgeography.com

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Scripture quotations marked (NLT) are taken from the Holy Bible, New Living Translation, copyright © 1996. Used by permission of Tyndale House Publishers, Inc., Wheaton, Illinois 60189. All rights reserved