Lecture 11: Future Winds and Global
Part I: Climate Change Primer
What does climate mean?
What factors influence climate?
Historical climate change
The greenhouse effect
Part II: Research on Torontos climate
Part 1: Climatic Change Primer
Climate versus Weather
In discussions of climatic change an important distinction should first be made
between the concepts of climate and weather. Weather can be defined as a description of
the current conditions of the atmosphere: temperature, pressure, humidity, winds, etc.
recall the quantities and instruments for observation from Lecture 1. A prediction of the
weather in the future consists of a set of estimates for the future values of these
quantities. The sensitivity of the weather to very small changes places a very short limit
(5-10 days) on our ability to make accurate predictions.
Climate, in contrast, is a description of typical atmospheric conditions typical
weather. This can take the form of statistical functions such as averages, variabilities, or
extreme values of the quantities listed above. Because of the large amount of variability
in weather conditions, at least 30 years of observational data should be used to describe
climate, and ideally much more. Knowledge of climate allows us to form long-term
expectations of what the weather will be like, although it doesnt provide specific predictions for example, our knowledge of climate in Toronto tells us that a typical July
day will be hot and sunny, but we know that some days will be cool and wet.
Predictions of climatic change, as we will see, are predictions of how typical
weather conditions will change over a long period of time.
What factors influence climate?
The latitude of a location affects the angle of incidence of sunlight. The part of
the Earths surface that is perpendicular to sunlight receives the greatest amount of
radiation per unit of surface area in spring and autumn this is near the equator. Because
of the Earths axial tilt, the angle of incidence at any location changes with the seasons;
in the Northern Hemisphere we receive the most concentrated sunlight in June, when the
sun is highest in the sky (we also get more hours of sunlight per day at this time).
We have seen in earlier lectures that prevailing winds have persistent effects on
local weather conditions. Jet streams high overhead can affect climate too, by controlling
the creation and movement and thus frequency of storms. Ocean currents also affect
local climates by transporting warm water from the equator to higher latitudes, and thus
redistributing heat to different parts of the globe.
Air masses pushed around by prevailing winds and topography provide
transportation of warm or cold, moist or dry air.
Geographical features such as oceans or mountains strongly affect local climates
see for example the land/sea breeze.
Urban heat islands are caused by changes in surface albedo, evapotranspiration,
heat capacity and topography. Other land surface types such as forests, deserts or fields
of crops also have a strong influence on their own climate.
Historical climatic change
Volcanic eruptions e.g. Mt. Pinatubo in 1991
Particularly powerful volcanic eruptions are capable of launching dust and
sulfuric acid particles into the stratosphere. These aerosols (tiny particles suspended in
the air) can remain in the stratosphere for several years, as there is no rain to wash them
out as happens in the troposphere (sometimes in the form of acid rain). They are too
small to fall very quickly, so it takes a long time for them to settle back into the lower
While they remain in the atmosphere, these particles have the property of
reflecting sunlight, reducing the amount that reaches the Earths surface (i.e. they
increase the albedo of the Earths system). This causes noticeably cooler conditions
around the world for a short period of time.One particularly alarming example of this occurred in 1816, known colloquially
as the Year Without a Summer or Eighteen Hundred and Froze To Death. Massive
eruptions occurred in the preceding few years, combining to load the stratosphere with
reflective aerosols. In 1816 there were snowstorms in June in North America and Europe
and snow cover lasting into July. Some victims froze to death, and even more starved as
a result of massive crop failures.
Changes in the strength of the sun alter climate on Earth for obvious reasons. In
Lecture 1 we talked about the suns gradual increase in strength on a billion year time
scale when we discussed the Gaia Hypothesis.
Cycles in solar features that have a period of decades or longer have been
observed, and may indicate chanths in solar strength that could cause climatic change on
Earth. For example, in the 17 century the sunspot cycle came to a halt, and no sunspots
were observed for several decades an event called the Maunder Minimum. This
roughly coincided with a climatic period called the Little Ice Age, where anecdotal
reports of temperatures in Europe indicate a temperature drop of between 0.5 and 1C.
However, there is significant dispute over whether this change in temperature was a local
or global phenomenon, and in any case it is unproven that the low temperatures were
caused by an actual decrease in solar strength.
Direct observations of solar strength have only been available since the
development of human-built satellites in the 1970s. Through these observations we have
observed a slight change (0.01%) in solar s