(Quote by Walter Lippmann – in notes) This is a truism as far a climate change and
what we do affect everywhere on earth. The quote was done in 1913 so he wasn’t
referring to global change; he referred to the start of WW1. He was an American.
What is ‘climate’?
There is some confusion between weather and climate.
Weather is the day to day changes in climate. They are the long term conditions
including seasonal changes. These include the extremes and the variation for a
specific location/region on earth. Environment Canada will ask what the climate on
the Prairies is. They will then average over the last 30 years for example. Roughly
it is 30 years that they average so the way you can distinguish between the two is
climate is what we expect to get and weather is what we actually get.
Weather is naturally variable and that is a problem. You can probably look today at
the forecast and there is a good chance they could be wrong. It can change over
weeks, months, and years. Weather is a result/consequence of an inter-play of a
number of factors; rapid shifts in air circulation, slower variations in ocean
conditions, and seasonal changes in sunshine.
If we look at climate it can also vary from average conditions. It is variable. One
year is colder or warmer than the next so if you have it change over time what has
to be distinguished is the variation caused by short-term variability from long-term
trends. You have to have a baseline. The baseline here with respect to climate is
important to have. It has to be consistent. One extreme year in
temperature/precipitation isn’t enough but if it goes on for 10 or 20 years or more
then you can be confident that maybe you have a problem.
Now the size of the change. If the change is very small over time it is difficult to
distinguish that from natural variation. If the change is large you have a better
handle of what is going on.
From a global perspective we are not interested so much what happens in Toronto
but on the entire face of the planet.
What is ‘climate change’?
BGYC58H3F.September ,18, 2007 LECTURE 2 2