How big are the temperature differences?
In fact, the general trend in the first part of this graph seems to be that temperatures rise and fall, but overall they decline a little. In fact, the 1500s to 1700s have sometimes been called the "Little Ice Age" in Europe.
During the Little Ice Age, the growing season was shortened by as much as two months across Europe, grain yields fell, and rivers and canals froze over. Even artists began to pay attention to the weather, producing paintings full of snow, ice, and menacing weather.
So, how big was this temperature difference ON AVERAGE?
Does 0.2 or 0.3 degrees sound like a small difference? Tiny even?
The differences we are talking about are not huge, but they are noticeable. Less than half a degree makes the difference between a normal winter and a winter filled with ice and snow. How can this be?
First, remember that we are talking about degrees Celsius, which are about twice as big as Fahrenheit. So, if you are used to Fahrenheit, you need to adjust your perceptions.
Secondly, remember that this is a WORLD average. During the Little Ice Age, Europe cooled down, but other parts of the world may have stayed the same. So a 0.5 degree Fahrenheit difference in WORLD average temperature could be 1 or 2 degrees in EUROPEAN average temperatures.
Thirdly, remember that this is an ANNUAL average. Let's say 3 months out of the year are much colder, but the rest of the year is the same. In that case, the EUROPEAN YEAR-ROUND average of 2 degrees becomes a EUROPEAN WINTER-TIME average difference of 8 degrees!!
Finally, remember that what really defines a winter is not the average temperature, but the cold snaps, right? The average temperature may decrease by 8 degrees, but the cold snaps may be 15 or 20 degrees colder.
Now we're talking mini-ice-age material!
Or, in summary, the differences you see on the hockey stick graph look small because
- they are in Celsius
- they are Northern Hemisphere averages
- they are annual averages
- they don't really account for cold snaps / heat waves.
In case you're curious, the temperature decline during a full-blown, world-wide, mile-of-ice-over-your-head, 50-thousand-year-long glacial period is only about 8 degrees Celsius.
Copyright University of Maryland, 2007
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