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2.1 Global warming through time

Activity 2 Global warming

Timing: Allow approximately 10 minutes

What do you understand by the term ‘global warming’?

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In brief, thousands of land measurements made over time and in different places are combined into a single, globally averaged temperature. An upward trend in the globally averaged temperature is referred to as global warming.

Climate scientists use the term global mean surface temperature (GMST) to describe the globally averaged temperature. This plays a key part in our current knowledge about climate change.

• Read the following statement from the IPCC and guess the missing value:

The amount of global warming in the period 1880–2012 is ___ degrees Celsius (IPCC, 2013).

• The amount of global warming in the period 1880–2012 is 0.85 degrees Celsius (IPCC, 2013). How close were you? Scientists need to be able to make sensible ‘guess-timates’, and practice helps to improve that skill. You should also note that, in many cases, changes measured in climate are surprisingly small, although their impact may be large.

The full statement from the IPCC also has an uncertainty range. They estimate there is a 9 in 10 chance of the temperature change being between 0.65 and 1.06 degrees Celsius. So, if your guess was in this range, or a little bit outside, you were also right!

Figure 4 shows the observed changes in global mean surface temperature (GMST) for the period 1850–2012 in degrees Celsius (IPCC, 2013).

Figure 4 Annual global mean surface temperature change for the period 1850–2012 (IPCC, 2013).

The x-axis is the year. Each of the data points is an annual mean: the mean of one year of data. The data points are joined by lines to show the changes more clearly.

The y-axis is ‘temperature change relative to 1961–1990 in degrees Celsius’. This is the temperature change relative to the average temperature during the 30 years of what we term as the baseline period of 1961–1990. The average temperature over this period is zero on the y-axis.

You can see there has been an overall upward trend in GMST. There are also short-term large fluctuations over about one to three years, which are known as interannual variability.

The video below shows another powerful way of communicating the same data: through music.

Download this video clip.Video player: Video 1 A Song of Our Warming Planet by Daniel Crawford.
Skip transcript: Video 1 A Song of Our Warming Planet by Daniel Crawford.

Transcript: Video 1 A Song of Our Warming Planet by Daniel Crawford.

[SOUND EFFECTS PLAYING]
[WATER DRIPPING]
DANIEL CRAWFORD:
I was in a class with Professor Scott St. George in the geography department and at one point, he posted a slide advertising for interns in his dendrochronology lab. And I was lucky enough to get that job.
He came to me with a set of data with the task of turning it into a piece of music, and we wound up with "A Song of Our Warming Planet." In the piece of music, each note will correspond to a year. And then the pitch of that note will represent the temperature of that year. So then for these really high pitches, that would mean a warmer year and then the lower pitches would be a cooler year.
The data comes from the Goddard Institute for Space Studies at NASA. It's a compilation of global annual surface air temperatures. Climate scientists have a standard toolbox to communicate their data, and what we're trying to do is we're trying to add another tool to that toolbox; another way to communicate these ideas to the people who might get more out of this than out of maps, graphs, and numbers.
Climate change is a defining issue of our generation, and it's still something that a lot of people don't fully understand. And what we're trying to do is to represent with the music, sort of, the immediacy and the importance that this issue has right now. And if we act on that, then maybe it won't be as much of an issue for the future.
[MUSIC PLAYING]
[MUSIC - DANIEL CRAWFORD AND SCOTT ST. GEORGE, “A SONG OF OUR WARMING PLANET”]
[MUSIC PLAYING]
End transcript: Video 1 A Song of Our Warming Planet by Daniel Crawford.
Video 1 A Song of Our Warming Planet by Daniel Crawford.
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Global warming of 0.85 °C in around 160 years does not sound like much. But humans do not feel global mean temperature: we feel local changes, and we are most affected by extremes (the hottest and coldest days).

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