◄Previous: 2 Taking Earth’s temperature

# 2.1 Global warming through time

## Activity 2 Global warming

Allow approximately 10 minutes

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

(A text entry box would appear here, but your browser does not support it.)

### Answer

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.

This browser does not support video playback.

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

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).

◄Contents►Next: 2.2 Changes in local and extreme temperatures

OpenLearn - Could we control our climate?
Except for third party materials and otherwise, this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 Licence, full copyright detail can be found in the acknowledgements section. Please see full copyright statement for details.