Unit 1 Prosperity, inequality, and planetary limits

1.3 Another hockey stick: Climate change

Using GDP as a measure of living standards ignores the importance of the environment for our current and future wellbeing. Evidence that our use of fossil fuels—coal, oil, and natural gas—has profoundly affected the natural environment of the planet is shown in Figures 1.2a and 1.2b. Each figure has the hockey stick shape. After having remained relatively unchanged for many centuries, increasing emissions of carbon dioxide (CO2) into the air during the twentieth and twenty-first centuries have resulted in measurably larger amounts of CO2 in the earth’s atmosphere (Figure 1.2a) and brought about perceptible increases in the northern hemisphere’s average temperatures (Figure 1.2b). Figure 1.2a also shows that CO2 emissions from fossil fuel consumption have risen dramatically since the late 1800s.

Figure 1.2b shows that the mean temperature of the earth fluctuates from decade to decade. Many factors cause these fluctuations, including volcanic events such as the 1815 Mount Tambora eruption in Indonesia.

There are 2 line charts. In line chart 1, the horizontal axis shows years from 1000 to 2020. The vertical axis shows atmospheric CO 2 in parts per million, and ranges from 250 to 450.  Between 1010 and 1800, atmospheric C O 2 was fluctuating around 280 parts per millions. It increased to slightly above 400 parts per million between 1800 and 2020. In line chart 2, the horizontal axis shows years from 1000 to 2020. The vertical axis shows global carbon emissions from fossil-fuel burning in millions of metric tonnes, and ranges from 0 to 40,000, with each increment going up by 8000. Data for carbon emissions is only available from 1750. Carbon emissions increased significantly from almost 0 millions of metric tonnes in 1750 to almost 40,000 millions of metric tonnes in 2018.
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Figure 1.2a Carbon dioxide in the atmosphere (1010–2020) and global carbon emissions from burning fossil fuels (1750–2018).

Pierre Friedlingstein, Matthew W. Jones, Michael O’Sullivan, et al. 2019. ‘Global Carbon Budget 2019’. Earth System Science Data 11: pp. 1783–1838. doi: 10.5194/essd-11-1783-2019.; Pieter Tans NOAA/GML and Ralph Keeling, Scripps Institution of Oceanography. 2022. ‘Trends in Atmospheric Carbon Dioxide’.; D. Gilfillan, G. Marland, T. Boden, and R. Andres, R. 2021. ‘Global, Regional, and National Fossil Fuel CO2 Emissions’. Carbon Dioxide Information Analysis Center (CDIAC) Datasets. Accessed: September, 2021.

Mount Tambora spewed so much ash that the earth’s temperature was reduced by the cooling effect of these fine particles in the atmosphere, and 1816 became known as the ‘year without a summer’.

Since 1900, average temperatures have risen in response to increasingly high levels of greenhouse gas concentrations. These have mostly resulted from the CO2 emissions associated with the burning of fossil fuels. And in each year of the twenty-first century, the average temperature has been higher than at any time in the previous millennium.

In this line chart, the horizontal axis shows years from 1000 to 2019. The verticxal axis shows the deviation from the 1961-1990 mean temperatur in Celsius degrees. The deviation was almost null until 1100. It fluctuated between negative 0.2 and negative 0.4 until 1300, between 0 and negative 0.6 until 1450, between negative 0.2 and negative 0.6 until 1700, between negative 0.4 and negative 0.6 until 1800, and then it started increasing until 1 degree Celsius in 2019.
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Figure 1.2b Northern hemisphere temperatures over the long run (1000–2019). The figure shows 5-year moving averages.

Michael E. Mann, Zhihua Zhang, Malcolm K. Hughes, Raymond S. Bradley, Sonya K. Miller, Scott Rutherford, and Fenbiao Ni. 2008. ‘Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia’. Proceedings of the National Academy of Sciences 105 (36): pp. 13252–13257.; C. P. Morice, J. J. Kennedy, N. A. Rayner, and P. D. Jones. 2012. ‘Quantifying uncertainties in global and regional temperature change using an ensemble of observational estimates: The HadCRUT4 dataset’, Journal of Geophysical Research 117. D08101, doi:10.1029/2011JD017187.

The authoritative source for research and data about climate change is the Intergovernmental Panel on Climate Change.

The human causes and the reality of climate change are no longer widely disputed in the scientific community. The likely consequences of global warming are far-reaching: melting of the polar ice caps, rising sea levels that may put large coastal areas under water, and potential changes in climate and rain patterns that may make some densely populated parts of the world uninhabitable and destroy the world’s food-growing areas.

We can see that the hockey sticks for GDP per capita and for atmospheric CO2 have risen together. It is also the case that richer countries have, on average, higher emissions per capita. In Unit 2, we explore this link between income and emissions, and consider whether it will be possible, in future, to raise living standards around the world without further damage to the climate.

Exercise 1.1 How much difference does a couple of degrees warmer or colder make?

Between 1300 and 1850 there were a number of exceptionally cold periods, as shown in Figure 1.2b. Research this so-called ‘little ice age’ in Europe and answer the following questions.

  1. Describe the effects of these exceptionally cold periods on the economies of these countries.
  2. Provide examples of groups of people within a country or region who were exceptionally affected by climate change.

Question 1.2 Choose the correct answer(s)

Figure 1.2b shows the northern hemisphere’s temperature since year 1000, reported as the deviation from the 1961–1990 mean (average) temperature. Based on this figure, read the following statements and choose the correct option(s).

  • The 1961–1990 mean temperature was 0.2 to 0.6 degrees higher than the temperatures between 1450 and 1900.
  • The negative numbers on the graph indicate that the temperature consistently fell between 1100 and 1900.
  • A consistent rise in temperature is only a post-1980 phenomenon.
  • The consistent rise in temperature after 1980 suggests that temperatures will continue to rise in every year following 2000.
  • The graph shows that the temperature between 1450 and 1900 was 0.2 to 0.6 degrees below the 1961–1990 mean temperature.
  • The vertical axis variable shows the difference between the temperature at a given time and the mean temperature from 1961 to 1990. Negative numbers on the graph indicate that the temperature during those years was consistently below the 1961–1990 mean.
  • There are earlier instances where the temperature rose consistently over a period, for example, the early 1900s.
  • It is true that temperatures have been rising consistently since 1980, but this alone does not suggest that temperature will continue to rise in every following year. There are many factors that affect temperature in any given year, making it difficult to predict exactly what the temperature will be in the future.