Climate science for beginners (Aug 2007)

Notes of a workshop given by Stuart Parkinson, SGR, at the Camp for Climate Action, on 15 August, 2007
 

Presentation

Outline of problem and basic jargon

  • Greenhouse gas (GHG)
    • gas present in the atmosphere which traps heat thereby warming the Earth, e.g. carbon dioxide (CO2)
  • Greenhouse effect
    • warming of the Earth caused by greenhouse gases (has some similarities to the way a greenhouse works)
    • natural greenhouse effect - due to natural levels of GHGs; Earth is 33ºC warmer because of this
    • enhanced greenhouse effect (global warming) - extra warming due to human emissions of GHGs
  • Climate change
    • extra heat trapped in atmosphere leads to changes in air/ ocean circulation patterns, ie a change in climate

Climate change: the details

  • Human activities releasing large amounts of greenhouse gases [1]

GHG

Main artificial sources

Increase in atmospheric level

(1750 to 2005)

% contribution to global warming

Carbon dioxide (CO2)

burning fossil fuels (coal, oil, gas); deforestation

35%

63%

Methane (CH4)

gas pipeline leaks; cattle; paddy fields

148%

18%

Nitrous oxide (N2O)

nylon production; artificial fertilisers

18%

6%

'F' gases (HFCs, PFCs, SF6)

refrigerators; air-conditioning; electronics industry

(did not exist in 1750)

13%

(calculated from IPCC data)

  • CO2 levels are now higher than for at least 650,000 years [1]
  • These GHG emissions are causing the average global temperature to rise [1, 2]
    • Current temp is 0.76ºC higher than in ~1875 - probably higher than at any time in the last 1300y
    • Predicted temp in 2100 will be between 1.1ºC and 6.4ºC higher than 1990. Current evidence indicates that the upper end of this range would represent a faster change than at any time in the last 50 million years. (For comparison, the temperature difference between the Ice Ages and the warm interglacial periods such as at present has been 4-7ºC.)
    • Figure 1 (below) - recent & projected warming (1900-2100)

  • Broad climatic effects [1]
    • Sea level rise due to water expansion + ice melting
    • 'More energetic hydrological cycle' - ie more severe weather, such as storms, floods in some areas, with heatwaves, droughts in others
    • Large regional changes in climate
    • Risk of dramatic/ irreversible climate shifts (see below)

  • General impacts on humans and wildlife [3]
    • more water shortages, heat-stress deaths
    • more storm/ flood/ landslide deaths & damage
    • expansion in ranges of some diseases, eg diarrhoeal disease
    • disruption of agriculture
    • increase in environmental refugees
    • poorer countries and peoples are most vulnerable
    • major loss of wildlife, especially endangered species
    • climate change impacts will interact with and compound existing problems, eg poverty, population growth, resource depletion, other pollution

  • What effects have been observed already? [1, 3, 4]
    • sea level - ~17cm rise over 20th century
    • ice cover - thinning of Arctic ice sheet, retreat of most glaciers, some melting of permafrost
    • extreme weather - widespread increases in storm activity (including more intense hurricanes in some regions), increases in occurrences of drought
    • earlier spring/ later autumn - evident in plant, animal changes
    • increase in coral bleaching
    • World Health Organisation study suggested that current global death rate due to climate change could already be around 150,000 a year

  • Some predictions of effects that are likely to happen in future [1, 3]
    • strongly dependent on what humans do over the next few decades
    • sea level - 18-59cm rise by 2100 (potential for it to be significantly higher as some feedbacks have not been taken account of in these estimates)
    • water-shortages
      • Africa: 75-250 million projected to be exposed to greater 'water stress' by 2020 (water stress is when a community does not have enough water to meet its basic needs, ie <1700 cubic metres per person per year)
      • Asia: >1 billion may be adversely affected by 2050s
    • flooding likely to affect millions more per year by late century
    • adverse health effects likely to affect millions more people per year
    • 20-30% of plant & animal species at increased risk of extinction if global temperature rises by 1.5-2.5ºC above 1990 level
    • most studies have only looked at changes up to 2100 but effects will continue well beyond that and are likely to be more severe
    • some impacts will be positive, eg reduction in deaths due to cold, but the negative effects will dominate
    • For more details, see Figure 2 (below)

  • Dramatic & irreversible* climate shifts [1, 3, 5, 6]
    1. Melting of Greenland ice sheet - if global temperature rises to between 1.9ºC and 4.6ºC above the pre-industrial level, and remains there, then the ice sheet will eventually disappear completely leading to a sea level rise of 7m. This may take millennia to complete, although some scientists argue it could happen as quickly as a single century. West Antarctic ice sheet is also at risk.
    2. Shutdown of ocean conveyor - The global ocean current that includes the Gulf stream (which keeps the UK warm) could shutdown as ice dynamics change, eg due to (a) above, although this is thought to be very unlikely this century.
    3. Release of frozen methane - 5 trillion tonnes of methane locked away in frozen hydrates in deep oceans. Warming will start to release it accelerating the warming potentially very rapidly.
    4. Die-back of Amazon rainforest - Climate models suggest that by mid-century temperature and rainfall changes will cause the shrinking of the Amazon rainforest, with major loss of wildlife. The entire forest could be lost eventually.

*irreversible over periods of at least thousands of years


  • Scale of cuts in GHG emissions needed [7, 8]
    • difficult to be exact because of significant uncertainties in climate models and impacts
    • growing number of scientists argue that we should aim to prevent global temperature change of over 2ºC above pre-industrial levels to prevent 'dangerous climate change'
    • to limit global temperature increase in the region of 2.0-2.4ºC (above the pre-industrial level), global GHG emissions need to peak in the period 2000-2015 (ie about now!) and then reduce by 50-85% by 2050
    • this is a huge task, but the longer the delay in reduction, the bigger the impacts will be

  • How do we know all this? [1, 2]
    • Physics of greenhouse effect well understood, ie observations of planets
    • Wide range of data on past climate - direct temp measurements & 'proxy' data which vary with temp, eg tree rings, coral, ice cores
    • Eg ice cores show carbon dioxide and temperature have varied together over past 650,000y
    • Figure 3 (below) shows, for example, atmospheric CO2 and temperature variations over past 420,000y
    • Understanding of global carbon cycle (& other mineral cycles) - measurements of how carbon moves through atmosphere, oceans, ecosystems etc
    • Wide range of climate models calibrated on past changes used to predict future changes
    • Of 29,000 good quality environmental data sets that are available, 89% show changes consistent with a warming world
    • Evidence gathered together by scientific body Intergovernmental Panel on Climate Change (IPCC). Set up by UN Environment Programme in 1988, it compiles evidence on the issue. The last major assessment in 2007 involved 3,500 scientists.

References

[1] IPCC WGI (2007). Climate Change 2007: The physical science basis. (Summary for policy-markers.) Working Group I of the Intergovernmental Panel on Climate Change. http://www.ipcc.ch/WG1_SPM_17Apr07.pdf

[2] IPCC (2007). Frequently Asked Questions. http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Pub_FAQs.pdf

[3] IPCC WGII (2007). Climate Change 2007: Impacts, adaptation and vulnerability. (Summary for policy-markers.) Working Group II of the Intergovernmental Panel on Climate Change. http://www.ipcc.ch/SPM13apr07.pdf

[4] World Health Organisation (2003). Climate Change and Human Health - risks and responses. WHO Press. http://www.who.int/bookorders/anglais/detart1.jsp?sesslan=1&codlan=1&codcol=15&codcch=551

[5] Pearce F. (2005). Climate Change: Awaking the sleeping giants. New Scientist, 12 February, p9-11. http://environment.newscientist.com/article/mg18524864.400.html See also: http://www.stabilisation2005.com/

[6] Hansen J. et al (2007). Climate Change and Trace Gases. Philiosophical Transactions of the Royal Society - A. Vol 365, pp 1925-1954. http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_2.pdf

[7] IPCC WGIII (2007). Climate Change 2007: Mitigation of climate change. (Summary for policy-markers.) Working Group III of the Intergovernmental Panel on Climate Change. http://www.ipcc.ch/SPM040507.pdf

[8] Pearce F. (2005). Climate Change: Act now, before it's too late. New Scientist, 12 February, p8. http://environment.newscientist.com/article/mg18524864.300.html See also: http://www.stabilisation2005.com/

NB Web-links correct as of 09/08/07

Figures


Figure 1: Global average surface temperature change 1900-2100.

1990-2000 using historic data; 2000-2100 using IPCC scenarios. From IPCC WGI (2007) [1]

 

Figure 2 - Projected impacts of climate change relative to increase in global temperature From IPCC WGII (2007) [3]