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December 2002

December 2002. Section 3 Attribution of Past Changes in Climate. Incoming solar energy heats the Earth, and outgoing heat radiation cools it off. Incoming Energy. Outgoing Energy. Reflected Energy. Energy Trapped By Greenhouse Gases.

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December 2002

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  1. December 2002 Section 3Attribution of Past Changes in Climate

  2. Incoming solar energy heats the Earth, and outgoing heat radiation cools it off Incoming Energy Outgoing Energy Reflected Energy Energy Trapped By Greenhouse Gases

  3. Solar and heat energy passing through the climate system is reflected, absorbed and re-radiated in many different ways Slide showing energy flux through atmosphere

  4. Natural factors can affect the flow of energy into the climate system • Decades to centuries -Solar intensity -Volcanic dust • Millennia and longer • -Changes in orbit • -Geophysical processes

  5. Water vapour and carbon dioxide are the primary contributors to the natural greenhouse effect ~10% ~25% ~65%

  6. However, there are many complex interactions and feedbacks within the global climate system

  7. The ocean circulation system has a major influence on global and regional climates

  8. GCM1: 1970s GCM2: 1980s CGCM1/CGCM2: 1990s Climate models are the primary tool for making quantitative projections of future climate change

  9. 1 Radiative forcing (W/m2) 0 -1 -2 -3 -4 1900 1950 2000 Solar and volcanic forces have affected the climate system

  10. Climate model equations are solved numerically on supercomputers at the Canadian Meteorological Centre 1 Gflop = 1 billion arithmetic operations per second • 128 Gflop peak speed • 128 Gbytes memory • Model simulates 2-3 years of climate per day

  11. Modelled response to natural forcings differs from observed temperatures during past 50 years

  12. Proxy data also indicate that the recent warming is likely unprecedented in at least the past millennium Source: IPCC(2001)

  13. Ice cores show evidence of a close relationship between greenhouse gas concentrations and climate

  14. 380 360 340 $ CO2 Concentration (ppmv) 320 $ $ $ $ $ $ $ $ $ 300 $ $ $ Highest concentration in last 400,000 years $ $ $ ! $ $ $ ' $ # ! ! $ ' ' $ ' # $ ' # ! ' ' ' ! ' ! 280 ' ' # ! # ! $ ! $ $ ' # ' ! ' ' $ $ ' ' ' ' ' ' 260 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 CO2 concentrations are now unprecedented in at least the past 400,000 years

  15. Carbon dioxide emissions from human sources have increased steadily over the past century Fossil fuel emissions Billion tonnes of carbon per year (GtC/yr) Land use change emissions Year

  16. Concentrations of other greenhouse gases and of sulphate aerosols have also increased dramatically

  17. Other greenhouse gases and aerosols also affect the climate • CFCs, HCFCs • already controlled under the Montreal Protocol • HFCs, PFCs, SF6 • HFCs are replacements for CFCs and HCFCs, while PFCs are produced through industrial processes • Ozone • short lifetime, spatially variable • increasing in the lower atmosphere, decreasing in the stratosphere • Non-sulphate aerosols • Soot • Biomass burning, mineral dust

  18. The abundance, atmospheric lifetime, and Global Warming Potential of GHGs vary considerably

  19. Concentrations of some greenhouse gases are beginning to decline because of controls

  20. Stratospheric ozone depletion also affects the surface climate Deviation from 1979-87 mean % Year

  21. The various human and natural factors have affected the climate differently 3 2 1 0 -1 -2 Accumulated forcing since 1750 Radiative forcing (W/m2) High Med. Med. Low Very low Very low Very low Very low Very low Very low Very low Very low Level of Confidence

  22. Trends in key human forcings during the past century are dominated by greenhouse gases but partially offset by other factors Radiative forcing (W/m2) Year

  23. Modelled response to human forcing agrees reasonably well with observed temperature

  24. Trends in combined effect of human and natural forcings GHG + sulphates only All forcings 3 2 1 0 Radiative forcing (W/m2) -1 -2 1900 1950 2000 Year

  25. Modelled response to all forcings agrees best with observations

  26. Intergovernmental Panel on Climate Change 2001 concludes that: “ There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities. ”

  27. Are recent weather extremes due to natural variability or to climate change? • Analyses suggest increases have occurred in some types of weather extremes in some, but not all areas • Individual extreme events occur rarely and hence are difficult to link directly to specific “causes” • However, many of the events are broadly consistent with climate change projections • Hence these events are good examples of what may happen more often in the future

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