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An update on the science of climate change

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  1. An update on the science of climate change David Karoly School of Earth Sciences, University of Melbourne TC Larry, 2006 From Bureau of Meteorology

  2. Global warming alarmism?

  3. Garnaut Climate Change Review (2008) concluded • Climate change is a diabolical policy problem • Australia has a larger interest in a strong mitigation outcome than other developed countries • We are already a hot and dry country; small variations in climate are more damaging to us than to other developed countries.

  4. Introduction • What is the greenhouse effect? • The latest assessment of climate change and its causes - IPCC 2007 • Updates since 2007 • International agreements and stabilising climate change

  5. IPCC AR4 WGI FAQ1.3 Fig 1

  6. Greenhouse effect • Most important greenhouse gas (ghg) is water vapour but its concentration is determined by temperature • Important long-lived ghgs are CO2, CH4, N2O • Absorption by ghgs seen in satellite infrared spectra • Absorption proportional to log(concentration), so doubling ghg concentration gives same heating

  7. Intergovernmental Panel on Climate Change (IPCC) • Joint body of UN Environment Program and World Meteorological Organization, established in 1988 • Every 5-6 years, carries out a comprehensive assessment of climate change science, impacts, and approaches for mitigation and adaptation to climate change • Includes representatives from all countries • Fourth Assessment Report prepared by more than 500 scientists over the last three years • Summaries for Policy Makers approved by consensus (including representatives of the Australian govt) at meetings in Paris (Feb 07), Brussels (Apr 07) and Bangkok (May 07) • Received the 2007 Nobel Peace Prize jointly with Al Gore

  8. ‘Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.’ (IPCC 2007) WGI Fig SPM.3

  9. ‘Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increasedmarkedly as a result of human activities since 1750 and now far exceed pre-industrial valuesdetermined from ice cores spanning many thousands of years.The global increasesin carbon dioxide concentration are due primarily to fossil fuel use and land-use change, while those ofmethane and nitrous oxide are primarily due to agriculture.’ WGI Fig SPM.1

  10. Causes of climate change In 2005, greenhouse gas concentration was 455 ppm CO2-eq. A large part of the warming influence is masked by aerosols. WGI Fig SPM.2

  11. Climate modelling • Physically-based tools for studying climate variability and change • Use mathematical representations of physical laws, including Newton's second law of motion, the laws of conservation of mass and energy, laws of thermodynamics, and the ideal gas law • Represent important processes in atmosphere, ocean, land surface and ice, as well as coupling between them • More than twenty different models developed independently around the world

  12. IPCC AR4 WGI FAQ1.2 Fig 1

  13. Annual mean precipitationObservations 1980-99Multi-model ensemble mean, 1980-99 WGI Fig 8.4

  14. ‘Most of the observed increase in global average temperatures since the mid-20th century is very likely (more than 90% certain) due to the observed increase in anthropogenic greenhouse gas concentrations.’ IPCC(2007) WGI Fig TS.23

  15. ‘It is likely that there has been significant anthropogenic warming over the past 50 years averaged over each continent except Antarctica.’ WGI Fig SPM.4

  16. ‘Continued greenhouse gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.’ WGI Fig SPM.5

  17. Projected temperature changes for the early and late 21st century WGI Fig SPM.6

  18. Projected precipitation changes for the late 21st century WGI Fig SPM.7

  19. ‘There is now higher confidence in projected patterns of warming and other regional-scale features, including changes in circulation patterns, precipitation, and some aspects of extremes and of ice.’ • It is very likely that hot extremes, heat waves, and heavy precipitation events will continue to become more frequent. • Snow cover is projected to contract. Sea ice is projected to shrink in both the Arctic and Antarctic. • Storm tracks are projected to move poleward, with changes in wind, precipitation, and temperature patterns. • Increasing atmospheric CO2 concentrations lead to increasing acidification of the ocean. • 21st century anthropogenic CO2 emissions will contribute to warming and sea level rise for more than a millennium, due to the long timescales required for removal of this gas.

  20. Observations to 2005 From Stroeve et al, GRL, 2007

  21. Sea ice in Sept 2007 From Stroeve et al, GRL, 2007 Sept 2005

  22. Observed and projected Australian rainfall Best estimate projected rainfall change for 2070(from “Climate change in Australia”) Observed trend in annual rainfall 1970-2007

  23. Projections of sea level rise Past sea level and sea-level projections from 1990 to 2100 based on global mean temperature projections of the IPCC TAR. From Rahmstorf, Science, 2007 From IPCC AR4

  24. UN Framework Convention on Climate Change (UNFCCC) • Established following the United Nations conference on Environment and Development in Rio de Janeiro in 1992 • Objective is “stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system” • “Such a level should be achieved within a time frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened, and to enable economic development to proceed in a sustainable manner” • Ratified by 192 countries, including USA and Australia, and came into force in March 1994

  25. Who has caused the problem? UNFCCC includes principle that: “Parties should protect the climate system...on the basis of equity and in accordance with their common but differentiated responsibilities and respective capabilities. Accordingly, the developed country Parties should take the lead in combating climate change” (UNFCCC, Art.3.1). Regional greenhouse gas emissions in 2004 SyR Fig 2.2a

  26. Stabilisation scenarios • 455 ppm CO2-eq in 2005, 379 ppm CO2 conc • I: CO2-eq stabilisation at 445-490 ppm, emissions peak in 2000-2015, global CO2 emissions -85% to -50% in 2050, warming of 2.0 to 2.4C above pi • II: CO2-eq stabilisation at 490-535 ppm, emissions peak in 2000-2020, global CO2 emissions -60% to -30% in 2050, warming of 2.4 to 2.8C above pi • Assuming equal per capita emissions, 50% global emission reduction in 2050 means ~90% emission reduction for US and Australia SyR Fig SPM.11

  27. Australian greenhouse gas emissions Dept of Climate Change “Tracking to the Kyoto target 2007” Australian emissions from energy use and transport have grown at more than 20% per decade. Australia is close to its Kyoto target only because of one-off reductions in land clearing. Sector % change in 2010 in 2020 Stationary energy +56% +64% Transport +42% +67 Land use change -68% -68% Total +8% +20%

  28. Probability distribution of committed global warming (relative to preindustrial) for greenhouse gases in the atmosphere in 2005 From Ramanathan and Feng, PNAS, 2008

  29. Summary • IPCC concluded in 2007 • warming of the climate system is unequivocal • most of the global average warming is due to the increasing greenhouse gases • warming will increase over the 21st century • Climate change due to increasing greenhouse gases will lead to • higher temperatures, increased evaporation, more bush fires • reduced winter precipitation but more intense precipitation • Australia is becoming a “land of more drought and more flooding rains” • Minimising dangerous climate change requires removal of greenhouse gases from the atmosphere, either through natural processes or anthropogenic sequestration (not further emissions)

  30. Climate change references • IPCC web site http://www.ipcc.ch/ • UNFCCC web site http://unfccc.int/ • Climate change in Australia site http://www.climatechangeinaustralia.gov.au/ • Bureau of Meteorology climate education http://www.bom.gov.au/lam/climate/index.htm • “Teaching climate change” Australia Institute http://www.teachingclimatechange.com.au/ My contact information: Prof David Karoly, School of Earth Sciences dkaroly@unimelb.edu.au