The context: 6.7 billion people 1 planet. Is there a future?

Transcription

1 Global Warming: The Scientific Basis for Anthropogenic Climate Change

2 The context: 6.7 billion people 1 planet. Is there a future?

3 The global average net effect of human activities since 1750 has been one of warming, with a radiative forcing of 1.6 Wm -2 (IPCC 2007). Mean global CO 2 concentrations are now at 386ppm (2008 mean) which is 30% greater than at anytime in the past 800,000 years, while the rate of increase is 200 times faster than at any time over the same period. Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air temperature, widespread melting of snow and dice, and rising i global laverage sea level l (IPCC 2007).

4 If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, palaeoclimate evidence and ongoing climate change suggest that CO 2 will need to be reduced from its current 386ppm to at most 350ppm. If the present overshoot of this target CO 2 is not brief, there is a possibility of seeding irreversible catastrophic c events. e (Hansen et al. p1, 2008). Human population p growth is a root cause of the stress that humanity is placing upon the global environment and upon the other species sharing our planet s resources. A deliberate policy of population growth (as promoted by Australia) is inconsistent with preservation of climate and nature (Hansen 2009).

5 Recent Climate Change Global average air temperature 100-year linear trend of temperature increase 0.74 [0.56 to 0.92] o C for Average ocean temperature increased to depths of at least 3000 m ocean has absorbed 80% of heat added > seawater expansion - Sea Level Rise. Annual average Arctic sea ice extent shrunk by 2.7 % per decade, decreases in summer 7.4 %. The maximum area covered by seasonally frozen ground has decreased by about 7% in the Northern Hemisphere since 1900, in spring of up to 15%. (Source: IPCC 2007)

6 Global warming the scientific basis for human induced climate change Evidence of human induced climate change how does it work? Climate forcing by greenhouse gases and landuse change. Our future climate.

7 Images of climate change: Glacier and Ice cap retreat

8 Rhone Glacier, Switzerland

9 (Source: National Snow and Ice Data Centre, USA) Arctic Sea Ice Loss

10 Evidence of Past Climate Change (Source Petit et. al. 1999) Ice cores provide excellent geologic archives of climate variability and changes in atmospheric trace gas concentrations, i.e. CO 2, CH 4. This record (eg Vostock) shows that the rapid increase in greenhouse gases This record (eg Vostock) shows that the rapid increase in greenhouse gases (CO 2 ) monitored over the last 50 yrs and the corresponding rate of temperature change has not been exceeded for at least the last 425ka yrs.

11 CO 2 CH 4 The atmospheric concentration of CO 2 and CH 4 in 2009 exceeds by far the natural range of the last 650,000 years

12 The Hockey Stick Curve The Mann temperature curve identified for the first time the recent rapid increase in air temperature.

13 Evidence of Anthropogenic Forced Climate? Are we starting to cool? ) Te emperatu ure anom maly ( C (Reference ) YEAR (Source: Climate Research Centre, UEA, Norwich, UK)

14 ENSO forcing of recent global temperatures El Niño events correlate with warmer years, while La Nina correlate with cooler years. Volcanic eruptions increase global albedo and result in a cooling IF the eruption is of sufficient size. (Source: Hansen et al 2009)

15 Solar forcing The current solar cycle has lasted about 2 years longer than usual. A possible cause for slowing of the warming trend? If it doesn t recover, the associated negative forcing relative to the mean solar irradiance is equivalent to about 7 years of CO 2 increase at current rates so no new Ice Age!!

16 IPCC (2007). Spatial trends in global warming

17 Global Mean Temperature Trends (IPCC 2007) FAQ 3.1, Figure 1

18 Recent Change in Australian Climate Observed change in maximum air temperature t ( C/decade)

19 Observed change annual total t rainfall (mm/decade) d

20 The Basic Cause of Global Warming: Modification of the Global Energy Balance Under ideal conditions the global energy balance is in equilibrium, i.e. 342 Wm -2 incoming solar radiation is balanced by 235 Wm -2 of outgoing longwave and 107 Wm -2 of reflected solar radiation. Disruption of this system causes global warming or cooling. Source: Kiehl and Trenberth (1997).

21 Modification of the Radiation Budget and Energy Balance: The Cause of Global Warming? Change in atmospheric composition (greenhouse gas emissions). Change in land surface type (land clearing, reduced snow & ice cover). Change in cloud cover.

22 Atmospheric absorption of radiation 1 Absorptivit ty Window Short wave Long wave CH 4 N 2 O O and O 2 3 CO 2 H 2 0 Gre eenhouse e Gases Atmosphere Wavelength ( m) Figure 2.12 Absorption of short- and long-wave radiation by consitituents of the atmosphere and by the atmosphere as a whole (after Fleagle l & Businger 1980).

23 Atmospheric absorption of radiation 1 Ab bsorptivity W indow Short wave Long wave CH 4 N 2 O O and O 2 3 CO 2 H 2 0 Gre eenhouse e Gases Atmosphere Wavelength ( m) Figure 2.12 Absorption of short- and long-wave radiation by consitituents t of the atmosphere and by the atmosphere as a whole (after Fleagle & Businger 1980).

24 Radiative Forcing and our Understanding (IPCC 2007)

25 Anthropogenic factors Human activities that affect climate through: Variable Scale of effect Sources of changed change Atmospheric composition Local-global Release of aerosols and trace gases Surface properties; energy budgets Regional Deforestation; desertification; urbanization Wind regime Local-regional Deforestation; urbanization Hydrological cycle components Local-regional Deforestation; desertification; irrigation; urbanization

26 100 Year Global Warming Potentials for selected greenhouse gases and atmospheric lifetimes Greenhouse Gas Global Warming Potential Lifetime CO2 (carbon dioxide) 1 variable CH4 (methane) e) yrs ys N2O (nitrous oxide) yrs HFC (hydrofluorocarbons) yrs CFC (chlorofluorocarbons) PFC (perfluorocarbons) yrs SF6 (sulfur hexafluoride) yrs

27 Modification of atmospheric composition Enhanced warming by greenhouse gas emissions since 1765AD is estimated at 1.6 W m -2 ( W m -2 ). Human emissions of CO 2 are believed to contribute to 60% of this warming, CH 4 20%, CFCs 12% and NO 6%. The warming has been attributed to increased absorption of L. CFCs have also lead to a dramatic depletion of stratospheric O 3 resulting in modification of stratospheric temperature. Aerosols may cause either a warming or cooling or both, i.e. black carbon absorbs solar radiation thereby changing the vertical temperature structure t where minerals such as Ca may cause a cooling. Water soluble inorganic species (SO 2 (sulphur dioxide), NO 3 (Nitrate) and 2 3 NH 4 (ammonium)) may backscatter the solar beam (direct forcing) and/or affect cloud micro-physical processes (increase cloud lifetime).

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29 Longest (most reliable) measured record of CO 2, Mauna Loa, Hawaii CO2 Mauna Loa : 386 ppm CO2 ppm Exceeding 400ppm is now believed to be a possible trigger for dangerous climate change (2013?) Year

30 Atmospheric concentrations in CO 2, CH 4, N 2 O Atmospheric concentrations of carbon dioxide, methane and nitrous oxide over the last 10,000 years (large panels) and since 1750 (inset panels). Measurements are shown from ice cores (symbols with different colours for different studies) and atmospheric samples (red lines). The corresponding radiative forcings are shown on the right hand axes of the large panels

31 GHG Emissions by Source (IPCC 2007)

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33 Change in Land Cover Occurs at a range of scales urban heat islands to Amazon deforestation. Australian land cover change: clearing of 1.2 million km 2 (~13%) of the continent since European settlement. Global land cover change: 25 30% of GHG Global land cover change: 25-30% of GHG emission each year are from deforestation.

34 Example of land clearing in western Queensland 34

35 Modeling the impact of landcover change in Australia. Uncoupled CSIRO Mark 3 atmospheric GCM (T63); Two sets of model simulations (ensemble of 10 each) for the period , (a) pre-european and (b) Modern Day Australian Vegetation; The mapping of Australian LCC was derived from the structural and floristic vegetation maps of Australian vegetation; Analysed the annual averages and seasonal means for Analysed the annual averages and seasonal means for the period averaged over all model ensembles for temperature and rainfall.

36 Results: Difference in the ensemble annual climate averages ( ) between pre-european and modern day conditions Temp ( o C) Rainfall (% Change) Soil Moisture (% Change) Surface Wind Speed (m/sec)

37 Results: Seasonal Climate DJF (Summer) Temp ( o C) JJA (Winter) Temp ( o C) Summer Rainfall (% Change) Winter Rainfall (% Change) 37

38 Land cover change and climate Modification of the surface energy balance. Reduced evaporation/evapotranspiration and lowered soil moisture meaning more net radiation is converted into sensible heat. Changes in surface roughness. Removal of trees increases wind speeds higher evaporation rates and moisture divergence. Changes in seasonal land cover and vegetation types influence exchanges of heat, moisture and momentum between the atmosphere and surface. Changes in surface temperature influence synoptic scale pressure field patterns leading to change in regional circulation patterns.

39 Where are we heading: IPCC 4 th Assessment On average 0.6 C globally over the last 100yrs to mid 1940s considerable warming of 0.4 C. Mid 1940s to early 1970s temperature oscillations with a range of 0.4 C with the northern hemisphere cooling slightly and the southern hemisphere remaining fairly constant. Mid 1970s to present has witnessed a pronounced warming of 0.5 C. In a few regions temperature has increased > 1 C Antarctic peninsula has experienced a warming of >2.5 C in the last 50 yrs Mid-troposphere temperatures above the Antarctic have risen between 0.5 C to 0.75 C in the last 30 yrs

40 Future scenarios Modeled predictions of future climate run a wide range of scenarios, e.g. Scenario A1F1 Assumes a fossil fuel intensive society where fossil fuels are used to promote economic development. It is the most CO 2 heavy scenario and assumes of tripling of CO 2 level by 2100 (1134ppm) with coal being used extensively to drive economic development in developing economies coupled with lower population growth (worse case scenario perhaps?).

41 IPCC 4 th Assessment Predictions Global GHG Emissions Global surface warming (IPCC 2007)

42 But how good are IPCC predictions? The IPCC is heavily influenced by politics. Leads to dumbing down of predictions to the lowest denominator. Climate change scenarios used by the IPCC are more than 10 years old. Incorporate scientific findings up to 2005/06. IPCC predictions do no consider recent rapid growth in GHG emissions from China and India. They assume a certain amount of spontaneous decarbonisation without direct policy intervention. In seeking global consensus I believe they may be highly conservative in their predictions of future climate.

43 Temperature Predicted v. Observed Temperature predictions good Sea Level Sea level well? (Source: Pielke 2008)

44 Sea level Sea level rise is predicted by the IPCC(2007) to range from 18 to 59cm by A further 10 to 20cm may occur due to melting of ice sheets. However further ice sheet contributions cannot be discounted or at present quantified. 20,000 yrs BP when temperatures were 4 to 7 C less than present sea level was 120m below present. In the Pliocene 3 million years ago temperatures were 2 to 3 C warmer and sea level was 25 to 35 m higher than present. Sea level would therefore appear to respond to a change in temperature of 1 C on the order of 10 to 30m!!

45 Future Sea Level Prediction of future sea level is difficult because we do not have adequate physical models to model all associated physical processes. Rahmstorf (2007) developed a semi-empirical model based on the simple relationship between temperature change and sea level change.

46 Predicted Sea Level Change Rahmstorf (2007) (1.4 to 5.8 C warming) IPCC (2007)

47 The Future for the Gold Coast?

48 Assessment of Target CO 2 Phenomenon Target CO 2 (ppm) 1. Arctic Sea Ice Ice Sheets/Sea Level Shifting Climatic Zones Alpine Water Supplies Avoid Ocean Acidification Initial Target CO 2 = 350* ppm *assumes CH 4, O 3, Black Soot decrease Reference: Hansen et al. Target Atmospheric CO 2, Open Atmos. Sci., 2008

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