Climate Science Briefing Dr Stephen Rintoul Interim Director, CSIRO Climate Science Centre 26 September 2016
Approach • Present evidence from peer ‐ reviewed, publicly available material as summarised in the State of the Climate 2014 report published by CSIRO and the Bureau of Meteorology and other sources. • Focus on empirical observations. • Assess the evidence that human activities have caused climate change.
Change in Australian temperature between 1910 and 2013 Source: State of the Climate 2014 (CSIRO and Bureau of Meteorology) Data source: Bureau of Meteorology Data available at: http://www.bom.gov.au/climate/change/acorn ‐ sat/index.shtml#tabs=Data ‐ & ‐ network
Change in Australian annual average temperature Source: State of the Climate 2014 (CSIRO and Bureau of Meteorology) Data source: Bureau of Meteorology Data available at: http://www.bom.gov.au/climate/change/acorn ‐ sat/index.shtml#tabs=Data ‐ & ‐ network Anomalies are departures from the 1961 ‐ 1990 average. Sea surface temperature averaged over Australian region (4°S to 46°S, 94°E to 174°E)
Change in frequency of warm and cool months Since 2001, the number of extreme heat records in Australia has outnumbered extreme cool records by almost 3 to 1 for daytime maximum temperatures, and almost 5 to 1 for night ‐ time minimum temperatures. Source: State of the Climate 2014 (CSIRO and Bureau of Meteorology) Data source: Bureau of Meteorology Data available at: http://www.bom.gov.au/climate/change/acorn ‐ sat/index.shtml#tabs=Data ‐ & ‐ network Standardised anomalies are with respect to the 1951 ‐ 1980 base period. Very warm and very cool months correspond to 2 standard deviations or more from the mean.
Change in Australian rainfall, northern wet season (Oct ‐ Apr) Source: State of the Climate 2014 (CSIRO and Bureau of Meteorology) Data source: Bureau of Meteorology Data available at: ‐ http://www.bom.gov.au/jsp/awap/rain/index.jsp http://www.bom.gov.au/climate/data/ October – April rainfall deciles since 1995 ‐ 96, relative to the entire national rainfall record from 1900.
Change in Australian rainfall, southern wet season (Apr ‐ Nov) Source: State of the Climate 2014 (CSIRO and Bureau of Meteorology) Data source: Bureau of Meteorology Data available at: ‐ http://www.bom.gov.au/jsp/awap/rain/index.jsp http://www.bom.gov.au/climate/data/ April ‐ November rainfall deciles since 1996, relative to the entire national rainfall record from 1900.
Change in heatwaves The duration, frequency and intensity of heatwaves have increased across large parts of Australia since 1950. Source: State of the Climate 2014 (CSIRO and Bureau of Meteorology) Data source: Bureau of Meteorology Data available at: http://www.bom.gov.au/climate/change/acorn ‐ sat/index.shtml#tabs=Data ‐ & ‐ network
Change in fire weather Forest Fire Danger Index ( a function of wind, humidity, temperature and drought) increased at 16 of 38 reference sites between 1973 and 2010. Extreme fire weather values have become more extreme at 24 of 38 sites since the 1970s. Source: State of the Climate 2014 (CSIRO and Bureau of Meteorology) Data source: Bureau of Meteorology, CSIRO and Office of Environment and Heritage (NSW) Data available at: http://www.bom.gov.au/climate/change/acorn ‐ sat/index.shtml#tabs=Data ‐ & ‐ network Trends in extreme fire weather days (annual 90 th percentile of daily Forest Fire Danger Index values). Larger circles represent larger trends.
Changes in ocean heat content More than 90% of the extra heat stored by the earth since 1970 is found in the ocean. Source: State of the Climate 2014 (CSIRO and Bureau of Meteorology) Data source: update of Domingues et al. (Nature, 2008) Data available at: http://www.cmar.csiro.au/sealevel/thermal_expansion_ocean_heat_timeseries.html http://www.cmar.csiro.au/argo/dmqc/index.html Change in ocean heat content (Joules) from the full ocean depth, 1960 to 2013. Shading indicates confidence range of the estimate.
Change in sea level Source: State of the Climate 2014 (CSIRO and Bureau of Meteorology) Data source: Church and White (Surveys in Geophysics, 2011, http://link.springer.com/article/10.1007%2Fs10712 ‐ 011 ‐ 9119 ‐ 1) Data available at: http://www.cmar.csiro.au/sealevel/sl_data_cmar.html Sea level change from 1880 from tide gauges (green line, shading shows confidence range). Sea level change from satellite altimeter (orange line) from 1993.
Changes in greenhouse gases in the atmosphere Source: State of the Climate 2014 (CSIRO and Bureau of Meteorology) Data source: CSIRO Data available at: http://cdiac.ornl.gov/GCP/ Emissions in gigatonnes of carbon per year
Sinks of carbon dioxide Source: State of the Climate 2014 (CSIRO and Bureau of Meteorology) Data source: CSIRO Data available at: http://cdiac.ornl.gov/GCP/ Uptake of carbon in gigatonnes of carbon per year by the ocean and the land
Changes in atmospheric composition Source: State of the Climate 2014 (CSIRO and Bureau of Meteorology) Data source: CSIRO Data available at: ‐ http://www.csiro.au/greenhouse ‐ gases/ and http://ds.data.jma.go.jp/gmd/wdcgg/ Atmospheric concentration of CO 2 (red line, ppm) and carbon ‐ 13 isotope ratio in CO 2 ( δ 13 C, per mil) as measured in air bubbles in ice cores and atmospheric samples at Cape Grim.
Changes in atmospheric oxygen concentration Burning of fuel produces carbon dioxide and consumes oxygen. Burning of fossil fuels has reduced the concentration of oxygen in the atmosphere, as well as increased the concentration of carbon dioxide. Data source: CSIRO Data available at: http://scrippso2.ucsd.edu/osub2sub ‐ data Measurements of the oxygen to nitrogen ratio (top plot) and carbon dioxide (bottom plot) at Cape Grim observatory in Tasmania.
Change in greenhouse gas concentrations Atmospheric concentrations of major greenhouse gases, including CO 2 , methane (CH 4 ), nitrous oxide (N 2 O), and a group of synthetic greenhouse gases, are increasing. The impact of all greenhouse gases in the atmosphere combined can be expressed as an ‘equivalent CO 2 ’ atmospheric concentration, which reached 480 ppm in 2013 Source: State of the Climate 2014 (CSIRO and Bureau of Meteorology) Data source: CSIRO Data available at: ‐ http://www.csiro.au/greenhouse ‐ gases/ and http://ds.data.jma.go.jp/gmd/wdcgg/
Evidence that humans have caused climate change 1. Carbon dioxide is a greenhouse gas. The natural greenhouse effect makes the planet habitable: the average temperatue of the earth is 33°C warmer than it would be in the absence of greenhouse gases. Laws of physics and direct measurements confirm that carbon dioxide is a greenhouse gas.
Evidence that humans have caused climate change 2. Carbon dioxide concentrations in the atmosphere have increased since the industrial revolution. Atmospheric carbon dioxide levels have increased by more than 40% since pre ‐ industrial times. Source: State of the Climate 2014 (CSIRO and Bureau of Meteorology) Data source: CSIRO Data available at: ‐ http://www.csiro.au/greenhouse ‐ gases/ and http://ds.data.jma.go.jp/gmd/wdcgg/ Atmospheric concentration of CO 2 (red line, ppm) and carbon ‐ 13 isotope ratio in CO 2 ( δ 13 C, per mil) as measured in air bubbles in ice cores and atmospheric samples at Cape Grim.
Evidence that humans have caused climate change 3. The extra carbon dioxide in the atmosphere comes from human activities. • The isotopic composition of CO 2 in the atmosphere shows that the CO 2 added to the atmosphere has come from burning fossil fuels. • Oxygen concentrations in the atmosphere have declined, at the rate expected from burning carbon ‐ rich fuels. • CO 2 in the atmosphere has increased as human emissions have increased (the two are correlated). • In recent decades, nature has absorbed more CO 2 than it has emitted, so natural sources cannot explain the observed increase in the atmosphere.
Evidence that humans have caused climate change 3. The extra carbon dioxide in the atmosphere comes from human activities. • Models can reproduce the record of global averaged temperature if we include the effects of increased greenhouse gas forcing, but cannot do so with natural forcings alone. Source: IPCC 5 th Assessment Report, Working Group I Summary for Policy Makers
Evidence that humans have caused climate change 4. The additional carbon dioxide added to the atmosphere by human activities has enhanced the greenhouse effect: less energy is leaving the top of the atmosphere in the wavelengths absorbed by carbon dioxide and other greenhouse gases. Harries et al., Nature (2001)
Evidence that humans have caused climate change 5. The earth has warmed as a result of the enhanced greenhouse effect. Lower troposphere ocean heat content Surface temperature (°C) Source: Surface air and lower troposphere temperature: Bulletin of the American Meteorological Society, State of the Climate 2015, supplement to Vol. 97, No. 8, August 2016 Ocean heat content: http://www.cmar.csiro.au/sealevel/thermal_expansion_ocean_heat_timeseries.html
Evidence that humans have caused climate change 6. Observed changes in the climate system are consistent with an enhanced greenhouse effect. Other forcings (e.g. volcanoes, the sun, internal variability) cannot explain the magnitude, timing and distribution of observed trends. For example, enhanced greenhouse forcing causes warming of the lower atmosphere and cooling of the upper atmosphere, as observed. Increases in solar energy reaching the earth would warm both the upper and lower atmosphere.
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