Lecture 2: Climate Projections and Impacts - Murdoch University

Lecture 2: Climate Projections and Impacts (Dr. Jatin Kala)

Lecture Outline

  • Climate change and variability in Australia.

  • Climate projections for southwest Western Australia.

  • Impacts of climate change on agriculture.

Climate Change and Variability in Australia

  • March 2011 Anomalies (Bureau of Meteorology data):

    • Maximum Temperature Anomaly: Ranged from −6extoextC-6^ ext{o} ext{C} to 6extoextC6^ ext{o} ext{C} across Australia.

    • Minimum Temperature Anomaly: Ranged from −6extoextC-6^ ext{o} ext{C} to 6extoextC6^ ext{o} ext{C} across Australia.

    • Rainfall Anomaly: Ranged from −400extmm-400 ext{mm} to 400extmm400 ext{mm} across Australia.

  • February 2009 Anomalies (Bureau of Meteorology data):

    • Maximum Temperature Anomaly: Ranged from −12extoextC-12^ ext{o} ext{C} to 12extoextC12^ ext{o} ext{C}.

    • Minimum Temperature Anomaly: Ranged from −12extoextC-12^ ext{o} ext{C} to 12extoextC12^ ext{o} ext{C}.

    • Rainfall Anomaly: Ranged from −400extmm-400 ext{mm} to 400extmm400 ext{mm}.

  • Summer of 2013: Natural Climate Variability or Anthropogenic Signal?

    • The question of whether extreme events are part of natural variability or influenced by human activity is critical.

    • Lewis and Karoly (2013) Research (Geophysical Research Letters, 114, 3705-3709):

      • Methodology: Climate models were run under two conditions:

        1. With only natural forcings (e.g., solar variations, volcanic eruptions).

        2. With natural forcings and greenhouse gas emissions.

      • Objective: To determine the likelihood that the temperature anomalies experienced during 2013 were solely due to natural variability.

      • Key Finding: The research showed with greater than 90 ext{%} confidence that there was at least a 2.52.5 times increase in the odds of extreme heat due to human influences.

  • Climate Change and Variability in Southwest Western Australia (SWWA):

    • Rainfall: A distinct step decrease in rainfall has been observed in SWWA since the 1970s.

    • Temperature: A step increase in maximum temperature has been observed in SWWA since the 1970s.

    • This raises the same question: Is this due to natural climate variability or an anthropogenic climate change signal?

Climate Projections for Southwest Western Australia

  • Temperature Projections (using CMIP5 models and ACORN-SAT observations):

    • Data show annual average surface air temperature (in extoextC^ ext{o} ext{C}) relative to the 1950−20051950-2005 mean, from 1910−20901910-2090.

    • RCP Scenarios (Representative Concentration Pathways):

      • RCP8.5 (Purple): High emissions scenario, leading to significant warming.

      • RCP4.5 (Blue): Intermediate emissions scenario.

      • RCP2.6 (Green): Low emissions scenario, aiming for substantial reductions.

    • Across all scenarios, an increasing trend in temperature is projected for SWWA, with higher emission scenarios (like RCP8.5) showing the most pronounced warming by 2100.

    • Observations (ACORN-SAT) align with historical simulations and show a clear warming trend.

  • Rainfall Projections (using CMIP5 models and AWAP observations):

    • Data show annual rainfall (as a percentage change relative to the 1950−20051950-2005 mean) for 1910−20901910-2090.

    • RCP Scenarios: Similar trends observed across RCP2.6, RCP4.5, and RCP8.5.

    • A general decreasing trend in annual rainfall is projected for SWWA across all scenarios, with more significant reductions under higher emissions pathways.

    • Observations (AWAP) starting from 19011901 show a historical decrease.

  • Relative Change in JJASON (July, August, September, October, November) Rainfall:

    • Projections from CMIP5 and CMIP6 models indicate continued relative changes (decreases) in rainfall across the region.

  • Regional Projections and Resources:

    • The IPCC AR6 (Sixth Assessment Report), Working Group 1, provides regional fact-sheets for key parts of the globe, offering detailed climate projections.

    • Website: https://www.ipcc.ch/report/ar6/wg1/#Regional

The Model Resolution Issue with Global Climate Models (GCMs)

  • GCM Resolution: Global Climate Models typically operate at coarse resolutions, for example, HADCM2 has a resolution of 2.5extoimes3.75exto2.5^ ext{o} imes 3.75^ ext{o}.

  • Limitations: This coarse resolution means GCMs cannot resolve fine-scale topographical features, land-use variations, or regional weather phenomena effectively.

  • Downscaling: To address this, downscaling techniques are used to translate coarse GCM outputs to finer resolutions relevant for regional impact assessments.

    • Regional Climate Models (RCMs): These models operate at a much finer resolution, for example, 50extkm50 ext{km}, or even 5extkm5 ext{km}.

    • Dynamical Downscaling: This involves embedding an RCM within a GCM. The RCM uses the boundary conditions (e.g., temperature, humidity, wind) provided by the larger-scale GCM or re-analysis data to simulate regional climate processes at a higher resolution (e.g., GCMs at 150150 to 250extkm250 ext{km} feed into RCMs typically at 5050 to 5extkm5 ext{km} resolution).

Impacts of Climate Change on Agriculture

  • Climate Indices Relevant to Cereal Crops:

    • Research by Andrys et al. (2016, 2017) identified various climate indices relevant for cereal crop assessment:

      • W-MIR, W-CCS, W-ECH, W-CSI.

      • OBS SDII (Simple Daily Intensity Index), PRCPTOT (Annual total wet-day precipitation), CDD (Consecutive Dry Days), CWD (Consecutive Wet Days), FD (Frost Days), SU (Summer Days).

      • DTR (Diurnal Temperature Range), TXX (Maximum of daily maximum temperature), TNN (Minimum of daily minimum temperature).

      • Specific indices for growing season length (FD, SU).

  • Climate Indices Relevant to Viticulture:

    • Research by Firth et al. (2017) explored indices for viticulture:

      • Huglin Index.

      • Cold Night Index.

      • Growing Season Precipitation.

      • Projections indicate significant future changes in these indices, impacting grape growing regions.

  • Observed and Projected Impacts on Agriculture and Livestock (IPCC AR6, Climate Change 2022):

    • Disruption and Decline: Expected disruption and decline in agricultural production and increased stress in rural communities across south-western, southern, and eastern mainland Australia due to hotter and drier conditions.

    • Wheat Yields: By 20502050, a projected decline in median wheat yields of up to 30 ext{%} in southwest Australia and up to 15 ext{%} in South Australia.

    • Livestock Heat Stress: Increased heat stress in livestock by 31−4231-42 days per year.

    • Broader Impacts on Human Systems: The IPCC report highlights observed impacts attributed to climate change at global and regional levels with varying confidence levels:

      • Water Scarcity and Food Production: Increasing adverse impacts on crop yields, animal and fisheries production, and human water systems scarcity globally, with high to very high confidence.

      • Health and Well-being: Impacts on infectious diseases, heat, malnutrition, mental health.

      • Cities, Settlements, and Infrastructure: Impacts on inland flooding, storm-induced damages in coastal areas, damages to infrastructure and key economic sectors.

  • Economic Impacts on Livestock Enterprises:

    • Research explored the relationship between changes in operating profit at optimal sustainable stocking rates and historical growing-season rainfall across southern Australia.

    • Using a mean of four GCMs (CCSM3, ECHAM5/MPI-OM, GFDL-CM2.1, UKMO-HadGEM1), projected changes in operating profit for livestock enterprises (weighted by economic value) for:

      • 20302030: −0.27-0.27

      • 20502050: −0.32-0.32

      • 20702070: −0.48-0.48

    • These figures indicate substantial declines in operating profit under projected climate change scenarios, especially in regions with a history of lower growing-season rainfall.

Take Home Messages

  • The climate of Australia, while naturally highly variable, shows clear evidence of human influence on recent changes.

  • The southwest of Western Australia has been experiencing a significant warming and drying trend since the 1970s.

  • Climate models project with high confidence that these trends (warming and drying) will continue into the future.

  • The impacts of climate change on agriculture are significant and adverse, including drought-induced declines in crop yields and increased heat stress for livestock.

  • Agriculture itself contributes to global warming through emissions, particularly methane.

  • While reductions in methane emissions are necessary, they alone will not solve the climate issue; urgent efforts to decarbonize and significantly reduce CO2CO_2 emissions are also crucial.

  • Agriculture is not only a contributor to, but also a major victim of, climate change.

  • The future of agriculture must focus on becoming low-emissions and building resilience to unavoidable changes in climate.

  • Considerable research and practical work are currently underway in this critical space, but much more effort is needed globally.