METR 112: Global Climate Changes – Lecture 9 Global Climate Models and the Future ▪ Reading: Chapter 4, Pages 1-44 1 2 Class Meeting ▪ Watch the video for this lecture at: https://www.youtube.com/watch?v=5qHqzwzEcV0 Climate Model – What is it? ▪ A mathematical representation of the physical processes that control climate – Basically everything that affects climate ▪ Sun, atmosphere (greenhouse gases, aerosols), hydrosphere, cryosphere, biosphere, solid Earth ▪ Equations are complex – Some of the world’s largest supercomputers are running climate models 3 The Need for Climate Models ▪ Already seeing effects of global warming – 9 of the 10 warmest years during the instrumental record have occurred in the past 15 years – September Arctic sea ice extent was 50% lower in 2012 than in 1979 – Global average sea level rose by 20 cm (~8 in) from 1900 to 2000 The Need for Climate Models ▪ Climate Models allow one to not only verify the causes of global warming, but examine how climate will change in the coming decades Global Temperature: 1880-2020 https://data.giss.nasa.gov/gistemp/graphs/graph_data/Global_Mean_Estimates_based_on_Land_and_Ocean_ Data/graph.png 7 Summer Arctic Sea Ice Decline Area Arctic summers could be ice-free by 2050! Sea Level Rise 2 main causes: - melting of continental ice - thermal expansion Carbon Dioxide, Methane, Nitrous Oxide 10 Carbon Dioxide (CO2) ▪ Most important anthropogenic greenhouse gas (AGHG), in terms of concentration and total effect ▪ Responsible for about 33% of (human induced) global warming ▪ CO2 emissions from fossil fuel burning increased by 58% from 1980 to 2006 Increase in CO2 emissions: 1850-2010 Methane (CH4) ▪ 2nd most abundant AGHG ▪ Culprit for about 15% of global warming ▪ Most of the world’s rice is grown by flooding of paddies, which can lead to microbes emitting CH4 ▪ Emissions also result from livestock ▪ Natural gas is mainly made up of CH4 – Can be released in many ways Ozone (O3) ▪ Accountable for about 13% of global warming ▪ Originates from smog generated by reactions of carbon monoxide (CO) and nitrogen oxides (NOx) – These chemicals can be emitted during transportation, power generation, and manufacturing ▪ Tropospheric concentrations have increased Nitrous Oxide (N2O) ▪ Approximately 6% of global warming is due to N2O ▪ Primarily emitted from agricultural activities Global Climate Models: Core Concepts ▪ 1. GCMs separate Earth into at least two sections – atmosphere and ocean ▪ 2. Each section is further broken up into submodels ▪ 3. GCMs break up Earth into grid boxes, each of which obey laws of physics Global Climate Models ▪ Model accuracy improves as grid boxes become smaller and time step decreases – However, this increases running time ▪ Over time, model resolution has increased Figure 4.6 Main floor of the Earth Simulator Center in Yokohama, Japan Figure 4.7 Elements of a global climate model Figure 4.8 Genealogy of atmosphere GCMs Figure 4.9 Examples of grid box systems Figure 4.10 GCMs characterize fluxes into and out of a grid box during a time step Input and Output of a Climate Model Changes in atmospheric GHG concentrations, changes in albedo due to aerosols Climate Model Future Climate (how temperature, precipitation, sea level will change) 24 Emission Scenarios ▪ Because it is unknown exactly how emissions will change in the future, scenarios are developed ▪ What factors can affect greenhouse gas emissions? Increase in CO2 emissions: 1850-2010 Factors affecting emissions ▪ Global Population – Currently at 7+ billion, projected to increase ▪ Energy Generation – Fossil fuel intensive or renewable? ▪ Economic Growth ▪ Type of Economy – Material based or science + technology based? ▪ Cooperation among countries – More Homogenous: Share technologies – More Isolated: Greater separation between rich + poor countries Storyline Scenarios ▪ There are four main storyline scenarios – A1 – A2 – B1 – B2 Scenarios High Emission Scenario A: A world of rapid economic growth and rapid introductions of new and more efficient technologies Low Emission Scenario B: A world of “dematerialization” and introduction of clean technologies Figure 4.16 Emissions scenarios (Part 2) Scenarios ▪ A1 storyline – World of rapid economic growth – Population peaks in 2050 – Different branches dependent on energy type/use ▪ A1FI – Fossil (Fuel) intensive ▪ A1T – Non-fossil intensive energy use (Technology) ▪ A1B – Balance between fossil and non-fossil ▪ A2 storyline – Heterogeneous world – technologies not shared across borders – Population continues to increase 31 Scenarios ▪ B1 storyline – Similar population as A1 – Global exchange/cooperation between countries – Focus on social and economic sustainability ▪ B2 storyline – Population like A2 – Similar environmental/social focus like B1 – More heterogeneous world than B1 32 Figure 4.18 Past and predicted changes in global average atmospheric CO2 concentration Model Verification: Can it be done? ▪ Before you can trust any of these models, they must be verified. – Observed past climate can be used as a test. If a climate model can simulate the past climate, then there is a reasonable chance that the model can accurately predict future climate. 34 Can we predict changes in past climate? Figure 4.29 Observed global temperature changes versus simulations via the HadGEM1 GCM Conclusions 1. Models can reasonably predict temperature variations over the last 150 years. 2. Most of the observed warming in the past 50 years is attributable to human activities. 37 Future Projections 38 Figure SPM.5 2000-2100 global warming based on six emission scenarios ▪ Best estimates: – 1.8°C to 4.0°C (3.2°F to 7.2°F) ▪ Likely range: – 1.0°C to 6.6°C (1.8°F to 11.8°F) ▪ Remember: 1.33°C (2.39°F) from 1916 to 2016 Figure 4.34 Projected changes in surface temperatures comparing data (Part 2) Starting from 1961-1990 Changes in Temperature ▪ Future changes in surface temperature are not uniformly distributed around the globe ▪ Land surface temperatures are expected to increase more than sea-surface temperatures – Why? ▪ Arctic regions are likely to warm more than other latitudes – Why? Figure 4.38 Projections of 21 GCMs about changes over the present century in precipitation Changes in Precipitation ▪ Polar and equatorial regions are likely to become wetter ▪ Parts of middle latitude regions will become drier ▪ Overall, precipitation should increase – Warmer air can hold more water vapor ▪ This can lead to more clouds and precipitation Figure 4.35 Past and future sea ice and sea level September Sea Level Rise ▪ Sea Level will increase – why? – Thermal expansion – Melting of continental ice and snow Sea Ice Area Decline ▪ Warmer temperatures lead to sea ice melt ▪ Process will be accelerated by ice-albedo feedback ▪ Two climate models projections from ~2007 show ice free Arctic summers by 2050/2070 – Recent trends suggest that it could be sooner Hurricane Intensity ▪ As ocean temperatures increase, there will be more energy for hurricanes – Intensity expected to increase ▪ Uncertainties remain as to how global warming will affect frequency Forest Fires ▪ Wildfires are more likely to occur in hot, dry, weather – In the mid-latitudes, frequency will increase 50 ▪ Therefore, stabilizing emissions is not enough to reduce the radiative forcing ▪ Based on above, how much will emissions have to decline in % to stabilize CO2 at 550 ppm? 51 Metr 112: Activity 7 1. Based on the A1FI emission scenario, what is the predicted atmospheric CO2 concentration in 2100, along with the global temperature change and sea level change from 2000 to 2100? (3 points) 2. Based on the B1 emission scenario, what is the predicted atmospheric CO2 concentration in 2100, along with the global temperature change and sea level change from 2000 to 2100? (3 points) 3. Explain the differences between the two projections, both in terms of magnitude of effects and scenario type. Use 3-5 sentences for your response. (4 points) Discussion Questions 1. What is a climate model? 2. Why are climate models important when studying global warming? Give two reasons. 3. How have global climate models changed over time? 4. What are five factors that affect greenhouse gas emissions? 5. Can climate models reasonably reconstruct global temperature variations from 1880 to present? 6. How will San Jose's average temperature and precipitation change from 2000 to 2100? 7. How is global warming affecting hurricanes? 8. How is global warming affecting forest fires in the mid-latitudes? 
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