Climate Sensitivity PDF

Climate Sensitivity OCN/ATMO-310 October 18, 2024 Overview Formation and history of the Earth System to understand past climate variability and natural variability Science of the Earth’s climate as a coupled system Looked into how we know this What can we expect in the future...

Climate Sensitivity OCN/ATMO-310 October 18, 2024 Overview Formation and history of the Earth System to understand past climate variability and natural variability Science of the Earth’s climate as a coupled system Looked into how we know this What can we expect in the future? Historical Overview of Climate Science Evidence seems to show: 1. Unprecedented rates of warming 2. Higher probability of extreme events 3. Links to excess and rapid GHG production Related? What to do about it? John Tyndall (1820-1893) In 1859 determined that certain gases in the atmosphere could trap heat James Croll (1821-1890) In 1875 wrote that changes in the Earth’s orbit could lead to ice ages Svante Arrhenius (1859-1927) In 1896 determined that a reduction in CO2 by half would lower the temperature in Europe by 4-5 oC G. S. Callendar (1898-1964) Study of absorption spectrum (Callendar effect) Global issue – Global solution Can we solve this via regulation? First need to understand the situation Policy 1947: The World Meteorological Organization (WMO) is formed as a specialized agency of the United Nations responsible for promoting international cooperation on atmospheric science, climatology, hydrology and geophysics 1972: The United Nations Environment Programme (UNEP) is formed to coordinate responses to environmental issues within the United Nations system and provides leadership, delivers science and develops solutions on a wide range of issues, including climate change, the management of marine and terrestrial ecosystems, and green economic development.  1979 statement by the World Meteorological Agency (WMO): “When it is assumed that the CO2 content of the atmosphere is doubled and statistical thermal equilibrium is achieved, the more realistic of the modeling efforts predict a global surface warming of between 2°C and 3.5°C, with greater increases at high latitudes. … “ This is a statement about climate sensitivity  Climate as distribution: change in mean Folland et al. 2001.  Climate as distribution: change in variance Folland et al. 2001.  Climate as distribution: change in mean and var Folland et al. 2001. Climate Sensitivity Term used by IPCC to express the relationship between the human- caused emissions that add to the Earth’s greenhouse effect — carbon dioxide and a variety of other greenhouse gases — and the temperature changes that will result from these emissions. How much will global mean surface temperature increase if CO2 is doubled? Measures of Climate Sensitivity 1. Transient Climate Response (TCR). The amount of warming that might occur at the time when CO2 doubles, having increased gradually by 1% each year. TCR more closely matches the way the CO2 concentration has changed in the past. It differs from ECS because the distribution of heat between the atmosphere and oceans will not yet have reached equilibrium. Measures of Climate Sensitivity 2. Equilibrium Climate Sensitivity (ECS): The Earth’s climate takes time to adjust to changes in CO2 concentration. For example, the extra heat trapped by a doubling of CO2 will take decades to disperse down through the deep ocean. ECS is the amount of warming that will occur once all these processes have reached equilibrium. Measures of Climate Sensitivity 3. Earth System Sensitivity (ESS), includes very long- term Earth system feedbacks, such as changes in ice sheets or changes in the distribution of vegetative cover. Example CO2 has increased from its pre-industrial level of 280 parts per million (ppm) to around 410 ppm today. Without actions to reduce emissions, concentrations are likely to reach 560 ppm – double pre- industrial levels – around the year 2060. TCR tends to be notably lower than ECS. The Intergovernmental Panel on Climate Change (IPCC) fifth assessment report gave a likely ECS range of 1.5oC to 4.5oC of warming for a doubling of atmospheric CO2 concentrations, but a likely TCR of only 1oC to 2.5oC. This sensitivity depends primarily on feedback effects that act to amplify or diminish the greenhouse effect. There are three primary ones: 1. Clouds 2. Sea ice 3. Water vapor NOTE: Without feedbacks, the change would be 1oC Virtually all of the controversies over climate science hinge on just how strong the various feedbacks may be — and on whether scientists may have failed to account for some of them. Feedbacks Cause Uncertainty Feedbacks include water vapor, clouds, surface reflectivity and other factors that will (may?) change as the Earth warms. Recall these feedbacks can amplify (positive feedbacks) or diminish (negative feedbacks) the effect of warming from climate forcing. “Simple” physics shows the world will warm by a bit more than 1oC once CO2 doubles if feedbacks are not taken into account. There is extremely strong evidence that feedbacks will amplify this warming, based on the Earth’s past and the physical processes involved. Feedbacks: Example Water vapor is the single largest and one of the best-understood climate feedbacks. As the world warms, the amount of water vapor in the atmosphere is expected to increase and, therefore, so too will the greenhouse effect. Measurements from satellites confirm that water vapor concentrations have been increasing with temperatures in the atmosphere over the past few decades. Feedbacks: Example A warmer and wetter atmosphere will also affect cloud cover. However, it is much more uncertain how changes in cloud cover will influence climate An increase in low-altitude clouds would tend to offset some warming by reflecting more sunlight back to space, whereas an increase in the height of high-altitude clouds would trap extra heat. Meanwhile a shift in sun-blocking clouds from the tropics towards the poles, where the incoming sunlight is less intense, would decrease their power to block sunlight. Feedbacks: Example Changes in the composition of clouds also matter: clouds that contain more water droplets are “optically thicker” and more effective at blocking sunlight than those composed mainly of ice crystals. All this means the global net effect of cloud feedbacks is complex and hard to model precisely. A warming world will also have less ice and snow cover. With less ice and snow reflecting the sun’s rays, melting will decrease Earth’s albedo and amplify warming. Feedbacks Cause Uncertainty The combination of these and other feedbacks converts the ~1oC warming from doubled CO2 alone into an uncertain range of possible warming, from around 1.5oC to 4.5oC. How to quantify? Recall that the Earth’s radiative balance includes incoming shortwave radiation from the sun and outgoing longwave radiation to space. If these two heat fluxes are exactly equal, i.e., no change in radiative forcing, then temperature does not change If the heat balance does change, the Earth either needs to store the excess, or release the excess  How to quantify? Energy Equation: !# ! !! = " + !# !$ " Climate = Heat + Heat Forcing Storage Loss In equilibrium, temperature change is constant with time and so, !! = " #!" 𝜆 is a measure of climate sensitivity; ˚K per Wm-2 of climate forcing  !# ! !! = " + !# !$ " To project future climates by using the observed record of climate over the past century, we need to know three things to interpret the temperature time series: Climate Forcing = 𝛥Q (Wm-2) Heat capacity = C (J oK-1 m -2) Climate sensitivity = 𝜆 (oK per Wm-2) Greenhouse Effect: The amount by which the atmospheric reduces the longwave emission from Earth. Greenhouse effect = Surface infrared emission - Earth infrared emission 155 Wm-2 = 390 Wm-2 - 235 Wm-2 Greenhouse effect = Surface longwave emission - Earth emission Radiative Forcing Various factors in the Earth’s atmosphere can change the amount of short-wave radiation that reaches the Earth’s surface and the amount of long-wave radiation that will escape the atmosphere to outer space. These are referred to as “radiative forcing terms” Greenhouse gases, clouds, albedo, etc. They are usually “small” compared to the net, but are extremely important Components contributing to the 155 W/m2 What the Intergovernmental Panel on Climate Change did not discuss was an even more radical potential response — one that would re-engineer Earth’s stratosphere to create a massive heat shield by effectively duplicating the fallout that follows a volcanic eruption. This kind of revolutionary “solar geoengineering” — known by some as the “Pinatubo Strategy,” after a volcano whose 1991 eruption shrouded the planet in a sulfurous cloud  Numerical Modeling Part 2: Coupled Climate Models OCN 310 October 16, 2024 Review Numerical models are a form of modeling that uses discrete forms of governing equations that are solved iteratively (on a computer) We talked about general circulation models for the atmosphere and, separately, for the ocean General Circulation Models “stand-alone” ocean or atmosphere, used for forecasts and/or “hindcast” Ocean General Circulation Models (OGCM): Ocean dynamics modeled, forcing applied is atmospheric winds (stress at surface), heat and freshwater fluxes Typically 10 to 100 km horizontal, ~10 to 50 vertical levels Atmospheric General Circulation Models (AGCM): Typically forced by surface temperatures and upward heat flux  Atmosphere GCM Atmospheric models require: 1. Forcing at the surface: temperature 2. Boundary conditions if not basin-wide Atm models provide: 1. Velocity/movement 2. Heat fluxes 3. Precipitation  Ocean GCM Ocean models require: 1. Forcing at the surface: wind, heat, freshwater 2. Boundary conditions if not basin-wide Ocean models provide: 1. Velocity/movement 2. Temperature 3. Salinity Considerations Equations are (can be) exact, numerical discretization is an approximation Sub-gridscale parameterizations important Compromise between resolution (time and space), domain size (again, size and space) and integration time  Coupled Climate Models Why is there a need for considering coupled models? Realistic description of climate cannot be done without considering the atmosphere and ocean (and maybe even biology) at the same time: Tele-connections and feedbacks Thermohaline circulation Radiative feedbacks Coupled Models Boundary conditions for AGCM provided by OGCM and vice versa Usually used to forecast future conditions, but also to experiment with different forcing scenarios, e.g., GHG adjustments Coupled models have evolved to “Earth System Models” or ECM’s Used for climate studies Evolution of Climate Models Based on IPCC recommendations via a series of reports  Earth System Model (ESM) Closing the Carbon Cycle Atmospheric circulation and radiation Climate Model Sea Ice Land physics (CGCM) Ocean circulation and hydrology Atmospheric circulation and radiation Allows Interactive CO2 Earth System Sea Ice Model (ESM) Ocean ecology and Plant ecology and land use Biogeochemistry Land physics Ocean circulation and hydrology  New Capabilities in ESMs Prognostic carbon cycle (some with prognostic nitrogen) Ocean biogeochemistry, micronutrient limitation, trophic structure Emerging capability for land use change and dynamic fire modeling Emerging capability for biogeography and successional processes Expanded treatment of aerosols and atmospheric chemistry (Interactive ice sheets) Complexity = Expensive Runs include a large array of physics, chemistry and biology Climate experiments are by nature long integrations Requires (usually) a dedicated super computer  Spinup and Drift Examples of model integrations (or runs, simulations or experiments), starting from idealized or observed initial conditions. Spin-up to equilibrated model climatology is required (centuries for deep ocean). Model climate differs slightly from observed (model bias) Example Earth Simulator Was the fastest supercomputer in the world from 2002-2004 Used to run “global climate models to evaluate the effects of global warming and problems in solid earth geophysics” 35.86 trillion floating point calculations per second (trillion = 1012, aka teraflop) Earth Simulator  2020 was “Summit” (DoE) 200 petaflops, or 200,000 trillion calculations per second 3 billion billion mixed precision calculations per second $200M The Fugaku supercomputer, developed by Fujitsu and Japan's national research institute Riken 442 petaflops, or quadrillions of floating point operations per second Frontier, the new number 1, is built by Hewlett Packard Enterprise (HPE) and housed at the Oak Ridge National Laboratory (ORNL) in Tennessee, USA. reaching 1102 petaFlops = 1.102 x 1018  Large resources needed: climate modeling centers IPCC provides guidance Look ahead: IPCC The Intergovernmental Panel on Climate Change Consequences Coupled climate models are large and complex, and expensive to run Climate models are not forecast models, more used to test hypotheses Large modeling centers (~50) around the world run these Non-linearity requires “ensemble runs” Need base set of experiments IPCC Climate Modeling Validation Models are getting much more sophisticated and (hopefully) realistic, but how good are they? NCAR_CCSM3 coupled simulation SST climatology (20th century run, 1979-2000) – December-February MODEL OBS NCAR_CCSM3 coupled simulation SST climatology (20th century run, 1979-2000) – June-August MODEL OBS  Simulation vs. Obs 1 Simulated Precipitation Observed Precipitation  Simulation vs. Obs 1 Simulated Precipitation Difference: Sim-Observed  Simulation vs. Obs 2 Simulated Land Temp Observed Land Temp  Simulation vs Obs 2 Simulated Land Temp Difference: Sim- Observed Annual Mean Precipitation (1980- 1999) Observations 23 GCM ensemble mean  Ocean Temperature (1957-1990) 18 model ensemble minus observations Regional Climate Models Low-resolution of coupled models usually prohibits any meaningful investigation of regional impacts 1. Statistical Downscaling Understand processes and impacts Use model statistics and relationships to “downscale” larger results 2. Dynamical Downscaling Run “nested” model à large model provides boundary conditions for smaller domain Part of Global Climate Model at 2.5o by 3.75o resolution (lat x lon) Regional Global Climate Model at 0.5o by 0.5o resolution (lat x lon) Resolution Issues: Regional Climate Models Summary Models can be effective tools for studying complex problem for which more traditional experiments are difficult (impossible) Numerical models are approximations, but information can be learned using idealized experiments, statistics and first principles Climate models form part of the basis of IPCC conclusions but have their limitations Numerical Modeling OCN 310 October 11, 2024 October 14, 2024 Science Paradigm "Predictions are hard, especially about the future.” –Yogi Bera Science started as empirical: describing natural phenomena Evolved to include experimentation and theory Models were a natural extension of this Models (why/when) Sometimes experiments are impossible (formation of the solar system) Sometime experiments are not wanted (flooding, nuclear tests) Experiments can be too costly or time-consuming (crash tests) Outline —We’ve discussed the mean, large-scale patterns of ocean and atmosphere circulation —How to we now take what we know and make projections, or forecasts, for future climate? Numerical models à Numerical simulations Physical System Mathematical Model Simulation Prediction Necessity/Utility of Models in Climate Science Individual components of the climate system, atmosphere, ocean, land, ice, etc., are extremely complex, numerical models allow for experimentation and hypothesis testing Models allow for forecasting, both in the sense of predicting future events, but also to understand impacts of changes in individual components. Some climate change signals are extremely long temporally, and there are insufficient observations to adequately study them Challenges Processes in ocean and atmosphere range from millimeter- scale to planetary waves, seconds to decades. It would be impossible to include all these space- and time-scales, so rely instead on approximations, a.k.a., sub-gridscale parameterizations The Earth system has many components (hydrosphere, cryosphere, biosphere, etc.), and these all interact, but it’s not clear what the exact feedbacks are The system could be highly no-linear, so small changes could lead to very different results Land surface model: soil moisture and evapotranspiration Precipitation Evapotranspiration Aerodynamic resistance Canopy Interception Leaf Canopy (stomatal) area resistance index Runoff Soil capacity Soil moisture Sea ice model processes Modeling Basics Take known or approximate physics in the form of a continuous set of equations Discretize the equations to solve iteratively Keys: Forcing, i.e., what makes it go Initial conditions, i.e., how to start Boundary conditions, i.e., how to include processes outside the model domain Example I live in Aina Haina and bike home from UH Manoa How long will it take me to get home? 1. Governing equation(s): velocity = distance / time time = distance / velocity ∂x 2. Discretize V = ∂t Δx End − Start t= = v speed  Average speed ~12 miles/hour Distance school to home ~6 miles Time to get home ~0.5 hour Initial condition: leave at 6:00PM Forecast: arrive home at 6:30PM Δx End − Start t= = v speed  Used a “finite difference” on a “regular grid” Grid cell 6 miles Assumed no external forcing No feedbacks 6 2 miles miles Ocean/Atmosphere Models Three-dimensional problem, so need a “grid” in both the horizontal and vertical Started with numerical weather prediction based on early theory by Bjerknes in 1904 Later ”demonstrated” by Lewis Fry Richardson in 1922 Richardson foresaw a “forecast factory,” where he calculated that 64,000 human “computers,” each responsible for a small part of the globe, would be needed to keep “pace with the weather” in order to predict weather conditions. They would be housed in a circular hall like a theater, with galleries going around the room and a map painted on the walls and ceiling. A conductor located in the center of the hall would coordinate the calculations using colored lights...  Scales of Atmospheric Motions/Processes Resolved Scales Global Models Future Global Models Cloud/Mesoscale/Turbulence Models Cloud Drops Microphysics CHEMISTRY Anthes et al.  Atmospheric Model Grid For each grid cell, single value of each variable (temp., vel.,…) Finite number of equations Vertical coordinate follows topography, grid spacing varies Effects passed from neighbor to neighbor until global Budget gives change of temperature, velocity, etc., one time step (e.g. 15 min) later 100yr=4million 15min steps Subgrid-scale processes  “typical” atmospheric forecast model: ~1-degree (100 km) for global High-res would be ¼-degree (25 km) ~1-km for regional model  “typical” ocean model: ~0.5-degree (50 km) for global High-res would be ~5 km ~100m for regional model Circulation Models Typically “stand-alone” ocean or atmosphere (used for forecasts and/or “hindcast” Ocean General Circulation Models (OGCM): Typically 10 to 100 km, ~10 to 50 vertical levels Ocean dynamics modeled, forcing applied is atmospheric winds (stress at surface), heat and freshwater fluxes Atmospheric General Circulation Models (AGCM): Typically forced by surface temperatures and upward heat flux Regional models typically higher resolution, but require boundary conditions Summary Atmospheric model Equations of motion based on sphere Forcing includes incoming solar radiation, outgoing longwave (from Earth, i.e., land and ocean temperatures), evaporation Output includes wind speed/direction, precipitation, etc. Ocean model Forcing includes wind stress, precipitation, heat flux Output includes currents, salinity, temperature Summary (cont’d) Equations are (can be) exact, numerical discretization is approximation Sub-gridscale parameterizations Compromise between resolution (time and space), domain size (again, size and space) and integration time Cost of Modeling Typically large computing power needed Global vs regional model For example, ocean processes 1 second, 1 mm 360 x 360 x 110 x 110 x 1000 x 1000 x 1000 x 1000 x 4000 x 1000 x 1000 = 6x1030 grid cells 86400 x 365 = 3 x 107 time points per year 2x1038 operations  Coupled Climate Models Why is there a need for considering coupled models? There are at least three major reasons why it is clear that realistic description of climate cannot be done without considering the atmosphere and ocean at the same time: Teleconnections Thermohaline circulation Radiative feedbacks Outline Discussed a variety of modeling techniques One type, numerical modeling, can be used to both “hindcast” and “forecast” various aspects of the Earth system (atmospheric and oceanic circulation) AGCM’s Require boundary conditions at the air/sea and air/land interface (heat, freshwater) and provide estimates of winds, rain, temperature, etc. OGCM’s Require boundary conditions at the air/sea interface (wind, heat, freshwater) and provide estimates of ocean currents, temperature, salinity, sea level, etc.  https://pacioos.org/voyager Intergovernmental Panel on Climate Change ATMO/OCN-310 October 21, 2024 Overview Formation and history of the Earth System to understand past climate variability and natural variability Science of the Earth’s climate as a coupled system Looked into how we know this What can we expect in the future? Historical Overview of Climate Science Evidence seems to show: 1. Unprecedented rates of warming 2. Higher probability of extreme events 3. Links to excess and rapid GHG production Related? What to do about it? Global issue – Global solution Can we solve this via regulation? First need to understand the situation WMO, UNEP  1985 a joint UNEP/WMO/ICSU Conference on the "Assessment of the Role of Carbon Dioxide and Other Greenhouse Gases in Climate Variations and Associated Impacts" assessed the role of carbon dioxide and aerosols in the atmosphere, and concluded that greenhouse gases "are expected" to cause significant warming in the next century and that some warming is inevitable.  1988 WMO recognizes climate change as a common concern for humankind and establishes the Intergovernmental Panel on Climate Change (IPCC) 1987 – Montreal Protocol Though not intended to tackle climate change, the Montreal Protocol was an historic environmental accord. Every country in the world eventually ratified the treaty, which required them to stop producing substances (e.g., CFCs) that damage the ozone layer. The protocol has succeeded in eliminating nearly 99% of these ozone-depleting substances. 1992 – UN Framework Convention on Climate Change (UNFCCC) The first global treaty to explicitly address climate change. It established an annual forum, known as the Conference of the Parties, or COP, for international discussions aimed at stabilizing the concentration of greenhouse gases in the atmosphere. Identified three key areas of response: Promoting the science needed as a sound basis for decision making on mitigation and adaptation Mitigation by reducing greenhouse gas emissions Adaptation to the changes that are inevitable, no matter what mitigative action is taken 2005 – Kyoto Protocol The first legally binding climate treaty. It required developed countries to reduce emissions by an average of 5% below 1990 levels, and established a system to monitor countries’ progress. It extended the UNFCCC and commits state parties to reduce greenhouse gas emissions, based on the scientific consensus that global warming is occurring and that human-made CO2 emissions are driving it. The major distinction between the Protocol and the Convention is that while the Convention encouraged industrialized countries to stabilize GHG emissions, the Protocol commits them to do so. 2015 – Paris Agreement Governments set targets, known as nationally determined contributions (NDCs), with the goals of preventing the global average temperature from rising 2oC above preindustrial levels and pursuing efforts to keep it below 1.5oC. It also aims to reach global net-zero emissions, where the amount of greenhouse gases emitted equals the amount removed from the atmosphere, in the second half of the century. (This is also known as being climate neutral or carbon neutral.)  Intergovernmental Panel on Climate Change (IPCC) Established in 1988 by WMO and UNEP Supports the UN Framework Convention on Climate Change (UNFCCC) Adopted in 1992 and entered into force in 1994 Overall policy framework for climate change issue Role of the IPCC "assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio- economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation" (source: www.ipcc.ch)  Role of the IPCC (cont’d) Review by experts and governments is an essential part of the IPCC process. The Panel does not conduct new research, monitor climate-related data or recommend policies. It is open to all member countries of WMO and UNEP. IPCC is policy relevant, but not policy prescriptive! Although the reports are supposed to be objective and purely scientific, the process is to some degree political (plenary, open for all countries, topics covered, criticism on process and authors). Role of the IPCC (cont’d) The IPCC does not carry out research nor does it monitor climate related data or other relevant parameters. It bases its assessment mainly on peer reviewed and published scientific/technical literature. (source: www.ipcc.ch) IPCC Organization IPCC working groups Working Group I - "The Physical Science Basis” Working Group II - "Impacts, Adaptation and Vulnerability” Working Group III - "Mitigation of Climate Change” Task Force on National Greenhouse Gas Inventories (source: www.ipcc.ch)  Working group 1: The physical science 1. Historical Overview of Climate Change Science 2. Changes in Atmospheric Constituents and in Radiative Forcing 3. Observations: Surface and Atmospheric Climate Change 4. Observations: Changes in Snow, Ice and Frozen Ground 5. Observations: Oceanic Climate Change and Sea Level 6. Paleoclimate 7. Couplings Between Changes in the Climate System and Biogeochemistry 8. Climate Models and their Evaluation 9. Understanding and Attributing Climate Change 10. Global Climate Projections 11. Regional Climate Projections  Working group 2: Impacts, adaptation, vulnerability Assessment of observed changes and responses Asia in natural and managed systems Australia and New Zealand New assessment methods and the characterisation of future conditions Europe Freshwater resources and their management Latin America Ecosystem, their properties, goods and services North America Food, fibre and forest products Polar Regions (Arctic and Antarctic) Coastal systems and low-lying areas Industry, settlement and society Small islands Human health Assessment of adaptation practices, options, constraints and Africa capacity Inter-relationships between adaptation and mitigation Assessing key vulnerabilities and the risk from climate change Perspectives on climate change and sustainability Working group 3: Mitigation Introduction Industry Framing Issues Agriculture Issues related to mitigation in Forestry Waste management the long-term context Mitigation from a cross-sectoral Energy Supply perspective Transport and its infrastructure Sustainable Development and Residential and commercial mitigation buildings Policies, instruments, and co- operative arrangements Role of Governments Governments request the scientific community to conduct comprehensive assessments Governments elect a Bureau to ensure assessments are conducted following the IPCC Rules and Procedures Proposed outlines are discussed and approved line-by-line by the governments in a Plenary Bureau approves the chapter author teams Based on scientific expertise, geography, & gender Role of Governments (cont’d) Governments participate in the review process and in the IPCC Plenary sessions, where main decisions about the IPCC work program are taken and reports are accepted, adopted, and approved Summary for Policymakers approved line-by-line by the governments in a final Plenary IPCC and Climate Projections Climate models, rather than providing a forecast, can be used to test hypotheses of climate change: Climate sensitivity Feedbacks Expensive to run, need big modeling centers How to use these to understand future climate? Climate modeling Recall that model experiments require: 1. Initial conditions 2. Boundary conditions 3. Forcing Since climate models have both atmospheric and oceanic physics, forcing is “internal”, and there is no need for boundary conditions How to best address this across different models? IPCC effort to “homogenize” model experiments All start from initial state, e.g., “pre-industrial” spin up All integrate forward for 150 years, “present day” or “historical” run Use this to initiate future climate runs How to best represent problem? In 1990 the IPCC released “emission scenarios” to be used for driving global circulation models called SA90. These were later revised in 1992. The so-called IS92 scenarios were the first global scenarios to provide estimates for the full suite of greenhouse gases. They were used from 1992 to 2000. The next revision included improved baselines on emissions and new information on technology trends and economics  IPCC then developed “Special Report on Emission Scenarios” or SRES These provide guidelines for modeling centers to following when designing climate model runs They include socio-economic changes and the anticipated change to emissions, for example, “one possible future scenario is no changes are made” and this would lead to an experiment forced with constant rates of change in GHG’s The SRES Story Lines Altogether 40 SRES scenarios were developed by six modeling teams. All are equally valid with no assigned probabilities of occurrence. The set of scenarios consists of six scenario groups drawn from the four families: one group each in A2, B1, B2, and three groups within the A1 family, characterizing alternative developments of energy technologies: A1FI (fossil fuel intensive), A1B (balanced), and A1T (predominantly non-fossil fuel). Atmospheric CO2 (input) Temperature (output) Actual Emissions Compared to the SRES Scenarios A1B A1FI A2 B1 A1T B2 Adapted from Leggett & Logan Different Models Run the Same Scenario, but Get Different Answers SRES A2 Scenario Issues: These things are incredibly difficult to predict and it is becoming increasingly likely that regulations will be based on limiting warming rather than emissions directly. The SRES did not directly answer questions on how to keep planet below 2ºC They did not address the effectiveness of Kyoto or Paris agreements Solution: RCP – The Representative Concentration Pathways fixed allowable future radiative forcing. The allowable global emissions can be determined from the models for each of the RCPs.  5th Assessment Report: Representative Concentration Pathways RCPs RCP 2.6 representative of scenarios in the literature that lead to very low greenhouse gas concentration levels. It is a “peak-and-decline” scenario; it’s radiative forcing level first reaches a value of around 3.1 W/m2 by mid-century, and returns to 2.6 W/m2 by 2100. RCP 4.5 stabilization scenario in which total radiative forcing is stabilized shortly after 2100, without overshooting the long-run radiative forcing target level RCPs RCP 6 stabilization scenario in which total radiative forcing is stabilized shortly after 2100, without overshoot, by the application of a range of technologies and strategies for reducing greenhouse gas emissions RCP 8.5 increasing greenhouse gas emissions over time, representative of scenarios in the literature that lead to high greenhouse gas concentration levels  Special Report on Emission Scenarios (SRES) outlined specific model experiments to be run by all modeling centers (e.g., 2% CO2 increase to doubling) Next used “Representation Concentration Pathways” or RCP Take advantage of ESM and mitigation strategies  SRES/RCP equiv Name Radiative Forcing CO2 Temp Pathway SRES RCP-8.5 8.5 W/m2 in 2100 1370 4.9 rising A1F1 RCP-6.0 6.0 W/m2 post 2100 850 3.0 Stabilization without overshoot B2 RCP-4.5 4.5 W/m2 post 2100 650 2.4 Stabilization without overshoot B1 RCP-2.6 3.0 W/m2 before 2100, 2.6 490 1.5 Peak and decline N/A by 2100  Long Term Experiments Control 500+ years Historical ~1850 to 2005 Projection 1850 2005 2100 2006 to 2100 RCP4.5 (stabilization near 2100) RCP8.5 (GHG continue to increase) NOTE: ECP = Extended Concentration Pathway RCPs versus SRES RCPs Allowable Carbon Emissions https://tntcat.iiasa.ac.at/RcpDb/dsd?Action=htmlpage&page=compare Long term experiments Control, historical, and paleo Future scenarios (RCPs) Diagnostic simulations (feedbacks) Attribution runs (single and multi-factor) Simulations only performed by ESMs… Forced by fossil fuel emissions and land use changes, as opposed to concentrations Next Generation: Shared Socio-economic Pathways (SSP’s) In the lead up to the IPCC’s Sixth Assessment Report new scenarios have been developed to more systematically explore key uncertainties in future socioeconomic developments Five Shared Socioeconomic Pathways (SSPs) have been developed to explore challenges to adaptation and mitigation. Shared Policy Assumptions (SPAs) are used to achieve target forcing levels (W/m2). Source: Riahi et al. 2016; IIASA SSP Database; Global Carbon Budget 2016 Examples of SSP Implications SSP3: Regional Rivalry SSP5: Fossil-fuel devel Multi-pole cold war Rise of the global middle class Conflict, focus on security Rapid technology progress Barriers to trade, migration Large investments in human Little investment in health, health and education education Well functioning institutions Slow technological progress Rapid economic growth Weak institutions Fossil-centered energy system Slow income growth Based on KC and Lutz, 2015 Based on Jiang and O’Neil, 2015 Based on Dellink et al., 2015 Based on van Vuuren et al., 2014 Pathways That Avoid 2oC of Warming According to the Shared Socioeconomic Pathways (SSP) that avoid 2°C of warming, global CO2 emissions need to decline rapidly and cross zero emissions after 2050 Riahi et al. 2016; IIASA SSP Database; Global Carbon Budget 2017 Summary Climate models are expensive and time-consuming to run Run by modeling centers, guided by the IPCC Initialization, spin-up prescribed Emission scenarios (SRES) followed by Representative Concentration Pathways (RCP’s) Common runs can be directly compared IPCC Reports ATMO-310/OCN 310 October 25, 2024 Honolulu Star Advertiser 10/25/2024 Sixth Assessment Rerport AR6 Synthesis Report: Climate Change 2023 AR6 Climate Change 2022: Impacts, Adaptation and Vulnerability AR6 Climate Change 2022: Mitigation of Climate Change AR6 Climate Change 2021: The Physical Science Basis https://www.ipcc.ch/ Physical Science Basis: Ten Key Points 1. Climate change is unprecedented 2. Climate change is caused by humans 3. Climate change affects everyone, everywhere 4. We can define our future 5. More warming, more changes Physical Science Basis: Ten Key Points 6. Less future warming, less severe extremes 7. The more we emit, the less nature can help 8. Some changes in the climate can be slowed and even stopped 9. Climate change will affect us in many ways 10. Future emissions will determine future warming 1. Climate change is unprecedented Human influence has warmed the climate at a rate that is unprecedented in at least the last 2000 years The Earth's surface is warming at a rate that is very unusual Unprecedented in at least 2000 years The Earth's surface is warming at a rate that is very unusual Unprecedented in at least 2000 years Warmest since the last 100,000 years The climate is warming because of human activity Current warming of 1.1 oC Natural factors are not causing this warming 2. Climate change is caused by humans Observed warming is driven by emissions from human activities, with greenhouse gas warming partly masked by aerosol cooling  Observed warming Current warming is caused by human activities Current warming of 1.1°C  Observed warming Contributions to warming Current warming is caused by human activities Current warming of 1.1°C Natural factors are not causing this warming  Observed warming Contributions to warming The warming effect of greenhouse gases is partly masked by air pollutants that have a cooling effect  Observed warming Contributions to warming Among all the greenhouse gases, carbon dioxide is the one contributing the most to warming, followed by methane 3. Climate affects everyone Each hexagon corresponds to a region of the world The hexagons indicate: Increase or decrease in the type of observed change (color) If the assessment of the changes is not conclusive (hatching) If there is not enough data or literature to assess (grey) Dots represent how robust the assessed human contribution is Observed changes in hot extremes and the human contribution to these observed changes in the world’s regions Today hot extremes have increased almost everywhere compared to the 1950s because of human-caused climate change Observed changes in heavy precipitation and the human contribution to these observed changes in the world’s regions Heavy precipitation has become more intense and frequent in many regions since the 1950s Observed changes in agricultural and ecological drought, and the human contribution to these observed changes in the world’s regions Agricultural and ecological drought has increase in some regions since the 1950s  4. We can define our future Future emissions cause future additional warming, with total warming dominated by past and future CO2 emissions Possible future emissions scenarios of carbon dioxide, other greenhouse gases, and air pollutants Different possible future emissions scenarios lead to different levels of future global warming Change in 2081-2100 relative to 1850-1900 (°C) Total warming (observed warming to date in darker shade), warming from CO2 and non-CO2 GHGs, and cooling from changes in aerosols and land use  Contribution to global surface temperature increase from different emissions, with a dominant role of CO2 emissions Change in 2081-2100 relative to 1850-1900 (°C) Total warming (observed warming to date in darker shade), warming from CO2 and non-CO2 GHGs, and cooling from changes in aerosols and land use Global warming is mainly caused by emissions of carbon dioxide  5. More warming, more changes With every increment of global warming, changes get larger in regional mean temperature, precipitation and soil moisture Annual mean temperature change (°C) at 1°C global warming Annual mean temperature change (°C) relative to 1850-1900 Annual mean precipitation change (%) relative to 1850-1900 Annual mean total column soil moisture change (standard deviation)  6. Less future warming, less severe extremes With every increment of global warming, changes get larger in regional mean temperature, precipitation and soil moisture  Hot temperature extremes over land Hot extremes become more intense and more frequent with increasing global warming Changes in previously 1 in 10 year hot temperature extremes over land Focus on 10-year event Hot extremes become more intense and more frequent with increasing global warming Changes in previously 1 in 50 year hot temperature extremes over land Focus on 50-year event Hot extremes become more intense and more frequent with increasing global warming  Changes in previously 1 in 10 year heavy precipitation extremes over land Focus on 10-year event Heavy precipitation over land Future changes in previously 1 in 10 year agricultural and ecological droughts Focus on 10-year event Agricultural and ecological droughts  7. The more we emit, the less nature can help The proportion of CO₂ emissions taken up by land and ocean carbon sinks is smaller in scenarios with higher cumulative CO₂ emissions With higher CO2 emissions, the amount of CO2 emissions taken up by nature is larger, but more of the emitted CO2 remains in the atmosphere Cumulative human-caused CO2 emissions (1850-2100) Illustrative greenhouse gas emissions scenarios Very low Low Intermediate High Very high The proportion of CO2 emissions taken up by nature from the atmosphere is smaller in scenarios with higher CO2 emissions (1850-2100) Very low Low Intermediate High Very high Illustrative greenhouse gas emissions scenarios 8. Some changes in the climate can be slowed and even stopped Human activities affect all the major climate system components, with some responding over decades and others over centuries Message 1: With rapid and strong reductions of GHG emissions, some changes can be stopped by the mid-century Global surface temperature change relative to 1850-1900 Message 1: With rapid and strong reductions of GHG emissions, some changes can be stopped by the mid-century  September Arctic sea ice area Message 1: With rapid and strong reductions of GHG emissions, some changes can be stopped by the mid-century  Global ocean surface pH (measure of acidity) Message 1: With rapid and strong reductions of GHG emissions, some changes can be stopped by the mid-century  Global mean sea level change relative to 1900 Message 2: Some changes are irreversible for centuries to millennia  (e) Global mean sea level change in 2300 relative to 1900 Message 3: low-likelihood, high impact storylines leading to very high sea levels cannot be ruled out (d) Global mean sea level change relative to 1900  9. Climate change will affect us in many ways Multiple climatic impact-drivers are projected to change in all regions of the world Assessed climatic impact-drivers relevant for impact and risk assessment interactive-atlas.ipcc.ch  Heat and Cold All regions are projected to experience further increases in hot climatic impact-drivers and decreases in cold CIDs. by 2050 compared to 1960-2014 (2°C global warming)  Wet and Dry At 2°C global warming and above, the magnitude of changes increases for droughts, heavy precipitation and associated flooding events, and for mean precipitation compared to those at 1.5°C. by 2050 compared to 1960-2014 (2°C global warming)  Wind Region-specific changes include intensification of tropical cyclones and/or extratropical storms. by 2050 compared to 1960-2014 (2°C global warming)  Snow and Ice Widespread loss of snow and ice and permafrost thaw is projected in all concerned regions at global warming of 2°C. by 2050 compared to 1960-2014 (2°C global warming)  Coastal Regional sea level rise contributes to increases in the frequency and severity of coastal flooding in low-lying areas and to coastal erosion along most sandy coasts. by 2050 compared to 1960-2014 (2°C global warming)  Open Ocean Open ocean regions are projected to experience widespread warming, increased marine heatwaves, loss of oxygen and increased surface salinity contrasts due to the intensified water cycle. by 2050 compared to 1960-2014 (2°C global warming)  10. Future emissions will determine future warming Every ton of CO₂ emissions adds to global warming Global surface temperature increase since 1850-1900 (°C) as a function of cumulative CO2 emissions (GtCO2) A near linear relationship between cumulative CO2 emissions and global warming Cumulative CO2 emissions since 1850 (GtCO2) Historical Projections Cumulative CO2 emissions between 1850 Cumulative CO2 emissions between 2020- and 2019 2050 How much more warming we will experience in the future mostly depends on how large our future global CO2 emissions will be  Intergovernmental Panel on Climate Change (cont’d) ATMO/OCN-310 October 23, 2024 How to best address this across different models? IPCC effort to “homogenize” model experiments All start from initial state, e.g., “pre-industrial” spin up All integrate forward for 150 years, “present day” or “historical” run Use this to initiate future climate runs How to best represent problem? In 1990 the IPCC released “emission scenarios” to be used for driving global circulation models called SA90. These were later revised in 1992. The so-called IS92 scenarios were the first global scenarios to provide estimates for the full suite of greenhouse gases. They were used from 1992 to 2000. The next revision included improved baselines on emissions and new information on technology trends and economics  IPCC then developed “Special Report on Emission Scenarios” or SRES These provide guidelines for modeling centers to following when designing climate model runs They include socio-economic changes and the anticipated change to emissions, for example, “one possible future scenario is no changes are made” and this would lead to an experiment forced with constant rates of change in GHG’s Different Models Run the Same Scenario, but Get Different Answers SRES A2 Scenario Issues: These things are incredibly difficult to predict and it is becoming increasingly likely that regulations will be based on limiting warming rather than emissions directly. The SRES did not directly answer questions on how to keep planet below 2ºC They did not address the effectiveness of Kyoto or Paris agreements Solution: RCP – The Representative Concentration Pathways fixed allowable future radiative forcing. The allowable global emissions can be determined from the models for each of the RCPs.  5th Assessment Report: Representative Concentration Pathways RCPs RCP 2.6 representative of scenarios in the literature that lead to very low greenhouse gas concentration levels. It is a “peak-and-decline” scenario; it’s radiative forcing level first reaches a value of around 3.1 W/m2 by mid-century, and returns to 2.6 W/m2 by 2100. RCP 4.5 stabilization scenario in which total radiative forcing is stabilized shortly after 2100, without overshooting the long-run radiative forcing target level RCPs RCP 6 stabilization scenario in which total radiative forcing is stabilized shortly after 2100, without overshoot, by the application of a range of technologies and strategies for reducing greenhouse gas emissions RCP 8.5 increasing greenhouse gas emissions over time, representative of scenarios in the literature that lead to high greenhouse gas concentration levels  Special Report on Emission Scenarios (SRES) outlined specific model experiments to be run by all modeling centers (e.g., 2% CO2 increase to doubling) Next used “Representation Concentration Pathways” or RCP Take advantage of ESM and mitigation strategies  SRES/RCP equiv Name Radiative Forcing CO2 Temp Pathway SRES RCP-8.5 8.5 W/m2 in 2100 1370 4.9 rising A1F1 RCP-6.0 6.0 W/m2 post 2100 850 3.0 Stabilization without overshoot B2 RCP-4.5 4.5 W/m2 post 2100 650 2.4 Stabilization without overshoot B1 RCP-2.6 3.0 W/m2 before 2100, 2.6 490 1.5 Peak and decline N/A by 2100  Long Term Experiments Control 500+ years Historical ~1850 to 2005 Projection 1850 2005 2100 2006 to 2100 RCP4.5 (stabilization near 2100) RCP8.5 (GHG continue to increase) NOTE: ECP = Extended Concentration Pathway RCPs versus SRES Long term experiments Control, historical, and paleo Future scenarios (RCPs) Diagnostic simulations (feedbacks) Attribution runs (single and multi-factor) Next Generation: Shared Socio-economic Pathways (SSP’s) In the lead up to the IPCC’s Sixth Assessment Report new scenarios have been developed to more systematically explore key uncertainties in future socioeconomic developments Five Shared Socioeconomic Pathways (SSPs) have been developed to explore challenges to adaptation and mitigation. Shared Policy Assumptions (SPAs) are used to achieve target forcing levels (W/m2). Source: Riahi et al. 2016; IIASA SSP Database; Global Carbon Budget 2016 Examples of SSP Implications SSP3: Regional Rivalry SSP5: Fossil-fuel devel Multi-pole cold war Rise of the global middle class Conflict, focus on security Rapid technology progress Barriers to trade, migration Large investments in human Little investment in health, health and education education Well functioning institutions Slow technological progress Rapid economic growth Weak institutions Fossil-centered energy system Slow income growth Summary Climate models are expensive and time-consuming to run Run by modeling centers, guided by the IPCC Initialization, spin-up prescribed Emission scenarios (SRES) followed by Representative Concentration Pathways (RCP’s) Common runs can be directly compared Results 5th Assessment Report https://www.ipcc.ch/report/ar5/syr/synthesis-report/ 6th Assessment Report https://www.ipcc.ch/assessment-report/ar6 What do the climate models tell us? We can look at historical runs to get confidence in individual model dynamics Model ensembles are be useful when looking at future climate Note: there are two types, single model run many times and different models grouped together Focus on: Temperature Sea level Precipitation  By the year 2100: RCP-2.6 models show a warming of 0.5 to 1.8 oC RCP-8.5 models show a warming of 3.0 to 5.5 oC  By the year 2300: RCP-2.6 models show a warming of 0.0 to 1.0 oC RCP-8.5 models show a warming of 3.0 to 13.0 oC  RCP2.6: more warming in the north and over land; cooling over Labrador Sea RCP8.5: patterns the same (?) just more extreme  By the year 2100: RCP-2.6 models show global mean SLR of 30 to 60 cm RCP-8.5 models show global mean SLR of 50 to 95 cm  RCP2.6 RCP8.5 NE US extreme Again, RCP8.5 similar pattern (?) just more extreme  RCP2.6 RCP8.5 Comments? Other Conclusions Natural v. Anthropogenic forcing Impacts Risk for Terrestria and Freshwater Species Risk for Marine Species Risk for Coastal Communties Food production https://tntcat.iiasa.ac.at/RcpDb/dsd?Action=htmlpage&page=compare https://psl.noaa.gov/ipcc/cmip6/ SPM-1: Observed Changes and Their Causes Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history. Recent climate changes have had widespread impacts on human and natural systems. *SPM: Summary for policy makers SPM-1.1: Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen. SPM-1.2: Anthropogenic greenhouse gas emissions have increased since the pre-industrial era, driven largely by economic and population growth, and are now higher than ever. This has led to atmospheric concentrations of carbon dioxide, methane and nitrous oxide that are unprecedented in at least the last 800,000 years. Their effects, together with those of other anthropogenic drivers, have been detected throughout the climate system and are extremely likely to have been the dominant cause of the observed warming since the mid- 20th century. SPM-1.3: In recent decades, changes in climate have caused impacts on natural and human systems on all continents and across the oceans. Impacts are due to observed climate change, irrespective of its cause, indicating the sensitivity of natural and human systems to changing climate. SPM-1.4: Changes in many extreme weather and climate events have been observed since about 1950. Some of these changes have been linked to human influences, including a decrease in cold temperature extremes, an increase in warm temperature extremes, an increase in extreme high sea levels and an increase in the number of heavy precipitation events in a number of regions. SPM-2: Future Climate Changes, Risks and Impacts Continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems. Limiting climate change would require substantial and sustained reductions in greenhouse gas emissions which, together with adaptation, can limit climate change risks. SPM-2.1: Cumulative emissions of CO2 largely determine global mean surface warming by the late 21st century and beyond. Projections of greenhouse gas emissions vary over a wide range, depending on both socio-economic development and climate policy. SPM-2.2: Surface temperature is projected to rise over the 21st century under all assessed emission scenarios. It is very likely that heat waves will occur more often and last longer, and that extreme precipitation events will become more intense and frequent in many regions. The ocean will continue to warm and acidify, and global mean sea level to rise. SPM-2.3: Climate change will amplify existing risks and create new risks for natural and human sys-tems. Risks are unevenly distributed and are generally greater for disadvantaged people and communities in countries at all levels of development. SPM-2.4: Many aspects of climate change and associated impacts will continue for centuries, even if anthropogenic emissions of greenhouse gases are stopped. The risks of abrupt or irreversible changes increase as the magnitude of the warming increases. SPM-3: Future Pathways for Adaptation, Mitigation and Sustainable Development Adaptation and mitigation are complementary strategies for reducing and managing the risks of climate change. Substantial emissions reductions over the next few decades can reduce climate risks in the 21st century and beyond, increase prospects for effective adaptation, reduce the costs and challenges of mitigation in the longer term and contribute to climate-resilient pathways for sustainable development. SPM-3.1: Effective decision-making to limit climate change and its effects can be informed by a wide range of analytical approaches for evaluating expected risks and benefits, recognizing the importance of governance, ethical dimensions, equity, value judgments, economic assessments and diverse perceptions and responses to risk and uncertainty. SPM-3.2: Without additional mitigation efforts beyond those in place today, and even with adaptation, warming by the end of the 21st century will lead to high to very high risk of severe, wide-spread and irreversible impacts globally (high confidence). Mitigation involves some level of co-benefits and of risks due to adverse side effects, but these risks do not involve the same possibility of severe, widespread and irreversible impacts as risks from climate change, increasing the benefits from near-term mitigation efforts. SPM-3.3: Adaptation can reduce the risks of climate change impacts, but there are limits to its effectiveness, especially with greater magnitudes and rates of climate change. Taking a longer-term perspective, in the context of sustainable development, increases the likelihood that more immediate adaptation actions will also enhance future options and preparedness. SPM-3.4: There are multiple mitigation pathways that are likely to limit warming to below 2°C relative to pre-industrial levels. These pathways would require substantial emissions reductions over the next few decades and near zero emissions of CO2 and other long-lived greenhouse gases by the end of the century. Implementing such reductions poses substantial technological, economic, social and institutional challenges, which increase with delays in additional mitigation and if key technologies are not available. Limiting warming to lower or higher levels involves similar challenges but on different timescales. SPM-4: Adaptation and Mitigation Many adaptation and mitigation options can help address climate change, but no single option is sufficient by itself. Effective implementation depends on policies and cooperation at all scales and can be enhanced through integrated responses that link adaptation and mitigation with other societal objectives. SPM-4.1: Adaptation and mitigation responses are underpinned by common enabling factors. These include effective institutions and governance, innovation and investments in environmentally sound technologies and infrastructure, sustainable livelihoods and behavioral and lifestyle choices. SPM-4.2: Adaptation options exist in all sectors, but their context for implementation and potential to reduce climate-related risks differs across sectors and regions. Some adaptation responses involve significant co-benefits, synergies and trade-offs. Increasing climate change will increase challenges for many adaptation options. SPM-4.3: Mitigation options are available in every major sector. Mitigation can be more cost-effective if using an integrated approach that combines measures to reduce energy use and the green-house gas intensity of end-use sectors, decarbonize energy supply, reduce net emissions and enhance carbon sinks in land-based sectors. SPM-4.4: Effective adaptation and mitigation responses will depend on policies and measures across multiple scales: international, regional, national and sub-national. Policies across all scales supporting technology development, diffusion and transfer, as well as finance for responses to climate change, can complement and enhance the effectiveness of policies that directly promote adaptation and mitigation. SPM-4.5: Climate change is a threat to sustainable development. Nonetheless, there are many opportunities to link mitigation, adaptation and the pursuit of other societal objectives through integrated responses (high confidence). Successful implementation relies on relevant tools, suitable governance structures and enhanced capacity to respond (medium confidence). Why 2 degrees Paris Climate Agreement Yes, our climate has always changed due to natural variability associated with planet's orbital changes (Milankovitch cycles), solar activity, volcanic eruptions, mountain-building and more. There is ongoing climate discussion on the level of climate sensitivity (recall climate sensitivity is the amount of warming as a function of changes to various parameters, e.g., greenhouse gas concentrations). Beyond 2 oC, scientific studies suggest that we "lock the climate" into a state of continuing loss of warm season arctic sea ice, sea level rise, amplified wildfire activity, shifts in agricultural yields, and greater stress on water supply. For many, it is seen as a tipping point.  https://www.forbes.com/sites/marshallshepherd/2015/12/13/the- paris-climate-agreement-why-2-degrees-c/?sh=398ab77541f0 https://www.carbonbrief.org/in-depth-qa-the-ipccs-sixth- assessment-report-on-climate-science  Plastics Dr. Christopher Sabine Professor of Oceanography UH Mānoa Vice Provost for Research and Scholarship  Question Does plastic recycling work? Should plastics be banned? How about single use plastics only? Is it possible to live today without plastic?  Plastic has Changed our Lives Making life safer: Plastics are used in safety equipment like bicycle helmets, child safety seats, and automotive airbags. Making food safer and fresher: Plastic packaging helps keep food and drinks safe and extends their shelf life. Making transportation more efficient: Lightweight plastic auto parts improve gas mileage and reduce greenhouse gas emissions. Making homes more energy efficient: Plastic insulation and sealants help reduce heating and cooling costs. Making medical advancements: Disposable medical gear has reduced the spread of diseases and greatly benefited modern medicine. Making products more affordable: Inexpensive plastics have raised the standard of living.  Plastics have Saved Lives From gloves and syringes to heart valves and blood bags, plastics have completely revolutionized the healthcare industry. Plastics have played an important part in transforming the healthcare industry. Single use plastics were essential for slowing the spread of Covid-19, including plastic gloves, face masks, covid testing kits, etc.  Have Plastics Helped or Harmed the Poor and Disadvantaged Benefits Plastics can be a low-cost, portable way for communities to access basic goods and resources. They can also help preserve food and provide access to clean drinking water and medicine. Plastics also make medical care much more affordable. However: Low-income communities often rely on single-use plastics, such as water bottles and shampoo sachets, which contribute to the global environmental crisis. Developing countries often lack plastic recycling programs and infrastructure, which leads to a lot of single-use plastic ending up in the environment. The health burdens of plastic are often not considered in cost-benefit analyses, which can lead to a disconnect between who benefits and who is burdened. Plastic pollution is a social justice issue that disproportionately impacts the poor, vulnerable, and children.  plastic has become an industry worth $712 billion a year Humans have produced more than 11 billion metric tons of virgin plastic since 1950 only 2 billion metric tons are still in use today 2017 Story in the India Times India generates 10.2 million tons per year of plastic waste, defined as that which ends up in the open environment rather than landfills. This is equivalent to nearly 20 percent of the global output. Macroplastic emissions into the environment (debris and open burned) in kg cap−1 year−1 for the year 2020 Worldwide plastic waste totals more than 57 million tons a year, with India creating more than any other country. Nigeria generates the second most plastic pollution of any country, but the amount, 3.9 million tons, is less than half that of India. Cottom et al.,Nature, 2024  Plastics Come From Oil In March 2023, a team of European scientists published a database of more than 16,000 chemicals found in plastics, only a quarter of which have been tested for health impacts.  Projections of global plastic production, waste generation and plastic stocks in use, by sector Plastics show the strongest production growth of all bulk materials and are already responsible for 4.5% of global greenhouse gas emissions. A doubling of global plastic demand by 2050 and more than a tripling by 2100 is predicted, with an almost equivalent increase in CO2 emissions. Stegmann et al, Nature, 2022 *Bottled water can cost up to 10,000 times more per gallon than tap water. Plastic Waste Doesn’t just Pollute the Land 4.8 – 12.7 million metric tonnes of plastic annually Nature Communications: 667 (2018) From land… …to the ocean  What is Marine Debris? Marine debris is “any persistent solid material that is manufactured or processed and directly or indirectly, intentionally or unintentionally, disposed of or abandoned into the marine environment or the Great Lakes.” Ala Wai Canal, HI 2011  Additional Information on the Model Model description and Dynamic display of summary of results monthly releases https://www.coaps.fsu.edu/our- expertise/global-model-for-marine- http://marinelitter.coaps. litter fsu.edu/  “Garbage Patches” The Great Pacific Garbage Patch is estimated to have 79,000 metric tonnes within 1.6 million km2 Nature Scientific Report 8 (2018)  An Interesting Case Study Time Magazine: https://time.com/6991350/plastic-microplastics-fiji-water-recycling/ Time Magazine: https://time.com/6991350/plastic-microplastics-fiji-water-recycling/ Fiji Water employs about 800 Fijians to produce half a billion of its iconic square plastic bottles every year. 300 suppliers employ hundreds more Fijians.  Top 10 items removed by weight >18 million pounds of trash picked up from beaches in one day 3rd Saturday of September each year. Sustainablecoastlineshawaii.org; 808cleanups.org Links Between Plastic Pollution and Climate Change Globally only 15% of plastics are recovered, with just 9% of it actually being recycled Recycling is an energy-intensive process that becomes more costly as additional steps such as post-consumer selection and washing are added. The new plastic is still relatively cheap to produce and creates a competitive environment in which added costs to the process make recycled plastic significantly more expensive.  The “Accelerating a Circular Economy for Plastics and Recycling Innovation Act of 2024” is the first comprehensive bipartisan effort by Congress in years to tackle plastics pollution in the United States. Tasking the EPA to establish national plastic recycling standards across the United States to increase the national recycling rate. Requiring a minimum recycled content mandate for plastic packaging of 30 percent by 2030. The current U.S. recycling rate for plastic packaging is around 13% Assigning the National Academy of Sciences to conduct a lifecycle study comparing the carbon impact and greenhouse gas emissions from comparable product materials that will guide informed policy. Establishing a legal framework for new recycling technologies to support continued investment and innovation.