GEL 10 Fall 2024 Climate Change Notes PDF

GEL 10: Fall 2024 Notes for Oct. 2 — 4 Part 2 (of 2) THE FUTURE COST OF GLOBAL WARMING How Hot is Hot in your life span? The answer to this question depends on the rate of atmospheric CO2 increase to the atmosphere — and that depe...

GEL 10: Fall 2024 Notes for Oct. 2 — 4 Part 2 (of 2) THE FUTURE COST OF GLOBAL WARMING How Hot is Hot in your life span? The answer to this question depends on the rate of atmospheric CO2 increase to the atmosphere — and that depends on future trends in the global use of fossil fuels and how quickly we decarbonize the economy. o Decarbonize means to: (1) put less CO2 into the atmosphere by replacing fossil fuels with green energy (solar, wind, hydropower, nuclear), and (2) remove existing CO2 from the atmosphere by nature-based or engineering technologies. CO2 emissions to the atmosphere are projected to continue to increase at least for the next couple of decades and possibly through though this century — how much is the key question. Before 2015, the world was on the ‘business as usual’ (i.e., no change in use of fossil fuels) track (now referred to as the ‘regional rivalry—rocky road’ scenario due to the resurgence in nationalism by several countries including the US over recent years) ▪ For this scenario, CO2 concentrations in the atmosphere could reach 750 to >1000 ppm — levels last seen on Earth well before humans evolved. ▪ And the amount of total global warming by 2100 under the business-as-usual scenario is projected to be ~4°C ▪ Then in 2015, 196 parties (countries) signed the Paris international Agreement — a treaty committing the world to reduce greenhouse gas emissions (primarily CO2) to maintain the total level of warming due to fossil-fuel burning — since the onset of the pre-industrial time — to ≤ 1.5°C. ▪ Why? Because the Paris Agreement recognized that a large body of scientific research indicates that, to avoid major climate change consequences, the total rise in global temperatures must be ≤1.5°C At this time (2024), it is doubtful that global warming can be kept below 2°C. Under current policies that aim to reach peak CO2 emissions by 2050 or 2075, the world is headed for ~ 2.4 to 2.7°C of total warming by late this century. What is needed?: To commit to and reach carbon (C) neutrality (net zero emissions) by 2045 to 2050. Doing so will permit the atmospheric CO2 levels to begin dropping. ▪ CA has committed to this, by law. IS THE WEATHER GETTING WORSE? ANSWER: A RESOUNDING ‘YES’ Some weather extremes are now 2 to 3 times more likely to happen than pre-2000 because of global warming Many of these events have no historical comparison for over 200 years. 1 GEL 10: Fall 2024 Notes for Oct. 2 — 4 Extreme Heat Conditions: Rising temps create circumstances for more frequent intense heat waves, which in turn fuel intense droughts, extreme precipitation events, and wildfires fires. Heat waves of summers 2022 through 2024 broke all-time records around the world. Places that are wet will get very wet & places that are drier will get drought: Why? Because, generally, a warmer atmosphere holds more water — increased evaporation of the oceans and increased water vapor in the atmosphere. Water cycling through the atmosphere intensifies as global temperatures rise. And the circulation patterns of the atmosphere are shifted with warming. Places that are ‘wet’ or highly seasonal (e.g., CA), are seeing not only ‘wetter’ wet times but also more ‘extreme precipitation events’. These are shorter, more intense periods of rain (and often, winds) that often lead to flooding. o Global warming is also increasing the number of severe tropical storms — they have tripled in last 30 years — including higher intensity hurricanes (Category 3 to 5; wind speeds well over 100 to 150 miles/hr) o This increasing intensity of extreme precipitation events and tropical storms will continue. o Why? Warmer air holds more moisture & has more stored energy — so tropical storms will become increasingly ‘wetter’, windier, and travel over land for longer distances. o And the oceans have absorbed 91% of the excess heat added to the climate system due to fossil-fuel burning. When surface ocean temperatures rise it fuels hurricanes, rapidly intensifying them, and keeping the storms energized so that they can travel further distance over land. And storms also move more slowly thus their impact in a given locatoin can be greater. Drought-prone (drier) regions — such as the western US, including CA — get drier — there will be more frequent and possibly longer durations of drought (called megadroughts). But what about all of the recent winter rains (Jan-March) 2023/2024) & the early rains fall 2023 (a hint of this in 2024 so far) — have they not ended the drought? Answer: Unlikely. The American West, including CA, has been in a minimally 22-year long drought — the longest lived and most intense drought of the past 1200 years occurred in 2022. o Recent wet winter & early fall rains may just be a perturbation superimposed on a continuing megadrought — time will tell if that is the case. Why does drought happen with global warming? (1) Because increased surface temperatures mean more evaporation of water from soils and other sources of water. (2) And because global warming changes atmospheric air circulation patterns — changing our normal rainfall patterns. o We’ll learn more about this in the Atmospheric Circulation lectures 2 GEL 10: Fall 2024 Notes for Oct. 2 — 4 Globally, if average temperatures increase by 3 to 4°C then 50% of all land on Earth will see major drought. What’s to come for CA? Weather Whiplash For CA our rainy season will be shorter with more rain coming in fewer months than previously. Years of very wet but short rainy seasons will be interspersed with interludes of drought — what climate scientists call ‘whiplash climate’. And warmer winters and warmer storms mean large declines in snowpack in western US o By 2100 C.E. there could be half to a quarter of the snowpack of recent years in the Sierra Nevada o There are already signs of this change: in 2015, the Sierra’s spring snowpack was the lowest in 500 years; in year (2020-21 it was ~67% of normal. ▪ Things look much better this past winter (2024). Climate Change knows no political or justice boundaries Drought does not follow international political boundaries — problems affecting our geographic neighbors also affect us. Estimates are that ~3 billion people will have to move from highly vulnerable locations — for 2°C of total warming, perhaps as many as 10s to 100s of millions per year. And it does not recognize societal inequities — for example: o Consider the months-long heatwaves in India, Pakistan & Southeast Asia and that led to historic rainfall and flooding (2022, 2023 & 2024), which has been show to be made 50% worse by climate change. o But these countries have contributed to the atmosphere — in all of their industrial history — only as much C as the US does per year — but they suffered some of the worst climate change impacts. Increased frequency & intensity of wildfires more extreme fire weather: o Over the past 2 decades, CA has experienced larger, more destructive and deadlier fires than in all of recorded history. o Acres burned per year, the intensity (temperatures) and the severity (how much damage) of fires has increased 5-fold o Over half of the largest wildfires in historical records for CA have happened in the past 5 years (drought years of 2020-2022). Why? What role does climate change play these wildfires? 3 GEL 10: Fall 2024 Notes for Oct. 2 — 4 o Answer: Some but not all; in part due to CA’s century-long policy of total fire suppression (i.e., extinguish every fire). o But increasingly these fires are due to extreme ‘fire weather conditions` — in large part due to climate change. Hotter summers overall with exceptionally hot heat dome events; more months of the year that are warmer than normal & the atmosphere is increasingly ‘thirstier’ for moisture leading to greater evaporation of soil and surface water sources. Record-breaking heat waves come with a lot of dry lightning (i.e. drier warmer storms that have lightning but no rain). CA is a Mediterranean climate with strong seasonal climate (dry summers & wet winters). The onset of the ‘fire season-ending rain’ that typically come by late Oct. has been delayed by 1 to 2 months for many years of the past couple of decades. Drying of soils and vegetation by evaporative wicking– creating lots of fire fuel And for those winters that experience intense precipitation events — growth of lots of underbrush and grasslands — these are the fuel for forest the next time the hot, dry weather comes. Windier conditions due to a warmer atmosphere Aging electrical grid infrastructure that provides ‘fire starters’..... and other human activities. o The sum result is (1) a doubling of risk of extreme fire weather conditions over the past couple of decades (which double again by 2050) and (2) a longer and more intense fire season for many recent (and future) years. o A big part of the answer is prescribed burns using Indigenous traditional practices. CHANGE IN THE OCEANS o Oceans cover > 70% of the Earth’s surface. Today, oceans are the hottest they have been in recorded history & it is due to human-created climate change. o Ocean has absorbed 91% of the excess heat that has been trapped in the atmosphere due to burning of fossil fuels (and secondarily agricultural practices and cement production). o Why? Because it has a higher heat capacity than land — they have absorbed large amounts of heat energy for decades with only a slight increase in temperature – but after decades of cumulative heat, the oceans are starting to show more rapid warming. o Food for thought: the oceans have delayed global warming impacts on humans considerably — up to 50% — but it comes with a cost. o A warming ocean negatively impacts marine ecosystems o And it leads to slowing ocean circulation — a major problem because: 4 GEL 10: Fall 2024 Notes for Oct. 2 — 4 o Ocean-atmosphere system controls the world’s climate o Ocean circulation provides the pump that transfers heat from warm tropics to cooler higher latitudes in both hemispheres — allows humans to live on land around the globe — rather than in a narrow belt in the mid-latitudes. A warming ocean has led to marine heat waves (doubled over last 50 years) — these are areas of extreme warm sea surface temperatures (SST) that persist for days to months: o They are created by a warmer than usual surface ocean and/or atmosphere (and the high air pressure cells above the warm ocean & weaker winds as a consequence) — due to global warming. o Marine heat waves decrease oxygen levels in the waters because warmer water holds less gas content (the oceans have already lost 2% of their oxygen and some tropical regions have oxygen levels down by 40%) o Warmer waters circulate less well so new oxygen cannot easily replenish waters that are oxygen-poor o Marine heat waves impact ecosystems, food webs, and fish stocks. For example, corals expel their algae symbionts when the waters are too hot – this causes coral bleaching. o Bacteria that are pathogens are proliferating in warmer waters, affecting people who eat the fish – far from the coast. Marine heat waves are expected to become 10s of times more frequent over the next few decades if global warming continues to increase. And some to much of the stored heat in the ocean will eventually return to the atmosphere warming the atmosphere further. AND WHAT ABOUT THE FATE OF FROZEN WATER & GLOBAL SEA LEVEL? o Mountain & polar glaciers will continue to melt for decades or centuries to come o The world’s glaciers have been retreating since the 1950s — unprecedented in past 2000 years. o Arctic temperatures have increased at 4 times the rate of the rest of the planet o Diminishing Arctic sea ice – melting at 10 to 15%/decade since early 1980s o Winter sea ice thickness is down by ~ 25% & the 12 lowest sea ice levels on record have been in the last 12 years. o The Arctic could be seasonally (summer) ice-free by 2035 or 2050 o Siberian Arctic — 5°C warmer (in some places up to 10°C) in recent years than the average of the past 40 years. These heat waves were at least 600 times more likely in response to human-created global warming than due to natural climate processes. 5 GEL 10: Fall 2024 Notes for Oct. 2 — 4 o This anomalous heat has caused increased loss of summer sea ice & encouraged widespread wildfires across the region that is normally frozen through most of the year. o And in turn, permafrost — which holds vast amounts of frozen methane (CH4) ice — is melting — releasing more greenhouse gases into the atmosphere. o The loss of permafrost carbon is irreversible for centuries. o Polar Ice Sheets: o Melting of Greenland ice sheet contributed to 21% of sea-level rise so far. o Some project that the temperature threshold for Greenland ice sheet to cross over to when its loss is inevitable is ~1.6°C above pre-industrial o when fully collapsed = 20 ft (6 m) of sea-level rise o Antarctic ice sheet has shrunk less in the last 2 decades — loss of ice mostly from Antarctic Peninsula and West Antarctica. o Could contribute to another ~ 6m of sea-level rise o And in response, sea level is rising. o Rates of sea level rise have tripled over the past century (faster than any time over the past 3000 years) & led to overall higher sea level by ~0.2 meters (8 inches) — due to ice melting as well expansion of seawater with warming. o Sea level will continue to rise by 0.3 to over a meter by 2100 depending on which trend of CO2 emission to the atmosphere we follow — and up to several meters by 2150. All coastal cities in the U.S., Asia, and Europe are under water at those levels. o With increasing sea level, there is an increase in high tide flooding events — in particular during major storms (storm surge). o In California, sea-level rise could lead to widespread flooding THE 6TH LARGEST EXTINCTION IN EARTH HISTORY We are currently living in the sixth major extinction event in Earth history & the greatest since the dinosaurs disappeared, 66,000,000 years ago. Up to 1 million plant and animal species are at risk of extinction Climate change is a major player in this extinction — altering habitats, ecosystem health, pushing the spread of invasive species, & changing how species interact with each other in their environment = reconfiguring ecosystems in an unprecedented way. Consider this: Humans have the distinction of being the only species on this planet to be individually responsible for a global extinction crisis. 6 GEL 10: Fall 2024 Notes for Oct. 2 — 4 Extinctions occur when climate change outpaces the capacity of species to adapt: Current rate of extinctions is 1000 times faster than past extinction rates 2°C of warming over pre-Industrial temperatures could double or triple the species extinction rates (Note: consider that in the context of what the anticipated amount of total global warming is (2.4 to 2.7°C). Study of past extinctions recorded in the ‘geologic record’ show us that new ecosystem communities that repopulate an area are of much reduced diversity Low-diversity ecosystems are in turn more vulnerable to further climate change Traditional natural resource management strategies are increasingly challenged by the impacts of climate change. Need policy and approaches that incorporate climate knowledge so as to reduce impacts, promote resilience, and increase the productivity/resources of these ecosystems. What can the past teach us regarding our future? The climate system may be approaching a threshold where climate change accelerates and can intensify quickly (in years or decades) even if the cause driving it doesn’t change. There are thresholds for everything in the climate system — e.g., sea ice and continental ice sheet stability, for storminess, for the viability of forests. The geologic record of past climate change (paleoclimate) tells us: climate change happens abruptly (in a decade or less) and can change in its rate of change because of feedbacks. it takes 1000s to 10s of thousands of years for natural processes on Earth to ‘sweep’ the atmosphere of residual greenhouse gases and for conditions to recover to pre-climate change conditions. So how we alter Earth’s atmosphere and its climate for generations to come will likely depend on the scientific and political decisions made in the next decade or two.... and the climate system often recovers to conditions that differ from those prior to the threshold. In the next lecture topic, we will look at systems (including the Earth System), what defines their conditions when they are stable or unstable, how feedbacks in the system behave and affect the rate and severity of climate change, the role that feedbacks play in helping the Earth recover from major climate change, and thresholds in the climate system. 7 GEL 10: Fall 2024 Notes for Oct. 2 — 4 And I remind you of something from Part 1 of this lecture set: IT IS NOT ALL DOOM & GLOOM? We are in a revolution – paradigm shift – future starting to look more promising with regard to global warming – due to global political awakening, an astonishing decline in price of clean energy, a rise in global policy ambition. It is true that big system changes in the use of fossil fuels at the government and company levels is more important than cutting individual carbon footprints. But appreciate that (1) there are many individuals whose daily life habits involve a lot of fossil- fuels and their individual changes can make a difference. (2) Individuals can play into a collective approach — convince others to take climate change seriously, changing what politicians and policies they support, actively post about global warming on social media, get involved in community action at the local level — it is at that level that most change will be happen. The world has made genuine progress in slowing climate change in recent years. In much of the world, solar and wind power are now cheaper than coal and gas. The cost of batteries has plummeted over the past few decades, making electric vehicles much more accessible. Governments and businesses are pouring hundreds of billions of dollars into clean energy. Inflation Reduction Act for example — could push warming down even more than previously estimated for the coming decades. 8