GEOL 1060

Laki, Iceland

-1783 AD -Giant eruption -12 km^3 -Vs. Mount St. Helens - 1 km^3

Aerosol Examples

-Acid droplets a. Sulfuric b. Hydrochloric -Very fine desert dust -Sea salt spray -Sulfate aerosols a. Combustion -Fertilizers a. Various nitrogen compounds -Soot a. Incomplete combusted carbon

Indirect Evidence

-Climate proxies: Something preserved that represents a particular aspect of climate -Proxy: Something that represents something else -Examples: a. Ice b. Fossils c. Pollen d. Tree-ring widths e. Sr/Ca in corals f. Isotopes g. Ice-rafted stones in mid-ocean sediment h. Hippos in England i. Polar bears in Oregon -Advantages: a. We can "see" climate farther into the past than the period covered by the instrumental record -Disadvantages: a. It is not a direct measurement b. We have to find a way to calibrate our proxy to temperature, which adds some additional uncertainty -If the planet is everywhere warming, glaciers everywhere should be getting smaller a. Yes, I would think so -Maybe they respond too slowly to see that yet -Glaciers are more sensitive to changes in snowfall, and maybe it is snowing more

Take Homes

-Ice cores: a. Never in 800,000 years has CO2 been as high as now b. Always the warmest times (interglacial) have high CO2 levels c. Coldest times are lowest CO2 levels d. The difference in CO2 between "glacial" (coldest) and "interglacial" (warmest) past times is ~100 units e. Increase in CO2 in past century is 120 units f. What is the equilibrium temperature for the modern CO2 levels? g. Independent measurements of CH4 -Pre-industrial CH4 level: ~700 ppb -Fall 2013 CH4 level: ~1800 ppb h. Increase of CH4 > CO2 i. Highs and lows of CO2 and CH4, independently measured, follow each other closely, and also follow temperature -CO2, CH4, CFCs, and NOxs a. Are much higher than at any time in the past 800,000 years b. Human enterprise has altered the trace gas content of the atmosphere and increased the greenhouse effect

Long-Term Changes in GHGs

-If we can recover continuous samples of the atmosphere trapped in an ice core, we may be able to reconstruct pass concentrations of GHGs in the atmosphere a. Be skeptical -How do we know those little air bubbles in the ice accurately record atmospheric CO2 concentrations? -Get a young ice core and compare it to an instrumental ice record b. To be convinced that tiny bubbles in ice accurately record the amount of CO2 at the time the surrounding snow fell, I would like to see: proof -Problem: It takes decades for snow to turn to ice that has trapped bubbles -Turn to ice cores in sites with the highest amount of annual snowfall -Ice cores preserve bubbles of trapped atmosphere from the time snow fell -Is there a link between CO2 and climate? a. Derive estimates of past temperatures from the isotopic ratios of hydrogen and oxygen in the ice of ice cores b. Compare CO2 levels with air temperatures from the exact same levels c. Reasonable correlation: d. When air temperatures are high, so are CO2 levels e. When air temperatures are low, so are the lowest CO2 levels

The Role of Sea Ice

-Important role in altering the salinity structure of surface water through brine rejection -Increase salinity of surrounding waters -Positive feedback of circulation of the ocean -On the large scale Thermohaline circulation

Explosive Volcanism

-Injects stuff into the stratosphere -Example: Pinatubo a. Shortly after Pinatubo erupted, climate modelers predicted how Earth's temperatures would change over the subsequent 5 years b. .5ºC c. Bold prediction because we would soon know if they were correct d. Impact was about 0.5ºC (1ºF) cooling across the entire planet for 3 years e. What do you think the climate models would predict would happen to Earth's temperature after a major explosive eruption? f. Troposphere would cool and the stratosphere would warm -Injects ash into the stratosphere, where gravity removes ash in weeks to moths a. No precipitation in the stratosphere -What do we know now about sulfate aerosols from explosive volcanism? a. Aerosols should be in the troposphere and stratosphere b. Short residence time in the troposphere, and longer in the stratosphere c. They are going to reflect and scatter the Sun's energy, and absorb Earth's -From the climate impacts of sulfate aerosols (shade and GHGs), and our estimates of residence times in the stratosphere and troposphere, what do you predict would be the climate impacts of a major explosive eruption injecting lots of sulfur gas into the troposphere and stratosphere on a. Temperature at Earth's surface: -Cools b. Temperature in the troposphere: -Cools c. Temperature in the stratosphere: -Warms -After a large explosive eruption injecting SO2 into the stratosphere and troposphere, Earth's surface would: a. Cool -After a large explosive eruption injecting SO2 into the stratosphere and troposphere, Earth's stratosphere would: a. Warm -After a large explosive eruption injecting SO2 into the stratosphere and troposphere, Earth's troposphere would: a. Cool b. Because Earth's surface is cooling, the troposphere has to cool

Origins of the Ocean

-Where did the water come from?... -Outgassing from the Earth's interior -i.e., Volcanoes -This is the same origin of the atmosphere -There have been oceans as far back as we can find rocks (~4 billion years) -There is still another ocean inside the Earth -Where did all the salt come from?... -The ocean has always been salty -Most of the "salt" delivered by rivers is sodium (Na), with very little chlorine (Cl) -New salt is added to the ocean from mid-ocean spreading

Sea Life and Circulation

-Why is primary productivity important? a. Where we catch all of those tasty fish we like to eat... b. Exerts strong control on the global carbon cycle c. Primary production removes CO2 from the atmosphere and sends it to the deep ocean

Climate Forcing

-Any mechanism that influences the amount of energy received or retained by the climate system, often expressed as a Radiative forcing in W/m2 a. We can compare all possible climate forcings by reducing their impacts to "Radiative forcing" b. Radiative forcing is loosely defined as the change in net irradiance at the Tropopause c. What must happen if the received solar radiation (or the Radiative forcing) at the top of the Tropopause steadily increases? d. Earth's temperature must adjust until the emitted radiation balances the increased received radiation e. What must happen if the Radiative forcing is continuously changing? f. The Earth system will seek, but not necessarily achieve, equilibrium or Radiative balance gThis is the current situation: Radiative forcing is continuously changing and the Earth system is moving toward a new equilibrium, but is still adjusting

Vegetation Change

-As the planet warms, boreal forests (evergreen trees) will expand northward, replacing the tundra. What might we predict would be a climate consequence of this change? a. Positive feedback due to vegetation change b. Albedo difference in the spring -Conversion of tundra (white in winter) to boreal forest (dark green in winter) with northward forest migration in warmer climate changes the energy balance of the northern regions, resulting in greater solar radiation absorbed in spring a. "Greening of the Arctic"

Water Vapor Change

-As the planet warms, from first principles, will there be a water vapor feedback and will it be positive or negative? a. Yes, positive feedback b. There will be a slow water vapor feedback c. Evaporation puts more water vapor into the atmosphere, which increases precipitation dWater vapor is a greenhouse gas -As the ocean surface water warms, the evaporation rate will increase (great flux of water from ocean to atmosphere), resulting in larger reservoir of water vapor in the atmosphere

Temperature Anomalies

-Because the absolute temperature varies greatly across the planet, the most effective way to monitor temperature change is to compare the various records as differences from their own averages -The magnitude of the departure of recent decades from the long-term average temperature -A departure from a reference value or a long-term average -A positive anomaly indicates that the observed temperature was warmer -A negative anomaly indicates that the observed temperature was cooler -First-order trend: a. 1900-2012 b~1.6 ºF -Second-order trend: a. Warming has structure b. We need to explain the warming trend c. But, you should always be skeptical -What are the assumptions over the warming in the past century? -What are some possible problems with direct measurements? a. Density of recording sights b. Natural climate cycles (fluctuations) c. Faulty thermometers (equipment) d. Seasonal contrasts e. Developing countries have shorter records f. Oceans cover 70% of Earth g. Heat Island Effect h. Spotty/moderate coverage -The temperature record of the past 100 or so years may be flawed because: a. Most of the Earth is ocean where there are no thermometers b. Towns are hotter, and most thermometers are in towns c. Not all countries have long thermometer records -Heat Island Effect: Which answer does not help explain why cities are hotter than their surroundings? a. Latent heat is released more often over cities b. Explanation of the Heat Island Effect: -Cities have lower albedos -Inversions in the lower atmosphere -Heat generated by cities can be trapped there -Not uncommon for cities to be 3 ºC (6 ºF) warmer than surroundings -Most stations are now outside of the city -Inequalities of warming: a. Land has warmed more than oceans -Is the land is warming more than the ocean because it has a lower albedo? a. No, the ocean has a lower albedo -The land has warmed more than the oceans because of conduction a. Land can only transfer energy by conduction b. Ocean transfers energy by convection c. Cooling by evaporation d. Higher heat capacity e. Even though the ocean absorbs more of the Sun than the land, the land still warms more than the ocean -The heat capacity of water is greater than land, and the ocean's mixed layer distributes heat over a much greater mass (convection) than conduction on land -The heat storage of the ocean is greater than for the land, and will eventually warm the entire ocean, but very slowly -Northern Hemisphere exceeds the Southern Hemisphere in warming a. North Hemisphere has much more land than the Southern Hemisphere b. Latent inequality -The Arctic has warmed the most a. The Arctic is warming more than anywhere else on the planet. This must be because it has strong positive feedbacks b. Warming is greatest in the Arctic despite less land there -Mostly due to sea ice loss and albedo feedbacks

Antarctic Sea Ice

-Because the planet warming, is sea ice around Antarctica also getting smaller? a. Antarctic sea ice extent is increasing b. Very slight increase on average -Sea ice is increasing around Antarctica when the planet is warming because of the Southern Hemisphere a. The Southern Hemisphere has a continent at the pole surrounded everywhere by ocean b. Strong polar vortex c. Isolates Antarctic by keeping warm, tropical air out d. Driven by the magnitude of the temperature gradient between the pole-equator e. As the planet warms, pole-equator temperature gradient decreases, vortex weakens, allowing ice to expand

Other GHGs

-CFCs (chloro-fluoro-carbons) a. They are benign to humans b. CFCs used to be used in refrigerators, AC units, etc. c. Because they are so benign, they don't interact d. Nothing in the atmosphere could get rid of them e. But they are GHGs f. Ozone killer -NOx a. Combinations of nitrogen and oxygen in various proportions b. Relatively small players

Greenhouse Gases

-Carbon dioxide has been increasing in the troposphere for at least the past 50 years. This is a... a. Fact -Why might we be concerned that carbon dioxide is increasing in the atmosphere? a. CO2 is a greenhouse gas -Greenhouse gases are transparent to solar radiation and absorb Earth's radiation a. Strong influence on planetary temperature -There has been concern about increasing CO2 in the troposphere since the 1800s -In 1896, Swedish chemist calculated that doubling CO2 in the atmosphere would raise the Earth's temperature 5-6 ºC a. Did not see this as a problem b. He figured that if industry continued to burn fuel at the 1896 rate, it would take 3,000 years for the CO2 level to double c. Now we except the atmospheric CO2 to double by 2050 -50 year record of CO2 (100 year residence time) shows: a. Steady increase from 315 to 400 ppmv b. Biosphere annual impacts on C-cycle -Trapped atm in ice cores tell us current CO2 levels unprecedented in >800,000 years -Only 1/3 of anthropogenic CO2 added each year remains in the atmosphere; oceans and vegetation are transient -Methane (10 year residence time) is a less important GHG; currently 2 times pre-industrial; increasing slowly, irregularly -GHGs increasing steadily since 1900 AD, but planetary temperature does not rise steadily -Consequently, GHGs alone cannot explain all the observed 20th century warming -1st order trend: a. Regular increase b. Rate of increase is itself increasing -What is the main reason that the concentration of CO2 in the atmosphere is increasing? a. Fossil fuel combustion -2000 AD = 368 ppm a. Mauna Loa, Hawaii -Wiggle = 8 ppm b. Niwot Ridge, Colorado c. Point Barrow, Alaska -Wiggle = 17 ppm d. American Samoa, Tropical Pacific e. South Pole / Tasmania, Australia = 366 ppm -The wiggles that are the second order CO2 trend must be related to... a. The annual cycle of plant grown and decay -2nd order trend: a. Biosphere breathing b. Primary productivity (plant photosynthesis) consuming CO2 during the summer months, and decomposing (oxidizing), releasing stored carbon as CO2 in the winter months c. Largest variation is where season contrasts are largest (high latitudes) and a large terrestrial biosphere (Northern Hemisphere) -Based on what we have seen, I expect the amplitude of the yearly cycle at Tutuila, American Samoa, Tropical Pacific, to be __________ than/as Hawaii a. Smaller -Based on what we have seen, we can explain the low amplitude of the yearly cycle at American Samoa to be a result of... a. Low seasonality at American Samoa b. Not much biosphere around American Samoa c. Year-round sunlight and warmth at American Samoa -Despite very large differences in the season amplitude of the CO2 levels, all our Northern Hemisphere sites had 368 ppmv, CO2 in the year 2000 AD. From this, we can conclude that... a. The Northern Hemisphere troposphere is very well mixed b. Southern Hemisphere? -Based on what we have seen, I expect the amplitude of the yearly cycle at the South Pole to be ___________ than as Hawaii because ____________? a. Smaller, because so little vegetation on Antarctica -Based on what we have seen, I expect the magnitude of the yearly cycle at the South Pole to be ___________ than as Hawaii a. Smaller -The South Pole has slightly less CO2 than any of the Northern Hemisphere sites. This suggests that... a. It takes a couple of years for CO2 to mix between the Northern and Southern Hemisphere -The entire Southern Hemisphere is well mixed, and primary productivity of the terrestrial biosphere must be much larger than the ocean biosphere a. Southern Hemisphere amplitude is smaller and opposite phase relative to Northern Hemisphere -3rd order trend: -Looks at a lot like ENSO, volcanism, and chaos a. Natural variability -Take homes from instrumental record (1957-2013): a. CO2 steadily increasing b. Troposphere is very well mixed -NH vs. SH -Weeks within; 1-2 year between c. Biosphere explains 2nd order trend wiggles d. Terrestrial NPP much bigger than ocean NPP e. Global Carbon Cycle -Active C-cycle -Explain steady climb in CO2? -Biggest reservoir of carbon is in carbonate rocks (40 m) -System is not in equilibrium -Visible changes -Atmosphere is gaining carbon -Source: Extra amount of carbon we are putting in the atmosphere from fossil fuel combustion -Sink: Biosphere and ocean are each extracting and storing 2 of these -Ocean is by far the largest active carbon reservoir -Increasing CO2 due mostly to fossil fuel combustion + some deforestation (burning) -2/3 fossil fuel CO2 emitted by fossil fuel combustion is taken up by ocean and vegetation, but these are a finite carbon sink -CO2 residence time in atmosphere is 100 years

Vertical Circulation

-Circulation is controlled by differences in density -Cold, salty water is denser (it sinks all the way to the bottom of the ocean) a. Sinking -> vertical circulation in the ocean -Thermohaline circulation: The North Atlantic a. Density driven circulation b. For surface water to sink, it needs to be denser than the water underneath it -Requires: cold, salty c. North Atlantic is especially salty -In the winter, that salty water cools -Becomes denser than underlying waters and therefore sinks d. 1,000-3,000 years to complete circulation e. North Atlantic Deep Water is very salty whereas Antarctic Bottom Water is not as salty -Because AABW is underneath NADW, we know for certain: AABW must be much colder than NADW f. Deep water forms in the northern North Atlantic and around Antarctica. Why does it now also form in the northern North Pacific? The surface waters there may be too fresh g. WHy is the North Pacific surface water so much fresher than North Atlantic surface water? Maybe it rains a lot more in the North Pacific / Maybe the surface current there is less salty h. What does the warm temperature at 1,000 m depth tell us about the salinity of Mediterranean Sea Outflow water? High salinity

Terms

-Climate forcing: a. Any mechanism that influences the amount of energy received or retained by the climate system b. Often expressed as a radiative forcing in W/m2 -Climate response: a. The response of the climate system to a particular forcing (or forcings), where the response may include climate feedback processes b. Direct response + positive/negative feedbacks c. Example: The climate response to CO2 forcing is dominated by water vapor feedback -Climate sensitivity: a. The ratio of response to forcing at equilibrium b. Often expressed as temperature change per W/m2 -Or, per "CO2 doubling"

Explaining the Mid-Century Dip

-Rapid industrialization during WWII (and post-war) with little regulation a. Led to a large aerosol release -Direct and indirect effects of aerosols counteracted increased GHG forcing a. Direct: Shading b. Indirect: Change in cloud coverage -Increasing regulation and cleaner burning fuels reduced aerosols and ironically led to increased warming -Natural variability probably played a role before and after this cooling interval a. GHG emissions currently dominate all other variables

Aerosols

-Composed of matter (not gases) a. Solid or liquid b. Tiny airborne particles of matter, either liquid droplets or solids -They are so small that hey remain suspended in the atmosphere for a long time c. Long residence time d. Types: -Soot a. Unburnt carbon b. Smaller than a particle of clay e. Volcanoes emit large volumes of sulfur dioxide (SO2) gas -SO2 reacts really quickly with oxygen and water vapor in the atmosphere to form tiny droplets of sulfuric acid droplets -Gas → Aerosol -Sulfuric acid aerosols reflect and scatter incoming solar radiation, reducing the energy received at Earth's surface -Consequently, they cool the Earth's surface -First order climate impact -But, they are behaving like a greenhouse gas in the way that they can absorb the wavelengths of Earth's outgoing infrared radiation (but are not transparent to Sun's incoming energy) f. Sulfuric acid aerosols are so small that gravity has little effect on them. Thinking about what removes volcanic ash from the atmosphere, in which reservoir would volcanic aerosols have the longest residence time? -Stratosphere -Gravity is inefficient on aerosols -There is no rain in the stratosphere

Soot

-Derived from incomplete combustion a. i.e., Coal, diesel, outdoor biomass burning, etc. -Essentially tiny particles of black carbon -Most common where inefficient burning occurs -Currently, largest sources are in Asia -Unlike other aerosols, soot is not shiny a. Black color → Low albedo b. Absorbs Sun's energy (solar radiation) c. → Warm surrounding atmosphere d. Opaque, so it shades the ground below -Soot is predominantly located in the Troposphere -Soot cools Earth's surface, but warms the Troposphere a. Typically more regional phenomenon -If soot falls on snow/ice, it lowers albedo, enhancing melting -Blocking effect -Creates instability -Rising air and condensation nuclei increase precipitation -With increased soot in the Troposphere, is there any reason to expect higher rainfall as a result? a. Yes, because soot enhances precipitation

Methane

-Differences in magnitude between Barrow, Alaska, and Mauna Loa, Hawaii compared to CO2 -Although the amplitude of CO2 changes differed between Alaska and Hawaii, the average values were the same. Yet for CH4, the average values are different; therefore... a. CH4 must have a shorter residence time than CO2 -Methane's source: Dead plant remains a. Differing process from CO2 -Derived by the decomposition of organisms without oxygen a. Swamps b. Rice paddies c. Permafrost d. Digestion process of certain animals (i.e., cattle) -Although the CH4 must have a shorter residence time than CO2 -Knowing methane sources, and the Hawaii-Alaska pattern, what would you predict would be the difference in methane levels between South Pole and Hawaii? a. Lower at the South Pole b. Opposite seasonality -Some anthropogenic sources a.Gas flaring b. Gas supply c. Coal mining d. Biomass burning e. Landfills -Some natural sources a. Livestock b. Swamps/wetland areas -Has been increasing over the period of instrumental observation since 1983 a. 1600 - 1800 ppb b. Although the rate of increase has been decreasing, CH4 is currently twice the pre-industrial level -Methane has a strong season cycle

20th Century Warming

-Direct evidence: a. Measured temperatures -Spatial distribution biased and of unequal duration -Heat Island: Cities are hotter than their surroundings -Temperature changes from satellites a. Microwave emissions are measured b. Troposphere and surface temperature records are (now) similar -The global compilations of temperatures take the identified problems into account -There is some uncertainty in the early measurements, but the overall trend is quite reliable -Replication is a fundamental precept of science

Sun

-Earth's temperature is set by the Sun a. Temperature of the Sun b. Earth's distance from the Sun c. Earth's greenhouse effect d. Earth's albedo -The Sun has been getting bigger and more luminous since Earth formed, 4.6 billion years ago a. True -If the Sun is getting steadily brighter, could its increase over the past century explain some of the observed warming? a. No, century is too short

Types of Volcanism

-Explosive volcanism -Fluid volcanism

Indirect Evidence of the 20th Century

-Glaciers and ice sheets -With very few exceptions, glaciers are retreating everywhere a. Arctic b. High mountains of mid-latitudes c. Tropics d. Southern Hemisphere e. Greenland Ice Sheet f. Antarctica Ice Sheet -Sea level rise -Sea ice melting a. Loss of sea ice does not impact the sea level -Ice shelves disappearing a. Arctic Canada: losing ice shelves b. Antarctica: losing ice shelves c. How does loss of ice shelves impact sea level? Sea level will not change d. Only if land-supported ice is lost will there be any impact on sea level -Permafrost melting in the Arctic a. Permanently frozen ground (ground temperatures never rise above 0º C during the year) at Earth's surface b. Is there a lot of permafrost? Siberia, etc. c. Some on land, some under the sea d. How can there be permafrost under the ocean? The ground froze when the ocean level was lower e. Arctic warming has resulted in permafrost warming, and reduction in the area of permafrost f. What are some of the effects of permafrost melting? -There are vast reserves of stored carbon (plant debris) stored in frozen ground -As the ground melts, carbon is released -Carbon-compound: decomposition a. If oxygen is present -> CO2 b. If no oxygen is present -> CH4 -Melting glaciers reveal humans and human tolls

Explanation

-Greenhouse gases a. CO2 b. CH4 c. CFCs / NOx -Sun a. Solar variability -Volcanism -Aerosols -Particulates -Clouds -Chaos -Additional Feebacks

Global Warming: The Evidence

-Has Earth warmed, on average, over the past century? -If it has indeed warmed, is the magnitude of warmth more than we would expect from natural climate variability? -Over the past century, Earth has warmed significantly -How do we know? Thermometers -Direct evidence -Temperature stations are not equivalent across land and population -Location and length of temperature records

Attribution

-How do we decide attribution? a. Mechanism: -The variable that we think is the causation for the observed change must have an established physical mechanism that would produce that change b. Correlation: -Changes in the observation and the cause must have similar patterns of change -The observed magnitude of change must be consistent with magnitude of change in the proposed cause

Limitations of Direct Evidence

-How do we know the observed trend is not part of a longer cycle? a. Possible solutions: -Use ice cores in place of thermometers to date back further

Making the Ocean Move

-Is there a difference between the stability of the ocean and the troposphere? - The ocean is more stable -Troposphere is fundamentally unstable because its lowest density is at the bottom and will always rise -The ocean is fundamentally stable because it is heated from the top and its lower density at the top -Concepts: a. Surface currents, winds b. Coriolis c. Ekman Spiral d. Ekman Transport e. Convergence -Surface water tends to pile up at the centers of gyres, where downwelling occurs f. Downwelling -Occurs with convergence; if it's hot, salinity increases as surface water evaporates g. Divergence -Where ocean currents evaporate; upwelling occurs h. Upwelling i. Primary productivity (biosphere) -Conversion of CO2 into organic matter by organisms through photosynthesis / chemosynthesis -First level of production -Horizontal flow vs. vertical flow of surface currents

Do GHGs Explain 20th Century Warming?

-Issues: a. Duration -Solved by ice cores b. Match -How well do GHG changes match the 120-year instrumental record of temperature change? a. They match part but not all of the record -Almost all GHG increasing steadily since 1900, but planetary temperature does not rise steadily -Roughly half of the observed warming occurred before significant anthropogenic GHG had been added to the atmosphere -GHG increase is consistent with warming, but GHG alone cannot explain all of the observed 20th century temperature change

Volcanism

-Laki, Iceland -Ben Franklin -Types of Volcanism -Releases -Explosive Volcanism -Fluid Volcanism

Solar Variability

-Long-term changes in luminosity -Systematic variations in the "solar constant" on decadal to centennial timescales -Why is it so hard to measure changes in the Sun's strength in real time? a. There isn't much change on these timescales b. Clouds influence measurements c. The Sun is only visible half the time -The long wish is to measure precisely subtle changes in solar irradiance were realized with satellites When the Sun has many sunspots, it is ___________ than when there are no sunspots... a. Hotter -Sunspots are dark areas on the Sun, cooler than elsewhere a. But, these dark spots are surrounded by larger, brighter areas b. So the Sun is actually brighter when there are lots of sunspots c. There is a link between solar irradiance and the number of sunspots visible on the Sun d. Sunspots follow the same 11 year cycle as solar irradiance -There is an 11 year cycle in solar irradiance; this is in some way related to the 22 year cycle in the Sun's magnetic field reversals e. Over the 11 year cycle, solar irradiance varies by about 0.1% (maximum is about 0.15%) f. The 11 year cycle is tracked by the Sunspot Number, with most sunspots linked to higher irradiance -Sunspot proxies for solar irradiance allow us to evaluate changes in the Sun's output before satellites could monitor directly -Based on what we know about the instrumental record of global temperature, could changes in solar luminosity help to explain some of the observed changes? a. Yes b. If the Sun is brighter, the planet should be warmer -#1 determinant -Collaborative Quiz: Based on what we know about the instrumental record of global temperature and now what we know about changes in sunspots (and therefore solar luminosity) over the past century, a. Describe in what way changes in the Sun's luminosity helps to explain some of the observed temperature changes b. First order trend: -The planet has warmed over the past century c. Second order trend: -Initial warming up until ~40s, ~50s; then is flat for a couple of decades -Second warming around ~60s, ~70s until 2010 d. Third order trend: -Wiggles e. Describe in what ways in the Sun's luminosity fails to explain some of the observed temperature change -Based on changes in solar luminosity reconstructed from sunspot numbers, the Sun might explain some of the observed early 20th century warming a. But, it not only cannot explain the late 20th century warming, changes in solar luminosity along predict global cooling, in opposition to the observed global warming -Solar variability take homes: a. Solar irradiance varies on an 11 year cycle, with the greatest irradiance when there are the most sunspots b. But, total variability is only 0.1% to 0.15% c. This is relatively small d. Observed spot numbers suggest that solar irradiance increased in the first half of the 20th century, at the same time that Earth's temperatures were rising e. But, observed sunspot numbers have been decreasing since 1950s (weaker Sun) at a time when Earth's temperatures were rising f. The Sun cannot contribute to late 20th century warming g. Future sunspot numbers projections show continued decline - may reduce future warming -Changes due to irregularities in Earth's orbital parameters (Earth-Sun distance) a. Precession of the equinoxes b. Tilt of the spin axis c. Elliptical orbit d. These three influence the Earth-Sun distance and amount of energy we get in different seasons e. All of these changes occur on timescales too slow to significantly influence planetary temperature over the past century f. Milankovich Effect g. Also not significant over the last 100 years h. We're left with sunspot cycles as the biggest effect -Solar irradiance gives us a decent match for early 20th century warming a. Magnitude b. 11 year cycle: +/- 0.1% c. Most current estimates are that maximum solar variability are no more than 0.15% d. Climate forcing e. Recall: annual average solar flux at the top of the atmosphere is 340 W/m2 (annual average across the sphere of Earth) f. 0.15% of 340 translates to a forcing of 0.5 W/m2 g. How does this compare to GHG Radiative forcing?

Can GHG increases explain 20th Century Warming?

-Mechanism: Does CO2 (CH4, etc.) have an accepted physical mechanism that would produce a warmer planet?a. Yes, CO2 is a GHG -Issues: a. Duration of CO2 record b. GHG instrumental record is too short to really test the correlation c. Match to observations -What happened before 1957 when CO2 started being recorded? a. How can we determine the level of GHG before 1957 if there was no measuring program them? b. Ice cores -Tiny bubbles of ancient atmosphere trapped in ice -Sealing of bubbles preserves the atmosphere

How Aerosols and Particulates Impact Climate

-Most are shiny a. → Reflect and scatter b. → Cools surface c. Reduce total flux of Sun's energy that reaches surface -If also dark (or GHGs), absorb/trap energy a. → Local atmospheric warming -Particulates act as nucleating particles for precipitation (cloud seeding) a. → Increase cloud cover b. Can have a role in increasing rainfall -Soot (black carbon)

Fluid Volcanism

-Only releases stuff into the troposphere -Less violent / explosive -Example: Big Island of Hawaii / Iceland a. Neither last long enough to change the climate system b. Need to inject stuff that lasts longer and impacts climate c. → Aerosols -Releases ash and gases into the troposphere, where precipitation and gravity scrub it out within days to weeks

Is the Magnitude of Observed Warming Outside the Range of Natural Climate Variability?

-Over the past century, the planet has warmed a. Why? What are the possible causes of global warming? -Increased greenhouse gases -Orbital changes; tilt / procession -Distance from the Sun -Planetary albedo; sea ice melting -Increase in the Sun's temperature; solar variability -Volcanism -Aerosols -Clouds -Chaos a. Natural, unforced variability

Horizontal Flow VS Vertical Flow of Surface Currents

-Overview: a. Surface currents driven by winds through the frictional coupling between atmosphere and sea surface (this will set the ocean currents in motion) b. Surface currents are restricted to top 100 m c. How deep is the ocean (on average)? - 4,000 m = 13,000 ft. d. Layering (surface layer (top) -> thermocline (transition) -> deep water (bottom)) -Do ocean surface currents follow the same path as surface winds? a. No, Coriolis causes water to flow differently b. No, gravity causes the water to sink c. No, because the continents get in the way -Coriolis surface currents are deflected to the right (Northern Hemisphere) or left (Southern Hemisphere) of prevailing winds a. This process is complicated by: -Continents -Ekman Spiral (Transfer of Coriolis Effect down through the water volume; responsible for the net motion of surface water) -Ekman Transport (Net effect is that the surface water moves at right angles to the wind; right of the wind in NH, left in SH; we can expect simple gyres) -What two factors control primary productivity? - Sun and nutrients -Why are there so few nutrients at the center of ocean gyres? - Something used them all up; they were transported to the seafloor; there is such a long transport time; there is no source of nutrients a. Nutrients consumed by primary production (photosynthesis) in the photic (sunlight) zone b. Primary producers are eaten by larger things that sink when they die, removing nutrients from the surface water c. Sinking dead things decompose in the deep ocean and most of their nutrients are returned to the water at depth (upwelling = vertical) -At the equator, there is equatorial upwelling -Divergence = upwelling -Upwelling brings nutrients to the surface -Coastal upwelling: Coastal winds can create upwelling along the coast -Offshore winds = upwelling -Onshore winds = downwelling

Releases

-Particulates -Aerosols

Particulates

-Particulates: a. Volcanic ash (tephra) b. Tiny bits of rock c. Often low density -Tephra is small; pumice is big d. Ash acts as a shade, reducing solar radiation at Earth's surface -Reflects and absorbs e. Short residence time f. In which reservoir (troposphere vs. stratosphere) would you predict that the residence time of volcanic ash would be longest? -Stratosphere g. What might remove volcanic ash from the troposphere? -Precipitation -Gravity h. What might remove volcanic ash from the stratosphere? -Gravity

The Ocean

-Plays an important role in the climate system -Is probably where life originated

Precipitation

-Precipitation is spatially much more variable than temperature -Precipitation records from over the oceans are almost exclusively from island stations -Precipitation has mediocre correlation with temperature a. After 1950, it was wetter on average than before, and that's about it

Result

-Primary drivers: a. GHGs - + b. Solar variability - +/- c. Volcanism - +/- -Secondary: a. Aerosols / Particulates - +/- -Rain b. Clouds - +/- c. Chaos - +/-

Distributions of Water on Earth

-Reservoir (noun): a. A volume or mass of something b. Ocean (water, salt, etc.) c. Atmosphere (oxygen, water vapor, etc.) -Flux (verb): a. The rate energy or matter is transferred between reservoirs -Residence time: a. The average time some component of a reservoir stays in that reservoir b. Ratio between reservoir and flux -After the ocean, snow and ice contain the greatest volume of water -The biosphere has the least volume of water -Reservoirs: a. Ocean -Mass (10^25 kg): 1,400,000 -Residence time: 3,000 years b. Snow and ice -Mass (10^25 kg): 43,400 -Residence time: Snow: N/A (few months in the winter); Ice: 10,000 years c. Groundwater -Mass (10^25 kg): 15,300 -Residence time: Variable (decades, centuries) d. Freshwater -Mass (10^25 kg): 360 -Residence time: Variable (days, years) e. Atmosphere -Mass (10^25 kg): 16 -Residence time: 12 days (2 weeks) f. Biosphere -Mass (10^25 kg): 2 -Residence time: 35 days (1 month)

Indirect Evidence

-Retreating glaciers a. Almost everywhere, but in the tropics/high latitudes in Southern Hemisphere? - Yes -Are tropical glaciers receding? a. Probably -What about the big ice sheets in Greenland and Antarctica? a. Loss of ice is by both direct melting and calving from outlet glaciers b. Ice shelves are breaking up c. As ice shelves break up, the glaciers behind them are free to flow more rapidly, delivering more ice to the ocean d. There is still negligible ice melt e. Greenland is melting more and more rapidly f. Antarctica is changing less rapidly g. Ironically, more snow is falling at the South Pole -If glaciers are retreating, sea level should be rising. Is it? a. Yes, of course b. How do we know? -Satellites a. Measure sea level -Tide gauges a. What controls tide gauges (relative sea level)? -The volume of water in the ocean - The volume of the ocean basin -Vertical motion of the continents -Average air pressure changes (currents) c. To capture true sea level changes, we need to analyze lots of tide gauges around the world and use satellites -Sea level rise a. Tide gauges: 1.8 cm/decade (100 years) b. Satellites: 2.5 cm/decade (20 years) -Sea level rising over the past century -Faster in most recent 30 years than past 100 years -Not obviously accelerating in recent decades -Where is the ice melt coming from? a. Some of the observed sea level rise must be from melting ice. The largest contributor is probably: b. Small glaciers and ice caps c. Melting the quickest -Why is sea level rising? a. Glaciers melting (50%) b. Calculating all of the glacier ice that has melted in the past century adds up to only about 9 cm of sea level, half the total observed sea level rise -What could explain the other half? a. Only half of the observed rise in sea level over the past century can be explained by melting glaciers. The rest of the rise might be best explained by: b. Global warming -The ocean is warming (50%) -Uplift under former ice sheets -Thermal expansion a. The ocean is warming b. Rule of thumb: -20 cm of sea level rise for every 1º C rise in temperature of the top 100 m -Sea ice a. The change in sea ice and land snow cover has a dramatic impact on the planetary energy balance -The most powerful feedback system b. Sea ice changes are difficult to predict because there are both thermal (freeze-melt) and dynamic (large-scale motion) components c. Why does the sea ice move north and disappear along western Svalbard? -This is the Gulf Stream d. How does loss of sea ice impact sea level? -Sea level will not change

Strong Positive Feedbacks on Warming

-Sea ice loss has positive feedbacks in both winter and summer -Snow cover decreases strong summer feedback -Ocean surface warming has strong positive feedback a. Increased water vapor in the atmosphere b. Water vapor itself is a greenhouse gas c. Putting more in the atmosphere increases the Greenhouse Gas Effect -Permafrost melting releases CO2 and CH4 a. Dead plants: b. Oxygenated: CO2 c. Non-oxygenated: CH4

Ben Franklin

-Studied eruption -In 1784, he wrote of a "constant dry fog" in London a. "Where collected in the focus of a burning glass, they would scarcely kindle brown paper." b. He tried to light a fire with a magnifying glass c. Way to demonstrate that the energy coming in from the Sun was so much smaller -Correctly associated the fog in London with Lakis, and recognized that something released by Laki resulted in reduced solar energy and that this was the primary cause of an unusually cold winter in the UK a. Fist to discuss the snow-albedo feedback

Clouds

-The complexity of changing cloud cover on temperature -Cloud forcing depends on cloud type a. Height (most controlling variable) -High clouds: Tend to warm the planet -Low clouds: Tend to cool the planet b. Problem: There are no proxies for cloud cover, let alone cloud height -Even climate models have a hard time predicting current clouds -Flowchart: a. Fossil fuel and fuelwood burning = Greenhouse warming and more aerosols b. → More and smaller cloud droplets c. → Less rain production d. → Clouds last longer -Climate impacts: a. → Sunlight decreases b. → Temperature decreases c. → Snowfall rate increases e. Are aerosols a positive or negative feedback in this case? -Positive feedback -Amplified our initial change of cooling and made it even cooler -Consensus: There will be more low-level clouds due to more aerosol condensation nuclei a. Difficult to predict, so uncertainty for past and future

Explaining Global Warming: Facts

-The planet has, on average, warmed -Arctic has warmed significantly more than planetary average -Glaciers and ice sheets are losing mass -As a partial consequence, the sea level is rising a. Glacier melt b. Ocean warming -Arctic sea ice is diminishing a. Area and volume -Permafrost is melting -Strong positive feedbacks

Chaos

-There is inherent variability in the climate system a. Unforced changes b. Things that take place naturally c. Even if nothing was going on, there would be some variability in climate -We would like to know the limits of natural variability to decide if current changes are outside this range C. Examples: a. ENSO (El Niño / Southern Oscillation) b. Best predictor of inter-annual variability c. There are other "natural" cycles that range from 2-3 year "beats" to 50-100 "beats" d. Mostly reflect changes in ocean surface water temperatures or atmospheric pressure patterns e. Confident that the current warming exceeds any know "unforced natural variability"

Global Warming is a Fact (Not a Theory)

-There is no doubt that Earth has warmed since 1900 A.D. a. Does this fact tell us why our planet is warming? -The century-scale patterns of temperature increase across the planet mirror the changes seen in the past decade

Direct Evidence

-Thermometer records show two-step warming and some inter-annual wiggles over the past century a. What about precipitation? -Because the planet has warmed over the past century, from first principles we expect that globally precipitation has: -Increased because evaporation from the ocean is greater -Measured temperatures -Warming in two steps over the past century

Additional Feedbacks

-Vegetation change -Water vapor change

20th Century Forcings

-Volcanic -Solar -Anthropogenic

Observations

-Warming since 1900s is virtually everywhere -Warming is greatest in the Arctic a. But, the warming has occurred in two steps -Was it the same pattern in the early 20th century warming as in the late 20th century? -The difference in geographic distribution of warming between the first and second halves of the 20th century tell us what? -The explanation for what caused the two warmings is probably different -Warming in the first half the 20th century was dominantly the Arctic a. 1960s → global warming -General warming of the planet on average over the past century, but it was not steady a. Rapid since the 1960s, and global in extent

Vertical Currents

-Why might the ocean move vertically? a. Surface water gets too heavy to float b. Gravity c. Surface water gets cold d. Surface water gets more saline -Deep ocean currents: a. Vertical circulation is controlled by differences in density -Just like air -Density is simply mass/volume (kg/liters) -For sea water, density is controlled by: a. Salinity b. Temperature -Salinity is the salt content of a water mass -The proportion of dissolved salt to pure water (measured in parts per thousand) -Typical ocean salinity = 35% -Sodium (55%) and chloride (31%) make up the salinity -Ocean composition is everywhere the same, even though salinity varies -If the composition of the ocean (the relative abundance of all the dissolved salts) of the ocean is everywhere the same, then residence times of salts must be long. -Because the composition of the ocean is everywhere the same, salts must have a long residence time in the ocean compared with ocean circulation -But, salinity does vary quite a bit around the ocean -Rules of thumb: a. Ocean composition is constant (local exceptions) b. Ocean salinity is variable -How density is controlled by temperature and salinity: a. More dense: -Colder -Higher salinity b. Less dense: -Warmer -Lower salinity -What if seawater gets colder and fresher? a. It "might" become less dense

Consequences

-With glaciers melting, sea levels must be rising a. Tide gauge records (100 yr.) b. Satellites (30 yr.) -Loss of fresh water sources a. Especially in the summer -Negative impact on tourism -Geologic records of past climates a. Losing ice-core records -Because the planet is warming, Arctic Ocean sea ice is shrinking; this will result in: a. Strong positive feedbacks b. Sea ice feedbacks (ice-albedo feedback) -Summer: a. As the planet warms, sea ice cover is reduced, greatly reducing albedo b. The ice free ocean (low albedo) now absorbs a much larger proportion of the solar energy in summer than when sea ice was present c. Although the ice-free ocean stores much of the solar radiation, it is distributed through the surface layer, so the air temperature warms only slightly -As the planet warms, sea ice cover is reduced, more energy is stored in the ocean a. The warmer ocean delays autumn freeze up, so the winter ice area decreases, and ice is thinner -Winter: a. Without sea ice, the atmosphere is no longer insulated from the ocean, which returns its stored heat to the atmosphere until freeze-up b. Because the polar atmosphere in winter is currently about -40 ºC and the ocean can't get below -1.5 ºC, the winter atmosphere warms greatly without sea ice insulation -Both summer and winter are very strong positive feedbacks -If the planet warms in the summer, snow cover over Arctic lands will melt earlier. The impact will be: a. Summer temperatures over land will warm more b. Temperature change over the land with snow change (rather than over the ocean with sea ice change) because the land energy is transferred only by conduction (whereas the ocean is convection) -Decreasing snow cover warms the land in summer more than sea ice loss warms the ocean in summer. Why? a. Conduction vs. convection b. Feedback from snow melt in a warming climate? c. If snow cover is less, continental albedo is lower, and more short-wave solar energy is converted to long-wave (heat) energy d. Absorbed energy only transferred into land by conduction so surface warms a lot (and so warms the atmosphere) e. Positive feedback in summer -If snow cover over land is less in summer because of warming, is there a positive feedback in winter? a. Yes, small positive feedback b. Feedback from snow melt in a warming climate? c. Stored extra heat in land surface from snow-free summer will warm the atmosphere for a while in the fall, but once new snow accumulates, this effect is very small d. Small positive feedback e. Positive feedbacks from snow and sea ice in both summer and winter f. → Polar amplification of global warming: -If the planet warms, because of strong positive feedbacks in the polar regions (especially the Arctic), should warm considerably more -When permafrost melts, CH4 (methane) and CO2 (carbon dioxide) are released - greenhouse gases a. Consequently, as the plane warms and permafrost melts, the release of CH4 and CO2 will produce: a. A positive feedback b. Arctic warming has resulted in permafrost thawing c. On land, carbon from plants preserved in permafrost is then released as CO2 or CH4, both GHGs, producing positive feedbacks on warming d. Vast amounts of methane clathrates frozen in sea floor permafrost have not yet started to be released, but are a potential larger feedback

Circulation of the Liquid Earth: The Oceans and the Hydrologic Cycle

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How do Glaciers Lose Mass?

a. Melting -Relatively inefficient -Slow: molecule by molecule b. Calving -Floating end of outlet glacier terminating in the sea or a lake breaks off -Efficient -Melting can take place somewhere else