NATS 101 Lecture Natural Climate Variability Artist’s rendition of snowball earth, 650 Mya

Perspective: Time Scales 13.7 Gya 4.6 Gya2.1 Gya 3.5 Gya 65 Mya Avg. human life span=0.15 s 21 s

1 ly = m ly=light year 13.7 Ga (+/- 1%) Perspective: Astronomic Space Scales

What is Climate Change? Climate change - A significant shift in the mean state and event frequency of the atmosphere. Climate change is a normal component of the Earth’s natural variability. Climate change occurs on all time and space scales. What is that evidence? How do we know what we know?We know that “a plethora of evidence exists that indicates the climate of the Earth has changed.” What is that evidence? How do we know what we know?

Causes of Climate Change Astronomical Surface Composition

Detecting Change With Proxies Scientifically, the best way to detect change is to directly measure it. Data available last yrs. Unfortunately for the timescales of interest in climate science, we were not always able (interested in?) to measure quantities such as temperature, precipitation, wind speed, direction, greenhouse gas levels, etc. But, obviously we want to know what these properties were and how they changed in the past to test our understanding of how climate changes. The study of past climate is known as paleoclimate science. Courtesy J. Thornton, U Wash

Detecting Change With Proxies Another property/qty that is a function of property of interest. The measured property is a PROXY for the one of interest. Think approximate Courtesy J. Thornton, U Wash

Record: 1000 ~ Present day “Length” of growing season Good versus stressed years Major fires Unlocking “Stored” Climate Change Modern Instrument Record Tree Rings Ice Cores Sediment cores Rock formations/types Courtesy J. Thornton, U Wash

Record: ~ 1Mya to 20 th cent Inert gases (CO 2, CH 4, N 2 O,…) Particulates (soot, ash, etc) Temperature?? Unlocking “Stored” Climate Change Modern Instrument Record Tree Rings Ice Cores Sediment cores Rock formations/types Courtesy J. Thornton, U Wash

Record: ~ 200 Mya Microfossils (ocean T), Volcanic glass Organic detritus Magnetic pole location Unlocking “Stored” Climate Change Modern Instrument Record Tree Rings Ice Cores Sediment cores Rock formations/types Courtesy J. Thornton, U Wash

Unlocking “Stored” Climate Change Modern Instrument Record Tree Rings Ice Cores Sediment Cores Rock formations/types Record: ~ 4.5 Gya Geologic formation Geochemical analysis Magnetic pole Continental Location Fossil record Banded Iron Formations BIFs tied up oceanic O 2 Prevented atmospheric O 2 Date no later than ~2 GYA

18 O/ 16 O low 18 O/ 16 O high 18 O/ 16 O lower 18 O/ 16 O lower still Water Cycle – Water Isotope T Proxy Courtesy J. Thornton, U Wash

T based on water isotope proxy Last Ice Age During last ice age (18,000 years ago) Temps 6 o C colder CO 2 levels 30% lower CH 4 levels 50% lower (Sea level was higher) than pre-industrial interglacial values Courtesy J. Thornton, U Wash Vostok Ice Core Record T and GHG correlated Causality?

 O 18 analysis of ocean sediments can be used to construct past temperatures Warm Cold

600 Million Years of Climate The past climate of the Earth can be deduced “by mapping the distribution of ancient coals, desert deposits, tropical soils, salt deposits, glacial material, as well as the distribution of plants and animals that are sensitive to climate, such as alligators, palm trees & mangrove swamps.” 542 Mya 65 Mya 490 Mya 200 Mya145 Mya 251 Mya 299 Mya 417 Mya 359 Mya 444 Mya 1.8 Mya

540 Mya of Climate Change from O 18

Snowball Earth!

Snowball Earth: Some Evidence dropstones Basic physics are understood: Runaway ice-albedo feedback How does earth thaw? CO 2 ? cap carbonates

Life is responsible for the “recent” rise of oxygen Use of sunlight for metabolism. Oxygen is a byproduct. Use of oxygen for metabolism. Water and CO2 are byproducts. Multicell organisms Cambrian explosion

Atmospheric constituents have changed radically through the ages Dimmer SunBrighter Sun

Long-Term Climate Change 250 million years ago, the world’s landmasses were joined together and formed a super continent termed Pangea. As continents drifted apart to their present configuration, they moved into different latitude bands. This altered prevailing winds and ocean currents. NA E-A Af SA India NA India Af SA E-A Ant Aus Ant Aus 180 M BPToday Ahrens, Fig 13.6

Long-Term Climate Change Circumpolar ocean current formed around Antarctica MY ago as Antarctica and Australia separated. Kept warm air from low latitudes from reaching into Antarctica. Absence of warm air accelerated growth of the Antarctic ice sheet.

Most Recent Ice Age Extend of continental glaciers 18,000 years BP. Sea level was m lower than present. Bering land bridge between Siberia and Alaska. Aguado and Burt, Fig 16-4

SST 18,000 years BP Much cooler over the North Atlantic Ocean. Ocean currents were undoubtedly different. North Atlantic Drift was probably much weaker. 18,000 BPToday Ahrens, Fig 13.2

Milankovitch Theory of Ice Ages Attempts to explain ice ages by variations in orbital parameters Three cycles: Eccentricity (100,000 yrs) Tilt (41,000 yrs) Precession (23,000 yrs) Changes the latitudinal and seasonal distributions of solar radiation.

Milankovitch Theory Change in daily solar radiation at top of atmosphere at June solstice Changes as large as ~15% occur

Milankovitch Theory of Ice Ages Ice ages occur if summers are cool and less snow melts. Partially agrees with observations, but many questions unanswered. What caused the onset of the first Ice Age?

Temperatures since the last Ice Age… the time that humans have flourished Younger-Dryas Rapid cooling at the start occurred over a period of 1,000 yrs. The abrupt warming at the end occurred in only a few yrs! Glacial retreat Rapid melt Glacial advance Apline advance Ahrens, Fig 13.3

FRESH WATER TO NORTH ATLANTIC As the ice sheets were retreating, a giant prehistoric lake formed called Lake Agassiz. The lake eventually broke through the ice sheet and drained into the North Atlantic. The freshening of the sea water shut down the Gulf Stream and the heat transport toward Europe, what happened then?? What caused the Younger Dryas?

Climate affects human societies Temperatures for Europe during the last 1200 years. Viking settlements lost in Greenland Viking colonization in Greenland Ahrens, Fig 13.4

Evidence of Climate Change Surface temperatures based on meteorological observations. Is the warming of the past century due to human activities? 0.6 o C warming past century Ahrens, Fig 13.5 Anthropogenic warming?

Complexity of Climate System The climate system involves numerous, interrelated components Feedback Mechanisms

Examples of feedbacks in the climate system with global warming Positive feedback = Enhances the warming Negative feedback = Mitigates the warming IF YOU HAVE THE FOLLOWING: MORE WATER VAPOR: Positive feedback because it’s a greenhouse gas. LESS SEA ICE: Positive feedback because more solar radiation is absorbed instead of reflected. MORE CLOUDS: Feedback can be positive or negative depending on the type of clouds. THIS IS STILL A BIG UNKNOWN… HiGH CLOUDS: Positive feedback LOW CLOUDS: Negative feedback MORE AEROSOLS: Negative feedback because more solar radiation is reflected.

Key Points: Climate Change Proxy data are used to infer the past climate. Data show that the Earth’s Climate Has changed in the past Is changing now And will continue to change There has been 1  F warming during the past century, half of which has occurred during the past 30 years.

Key Points: Climate Change The climate system is very complex. Contains hundreds of feedback mechanisms. Feedbacks are not completely understood. Biosphere-Atmosphere interactions.

Key Points: Climate Change Three general climate change mechanisms: 1)Astronomical 2)Atmospheric composition 3)Earth’s surface Humans modifying 2 and 3 on global scale. Are recent climate and weather changes due to natural causes or human activities? Next Time

Assignment for Next Lecture Anthropogenic Climate Change Reading- Ahrens 4th: th: Homework11- D2L 4th-Pg. 399: 14.12, 15, 16, 19 5th-Pg. 412: 14.12, 15, 16, 19 Do Not Submit D2L