Weather, Climate & Society ATMO 336 Natural Climate Variability

Perspective: Time Scales 4.6 b.y. 2.1 b.y. 13.7 b.y. 3.5 b.y. Origin of the Universe--Jan. 1 Origin of our galaxy--Jan 24 Solar system origin--Sept. 9 Earth Solidifies--Sept. 14 Life on Earth--Sept. 30 Sexual reproduction advent--Nov. 25 Oxygen atmosphere--Dec. 1 Cambrian explosion (600 mil years ago when most complex organisms appear, fish, trilobites)--Dec. 17 Land plants & insects--Dec. 19, 20 First amphibians--Dec. 22 First reptiles & trees--Dec. 23 First dinosaurs--Dec. 25 KT impact, mammal age, birds--10:00 AM Dec. 30 First primates--Dec. 30 Australopithicenes (Lucy, etc.)--10:00 PM Dec. 31 Homo habilis--11:25 PM Dec. 31 Homo erectus--11:40 PM Dec. 31 Early Homo sapiens--11:50 PM Dec. 31 Neanderthal man--11:57 PM Dec. 31 Cro-Magnon man--11:58:38 PM Homo sapiens sapiens--11:58:57 PM Dec. 31 Human history--11:59:39 PM Ancient Greeks to now--last five seconds Average human life span--0.15 seconds 65 m.y. 21 s Avg. human life span=0.15 s http://ocw.mit.edu/OcwWeb/Earth--Atmospheric--and-Planetary-Sciences/12-301Fall-2006/LectureNotes/index.htm

Perspective: Astronomic Distance Scales 13.7 Ga (+/- 1%) 1 lt.y.=1016 m http://ocw.mit.edu/OcwWeb/Earth--Atmospheric--and-Planetary-Sciences/12-301Fall-2006/LectureNotes/index.htm

http://en.wikipedia.org/wiki/Earth

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. It was stated 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?

Determining the Past Climate Paleoclimatology - the study of past climates. Past 100-200 years (weather observations) Must use indirect climate measures, proxies, to examine further into the past. Some proxies: - Tree rings (1,000+ years before present BP) - Trapped pollen (10,000+ years BP) - Glacial ice cores (100,000+ years BP) - Ocean sediment cores (1 Million+ years BP) - Geology (1 Billion+ years BP)

Detecting Change With Proxies Scientifically, the best way to detect change is to directly measure it. 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

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

Unlocking “Stored” Climate Change Record: ~ 1Mya to ~ 20th cent Inert gases (CO2, CH4, N2O,…) Particulates (soot, ash, etc) Temperature?? Modern Instrument Record Tree Rings Ice Cores Sediment cores Rock formations/types Courtesy J. Thornton, U Wash

Unlocking “Stored” Climate Change Record: ~ 200 Mya Microfossils (ocean T), Volcanic glass Organic detritus Magnetic pole location 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 Banded Iron Formations BIFs tied up oceanic O2 Prevented atmospheric O2 Date no later than ~2 GYA Record: ~ 4.5 Gya Geologic formation Geochemical analysis Magnetic pole Continental Location Fossil record

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

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

Courtesy J. Thornton, U Wash Vostok Ice Core Record During last ice age (18,000 years ago) Temps 6oC colder CO2 levels 30% lower CH4 levels 50% lower (Sea level was higher) than pre-industrial interglacial values Last Ice Age T based on water isotope proxy Courtesy J. Thornton, U Wash

O18 analysis of ocean sediments can be used to construct past temperatures Cold Warm http://en.wikipedia.org/wiki/%CE%9418O

600 Million Years of Climate 542 Mya 490 Mya 444 Mya 417 Mya 359 Mya 299 Mya 251 Mya 200 Mya 145 Mya 65 Mya 1.8 Mya http://www.scotese.com/climate.htm 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.”

540 Mya of Climate Change from O18 http://en.wikipedia.org/wiki/Oxygen_isotope_ratio_cycle

Snowball Earth! http://www.snowballearth.org/images/geologic_column.gif

Snowball Earth: Some Evidence dropstones http://www-eps.harvard.edu/people/faculty/hoffman/Snowball-fig11.jpg Basic physics are understood: Runaway ice-albedo feedback How does earth thaw? CO2? http://nai.nasa.gov/newsletter/03182005/snowball.jpg

Simple climate models exhibit hysteresis between ice-no ice states Delayed response between CO2 forcing and rapid jumps between ice free and snowball earth. http://www.snowballearth.org/slides/Ch7-6.gif

Snowball cycles show freeze-thaw-hothouse http://www.snowballearth.org/images/snwbltvst.gif

Is snowball earth a mechanism for jump starting evolutionary leaps? Metazoa and plants appear after last episode http://www.snowballearth.org/slides/Ch7-6.gif

Life is responsible for the “recent” rise of oxygen Cambrian explosion Multicell organisms Use of oxygen for metabolism. Water and CO2 are byproducts. Use of sunlight for metabolism. Oxygen is a byproduct. http://si.wikipedia.org/wiki/%E0%B6%BB%E0%B7%96%E0%B6%B4%E0%B6%BA:Oxygen_atmosphere.png

Atmospheric constituents have changed radically through the ages http://www.ozh2o.com/atmos.jpg

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

Long-Term Climate Change Circumpolar seaway leads to large latitudinal temperature gradient. Current S.H. Situation Circumequatorial seaway leads to small latitudinal temperature gradient. Situation 50 MYa http://www.ace.mmu.ac.uk/eae/Climate_Change/Older/Continental_Drift.html

Long-Term Climate Change Circumpolar ocean current formed around Antarctica 40-55 MY ago once Antarctica and Australia separated. This prevented warm air from warmer latitudes to penetrate into Antarctica. Absence of warm air accelerated growth of the Antarctic ice sheet. http://www.ace.mmu.ac.uk/eae/Climate_Change/Older/Continental_Drift.html

Most Recent Ice Age Extend of continental glaciers 18,000 years BP. Aguado and Burt, Fig 16-4 Extend of continental glaciers 18,000 years BP. Sea level was 100-125 m lower than present. Bering land bridge between Siberia and Alaska.

http://en.wikipedia.org/wiki/Image:Recent_Sea_Level_Rise.png

http://earthobservatory. nasa http://earthobservatory.nasa.gov/Study/BorealMigration/Images/pleistocene_modern.jpg

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

Temperatures since the last Ice Age… the time that humans have flourished Glacial advance Apline advance Glacial retreat Rapid melt Ahrens, Fig 13.3 Rapid warming occurred at end of Younger-Dryas period. Ice cores indicate that Ice Age conditions ended in 3 years!

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

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

Controversial “Hockey Stick”

Causes of Climate Change Atmospheric Composition - Anything that changes the radiative properties of the atmosphere (volcanic aerosols, carbon dioxide). Astronomical - Anything that alters the amount or distribution of solar energy intercepted by the Earth (solar variations, orbital variations). Earth’s Surface - Anything that alters the flow of energy at the Earth's surface or changes its distribution (desertification, continental drift).

Causes of Climate Change Astronomical Composition Surface

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 of Ice Ages Ice ages occur when summers are cool to melt less snow. Partially agrees with observations, but many questions unanswered. What caused the onset of the first Ice Age? http://en.wikipedia.org/wiki/Milankovitch_cycles

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

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

Closer Look at Climate System

Climate Feedback Mechanisms

Positive and Negative Feedbacks Assume that the Earth is warming. - Warming leads to more evaporation from oceans, which increases water vapor in atmosphere. -More water vapor increases absorption of IR, which strengthens the greenhouse effect. -This raises temperatures further, which leads to more evaporation, more water vapor, warming… “Runaway Greenhouse Effect” Positive Feedback Mechanism

Positive and Negative Feedbacks Again assume that the Earth is warming. - Suppose as the atmosphere warms and moistens, more low clouds form. - More low clouds reflect more solar radiation, which decreases solar heating at the surface. - This slows the warming, which would counteract a runaway greenhouse effect on Earth. Negative Feedback Mechanism

Positive and Negative Feedbacks Atmosphere has a numerous checks and balances that counteract climate changes. All feedback mechanisms… Operate simultaneously. Work in both directions. The dominant effect is difficult to predict. Cause and effect is very difficult to prove at the “beyond a shadow of a doubt” level.

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 Key question is determining whether recent changes are due to natural causes or man.

Key Points: Climate Change The climate system is very complex. Contains hundreds of feedback mechanisms Feedbacks are not completely understood. Three general climate change mechanisms: Astronomical Atmospheric composition Earth’s surface