Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System

1. Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System • We have discussed evidence that suggests the earth is warming due to human outgassing of carbon dioxide • Could we be wrong? Consider the major criticisms of the global warming hypothesis: • Instrumental error • Urban heat island • Others • A potential cause of the present warming may be due to natural variability in the climate system.

2. Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System • Natural variability can be classified by its forcing type (internal or external to the climate system) and whether it is periodic/cyclic or episodic. • Modes of Natural Variability that we know of: • timescale form forcing • Seasonal 90 days cyclic external • El nino 3-5 yrs cyclic internal • North Atlantic Oscillation decadal cyclic internal?? • Volcanism none episodic external • Ice ages 40,000 yrs cyclic internal • Pacific Decadal 20-50 yrs cyclic ????

3. http://sealevel.jpl.nasa.gov/science/images/el-nino-la-nina.jpghttp://sealevel.jpl.nasa.gov/science/images/el-nino-la-nina.jpg

4. Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System • Natural variability can be classified by its forcing type (internal or external to the climate system) and whether it is periodic/cyclic or episodic. • Modes of Natural Variability that we know of: • timescale form forcing • Seasonal 90 days cyclic external • El nino 3-5 yrs cyclic internal • North Atlantic Oscillation decadal cyclic internal?? • Volcanism none episodic external • Ice ages 40,000 yrs cyclic internal • Pacific Decadal 20-50 yrs cyclic ????

5. North Atlantic Oscillation • The NAO index is defined as the anomalous difference between the polar low and the subtropical high during the winter season (December through March)

6. The Negative NAO • The negative NAO index phase shows a weak subtropical high and a weak Icelandic low. • The reduced pressure gradient results in fewer and weaker winter storms crossing on a more west-east pathway. • They bring moist air into the Mediterranean and cold air to northern Europe • The US east coast experiences more cold air outbreaks and hence snowy weather conditions.

7. Positive NAO Index • The Positive NAO index phase shows a stronger than usual subtropical high pressure center and a deeper than normal Icelandic low. • The increased pressure difference results in more and stronger winter storms crossing the Atlantic Ocean on a more northerly track. • This results in warm and wet winters in Europe and in cold and dry winters in northern Canada and Greenland • The eastern US experiences mild and wet winter conditions

8. Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System • Natural variability can be classified by its forcing type (internal or external to the climate system) and whether it is periodic/cyclic or episodic. • Modes of Natural Variability that we know of: • timescale form forcing • Seasonal 90 days cyclic external • El nino 3-5 yrs cyclic internal • North Atlantic Oscillation decadal cyclic internal?? • Volcanism none episodic external • Ice ages 40,000 yrs cyclic internal • Pacific Decadal 20-50 yrs cyclic ????

9. Volcanic eruptions and climate: • The present atmospheric composition, Nitrogen-78%, Oxygen-21%, Argon-<1%, water vapor-0.4%, carbon dioxide-0.036% • How did the present atmospheric composition evolve? • Assume outgassing from early volcanoes provided the first atmosphere. • Composition of volcanic gasses: Water vapor-80%, Nitrogen-1%, Oxygen-0%, carbon dioxide-12%, sulphur compounds and others-7%

10. Volcanism and the early atmosphere: • So how did the atmosphere evolve from the volcanic composition to our present composition? • Water began to precipitate early – forming oceans • Carbon Dioxide dissolved rapidly in the early oceans reaching saturation and leading to precipitate of Calcium carbonate to the deep ocean • Nitrogen and argon built up slowly since it does not dissolve in sea water • Oxygen built up in the atmosphere due to by product of photosynthesis.

11. Earth’s Atmosphere Develops http://www.globalchange.umich.edu/globalchange1/current/lectures/first_billion_years/first_billion_years.html

12. The climate effects of volcanic eruptions: • What makes an eruption climatically significant? • nature of the eruption – lava vs. ash (ash is more significant) • composition – need high sulfur dioxide gas content • location – Tropical eruption spread globally In most eruptions, the particulates have only a minor effect. If the sulfur dioxide gas can reach the stratosphere, it converts to small sulfuric acid droplets that have long residence times in the stable stratosphere. It is this cloud of particles that spread and influence climate over long periods. Note Figure 4.3 in the book.

13. Natural variability can be classified by its forcing type (internal or external to the climate system) and whether it is periodic/cyclic or episodic. • Modes of Natural Variability that we know of: • timescale form forcing • Seasonal 90 days cyclic external • El nino 3-5 yrs cyclic internal • North Atlantic Oscillation decadal cyclic internal?? • Volcanism none episodic external • Ice ages 40,000 yrs cyclic internal • Pacific Decadal 20-50 yrs cyclic ????

14. Pacific Decadal Oscillation

15. Pacific Decadal Oscillation warm phase             cool phase

16. How does ocean circulation affect local climates? Answer: Heat release locations are warmer! Warm surface current- Less Dense Cold deep water current–More Dense Salty water anywhere- More Dense Intergovernmental Panel on Climate Change (IPCC), "Climate Change 2001: The Scientific Basis"

17. What directions do warm and cold water currents travel? Animation by Jack Cook (Woods Hole Oceanographic Institute)

18. Is it true that the North Atlantic current could shut down? The ocean surface transfers heat to the atmosphere! Animation by Jack Cook (Woods Hole Oceanographic Institute)

19. Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System • Air-Sea Interactions: • Ocean and atmosphere communicate with one another: • constituents: water (precipitation and evaporation), carbon dioxide, oxygen, trace gasses, etc • Energy – momentum through wind stress driving the surface currents • Heat – sensible heat and latent heat due to evaporation • Ocean structure: warm and relatively fresh mixed layer lying on top of a nearly isothermal cold and salty water mass

20. Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System The global thermohaline circulation: Cold Salty water in the north Atlantic becomes dense and convects downward, spreads southward and contributes to vertical overturning of deep ocean water on millennial timescales. Importance: Climate of northern Europe and Asia rely on heat and moisture supplied to atmosphere to keep climate habitable in extreme northern latitudes.

21. Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System Even though the oceans and atmosphere are both fluids, they have a fundamental difference – their density: Atmosphere 1 kg/cubic meter, Ocean – approximately 1000 kg/cubic meter. This density difference leads to large difference in heat capacity. Heat capacity is defined as the amount of temperature change in kelvin degrees for a unit input of heat energy. The ocean’s heat capacity is approximately 41 times that of the atmosphere. A 1 degree change in atmospheric temperature is equivalent to an 0.02 change in ocean temperature change.

22. Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System El Nino is an example of air-sea interactions that occur on annual time scales Note figures 4.8 and 4.9: Sea surface temperature (SST) patterns change fundamentally with the el nino cycle The atmosphere both forces and responds to the el nino cycle. Normal sst patterns: atmospheric forcing of sst is accomplished through easterly trade winds cooling the central and eastern equatorial pacific. Atmosphere responds to warm western pacific water by the occurrence of strong thunderstorms in that region

23. Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System An el nino is characterized by a general warming of the water in the central and eastern pacific. Atmosphere forces the ocean by a weakening of the easterly trades in the central and eastern pacific. Atmosphere responds by shifting thunderstorm activity eastward to the central pacific. Implications: Interruption of fishery along western margins of South America, failure and/or weakening of the Indian Monsoon impacting agriculture in that region.

24. Meteo 1020 – Lecture 4 The Natural Variability of the Earth-Atmosphere System El nino remote forcing: the modulation of the normal patterns in the equatorial pacific influence weather patterns around the world: In the U.S., the pacific storm track is shifted southward leading resulting in storminess over the southwestern U.S. and droughts over the Pacific Northwest. Precipitation is often reduced over the southeastern U.S.

25. What process could change the ocean circulation?

26. If air from the upper atmosphere is brought down to the surface in a hurricane, will it freeze us? • Closer to the Earth’s surface, the air pressure is higher than higher up in the atmosphere. As we bring the air down to the Earth the air pressure increases. As we apply pressure to air, air warms instantaneously! Bring air which is -80º C from 15km (tropopause) down to the surface • Temperature change because of pressure changes 15km*9.8º/km(for dry air)= +147ºC • Original temp + temp change = temp at surface -80ºC+147ºC=67ºC • Change to Fahrenheit 67ºC*(9/5)+32=152.6ºF

27. Can ice sheets melt and build overnight? • Ice Sheets and Glaciers • Immense mass prevents rapid melting of ice sheets. • Ex. Climate quickly changed at the end of last ice age • Decades and centuries later the ice sheets and deep ocean adjusted. (NSIDC) • The major ice sheets over North America at the peak of the last ice age took tens of thousands of years to build up. (NASA) http://daily.greencine.com/archives/day-after-tomorrow.jpg

28. What process could most likely change the climate? More moisture in the air Warmer climate More evaporation at the equator Circulation slows down and changes More moisture can be held in the air Water does not sink in the northern latitudes Melting Glaciers Ocean is not as salty and dense More rain at higher latitudes More freshwater in the ocean

29. What is happening with ice shelves today? • Today shifting climate • Antarctic Peninsula the ice shelves are no longer stable. The northern most limit for ice shelves has moved south over the past two decades by about 100 miles. (NSIDC) http://images.amazon.com/images/P/B0007PALRU.01.LZZZZZZZ.jpg

30. Three Glaciers Retreating • Source: C.L. Andrews. 1912, 1938. Denver Glacier: From the Glacier Photograph Collection . Boulder, CO: National Snow and Ice Data Center. Digital Media; Marion T. Millett. 1958. Denver Glacier: From the Glacier Photograph Collection . Boulder, CO: National Snow and Ice Data Center. Digital Media.

31. How do we know about past climates? • Photo by: Lonnie Thompson, Ohio State University • Ice sheets reveal annual layers • history of precipitation and air temperatures 100,000 years in the past.

33. http://www.whoi.edu/institutes/occi/images/occi_abrclimate_jk_lev_en.gifhttp://www.whoi.edu/institutes/occi/images/occi_abrclimate_jk_lev_en.gif

34. Sea Ice Concentration

35. Temperature and Ice Accumulation vs. Time