Natural Climate Variability: Short Term

Transcription

1 Natural Climate Variability: Short Term

2 Natural Climate Change Today: Natural Climate Change-1: Overview of processes, with focus on short to medium timescales

3 Natural Climate Change 1) Systems Revisited: Complexity, thresholds and unpredictability 2) Review of some rapid climate cycles: e.g. El Nino, PDO. 3) Last 1000 years- younger Dryas & little ice age- (Another story of ocean circulation change?) 4) Going farther back: Archives and Climate Records how we get this data?

4 1) complexity (briefly) Goal: clarify how do changes in a climate system at equilibrium come about? Will consider Four things: 1) Complexity- systems marked by nonlinear behavior stochastic (random) behavior variance (=scatter or variability) time lags

5 1) Complexity First- most systems have lots of parts and feedback loops that interact with each other.

6 A result of Complexity Complexity of these feedbacks leads to nonlinear behavior in systems. this means you can t easily predict outcome from knowing input variables! How?

7 2) Variance The variability (or scatter ) inherent any natural process- Why? typically arises because pretty much any phenomena is a combination of many contributing factors.. Each of which vary- Added together: get scatter -

8 Variance Variance = the wiggles around the mean of a given forcing (standard deviation is one way to measure of variance..)

9 Complexity + Variance Add Variance (in all natural phenomena), with Complexity of a feedback system: ==> And you end with (sometimes) inherently unpredictable results.

10 3) Unpredictable forcings There can be also random disturbances to a system that can t be predicted: Stochastic behavior River & Lake water evaporation rain river flow Atmosphere Water vapor rain Ocean water evaporation sublimation snow melting Greenland and Antarctic ice caps

11 Stochastic process A process which has basic element of randomness - knowing all inputs, you cannot predict outputs exactly. Also called non-deterministic

12 4) Time Lags most relationships between system parts take time to happen. (cause and effect usually don t happen at the exact same time) makes it quite difficult to study.. Have to guess at time lags.

13 Example: results of stochastic forcing Stochastic behavior ADDS on top of the other predictable, cyclic forcings that systems When critical thresholds are exceeded, drives a system out of equilibrium

14 Combine with threshhold idea Recall: Multiple stable state cartoon/ idea Threshold Combinations of periodic and stochastic forcing can cause the Earth system to move from one equilibrium state to another.

15 Stochastic forcing example Periodic Forcing is predictable

16 Stochastic forcing Stochastic Forcings are not predictable- have high variance

17 Stochastic + Periodic forcings COMBINATION of stochastic forcing on top of periodic forcing can exceed threshold- BUT you will never know exactly when it will happen

18 Understanding Climate Cycles Basis of Climate cycles or Climate Oscillations 1) Thresholds: when critical threshold is exceeded- then feedbacks can amplify stochastic disturbances of Earth system 2) Forcings: You may know what most forcings are.. So you can predict when a system is vulnerable to change- 3) Stochastic nature: but you may never be able to know exactly when and how it will change..

19 Some Sources of Natural Variability 1) Internal Behavior of the Earth System Climate cycles or Oscillations Geologic events 2) External Solar Forcing Sun spots Earth - Sun orbital configuration

20 1) Very rapid oscillations Constant Oscillations in climate modes which take place on time scales of years to decades

21 El Nino: topic of last lecture Example of interannual variability: El Niño. Normal El Niño Global Effects of El Niño

22 Positive Phase Negative Phase Another Example from the Atlantic: North Atlantic Oscillation Changes in strength of SUBTROPICAL HIGH & SUBPOLAR LOW. Results in Changes in STORMS in: Eastern U.S. Greenland Northern Europe Mediterranean

23 And closer to home...

24 Recognize this fellow?

25 Sardine fishery, early part of century..

26 Sardine landings..

27 But

28 They re back?

29 PDO.. Pacific Decadal Oscillation..

30 PDO.. Pacific Decadal Oscillation.. A somewhat longer oscillation of N Pacific Strongly linked to ENSO cycles.. thought to be ~20-50 yr time frames

31 PDO.. Last century approximately

32 PDO.. Last century approximately

33 PDO.. Last century approximately

34 Currently waiting to see..?

35 2) Natural Climate Changes on longer time frame.. There have been some really clear variations in the Last 1000 years..

36 The Holocene Period= post last ice age The height of the last glacial peridod was ~ 20,000 yrs ago. The Earth began to warm rapidly ~ 15,000 yrs ago, entered The Holocene Period. During this time, global sea level rose, glaciers melted, and erosion dramatically reshaped landscapes.

37 The Younger Dryas Event BUT : all this came to an abrupt, (but fortunately temporary!), end 13,000 yrs ago A reversal of climate occurred plunging parts of western and northern Europe back into what almost appears to be another iceage. This is commonly called The Younger Dryas Event (named after an Alpine flower common at the time.)

38 Greenland ice core data: Recall low precip means low temp. The Younger Dryas Event and Abrupt Climate Change Abrupt change Abrupt change Rapid termination of last glacial Last ice age.. Climate record punctuated by very rapid changes

39 A Possible Explanation One of best plausible explanations for the sudden nature of the changes in Younger Dryas is related to the formation of North Atlantic Deep Water. Recall NADW formation region and the processes involved

40 NADW Formation Region The Global Ocean Conveyor Belt

41 A Temporary Shutdown of NADW Formation? How? End of last glacial period, Arctic polar ice melt = large source of freshwater into the ocean. What influence would this freshwater have had on the rate of NADW formation? What influence would you imagine NADW formation might have on the Gulf Stream? What role does the Gulf Stream play in controlling climate of Europe?

42 The Westerlies and Storm Track In wintertime, cold air from N. America cools the Gulf Stream EUROPE Net transport of heat over Europe

43 The Gulf Stream and Global Warming ` The Gulf Stream is in part drawn northward by the sinking of NADW around Greenland. global warming due to increasing GHGs will be largest in the polar regions (snow-ice albedo feedback) This will lead to an increase in sea-ice melt, an associated freshening of the N Atlantic, and a reduction in the rate of NADW formation. As a result, the Gulf Stream will not be drawn as far north, meaning that northern Europe may become colder.

44 And the Feedbacks? If northern Europe is colder, this could mean longer winters, accumulation of snow and ice, and further cooling via the snow-ice albedo effect. What will be the end result? We can only speculate.. Too much untestable complexity.. But an abrupt change in climate like that which occurred during the Younger Dryas may be possible.

45 Is there any clear modern precedent for this idea?

46 1960 s: The Great Salinity Anomaly (GSA): A mass of ocean water in the N. Atlantic with anomalously low salinity, caused by Arctic sea-ice melt, that moved around the ocean until the 1970 s!

47 The GSA made the surface ocean fresher and less dense, reducing overturning and deep water formation rates.

48 The Great Salinity Anomaly

49 Overall: could a Younger Dryas-like event in future? Or will global warming dominate? New York City in the future??

50 More recent hickup hickup in climate history: The Little Ice Age also in Europe

51 Medieval warm period ( CE): Vikings were able to colonize and farm Greenland-

52 For this one, there is historical record

53 A Favorite Meteorological conditions recorded in works of art

54 Pieter Bruegel s Winter Landscape with Skaters (1565)

55 Conditions afterwards The Haywain, John Constable (1821)

56 Glacial Retreat in Europe Chamonix 1966 Chamonix Chamonix today Chamonix, 1850

57 Summary of some Natural Forcings (sources) of Such Short Term Climate Variability Variations in thermohaline circulation. Volcanic activity. El Nino Southern Oscillation. Solar variability. Precession of earth axis. Stochastic forcings.

58 4) To Go further back.. Climate Records

59 Why are we interested in more remote past climates? * direct evidence for importance of feedback loops. baseline for assessing future climate change (can see natural variations) information about the resilience of the climate system. Critical timescale information (i.e. how fast do things happen).

60 The Modern Instrumental Record: only goes back about 150 years..no context.. How do we interpret this? What is naturally induced? What is human induced? About 1C increase in 145 yrs

61 A Proxy Record for Earth Temperature Means that temperature has been reconstructed in the past, using paleoproxies - chemical signatures that record past earth conditions Interglacial periods (T~15C, 280ppm CO 2 ) Current interglacial called the Holocene Glacial periods (T~9-10C, 200ppm CO 2 )

62 Paleo Archives : Cored sediments 1000 Resolution (yrs) Deployable recorders Long-lived organisms ems.anu.edu.au/margo 1 Direct observation mclanelabs.com >10,000 Length of Record (yrs)

63 How do we know temperature in last past? Many proxies.. e.g: Tree Rings Tree ring density => temperature:

64 How do we know temperature in the past? Ice Cores Accumulation rate => temperature Chemistry of ice => temperature (& other things) Chemistry of air bubbles => GHG Particles in ice => dustiness

65 How do we know temperature in the past? Corals Chemistry of skeletal material => temperature

66 DEEP SEA PROTEINACEOUS CORALS (Gorgonians, Antipatharians, Colonial Anemones) Globally distributed 200 m 4 km water depth Annual growth rings

67 HAWAIIAN PROTEINACEOUS CORALS: EXTREME LONGEVITY Hawaiian Gerardia Collected live in 1997 C-14 Inner Age = 2730 yrs GOAL: ANNUALLY-RESOLVED 15 N RECORDS THROUGH HOLOCENE AND EARLIER Lifespans of Hawaiian deep sea corals Roark et al. PNAS cm

68 Corals Bulk 15 N ~ present ~ last 80 yrs: trend in 15 N in multiple bulk records- ( Also correlated with NAO/Temp Anomalies)

69 But what is cause? 1. Shift in NO 3 Source 15 N? (physical oceanographic change?) 2. Broad Shift in Trophic Structure? (linked to fisheries pressure, climate?) 1. The balance of N sources Trophic transfer Sewage/Manure Mean ocean NO 3 N-fixation Fertilizer AIR Denitrified NO 3 15 N ( ) +3-4 per trophic level N ( ) Trophic position

70 Fossil corals also suggest δ 15 N changes are recent In this region suggests Physical regime shift (currents w/ distinct NO 3 δ 15 N)

71 Climate change driven?

72 How do we know temperature in the Long past? Ocean Sediments- 100 s of thousands of yrs Chemistry of sediments/fossils => temperature Fossil species => temperature

73 Overall: Lessons from the Past Natural sources of large climate change exist. Potent climate feedbacks exist- makes outcome of forcings inherently unpredictable Changes between climate states can be quite rapid- not nice, slow change we may be expecting.. Will our times ongoing climate shifts result in any rapid (and unexpected) shifts???

74 END Next: going farther back..