The science and impact of climate change.

Transcription

1 The science and impact of climate change. University of Puerto Rico-Mayaguez The National Science foundation sponsored: "Coastal Area Climate Change Education (CACCE) Partnership". Mayaguez, Puerto Rico November 15, 2012 Franco Einaudi

2 Definition of weather and climate Weather is the state of the atmosphere at some place and time. Climate is a statistical concept involving average conditions over a period of a month or more and often of years of meteorological variables (temperature, humidity, precipitation, cloudiness, and winds, etc.), as well as probabilities of major events.

3 Weather and climate change on many different time scales Natural variability and climate change Natural variability refers to fluctuations about a mean that does not change. The time series is stationary. Climate change refers to long-term shifts that can be characterized by a uniform trend or by stronger or even sudden fluctuations Signals will in general have a random component and a deterministic component

4 Variability of day to day weather Timely, accurate and reliable weather warning and forecasts are essential to save lives and property

5 Record breaking events in 2011 More than 1000 lives lost in the US, almost double the yearly average NOAA estimates that 14 events each producing more than $1 billion damages occurred, the largest number since 1980 when the statistics began Previous record was nine in 2008

6 Value of Weather forecasting for life and property Galveston Hurricane (1900) versus Katrina (2005) Galveston hurricane Landfall in Texas at 5 PM 09/08/1900 > $500M (2008 dollars) in property damage ~10,000 fatalities (out of a population of ~40,000) No satellite data, no upper air network, no Numerical Weather Prediction (NWP) Katrina Landfall (2nd) in Louisiana at 6 AM 08/29/2005 > $90B in property damage (2008 dollars) > 1800 fatalities (out of a population of ~1.5M) Extensive satellite and conventional observations, good forecast 6

7 White cone 2003 Red cone :54 AM 7

8 8 Variability at the century and a few millennia time scale

9 Medieval warm period Little ice age Abrupt Change 15 o C increase in less than a decade 9

10 Variability at the thousands of millennia time scale 10

11 Global deep water ocean temperature

12 Why do we study climate?

13 Climate matters because of its impact on: Human health Food production Energy resources and use Economics Business activities Tourism Recreational opportunities

14 Natural processes: Intensification of storms and hurricanes Droughts Floods, etc. Sea level Air Quality

15 Policy decisions: Environmental regulations National security: Disputes for water availability and distribution and other resources Technology investments

16 International relations Economic development: affluent versus poorer nations Competition for natural resources Disputes for water availability and distribution Water scarcity forcing migrations

17 How do we study climate and climate change?

18 We study climate: Acquiring data By designing operational and research data networks, field campaigns, airborne and satellite missions. By designing instruments that satisfy science needs: radars, lidars, radiometers, etc. By interacting with engineers and project managers to ensure successful and safe operations in Space

19 Analyzing and handling data By developing algorithms for the analysis of data By designing data processing and storage By designing networking By designing visualization systems

20 Modeling and data assimilation By developing comprehensive models of the Earth System and attendant assimilation of data to: o Improve forecast of Weather and Climate o Understand the Earth System processes

21 Four Questions About Climate Change: Is the climate changing and what governs climate? Are humans responsible for climate change? What is the impact of climate change? What will the changes be in the next century or so?

22 Is climate change underway? Yes But climate has always changed: Natural Variability 22

23 Average Earth-Land Temperature since 1750

24 The World Has Warmed Globally averaged, the planet is about 0.75 C warmer than it was in 1860 Average surface temperature during the reference period : 14 C 24

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26 Disappearing Arctic Sea Ice? Source: National Center for Atmospheric Research

27 Himalayan (Rongbuk) Glacier Rongbuk, the largest glacier on Mount Everest s northern slopes, in 1968 (top) and Glaciers are receding rapidly world-wide, including the Rockies, Andes, Alps, Himalayas. Glaciers provide freshwater to rivers throughout the dry season and reduce spring flooding.

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29 What causes climate change? An energy imbalance: There is more incoming solar radiation than there is energy radiated back to space 29

30 Earth s Energy Budget (Balanced) incident 342 W/m W/m 2 radiated as heat 107 W/m 2 reflected 30

31 Energy Balance 342 W/m W/m W/m 2 Energy imbalance due mostly to increased trace gases 31

32 Earth s Energy Balance 32

33 What causes an energy imbalance? Forcings are environmental processes that influence the Earth s climate. The advantage of using the term forcing is to allow to express diverse changes using a common metric An energy imbalance can be caused by: o Changes in incoming solar radiation: Changes of orbit parameters Changes in solar brightness

34 o Changes in energy radiated back to space: Greenhouse Gases Cloud cover Aerosols Surface albedo o Changes due to natural variability: El Niño La Niña

35 Are humans responsible for creating such an energy imbalance?

36 Climate has always changed Global deep water ocean temperature

37 What does an ice core look like? 37

38 Change Has Been Constant During Earth s 4.5-Billion Year History Time (thousands of years before present) 38

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40 Natural Variability and the Variation of the Orbital Parameters (19,000 and 23,000 yrs) (100,000 and 400,000 yrs) (41,000 yrs) Orbital variations are producing changes in the seasonal and latitudinal distribution of incoming solar radiation at the top of the atmosphere. 40

41 Orbital Variations, insolation at 65 o N and Milankovitch theory 41

42 Orbital Variations, insolation at 65 o N and Milankovitch theory cont d Solar insolation at 65 o North displays a complex structure that includes the periodicities due to orbital variations Milankovitch theory: ice ages are triggered by minima in summer insolation near 65 0 N, enabling winter snowfall to persist The global mean forcing due to orbital variations only (i.e., no GHG and with fixed surface albedo) is ~0.25 W/m 2 Changes in surface albedo and GHG produce large positive feedbacks that bring the forcing due to orbital variations ( 0.25 W/m 2 ) to values of the order of 3 4W/m 2. 42

43 What has happened since the industrial revolution began? Are humans responsible for climate change?

44 2 400,000 Years Vostok, Antarctica Temperature Anomaly 127 Years Global Temperature Anomaly ( 0 C) Age [(Years before present (2008)] Date The current rate of warming is much more rapid than in the past 44

45 CO 2 as a function of time ,000 Years Vostok, Antarctica 2000 Years Law Dome, Antarctica 25 Years Mauna Loa, Hawai 350 Carbon Dioxide Parts per million Interglacial Ice age Industrial Revolution , ,000 2,500 2,000 1, Age Years before present (2008) 45

46 Human Fingerprints on the Climate Population doubled & then doubled again over the last century, from 1.65 billion to almost 7 billion inhabitants. Greenhouse Gases In that same span, there is a rise in the three most abundant persistent greenhouse gases that mirrors the growth in human population. Isotopic analysis and carbon cycle models established that the increase in carbon dioxide was due to fossil fuel consumption. With the rise in those greenhouse gases, Earth experienced an unusually rapid rise in its average temperature increasing ~0.75 C since 1880.

47 Radiative Forcings from Glacial to Interglacial Period a + b + c = d e Time (thousands of yrs before present) a: 0.25 W/m 2 is the forcing due to variations in the orbital parameters without GHG and albedo changes feedbacks b: 3W/m 2 is the forcing due to GHG feedback c: 3.5W/m 2 is the forcing due to albedo change feedback d: a + b + c is the total forcing due to orbital parameters, changes, and associated feedbacks e: 1.5W/m 2 is the forcing due to human activities since the industrial revolution 47

48 Comparison of forcings Forcings responsible for the transition from glacial to interglacial periods: 7 8 W/m 2 Forcings since the beginning of the industrial revolution: 1.5 W/m 2 48

49 Radiative Forcings Glacial to Interglacial Period Since the Industrial Revolution in 1750 W/m W/m ,000 Years Years 49

50 The overarching question: Can the small forces that drove millennial climate changes be now overwhelmed by human activities? This is a challenging question because the forcing since the beginning of the industrial revolution, 1.5 W/m 2, is of the same order of magnitude as the forcing, 7 8 W/m 2, responsible for the transition from glacial to interglacial periods. 50

51 Solar variation and volcanic activity GHGs and aerosols Such results suggest that anthro forcings provide plausible explanation for a substantial part of the obs temp change over the past century. 51

52 Change of climate forcings in W/m 2 between 1750 and 2000.

53 What is the impact of climate change?

54 Impact of Climate Change Why should we care about climate change? Because a few degrees can make a difference During ice ages the temperature was only C colder than today and the planet was essentially a different planet Glaciers several thousand feet thick cover much of North America and Europe Sea level 120 m lower than today because so much water was tied up in glaciers During the summer of 2003 a heat wave struck Europe and led to the death of several tens of thousand of people: the average temperature during that time was only C above the average over the past century

55 Impact of Climate Change (Cont.) If permafrost in Alaska melts, houses built on it will collapse Warming will increase amount of water vapor in the atmosphere More water vapor in the atmosphere will cause more rain fall

56 Impact of Climate Change (Cont.) More rain fall will cause heavier downpours: Soil saturates Remaining rain runs off Rain run off increases risks of erosion and flooding Less water available for ecosystems Heavier precipitation per event will tend to increase times between events Combined with warmer summers which will increase the rate of water lost from soil by evaporation, this will increase the frequency and intensity of droughts

57 Examples of possible effects of climate change

58 1 meter will be hard to avoid within a few centuries, just from thermal expansion and small glaciers melt.

59 Sea level rise of meter would have large impacts in many parts of the world. [From IPCC WG2 (2001).]

60 How will climate evolve? A difficult question to answer because the Earth System is complex. Examples: Feedback mechanisms Tipping points

61 Climate feedbacks and tipping points FE Positive feedbacks: mechanisms that reinforce and accelerate initial changes in climate Negative feedbacks: mechanisms that offset initial changes in climate Tipping points: climate configurations that when reached are irreversible, i.e., unstoppable 61

62 Feedbacks in the Climate System Water Vapor Feedbacks Temperature increases More evaporation from ocean and wet land surface More water vapor content More clouds Temperature increases Temperature decreases 62

63 Mechanisms to Affect the Energy Balance aerosols clouds 63

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66 Examples of Tipping points The great ice sheets on Greenland and Antarctica accelerate the melting The West Antarctic ice sheet begins to collapse Thawing of the permafrost accelerates

67 What will changes be in the next century or so?

68 Predictions versus Projections for climate Emission scenarios are assumed. The Intergovernmental Panel on Climate Change (IPCC) constructed four scenarios for the 21st century Such scenarios are inserted into climate models to produce statistics over time periods of years Example: projected warming over the 21 st century of C. Comment: over the 20 th century the warming was about C.

69 About forcings: Fundamental Concerns The forcing that triggered the transition from glacial to interglacial periods was of the order 0.25 W/m 2 (feedbacks came later). The forcing applied since 1750 is about 1.5 W/m 2 which is larger than 0.25 W/m 2 Forcing since 1750 has been acting over time scales of decades, not tens of thousands of years 69

70 Fundamental Concerns (Cont.) About temperature changes: The temperature has already values close to the maxima on record in the last thousands of millennia. The rate of temperature increase since the beginning of the industrial revolution is unprecedented: C in the last 100 years versus the average rate of warming since the height of the last ice age of C in 20,000 years, i.e., the present rate of warming in roughly times faster. Paleoclimate records show that warmings move faster than coolings 70

71 Fundamental Concerns (Cont.) About CO 2 changes: The concentration of CO 2 in the atmosphere has never been so high. The concentration of CO 2 has grown at an exceptional fast rate. 71

72 Fundamental Concerns (Cont.) Glaciers and ice sheets respond more quickly than anticipated Sea ice is declining faster than anticipated Positive feedbacks mechanisms in the Earth System could bring the climate towards tipping points 72

73 Is human kind carrying out an experiment? Is the mean temperature of the ground in any way influenced by the presence of the heatabsorbing gases in the atmosphere? Svante Arrhenius, Journal of Science, 1896 Human beings are now carrying out a large-scale geophysical experiment of a kind that could not have happened in the past nor be reproduced in the future. Roger Revelle & Hans Suess, Tellus,

74 The Earth s environment is changing and we are entering unfamiliar territory.

75 Thank you