1. Chapter 13: Climate Change and the causes of change

2. OUTLINES 1. Climate and Climate System 1.1 Weather versus Climate
1.2 Climatic Controls
1.3 Climate System Components
2. Forcing, Response, Coupling and Feedback
3. Climate Change Through Time
4. Causes of Change
5. Global Warming and Greenhouse Effects
6. Climate Modeling
4.1 Coupled Ocean-Atmosphere-Land-Ice Model
4.2 Role of Forcing Factors
Natural [volcanos + sun] Variability versus Human [GHG + sulfate] Effects
7. Summary

3. 1.1 Weather versus Climate
The condition of atmosphere at a given time and place
Short-term (and large) fluctuations that arise from internal instabilities
of the atmosphere
Occurs as a wide variety of phenomena that we often experience
Effects are immediately felt
Social and economic impacts are great but are usually localized
Many such phenomena occur as part of larger-scale organized systems
Governed by non-linear chaotic dynamics; not predictable
deterministically beyond a week or two.

4. 1.1 Weather versus Climate Climate
Defined as the average state of the atmosphere over a finite time
period and over a geographic region (space).
Can be thought of as the “prevailing” weather, which includes the
mean but also the range of variations
Intimate link between weather and climate provides a basis for
understanding how weather events might change under a
changing climate
Climate is what you expect and weather is what you get.
Climate tells what clothes to buy, but weather tells you what clothes to wear.

5. Weather and Climate

6. 1.2 Climatic Controls
The world's many climates are controlled by the same factors as affecting weather,
intensity of sunshine and its variation with latitude,
distribution of land and water,
ocean temperature and currents,
mountain barriers,
land cover,
atmospheric composition.
This map shows sea-level temperatures (°F).

7. 1.3 The Climate System Components

8. 1.3 Climate System Components
Atmosphere
Fastest changing and most responsive component
Previously considered the only “changing” component
Ocean
The other fluid component covering ~70% of the surface
Plays a central role through its motions and heat capacity
Interacts with the atmosphere on days to thousands of years
Cryosphere
Includes land snow, sea ice, ice sheets, and mountain glaciers
Largest reservoir of fresh water
High reflectivity and low thermal conductivity
Land and its biomass
Slowly changing extent and position of continents
Faster changing characteristics of lakes, streams, soil moisture
and vegetation
Human interaction
agriculture, urbanization, industry, pollution, etc.

9. 2. Climate: Forcing and Response
Input
Machine
Output

10. Forcing and Response: A Bunsen Burner Experiment
Three major kinds of climate forcing in nature:
Tectonic processes
Earth-orbital changes
Changes in Sun’s strength
Anthropogenic forcing
Urbanization
Deforestation
Burning fossil fuels
Agriculture
Response time depends on “materials” or “components”.

11. Response Times of Various Climate System Components

12. Climate System
Coupling of components
Positive coupling between A & B (A  B):
A incr. => B incr.; A decr. => B decr.
Negative coupling: A —o B
A incr. => B. decr.; A decr. => B incr.

13. Feedbacks
A feedback is a mechanism whereby an initial change in a process will tend to either reinforce the change (positive feedback)
or weaken the change (negative feedback).

14. (+) A’s body T B’s body T A’s blanket T B’s blanket T Correct setup
(–)
Incorrect setup
A’s body T
A’s blanket T
B’s blanket T
B’s body T
(+)

15. Equilibrium states
Correct elec. blanket setup with negative feedback loop => equilibrium state.
Stable equilibrium: Minor perturbation from this state will return to the same equilibrium.
Stable eq.
state
Stable eq.
state

16. Unstable equilibrium states
At an unstable equilibrium state, the smallest disturbance moves the system away towards a stable equil. state (if one exists).
System rarely stays at an unstable equil. state for long.

17. Example of a positive feedback
Think about the polar regions:

18. Example of a positive feedback
More energy retained in system
Albedo decreases, Less solar energy reflected
Warm temperatures
Ice and snow melt
If this were the only mechanism acting, we’d get a runaway temperature increase

19. Snow and ice albedo feedbacks in the polar regions are to blame for the large changes already observed.
1997
2000
Ninnis Glacier Tongue
Antarctica

20. Example of a negative feedback
More energy retained in system
Albedo decreases Less solar energy reflected
Warm temperatures
More evaporation More clouds

21. Example of a negative feedback
More energy retained in system
Albedo increases More solar energy reflected
Warm temperatures
More evaporation More clouds

22. 3. Climate Change Through Time

23. Holland in 1565 (Little Ice Age)

24. Climate Change Since the Last Glacial Maximum
Data important for estimating past climate include:
lake bottom sediment, ice cores, fossil evidence, written documents, coral isotopes, calcium carbonate layers in caves, borehole temperature, and dendrochronology or tree ring data.
These data have helped identify several important climate change events in the past 18,000 years.

25. The Earth’s Climate History
Over the last century, the earth’s surface temperature has increased by about 0.75°C (about 1.35°F).
Little Ice Age = Cooling during 1,400 A.D. – 1,900 A.D. (N.H. temperature was lower by 0.5°C, alpine glaciers increased; few sunspots, low solar output)
Medieval Climate Optimum (Warm Period) = Warming during 1,000 A.D. – 1,300 A.D. in Europe and the high-latitudes of North Atlantic (N.H. warm and dry, Nordic people or Vikings colonized Iceland & Greenland)
Holocene Maximum = 5,000-6,000 ya (years ago) (1°C warmer than now, warmest of the current interglacial period)
Younger-Dryas Event = 12,000 ya (sudden drop in temperature and portions of N.H. reverted back to glacial conditions)
Last Glacial Maximum = 21,000 ya (maximum North American continental glaciers, lower sea level exposed Bering land bridge allowing human migration from Asia to North America)
We are presently living in a long-term Icehouse climate period, which is comprised of shorter-term glacial (e.g., 21,000 ya) and interglacial (e.g., today) periods. There were four periods of Icehouse prior to the current one.
For most of the earth’s history,
the climate was much warmer than today.

26. Proxy Records of Climate
Recent times: instrumental
More recent times: historical, tree rings, ice cores
Proxies for more ancient climates are found in sediments or inferred from fossils and land forms.
Limted to usually last years except for ice cores
Can generally only resolve changes that occur over 100 years or greater

27. Yearly Temperature Change for the Last 1000 Years
Small climate changes (0.5°C)
Data from tree rings, corals, ice cores, and historical records are shown in blue. Data from thermometers are shown in red.
About 1000 y.a., the N.H. was cooler than now (e.g., average). Certain regions were warmer than others. Warm and dry summers in England ( ): vineyards flourished and wine was produced. Vikings colonized Iceland and Greenland.

28. Global temperature over the last 1000 years.
Global temperature over the past 1000 years.
The past 140 years
Global temperature over the last 1000 years.
Going back further in time, looking at the past 1000 years, we cna see that average temperatures are higher now than they have been in the past 1000 years. CO2 is also higher now than in the past 1000 years.

30. Yearly Temperature Change for the Last 140 Years
Data over the globe (land and sea).
Warming periods: (by 0.5°C), the mid-1970s to present.
The warmest decade: the 1990s. The warmest year: second warmest year on record. Over last 25 years warming ~ 0.5 C
Over past century warming ~ 0.75 C
Cooling periods:

31. Surface air temperature trends over the past century
The warming has been greatest at night over land in the mid-to-high latitudes of the northern hemisphere. The warming during the northern winter and spring has been stronger than at other seasons. In some areas, primarily over continents, the warming has been several times greater than the global average. In a few areas, temperatures have actually cooled, e.g., over the southern Mississippi Valley in North America.

32. local temp. trends

34. An increasing body of observations gives a
collective picture of a warming world and
other changes in the climate system
Global mean surface temperature increase
(NH, SH, land, ocean)
Melting of glaciers, sea ice retreat and thinning
Rise of sea levels
Decrease in snow cover
Decrease in duration of lake and river ice
Increased water vapor, precipitation and
intensity of precipitation over the NH
Less extreme low temperatures, more
extreme high temperatures

37. Recent Range Shifts due to Warming
Species Affected
Location
Observed Changes
Arctic shrubs
Alaska
Expansion into shrub-free areas
39 butterfly spp.
NA, Europe
Northward shift up to 200 km in 27 yrs.
Lowland birds
Costa Rica
Advancing to higher elevations
12 bird species
Britain
19 km northward average range extension
Red & Arctic Fox
Canada
Red fox replacing Arctic fox
Treeline
Europe, NZ
Advancing to higher altitude
Plants & invertebrates
Antarctica
Distribution changes
Zooplankton, fish & invertebrates
California, N. Atlantic
Increasing abundance of warm water spp.
Walther et al., Ecological responses to recent climate change, Nature 416:389 (2002)

38. Modes of Climate Variation
Periodic variation
Abrupt shift in climate state
Will show proxydata and model results
Warming or cooling to new climate state
Changes in amplitude or frequency of climate oscillations

39. 4. Mechanisms of Climate Variability and Change: External versus Internal Forcing
Changes in the Sun and its output, the Earth’s rotation rate,
Sun-Earth geometry, and the slowly changing orbit
Changes in the physical make up of the Earth system, including
the distribution of land and ocean, geographic features of the land,
ocean bottom topography, and ocean basin configurations
Changes in the basic composition of the atmosphere and ocean
from natural (e.g., volcanoes) or human activities
Internal
High frequency forcing of the slow components by the more rapidly
varying atmosphere
Slow variations internal to the components
Coupled variations: Interactions between the components

40. Factors that influence the Earth's climate

41. The Milankovitch Hypothesis
Milutin Milankovitch first proposed the following idea in the 1930s.
Changes in climatic cycles of glacial-interglacial periods were initiated by variations in the Earth’s orbital parameters (Earth-Sun geometry factors)

42. Eccentricity: Earth’s orbit around the sun
Orbit = Ellipse
(Eccentricity = 0.05 shown
today
maximum)
Orbit = Circle
(Eccentricity = 0)
Varies from near circle to ellipse with a period of 100,000 years
Distance to Sun changes  insolation changes

43. Obliquity: Tilt of the Earth’s rotational axis
Cycle of ~ 41,000 years
Varies from 22.2 to 24.5°
(The current axial tilt is 23.5°)
Greater tilt = more intense seasons
If Earth’s orbit were circular,
No tilt = no seasons
90° tilt = largest seasonal differences at the poles (6 mon. darkness, 6 mon. overhead sun)

44. Precession: positions of solstices and equinoxes in the eccentric orbit slowly change
Wobbling of the axis
Turning of the ellipse
Period of about 23,000 years

45. Earth’s Orbit Changes Through Time

46. Warming from the last glacial interval to the present was interrupted by several large and abrupt plunges back into cold periods. Evidence points the oceanic thermohaline conveyor belt as the mechanism for these rapid climate changes

47. Climate Change and Variations in Solar Output
More sunspots, stronger solar emissions from the Sun.

48. Sunspot History from Telescopes
The telescope records show:
11-year sunspot cycle.

49. 5. Global Warming and Greenhouse Effects

50. Natural or Anthropogenic?

51. Atmospheric CO2 Concentrations Are Increasing as a Result of of Human Emissions
CO2 levels in the atmosphere have increased from 280 parts per million in 1860, the beginning of the Industrial Revolution, to 370 parts per million in 1998, about a 30% increase.
CO2 concentration data from before 1958 are from ice core measurements (tiny air bubbles trapped in ice core samples) taken in Antarctica. Since 1957, scientists have been making continual measurements of atmospheric CO2 at an observatory in Mauna Loa, HI. [Annual variation is due to CO2 uptake by growing plants; the uptake is highest in the northern hemisphere springtime.]
Over the same time period (from 1860 to present), methane concentrations have almost tripled and nitrous oxide concentrations have risen by about 15%.
Greenhouse gases hang around in the atmosphere for long time periods before they are broken down. Increases in all of these gases in the atmosphere last from decades to centuries, so yesterday’s emissions are today’s visible impacts on the climate. Today’s emissions will be affecting the climate well beyond the 21st century. This is also known as our "commitment to climate change". That is, we are committed to a course of changing climate, even if we were to stop all CO2 emissions immediately, because of the long lag time of effects in the atmosphere.

52. Atmospheric CO2 concentrations--past 1000 years.

53. Global average temperatures are increasing with increases in CO2.
Global Average Temperature Is Increasing
The term global warming is used to describe the enhanced greenhouse effect resulting from human activities. The blue line shows CO2 records from ice cores, the tan line shows CO2 records from atmospheric measurements in Hawaii, and the red line shows mean yearly temperature trends.
This steady increase of CO2 in the atmosphere has caused greater retention of heat and a gradual warming of the earth: global average surface temperature has risen by about 1°F over the last century.
Temperature Trends in the U.S.
Data from climate stations across the U.S.A. show that most regions of the country have warmed over the past 100 years. Trend analysis shows that temperatures have warmed between 1.8 and 5.4°F (1–3°C) over much of the U.S. A.
Rainfall patterns have also changed across the U.S.A. Over, there has been an increase in precipitation events (rain and snow), and precipitation is coming down in fewer, more extreme events (floods and very heavy snowfalls).

54. CO2 (ppm)
CH4 (ppb)
1000
2000
N2O (ppb)

56. 6. Climate Modeling

57. Climate models Use quantitative methods to simulate
the interactions of the atmosphere,
oceans, land surface, and ice.
Climate models are mainly used for
predictions and simulations.

58. Dynamical/physical models
Using physical principles to describe the
relationship among different components of
climate system in the form of mathematical
equations. These mathematical equations are called
dynamical models. By solving the
equations, we can simulate and predict the
components of the earth climate system.

59. Climate Model – what does it do?
Starts with known physical laws – conservation of momentum, energy, & mass.
Views atmosphere, oceans, land as a continuum (i.e. all spatial scales present satisfying same laws).
Find and uses numerical approximations to the continuum physical laws.
Integrate in time to develop climate statistics same as observed-evaluate success by extent of agreement.
On global scale, this agenda very successful.

60. Climate Model Scaling/parameterization
Need to describe details within the grid boxes

61. Global climate model
These models are the most complex. The models divide atmosphere or ocean into a horizontal grid with a typical resolution of 2-4 degree latitude by 2-4 degree longitude and layers in the vertical. They directly simulate winds, ocean currents and many other processes. Feedback processes are simulated in the coupled atmosphere and ocean GCMs - water vapor, clouds, seasonal snow and ice.

62. Scheme of a coupled atmosphere ocean model and supplementary models.

63. Ideal gas

64. Newton's law

65. Navier Stokes Equations

66. Coriolis force

67. First law of thermodynamics

68. Model Grid:

71. The 21st century predicted by the HadCM3 climate model (one of those used by the IPCC) if a business-as-usual scenario is assumed for economic growth and greenhouse gas emissions. The average warming predicted by this model is 3.0°C.

72. Time evolution of globally averaged temperature change relative to the period The top graph shows the results of greenhouse gas forcing, the bottom graph shows the results of greenhouse gas forcing plus aerosol forcing.

73. Time evolution of globally averaged precipitation change relative to the period The top graph shows the results of greenhouse gas forcing, the bottom graph shows the results of greenhouse gas forcing plus aerosol forcing.

75. The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by two United Nations organizations, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) to assess the "risk of human-induced climate change".
IPCC: first assessment report in 1990
second assessment report in 1995
third assessment report in 2001
fourth assessment report in 2007
Intergovernmental Panel on Climate Change (

76. IPCC reports should be the most authoritative reports on climate change, and are widely cited in almost any debate related to climate change. The reports have been influential in forming national and international responses to climate change.
A small but vocal minority (less than 1.5%) of the scientists involved with the report have accused the IPCC of bias.

77. Evidence of some uncertainties:
(1) The individual models often exhibit worse agreement with observations.
(2) All models have shortcomings in their simulations of the present day climate of the stratosphere, which might limit the accuracy of predictions of future climate change.
(3) There are problems in simulating natural seasonal variability.
(4) Coupled climate models do not simulate with reasonable accuracy clouds and some related hydrological processes.

78. Confidence in the ability of models to project
future climate has increased
Simulated Annual Global Mean Surface Temperatures
Volcanic and solar activity
ghg and sulphate aerosols
all
(b) Able to explain most recent increases, but best fit given for (a)+(b)
This doesn’t exclude the possibility other forcings have played a role too.

79. Global warming  Heating  Temperature  & Evaporation 
water holding capacity  
atmospheric moisture 
 
greenhouse effect  & rain intensity 
Floods & Droughts

80. Growing Cooperation Between Modelers and Field-Scientists
“Your tools are terribly antiquated and imprecise”
“You produce junk and waste a lot of money”
Climate Modeler
Field-Geologist
Solution: interdisciplinary collaborations!
Requirement: understanding each others ‘language’

81. 7. Summary Climate change occurs through all time scales.
Climate conditions at a given period are a result of complex interactions among components of the climate system driven by specific forcing factors.
Climate modeling is a powerful approach to studying the cause-effect relationships.
Observed data (proxy and instrumental) are critical for calibrating climate models.
Understanding the causes and effects of global warming is one of the grandest challenges facing today’s scientists and the public.

82. Thank You!