1. An introduction to global climate change
On August 29, 2005, Hurricane Katrina landed east of New Orleans
The costliest ($134 billion in damage) storm ever
The deadliest storm (killing 1,800) since 1928
Leaving mountains of debris, ruined homes and lives
A month later, Hurricane Rita hit Louisiana and Texas
2005 had a record 27 named storms
2007 had 15 and 2008 had 18 named storms
There is a link between hurricanes and global warming
Warmer oceans create humid air, leading to hurricanes

2. Number of category 4 and 5 hurricanes

3. Structure and temperature of the atmosphere

4. Weather
Weather: day-to-day variations in temperature, air pressure, wind, humidity, precipitation
Climate: the result of long-term regional weather patterns
Meteorology: the study of the atmosphere (weather and climate)
The atmosphere-ocean-land system is a huge weather engine
Driven by the Sun and affected by Earth’s rotation and tilt
Solar energy is reflected (29%) or absorbed by Earth
Absorbed energy heats the ocean, land, and atmosphere

5. Solar-energy balance

6. Climate is …
Climate: the general patterns of weather that characterize different regions of the world
Climate results from all the combined elements of
General atmospheric circulation patterns and precipitation
Wind and weather systems
Rotation and tilt of Earth, which creates seasons

7. Synopsis of global climate change
In 2007, scientists from the Intergovernmental Panel on Climate Change (IPCC) sifted through thousands of studies and published the Fourth Assessment Report (AR4)
The report concluded that warming of the climate is unequivocal
The atmosphere and oceans are warmer
Sea levels are rising and glaciers are melting
There are more extreme weather events

8. Annual mean global surface temperature anomalies

9. The IPCC’s report
The report concluded that it is very likely (90% probability) that warming is caused by human factors
Increased greenhouse gases (GHGs) trap infrared radiation
GHGs come from burning fossil fuels
Along with deforestation
The major GHG: CO2
Responses to climate change
Mitigation: reducing GHG emissions
Adaptation: adjusting to climate change

10. Atmospheric carbon dioxide concentrations

11. IPCC
Founded in 1988 by the UN Environmental Program and the World Meteorological Society to provide accurate and relevant information leading to understanding human-induced climate change
The AR4 report had over 2,000 experts from 154 countries
Risk assessment: is the climate changing?
Risk management: how do we adapt and mitigate effects?

12. Third assessment The IPCC’s 2001 report showed
Increasing information shows a warming world
Humans are changing the atmosphere, which will affect climate
We have increased confidence in models of future climate change
Stronger evidence that most recent warming is human-caused
Human influences will continue to change the atmosphere
Temperature and sea levels are rising
We need more information and understanding

13. A Nobel Effort
The 2007 Nobel Peace Prize went to the IPCC and former Vice President Al Gore: the leading advocate of the need to take action on climate change
For their efforts to disseminate knowledge about man-made climate change and to lay groundwork to counter it
Gore also was awarded the Academy Award for his film An Inconvenient Truth

14. Climates in the past
It is harder to find evidence of climate change the further into the past we search
Records of temperature, precipitation, storms have been kept for only 100 years
Since 1880, especially since 1976, our climate warmed
Proxies: records providing information on climate
Using temperature, ice cover, precipitation, tree rings, pollen, landscapes, marine sediments, corals, etc.
Earth warmed from 1100 to 1300 A.D.
Little Ice Age: 1400–1850

15. Ice cores
Analyzing ice cores from Greenland and the Antarctic shows global climate can change within decades
Uses CO2 and CH4 (methane) and isotopes of O and H
Climate oscillates between ice ages and warm periods
Ice ages tie up water in glaciers, lowering sea levels
8 glacial periods occurred over the past 800,000 years
Ice ages have lower GHGs and temperatures
CO2 levels ranged between 150 and 280 ppm
Milanovitch cycles: climate oscillations due to Earth’s orbit
Periodic intervals of 100,000, 41,000, and 23,000 years

16. Rapid changes
Rapid climatic fluctuations during glaciation and warmer times
The Younger Dryas event: 11,700 years ago
Dryas: a genus of arctic flower
Arctic temperatures rose 7ºC in 50 years
Caused enormous impact on living systems
Warming was not caused by changing solar output

17. Oceans and climate Oceans play a dominant role in determining climate
They are a major source of water and heat
Evaporation: supplies water vapor to the atmosphere
Condensation: supplies heat to the atmosphere
Heat capacity: oceans absorb energy with heated water
Oceans convey heat through currents
Thermohaline circulation pattern: the effects of temperature and salinity on the density of seawater
This giant, complex conveyor belt moves water from the surface to deep oceans and back

18. The oceanic conveyor system

19. Thermohaline circulation affects climate
The movement of warm water toward the North Atlantic transfers enormous amounts of heat toward Europe, providing a much warmer than expected climate
The circulation pattern cycles over 1,000 years
It is vital to maintaining current climate conditions
In the past, the conveyor system has been interrupted
Abruptly changing the climate
Large amounts of fresh water lower water’s density
Preventing the sinking of surface waters
Slowing the northern movement of warmer, saltier water

20. Heinrich events
Heinrich events: fresh water from melting icebergs from the polar ice cap dilutes salt water
Six times in the past 75,000 years
Diluted water doesn’t sink
The conveyor system is shifted southward to Bermuda (instead of Greenland)
The climate cools in a few decades
Return of the normal pattern abruptly warms the climate
The Younger Dryas event involved dammed-up water from glacial Lake Agassiz entering the St. Lawrence

21. What if …? Extended global warming will
Increase precipitation over the North Atlantic
Melt sea ice and ice caps
The conveyor will decrease over the 21st century
The Achilles’ heel of our climate system: weakening of the conveyor and a changed climate
Especially in the northern latitudes

22. The Earth as a greenhouse
Factors that influence climate
Internal components: oceans, atmosphere, snow, ice
External factors: solar radiation, Earth’s rotation and orbit, gaseous makeup of the atmosphere
Radiative forcing: the influence of any factor on the energy balance of the atmosphere-ocean-land system
Positive (negative) forcing: leads to warming (cooling)
Forcing is measured in Watts/m2
Solar radiation entering the atmosphere = 340 W/m2
Radiation is acted on by forcing factors

23. Warming processes
Greenhouse gases (GHGs): water vapor, CO2, other gases
Light energy goes through the atmosphere to Earth
Earth absorbs and converts energy to heat
Infrared heat energy radiates back to space
GHGs (but not N2 and O2) in the troposphere absorb some infrared radiation
Direct it back to Earth’s surface
The greenhouse effect was first recognized in 1827
It is now firmly established

24. GHGs insulate Earth GHGs delay the loss of infrared heat (energy)
Without insulation, Earth would be -19°C instead of +14°C
Life would be impossible
Earth’s global climate depends on the concentration of GHGs
Changing amounts of GHGs change positive forcing agents, which would change the climate
Tropospheric ozone has a positive forcing effect
Varying with time and location

25. The greenhouse effect

26. Snow and ice contribute to albedo by reflecting sunlight
Cooling processes
Planetary albedo: sunlight reflected by clouds
Contributes to overall cooling by preventing warming
Low-flying clouds have a negative forcing effect
High-flying, wispy clouds have a positive forcing effect
Absorb solar radiation and emit infrared radiation
Snow and ice contribute to albedo by reflecting sunlight

27. Volcanoes and aerosols
Volcanic activity can lead to planetary cooling
Reflects radiation from particles and aerosols
Aerosols: microscopic liquid or solid particles from land or water
Industrial aerosols (pollution) cancel some GHG warming
Sulfates, nitrates, dust, soot from industry and forest fires
Sooty aerosols (from fires): warming effect
Reduced pollution in the U.S. and Europe decreased aerosols
China’s and India’s pollution has increased aerosols

28. Global warming and cooling

29. Solar variability
Variation in the Sun’s radiation influences the climate
Changes in solar radiation occur on 11-year cycles
Solar radiation increases during high sunspot activity
Sunspots block cosmic ray intensity
Solar output declined in 1985 and continued for 20 years
But global temperatures rose rapidly
The IPCC AR4 concluded that GHGs were 13 times more responsible for warming temperatures than solar changes

30. Thus …
Global atmospheric temperatures are a balance between positive and negative forcing from natural causes (volcanoes, clouds, natural GHGs, solar irradiance) and forcing from anthropogenic causes (sulfate aerosols, soot, ozone, increased GHGs)
Forcing agents result in climate fluctuations
It is hard to say any one event or extreme season is due to humans
But climate has shifted enough to generate international attention

31. Evidence of climate change
Weather varies naturally year to year
Local temperatures may not follow global averages
But the 10 warmest years on record were 1997–2008
2005 set a record high—the warmest since the late 1800s
The average global temperature has risen 0.6°C since the mid-1970s (0.2°C/decade)
Warming is happening everywhere
Most rapidly at high latitudes of the Northern Hemisphere
The warming is a consequence of an “enhanced greenhouse effect”

32. Ocean warming
Recently, the upper 3,000 meters of the ocean have warmed
Dwarfing warming of the atmosphere
90% of the heat increase of Earth’s systems
Over the last decade, oceans have absorbed most of the non-atmospheric heat
A long-term consequence: the impact of this stored heat as it comes into equilibrium with the atmosphere
It will increase atmospheric and land heat even more
A short-term consequence: unprecedented rising sea levels
Thermal expansion and melting glaciers and ice caps

33. The rise in global mean sea level

34. Other observed changes by the IPCC AR4
Changes are consistent with GHG-caused climate change
Increased warm temperature extremes
Decreased cold temperature extremes
Spring comes earlier, fall later, in the Northern Hemisphere
Ecosystems are out of sync
Tree deaths and insect damage
Heat waves are increasing in intensity and frequency
Droughts are increasing in intensity and frequency
60% of the U.S. is in a drought that started in the 1990s

35. More changes reported by the IPCC
Rising Arctic temperatures have caused major shrinkage of Arctic sea ice (11.7% in 10 years)
Alaska, Siberia, Canada have warmed 5°F in summer, 10°F in winter
Spring comes 2 weeks earlier than 10 years ago
The polar ice cap has lost 20% of its volume in 20 years
Permafrost is melting
Unprecedented melting of the Greenland Ice Sheet can raise ocean levels 23 feet

36. Decline of Arctic sea ice

37. Other changes reported by the IPCC
Antarctica temperatures have risen 0.5°–0.85°C
The West Antarctic Ice Sheet (WAIS) is shrinking and can raise sea levels by 16–20 feet
Accelerating glacier melting since 1990
Changing patterns of precipitation and flooding
Greater amounts from 30° N and S poleward
More intense and frequent tropical hurricanes
Marine fish populations have shifted northward
Ocean acidification: decreased pH due to CO2 absorption
The surface ocean’s chemistry is actually changing

38. Carbon dioxide levels
CO2 levels oscillate 5–7 ppm, reflecting seasonal changes in photosynthesis and respiration
Fall through spring: respiration increases CO2 levels
Spring through fall: photosynthesis decreases CO2
By 2009, atmospheric CO2 levels = 338 ppm
39% higher than before the Industrial Revolution
Higher than in the past 800,000 years
Fossil fuels increase CO2 levels
1 kg of fossil fuel burned releases 3 kg CO2
Eight billion tons (gigatons, Gt) of fossil fuel carbon/year

39. Sources of carbon dioxide
Half of fossil fuel carbon comes from industrialized nations
Burning forests
Over the past 50 years, release of carbon has tripled
Half of the carbon is removed by sinks
Sinks: burning fossil fuels should add 8 GtC/year to the air
But only 3.3 GtC/year are actually added
Carbon sinks (the ocean, biota) absorb CO2
Oceans take up CO2 by phytoplankton or undersaturation
But there are limitations to uptake
Forests are valuable for their ability to sequester carbon

40. Sources of carbon dioxide emissions from fossil fuels

41. Other gases Other gases absorb infrared radiation
Adding to the insulating effect of carbon dioxide
Most are anthropogenic sources and are increasing
Water vapor: the most abundant GHG
Its tropospheric concentration varies, but is rising
Higher temperatures increase evaporation and water vapor (humidity)
Higher humidity traps more heat, causing more warming (positive feedback)

42. Other GHGs Methane: 20 times more effective than CO2 in heating
From microbial fermentation (in wetlands), green plants
Two-thirds of emissions are from human sources: livestock, landfills, coal mines, natural gas, rice cultivation, manure
Rising at 0.8 ppb/year, it is more abundant than in the past 800,000 years
Nitrous oxide: has increased 18% over the last 200 years
From agriculture, oceans, biomass burning, fossil fuel burning, industry, anaerobic denitrification (fertilizers)
Warms the troposphere and destroys stratospheric ozone

43. Ozone and CFCs Ozone: a short-lived but potent GHG in the troposphere
From sunlight acting on pollutants
Has increased 36% since 1750
From traffic, forest fires, agricultural wastes
CFC and other halocarbons
Long-lived GHGs causing warming and ozone destruction
From refrigerants, solvents, fire retardants
They absorb 10,000 times more infrared energy than CO2
Levels are slowly declining but will remain for decades

44. Future changes in climate
Happening now: higher temperatures, rising seas, heat waves, droughts, intense storms, season shifts, melting ice
GHG levels are rising
Along with fossil fuel demand and population
Emissions will rise 35% (2030) and 100% (2050)
Modeling global climate: computing power has increased
Can explore the potential future impacts of rising GHGs
Atmospheric-ocean general circulation models (AOGCMs)
Simulate long-term climatic conditions

45. Significant findings of climate models
Equilibrium climate sensitivity: if atmospheric CO2 stays at 550 ppm (double preindustrial values), temperature will rise 3°C (2°–4.5°C) by 2050
Higher latitudes and continental interiors will warm most
But it will be warmer everywhere
Snow cover and sea ice will decrease, opening up the Arctic Ocean by 2100
Shrinking glaciers and ice caps will increase sea levels
90% of upper permafrost will thaw

46. More findings
Warmer, dilute upper layers of the North Atlantic Ocean will lead to decreased (but not collapsed) thermohaline circulation
Increased storm intensities, higher wind speeds and waves, more intense precipitation
More frequent, longer-lasting heat waves
Longer growing seasons, shorter frost days
Dry areas will get dryer, wet areas will get wetter
Extreme droughts will affect up to 30% of the world
Ecosystems (polar ecosystems, coral reefs, rainforests) will be profoundly affected, increasing species extinctions

47. What about the Antarctic?
The Antarctic could be a huge factor in rising sea levels
Greenland and Antarctic ice sheets hold enough water to raise sea levels 230 feet
Snowfall has not changed in the past 50 years
87% of the 244 glaciers are melting
The melting ice sheet is raising sea levels 0.4 mm/year
Higher continental temperatures (3°C)
Models project a 5% snowfall increase for each 1°C temperature rise

48. Climate change in the U.S.
All impacts are expected to continue and/or increase
Impacts are greater in Alaska than any other U.S. region
Changes in the U.S. over the past 50–100 years include
Average temperature has risen 2°F
Wetter areas are wetter, dryer areas are dryer
Heavy downpours and storms have increased
More extreme and frequent weather events
Stronger Atlantic hurricanes
Arctic sea ice is declining rapidly

49. Response to climate change
Industries and transportation network are locked into using fossil fuels
Massive emissions of GHGs will continue
Adaptation: anticipate harm and plan adaptive responses to decrease vulnerability of people, property, and the biosphere
Mitigation: take action to prevent emissions
Skeptics about global warming exist
Fossil fuel industry, Rush Limbaugh, conservative think tanks, some scientists