The greenhouse effect and global warming

1
Global Warming and the Climate System http//www.
motherjones.com/news/featurex/2006/03/oceans_index
.html
2
(No Transcript)
3
(No Transcript)
4
To understand how climate has changed in the
past, we need to use records of climate preserved
in ice cores, ancient tree rings, coral bands,
and other paleoclimatic sources
5
Temperature is a state variable of the Climate
System.
Changes in temperature are associated with
Climate Change
Understand processes that control TEMPERATURE
changes
6
A paleo perspective
CO2
Temperature
7
Whats the greenhouse effect?
greenhouse gases in the atmosphere trap heat at
the Earths surface and prevent it from escaping.

• These gases include
• Carbon dioxide CO2
• Methane CH4
• Nitrous oxide N2O
• Chlorofluorocarbons
• Water vapor H2O
• (this is the most important one, by far!)

8
The greenhouse effect occurs naturally...
9
A paleo prospective
CO2
5 C
Temperature
10
Changes in atmospheric CO2 induced by humans
11
CO2
changes in the last 300 yr
12
from thermometers
from paleo records
0.8 C
13
Why doesnt a 70 ppm change in CO2 correspond to
a 4 C change?
The climate system does not reach equilibrium
instantaneously Other processes can change the
equilibrium temperature.
14
Other greenhouse gases are also increasing
15
Evidence of Global Warming in the Climate System
16
Glacier melting
Evidence of Global Warming in the Climate System

• Kilimanjaro ice caps are 80 gone since early
  1900s
• All glaciers in tropics are melting rapidly
• Impacts water supply, power generation, tourism,
  local climate and ecology

17
(No Transcript)
18
Arctic - the most sensitive ecosystem?

• Arctic sea ice has shrunk by 1 million sq km and
  thinned from 3.1m to 1.8m average
• More freshwater, reduced ability to travel over
  ice
• All summer ice gone in this century
• Ecological consequences huge!

19
Arctic warming

• Sea ice melting
• Key feedback! (animation)
• Reduces albedo (reflectivity) of earth, allowing
  more radiation to be absorbed
• http//www.gsfc.nasa.gov/topstory/2003/1023esuice.
  html
• Warming temperature
• Melts permafrost
• Ice sheet stability? Key sea level question!
• Rate of warming 8x faster in last 20 years than
  in last 100

1979
2003
20
Arctic ecosystems impacts

• Reduced ice less algal production under ice
  undermines base of food chain
• Seal pups emerge just when ice is melting -
  earlier melt means they are exposed before ready
  to thrive
• Caribou need ice to island-hop they are falling
  through as ice thins
• Polar bears hunt on ice in winter, retreat to
  land in summer. Less ice forces them onto land
  earlier

21
More intense storms
Hurricanes get their energy and staying power
from warm water in the tropical oceans. As
waters get warmer, we expect that hurricanes will
become more intense.
22
Higher sea level

• As water warms, it expands (thermal
  expansion).
• Glaciers are melting
• Observation 3mm/yr in past few decades
• Prediction 0.5m rise by the end of this
  century, 2-4m in 500 years

• This will have a major impact on
• Developed coastal regions
• Low-lying island nations
• Intensity of coastal flooding during storm surges
• Coastal ecosystems (e.g. mangroves, estuaries)

23
What is the role of human emissions? Are we
responsible or is it just a natural cycle of the
climate system?
24
(No Transcript)
25
The temperature in the climate system is
controlled by many different processes, however
anthropogenic forcing by CO2 represents one of
the major contributors
26
(No Transcript)
27
What will happen in the future?
28
70 ppm
29
CO2
TEMPERATURE
4.5 C
30
Warmer temperatures
Prediction Doubled CO2 will warm the planet by
1.8-5.8C (before 2100) Some areas warm up more
than others. Continents warm faster than
oceans. Higher latitudes warm more than low.
Map of predicted temperature change for a
doubling of atmospheric CO2
31
Can we do anything about it?
32
stop emitting and fix the concentration
constant emissions
33
Who is responsible for CO2 emissions?(these data
are relatively correct even for today)

• Mainly the U.S. 25
• Other industrialized countries 25
• Developing world 30
• Remaining 20 split Mideast, former Soviet
  Union, E. Europe.

34
Personal choices make a difference!

• About one third of all GHG emissions in the US
  are related to personal choices
• How you travel
• Home energy use
• Waste production
• The remaining 2/3 is related to factors like
  industry, agriculture, and business uses

3.1 tons/yr CO2
14.3 tons/yr CO2!!
35
Is human-caused global warming for real?

• The evidence
• Greenhouse gases are rising due to human activity
• The greenhouse effect is real (past climate
  example)
• The Earth is warming up
• No other obvious causes are seen
• This point is no longer debated by climate
  scientists (IPCC)
• http//www.ipcc.ch/
• What can be done?
• Personal choices
• Political actions (e.g. a successor to the Kyoto
  treaty capping carbon emissions)
• Industry initiatives (e.g. hybrid gas-electric
  cars)

36
What can or should be done about global warming?

• Potential for dramatic irreversible consequences
• Evidence that changes are beginning
• But there is uncertainty about details of future
  change
• What gets in the way of action?
• Uncertainty
• (dont we always make decisions in the face of
  uncertainty?)
• Economics
• (is this really an issue? How are estimates of
  costs made, and what are the costs of doing
  nothing? What are the benefits of acting?
• Politics
• Do governments follow scientific advice?

37
Thermohaline circulation
Responable for heat transport
38
Slow/shut down thermohaline circulation?

• Future climate gt more precipitation over North
  Atlantic
• Surface ocean there will become fresher, less
  dense.
• Leads to weaker or failed thermohaline circulation

One possibility Predicted cooling of Europe
directly related to thermohaline collapse.
39
Changing where plants and animals can live
Plant and animal species are best adapted to
certain climate conditions.

• General pattern northward migration of
  ecosystems
• Also some areas get wetter (shrinking grasslands)
• Extinctions likely as new stresses are added to
  threatened species

40
(No Transcript)
41
Climate surprises we dont know enough about
climate to predict it perfectly
Even relatively simple things are hard to predict
accurately. Best guess is that the globe will
warm by about 3C, but

• Will El Niños become more frequent?
• Will another Dust Bowl-scale drought occur?
• Will the oceans thermohaline circulation
  collapse?
• Will the west Antarctic or Greenland ice sheets
  melt? (125,000 years ago - melting ice sea
  level 5 m above present)

42
(No Transcript)
43
(No Transcript)