2 (No Transcript) 3 Is the climate becoming warmer and warmer?
According to the National Academy of Sciences, the Earth's surface temperature has risen by about 1 degree Fahrenheit in the past century, with accelerated warming during the past two decades.
There is new and stronger evidence that most of the warming over the last 50 years is attributable to human activities.
Human activities have altered the chemical composition of the atmosphere through the buildup of greenhouse gases primarily carbon dioxide, methane, and nitrous oxide.
The heat-trapping property of these gases is undisputed although uncertainties exist about exactly how earth's climate responds to them.
4 Global temperature trendNote that these are surface temperatures and mostly overland. The temperature in upper levels may be different, even reversed. 5 What cause the temperature of the atmosphere to go up?
There are many possible mechanisms that can cause the warming of the atmosphere, for example
Natural variation the climate becomes warmer by internal chaotic dynamics of the earth-atmosphere system (that is, no external influence).
Solar activity either direct increase of solar energy output or indirect trigger mechanisms due to solar activity (though nobody knows how) may cause the surface temperature to go up.
Greenhouse effect increasing greenhouse gases such as CO2, CH4, NO, CFC,etc. (actually H2O is very efficient, too, but at present it is assumed to be in steady state).
The last one is presently thought to be the most likely cause of the global warming and hence we will examine it here in this section
6 The real greenhouse 7 The (Atmospheric) Greenhouse Effect
In the atmosphere, gases such as H2O, CO2, CH4, CFC, etc., are capable of absorbing the terrestrial radiation (peaking at infrared wavelength) and re-radiate in all directions.
Thus part of the re-radiation is sent back to the surface.
This means that in the presence of these gases, the atmosphere will be warmer than without them.
These gases thus play the role of glass panels in a greenhouse. (Hence the name greenhouse gases).
It is therefore reasonable to expect that increasing concentrations of greenhouse gases will cause warming in the atmosphere.
Currently, CO2 is the main suspect of causing global warming because combustion of fossil fuel naturally injects CO2 into the atmosphere.
Whereas other natural processes also inject CO2, the industrial combustion process seems to play a significant role in the concentration increase.
8 Atmospheric Carbon Dioxide
Keeling has kept track of the atmospheric concentration of CO2 since 50s.
The chart to the right shows a steady increase of CO2 concentration in the last five decades.
Although this chart is based on Mauna Loas data, the same trend has been found in many other places.
9 South Pole and Barrow, Alaska, show the same trend as Hawaii 10 How is the CO2 increase connected to the global warming?
Through the greenhouse effect, of course.
The connection is usually made via the use of a climate model.
A climate model is usually a kind of the atmospheric general circulation models which simulate the physical and dynamical processes of the atmosphere (and oceans in some models) by solving relevant equations describing these processes.
A control run of the model is performed first and the results are regarded as a reference.
Hopefully the reference results agree with observations to a certain extent.
Then other runs, in which the amounts of CO2 assumed in the model are increased (e.g., 2X or 4X), are performed and the results are compared with the reference.
If the new results show warmer surface condition than the control, then it is plausible to suspect that the increasing CO2 concentration in the atmosphere may cause warming.
11 How fast will the CO2 concentration increase?
There are various estimates of the CO2 increasing rate.
They are different in the statistical models used (for example, linear vs. nonlinear increase) and the future regulations.
12 Projection of future warming 13 Other speculations Of course the physical environmental change will lead to changes in the biosphere including our society. 14 Not everybody is convinced of the greenhouse gases - global warming theory
At this point, it appears that the warming itself is real the surface temperature indeed becomes higher in the last few decades.
The question is Is the warming caused by the greenhouse gases (especially CO2)?
Some groups, especially the IPCC members argue strongly for it. But there are other groups that are not convinced.
15 Not everybody is convinced of the greenhouse gases - global warming theory
World leaders gathered in Kyoto, Japan, in December 1997 to consider a world treaty restricting emissions of ''greenhouse gases,'' chiefly carbon dioxide (CO2), that are thought to cause ''global warming'' severe increases in Earth's atmospheric and surface temperatures, with disastrous environmental consequences.
Predictions of global warming are based on computer climate modeling, a branch of science still in its infancy.
The empirical evidence actual measurements of Earth's temperature shows no man-made warming trend.
Indeed, over the past two decades, when CO2 levels have been at their highest, global average temperatures have actually cooled slightly.
16 Some examples of criticisms
There are evidence showing that the current temperature isnt really that warm compared to what was two to three thousand years ago.
The figure to the right shows that the temperature of Sargaso Sea fluctuates in a range of 3.6C.
Also the trend depends on the data sets and the section of data you select to examine see the lower chart.
By using a different data set (here the satellite microwave sounding) and selecting a suitable section (for example, 1978-1998) you can actually show that there was a cooling, not warming.
Source Robinson et al. (1998) 17 Solar Warming There are also evidence showing that the solar activity seems to have some influence on atmospheric temperature. But there are many questions here. Especially on how and how much. 18 Global Warming More than a scientific problem - Aside from scientific problems, there are political problems as well.
At Climate Meeting, Unlikely Ally for Have-Nots
By AMY WALDMANNew York Times 1 Nov 2002
NEW DELHI, Friday, Nov. 1 When India's prime minister, Atal Bihari Vajpayee, finished speaking at the international conference on climate here on Wednesday, the fissure between richer and poorer countries over how best to tackle global warming could no longer be papered over.
In his speech, he argued that poorer countries could not be expected to invest money in tackling the causes of global warming. They bear little responsibility, he said, producing fewer greenhouse gases than industrialized countries, and yet have been hit harder by the natural calamities, from drought to floods, caused by climate changes. They have weaker economies, and with pressing needs in everything from health to education, can little afford to invest in clean-air technologies.
19 Global Warming More than a scientific problem - Aside from scientific problems, there are political problems as well.
At Climate Meeting, Unlikely Ally for Have-Nots
By AMY WALDMANNew York Times 1 Nov 2002 His speech articulated sentiments resentments, in some cases widely shared among developing nations. So while it produced little new of substance, the conference, the eighth since the United Nations Framework Convention on Climate Change was adopted in 1992, illuminated the challenges in crafting a global response to global warming.
It highlighted a divide between north and south, between the industrialized and developing worlds, over who should bear the obligations and burdens of trying to reduce the emissions that cause global warming.
But on several points, the south found itself with an unlikely ally the United States, which under the Bush administration has also blanched at joining efforts to reduce emissions.
Instead, the United States joined India and other developing countries in encouraging a focus on developing the technology and finding the resources to adapt to climate change.
20 Global WarmingSo, are we headed for a super interglacial? 21 Greenhouse Effect
We are altering the radiation budget of Earth by addition of greenhouse gases to the atmosphere
What will be the T response?
How will ecosystems respond?
What will be the social, political and economic consequences?
22 Radiation Balance A Review
fn of solar flux, orbital parameters
Absorption or reflection in atmosphere
fn of ozone, clouds, aerosols
Absorption or reflection from Earth surface
fn of surface albedo
Emitted long-wave radiation absorbed by clouds and greenhouse gases
GH gases added to atmosphere by mans activities represent a 1.9 addition to the natural GH Effect
Earth due to enter another glacial period soon
1940-1970 planet cooled slightly
Since 1970 Earth has warmed relatively rapidly, but erratically
25 Past Century Warming 26 Greenhouse Gases
GH gases absorb long wavelength radiation and scatter it, warming the atmosphere
Individual gases absorb different wavelengths
The heat production per unit gas also varies
Global Warming Potential (GWP) is a measure of the radiative effects of gases in the atmosphere
GWP depends on the concentration of a gas, its residence time, and the time period of the calculation
GWP is used to compare the GH effects of different gases CO2 is standard of GWP 1
27 Some Greenhouse Gases 28 Anthropogenic CO2
Fossil fuel burning
6.8 billion tons C as CO2 to atmosphere in 2000
Land use practices
1-2 billion tons C per year not well known
What happens to it all?
29 70 ppm 30 CO2 TEMPERATURE 4.5 C 31 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 32 Can we do anything about it? 33 stop emitting and fix the concentration constant emissions 34 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.
35 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
The remaining 2/3 is related to factors like industry, agriculture, and business uses
3.1 tons/yr CO2 14.3 tons/yr CO2!! 36 Is human-caused global warming for real?
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)
What can be done?
Political actions (e.g. a successor to the Kyoto treaty capping carbon emissions)
Industry initiatives (e.g. hybrid gas-electric cars)
37 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?
(dont we always make decisions in the face of uncertainty?)
(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?
Do governments follow scientific advice?
38 Thermohaline circulation Responable for heat transport 39 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. 40 (No Transcript) 41 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 stresses are added to threatened species
42 (No Transcript) 43 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)
44 Mauna Loa Record Atmospheric Increase Seasonal Cycles Winter Summer 45 Ice Core Records 90 ppmv in 300 years 46 Some Greenhouse Gases 47 Nitrous Oxide N2O
Natural sources microbial activity in soils and ocean
Produced by decay of organic matter by anaerobic bacteria
As much as 60 of methane flux to atmosphere may be anthropogenic
53 Methane Cycle 54 Increase in Atmosphere CH4 has doubled in past 200 yrs. Recent decrease in growth rate decreased fluxes from rice paddies and livestock and reduced natural gas leaks. CH4, ppmv 1978 2000 55 Some Greenhouse Gases 56 Halocarbons
C-based compounds w/ Cl, F, Br, or I
Include CFCs (chlorofluorocarbons) such as the freons
Local increases in S. Amer. and Africa due to biomass burning
61 Water Vapor
Principal GH gas in atmosphere
Provides initial positive feedback to warming because flux of water to vapor in atmosphere increases w/ inc. T
Water vapor content also influences types and distribution of clouds formed
62 Effects of Water Vapor
Changes in cloud formation in response to global warming very difficult to predict
Clouds generally have net cooling effect
Cooling estimated by satellite studies to be 13.2 w/m2
Compare to 2.8 w/m2 for GH warming for past 200 yrs
63 Greenhouse Gases Present Conc. Pre-indust. Conc. An. Rate Inc. Rel. Contrib. Gas 64 Global CO2 Emissions 2003, Nature Conservancy 65 Growth of Industrial Emissions80 of Total Emissions Flaring the controlled burning (flare) or release (vent) of natural gas that cant be processed for sale or use because of technical or economic reasons. Fossil fuels Total Liquids Solids Gases Flaring Cement 66 Industrial Emissions of CO2
8.5 billion tons C/yr
Top 6 countries 55 of industrial emissions
US - Japan
China - India
Russia - Germany
US alone responsible for 1/3 of total FF CO2 emissions since 1950
67 Cumulative Industrial CO2 Emissions by Country 68 Per Capita Emissions In 2000 1.12 metric tons/person global average US per capita emissions 5.43 metric tons 69 Per Capita CO2 Use by Sector 1973 vs 1991 70 Land Use Emissions
1.6 billion tons C/yr in 1990s
More important in developing countries
78 of Congo and 97 of Indonesia emissions are from land use
Numbers are less well constrained than industrial emissions numbers
71 Methane Sources by Sector
Rice cultivation 25
Oil and gas production 16
Solid waste disposal 16
Coal mining 13
72 (No Transcript) 73 Methane Sources by Region
Asia 52 (rice, livestock, coal)
US 10 (1/3 from solid waste)
Russian Federation 6
74 Nitrous oxide (N2O) Emissions
Difficult to quantify
In 1990s, anthropogenic flux 8 million tons/yr
1 million tons/yr from North America and Europe
75 (No Transcript) 76 Evidence of Global Warming in the Climate System 77 Glacier melting
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
78 (No Transcript) 79 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!
80 Arctic warming
Sea ice melting
Reduces albedo (reflectivity) of earth, allowing more radiation to be absorbed
Ice sheet stability? Key sea level question!
Rate of warming 8x faster in last 20 years than in last 100
1979 2003 81 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
82 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. Significant change not yet observed. Hurricane Andrew (above) was the most costly natural disaster in US history! Will we see more like this one? 83 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)
84 What is the role of human emissions? Are we responsible or is it just a natural cycle of the climate system? 85 Consequences of GH Effect
T and precipitation changes
Response of atmos-ocean system
deep water circulation, Sea Level
Response of atmos-land system
photosynthesis and respiration/decay rates shifts in biomes/habitats
Knowledge stems from models, historical and proxy records, observations of modern climate system
86 Temperature EffectsSurface Thermometer RecordsWeighted Average of Land and Sea Surface Ts 97-98 ENSO 0.6 C Pinatubo 87 Earth Surface T Effects
Global T increase 1861-2000 0.6 C
Regional conditions highly variable
0.1 to 0.2 C per decade for past 20 yrs
9 out of 10 warmest years on record since 1990
88 Tropospheric T Records
Radiosondes balloon-borne instruments released daily around world since 1940s
Satellites MSU Microwave Sounding Unit measures microwave radiation emitted by O2 in lower to mid-troposphere indicates T since 1960s
89 Tropospheric T Past 20 yrs - 0.1 C 90 Surface vs Troposphere T
Discrepancies in records may be partially due to errors in measurements
Also may be that troposphere warms more slowly
Cooling of troposphere from volcanic eruptions
Cooling of stratosphere because of ozone depletion
91 Stratospheric CoolingBalloon and Satellite Measurements Note that volcanic eruptions cause stratospheric warming. The temperature of the lower stratosphere increases because of aerosol absorption of terrestrial longwave and solar near-infrared radiation. Numerical models have shown that the direct radiative effect of volcanic aerosols causes general stratospheric heating and tropospheric cooling, 92 Future Temperature Change
Depends on rates of GH gas emissions
In turn, dependent on population growth and government policies on fossil fuel use, deforestation, and industry, agriculture and transportation practices
Projections also dependent on models and data used to build them
93 IPCC Projections
IPCC Intergovernmental Panel on Climate Change
Scenarios based on demographic, political, economic, social, and technological considerations
Usually also consider a BAU scenario Business as Usual in which we continue current trends
94 Projected CO2 Emissions Business as Usual Scenario 95 IPCC 2001 - CO2 Emissions (BAU) 96 Projected CO2 Concentration Business as Usual scenario 97 IPCC 2001 CO2 Concentrations 98 Projected Temperature IPCC 2001 prediction Range of 1.4 to 5.8C Depends on CO2 and SOx emission scenarios etc. 99 IPCC 2001 T Change 100 Global T ChangePredictions Note warmer N hemisphere and warmer continents 101 Precipitation Change Predictions Wetter in some regions Drier in others Will also affect soil moisture and crop yields 102 Ocean Response
Deep-water circulation slows down
Sea level rise
103 Effects of Global Warming on Thermohaline Circulation CO2 unchanged 2 X CO2 4 X CO2 1 Sv million cubic meters water/sec. 104 (No Transcript) 105 (No Transcript) 106 IPCC 2001 SL Rise 107 (No Transcript) 108 Threats to Coral Reefs
Rising SL should be able to keep up
Decreasing saturation state of SW will decrease calcification rates
Increased T stress more incidents of bleaching/death
109 Land Response
Increased T increased photosynthesis, respiration, and decay rates net result hard to model
Fertilization effect acts as a sink today in future, that C may be returned to atmosphere with greater respiration rates
Habitat and biome shifts
110 Today 111 Future Scenario 112 Models
Predictions based on GCMs
Observations often indicate less response to GH warming than predicted
Many factors other than GH gases contribute to global warming/cooling
Knowledge of these continuously improving (ex S and climate)
Models also being refined
113 (No Transcript) 114 (No Transcript) 115 Bottom Line
Greenhouse Effect exists and has influenced climate change in past
Humans are increasing levels of GH gases
General consensus is that global warming due to human activities is highly probable, or is already occurring