http://www.ipcc.ch/

Global warming

90 The Climate System: an Overview

and clouds, except in a transparent part of the spectrum called the“atmospheric window”, as shown in Figure 1.2. They emit in turninfrared radiation in all directions including downward to theEarth’s surface. Thus greenhouse gases trap heat within theatmosphere. This mechanism is called the natural greenhouseeffect. The net result is an upward transfer of infrared radiationfrom warmer levels near the Earth’s surface to colder levels athigher altitudes. The infrared radiation is effectively radiatedback into space from an altitude with a temperature of, onaverage, −19°C, in balance with the incoming radiation, whereasthe Earth’s surface is kept at a much higher temperature of onaverage 14°C. This effective emission temperature of −19°Ccorresponds in mid-latitudes with a height of approximately 5km. Note that it is essential for the greenhouse effect that thetemperature of the lower atmosphere is not constant (isothermal)but decreases with height. The natural greenhouse effect is partof the energy balance of the Earth, as can be seen schematicallyin Figure 1.2.

Clouds also play an important role in the Earth’s energybalance and in particular in the natural greenhouse effect. Cloudsabsorb and emit infrared radiation and thus contribute to warmingthe Earth’s surface, just like the greenhouse gases. On the otherhand, most clouds are bright reflectors of solar radiation andtend to cool the climate system. The net average effect of theEarth’s cloud cover in the present climate is a slight cooling: the

reflection of radiation more than compensates for the greenhouseeffect of clouds. However this effect is highly variable, dependingon height, type and optical properties of clouds.

This introduction to the global energy balance and thenatural greenhouse effect is entirely in terms of the global meanand in radiative terms. However, for a full understanding of thegreenhouse effect and of its impact on the climate system,dynamical feedbacks and energy transfer processes should alsobe taken into account. Chapter 7 presents a more detailed analysisand assessment.

Radiative forcing and forcing variabilityIn an equilibrium climate state the average net radiation at the topof the atmosphere is zero. A change in either the solar radiationor the infrared radiation changes the net radiation. The correspon-ding imbalance is called “radiative forcing”. In practice, for thispurpose, the top of the troposphere (the tropopause) is taken asthe top of the atmosphere, because the stratosphere adjusts in amatter of months to changes in the radiative balance, whereas thesurface-troposphere system adjusts much more slowly, owingprincipally to the large thermal inertia of the oceans. Theradiative forcing of the surface troposphere system is then thechange in net irradiance at the tropopause after allowing forstratospheric temperatures to re-adjust to radiative equilibrium,but with surface and tropospheric temperatures and state held

235 OutgoingLongwaveRadiation235 Wm−2

IncomingSolar

Radiation342 Wm−2

Reflected SolarRadiation107 Wm−2

Reflected by Clouds,Aerosol andAtmosphere

342107

77

77

67Absorbed byAtmosphere

Emitted byAtmosphere 165 30

40AtmosphericWindow

324Back

Radiation

390Surface

Radiation

350 40

78LatentHeat24

168Absorbed by Surface

78 Evapo-

transpiration

GreenhouseGases

324Absorbed by Surface

Reflected bySurface

30

24Thermals

Figure 1.2: The Earth’s annual and global mean energy balance. Of the incoming solar radiation, 49% (168 Wm−2) is absorbed by the surface. That heat isreturned to the atmosphere as sensible heat, as evapotranspiration (latent heat) and as thermal infrared radiation. Most of this radiation is absorbed by theatmosphere, which in turn emits radiation both up and down. The radiation lost to space comes from cloud tops and atmospheric regions much colder than thesurface. This causes a greenhouse effect. Source: Kiehl and Trenberth, 1997: Earth’s Annual Global Mean Energy Budget, Bull. Am. Met. Soc. 78, 197-208.

Most important greenhouse agents

Water vapor

Carbon dioxide

Methane

Carbon dioxide

burning fossil fuel

deforestation

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Department of Energy and Environmental Protection Agency/ Carbon Dioxide Emissions from the

Generation of Electric Power in the United States2

5 Caution should be taken when interpreting year-to-year changes in the estimated emissions and generation due to an undetermineddegree of uncertainty in statistical data for the 1999 estimates. Also, differences in the 1998 and 1999 estimation methodologies have anundetermined effect on the change from 1998 to 1999 estimates. See Appendix B, “Data Sources and Methodology,” for further information.For more information on uncertainty in estimating carbon dioxide emissions, see Appendix C, “Uncertainty in Emissions Estimates,”Emissions of Greenhouse Gases in the United States, DOE/EIA-0573(98) (Washington, DC, October 1999). Also, because weather fluctuationsand other transitory factors significantly influence short-run patterns of energy use in all activities, emissions growth rates calculated overa single year should not be used to make projections of future emissions growth.

6 About 37 percent of CO2 emissions are produced by electric utility generators, as reported in the greenhouse gas inventory for 1998.An additional 3.5 percent are attributable to nonutility power producers, which are included in the industrial sector in the GHG inventory.

7 Energy Information Administration, Emissions of Greenhouse Gases in the United States 1998, Chapter 2, “Carbon Dioxide Emissions,”DOE/EIA-0573(98) (Washington, DC, October 1999). Data for 1999 will be available in October 2000.

fuels rose slightly, a reduction in the emission rate forcoal-fired generation combined with growth in themarket share of gas-fired generation contributed to themodest improvement in the output rate.5

In the United States, about 40.5 percent6 of anthro-pogenic CO2 emissions was attributed to the combustionof fossil fuels for the generation of electricity in 1998, thelatest year for which all data are available.7 The available

Table 1. Summary of Carbon Dioxide Emissions and Net Generation in the United States, 1998 and 1999

1998 1999 p

Change

Percent

Change

Carbon Dioxide (thousand metric tons)a

. . . . . . .

Coal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1,799,762 1,787,910 -11,852 -0.66

Petroleum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110,244 106,294 -3,950 -3.58

Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291,236 337,004 45,768 15.72

Other Fuels b

. . . . . . . . . . . . . . . . . . . . . . . . . . 13,596 13,596

U.S. Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2,214,837 2,244,804 29,967 1.35

Generation (million kWh)

Coal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1,873,908 1,881,571 7,663 0.41

Petroleum . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126,900 119,025 -7,875 -6.21

Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488,712 562,433 73,721 15.08

Other Fuels b

. . . . . . . . . . . . . . . . . . . . . . . . . . 21,747 21,749 2

Total Fossil-fueled . . . . . . . . . . . . . . . . . . . . 2,511,267 2,584,779 73,512 2.93

Nonfossil-fueled c

. . . . . . . . . . . . . . . . . . . . 1,105,947 1,106,294 347 0.03

U.S. Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3,617,214 3,691,073 73,509 2.04

Output Rate d (pounds CO2 per kWh)

Coal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.117 2.095 -0.022 -1.04

Petroleum . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.915 1.969 0.054 2.82

Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.314 1.321 0.007 0.53

Other Fuels b

. . . . . . . . . . . . . . . . . . . . . . . . . . 1.378 1.378

U.S. Average . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.350 1.341 -0.009 -0.67

a One metric ton equals one short ton divided by 1.1023. To convert carbon dioxide to carbon units, divide by 44/12.

b Other fuels include municipal solid waste, tires, and other fuels that emit anthropogenic CO2 when burned to generate

electricity. Nonutility data for 1999 for these fuels are unavailable; 1998 data are used.

c Nonfossil includes nuclear, hydroelectric, solar, wind, geothermal, biomass, and other fuels or energy sources with zero or

net zero CO2 emissions. Although geothermal contributes a small amount of CO2 emissions, in this report it is included in

nonfossil.

d U.S. average output rate is based on generation from all energy sources.

P = Preliminary data.

= No change.

Note: Data for 1999 are preliminary. Data for 1998 are final.

Sources: Energy Information Administration, Form EIA-759, “Monthly Power Plant Report”; Form EIA-767, “Steam-Electric

Plant Operation and Design Report”; Form EIA-860B, “Annual Electric Generator Report Nonutility”; and Form 900, “Monthly

Nonutility Power Report.” Federal Energy Regulatory Commission, FERC Form 423, “Monthly Report of Cost and Quality of

Fuels for Electric Plants.”

Methane

Landfills, cows

Termites

....

Perhaps 100 million ton of methane produced by (3?) tropical dams (in Brazil?), a sizable contribution to global warming.

NEWS

Nature

Published online: 28 November 2006; | doi:10.1038/444524a

Methane quashes green credentials of hydropowerEmissions from tropical dams can exceed fossil-fuel plants.

Ozone layer - Increase of UVB

CFC - ChloroFluoroCarbons

(regulated since 1987)

NOx - contributes also to

greenhouse effect

Consequences

Increase in temperature

sea surface temperature

on land

methods of analysis and the fact that the SAR decided not updatethe value in the First Assessment Report, despite slight additionalwarming. The latter decision was likely to have been due to acautious interpretation of overall uncertainties which had at thattime to be subjectively assessed.

2.2.2.4 Are the land and ocean surface temperature changes mutually consistent?

Most of the warming in the 20th century occurred in two distinctperiods separated by several decades of little overall globallyaveraged change, as objectively identified by Karl et al. (2000)and discussed in IPCC (1990, 1992, 1996) and several referencesquoted therein. Figures 2.9 and 2.10 highlight the worldwidebehaviour of temperature change in the three periods. These lineartrends have been calculated from the Jones et al. (2001) griddedcombination of UKMO SST and CRU land-surface air tempera-ture, from which the trends in Table 2.2 were calculated. Optimumaveraging has not been used for Figures 2.9 and 2.10, and onlytrends for grid boxes where reasonably complete time-series ofdata exist are shown. The periods chosen are 1910 to 1945 (first

warming period), 1946 to 1975 (period of little global temperaturechange), 1976 to 2000 (second warming period, where all fourseasons are shown in Figure 2.10) and the 20th century, 1901 to2000. It can be seen that there is a high degree of local consistencybetween the SST and land air temperature across the land-oceanboundary, noting that the corrections to SST (Folland and Parker,1995) are independent of the land data. The consistency withwhich this should be true locally is not known physically, but isconsistent with the similarity of larger-scale coastal land andocean surface temperature anomalies on decadal time-scalesfound by Parker et al. (1995). The warming observed in the periodfrom 1910 to 1945 was greatest in the Northern Hemisphere highlatitudes, as discussed in Parker et al. (1994). By contrast, theperiod from 1946 to 1975 shows widespread cooling in theNorthern Hemisphere relative to much of the Southern, consistentwith Tables 2.1 and 2.2 and Parker et al. (1994). Much of thecooling was seen in the Northern Hemisphere regions that showedmost warming in 1910 to 1945 (Figure 2.9 and Parker et al.,1994). In accord with the results in the SAR, recent warming(1976 to 2000) has been greatest over the mid-latitude Northern

116 Observed Climate Variability and Change

(a) Annual temperature trends, 1901 to 2000 (b) Annual temperature trends, 1910 to 1945

(c) Annual temperature trends, 1946 to 1975

Trend (°C/decade)0 0.2−0.2 0.4−0.4 0.6−0.6 0.8−0.8 1−1

(d) Annual temperature trends, 1976 to 2000

Figure 2.9: (a) to (d) Annual surface temperature trends for the periods 1901 to 2000, 1910 to 1945, 1946 to 1975, and 1976 to 2000, respectively(°C/decade), calculated from combined land-surface air and sea surface temperatures adapted from Jones et al. (2001). The red, blue and greencircles indicate areas with positive trends, negative trends and little or no trend respectively. The size of each circle reflects the size of the trendthat it represents. Trends were calculated from annually averaged gridded anomalies with the requirement that annual anomalies include aminimum of 10 months of data. For the period 1901 to 2000, trends were calculated only for those grid boxes containing annual anomalies in atleast 66 of the 100 years. The minimum number of years required for the shorter time periods (1910 to 1945, 1946 to 1975, and 1976 to 2000)was 24, 20, and 16 years, respectively.

global land in 1910 to 1945 (seen in Table 2.1) is within theuncertainties of either data set, as a slightly slower warming ofthe ocean might be expected on physical grounds.

Figures 2.7a to c show annual time-series of anomalies ofcombined land-surface air temperature and SST for thehemispheres and globe since 1861, based on the latest CRU landair temperature data and the UKMO SST data. Jones et al. (2001)temperature data have been averaged by both a standard weightingmethod, used in the SAR, as shown by the dashed smoothedcurves, and by an optimum averaging method (Shen et al., 1998;Folland et al., 2001) as shown by the bars and solid smoothedcurves. The latter method uses the variance-covariance matrixinstead of correlation functions (Kagan, 1997). The calculateduncertainties (twice the standard error) in the annual values arealso shown (including the independent urbanisation and SST biascorrection uncertainties). Optimum averaging gives less weight toareas of high data uncertainty than do ordinary averagingmethods, and it takes much better account of data gaps. It alsogives more weight to Antarctica, the great bulk of which (awayfrom the Antarctic Peninsula) has warmed little in the last twodecades (Comiso, 2000). Optimum averages can affect individual

years markedly when data are sparse. Thus extra warmth of thewarm year 1878 (strongly affected by the 1877/78 El Niño) in theNorthern relative to the Southern Hemisphere in the area weightedaverage (not shown) disappears when optimum averages are used.In the Northern Hemisphere, the optimum averages are littledifferent from area weighted averages, but they are consistentlywarmer in the sparsely sampled Southern Hemisphere before1940, often by more than one tenth of a degree. The overall effecton global temperature is small, however (Figure 2.7c)

The five warmest global optimally averaged years since thebeginning of the record in 1861 all occurred in the 1990s with1998 having the warmest anomaly (0.55°C). This year was signif-icantly warmer than the second warmest year, 1995 (0.38°C),while 1999 was fourth warmest year, despite the strong La Niñaevent. The remarkably consistent monthly global warmth of 1998is discussed in Karl et al. (2000).

Table 2.2 shows linear trends of the annual optimumaverages, and twice their standard errors, for the globe andhemispheres using the restricted maximum likelihood method asin Table 2.1 and allowing for the annual uncertainties due to datagaps, urbanisation over land, and bias corrections to SST. Since

113Observed Climate Variability and Change

1860 1880 1900 1920 1940 1960 1980 2000Year

−0.6

−0.4

−0.2

0.0

0.2

0.4

0.6

0.8re

lativ

e to

196

1 to

199

0G

loba

l ano

mal

y (°

C)

UKMO SST (adapted from Jones et al., 2001)UKMO NMAT (adapted from Parker et al., 1995)CRU LSAT (Jones et al., 2001)

1860 1880 1900 1920 1940 1960 1980 2000−0.4

−0.2

0.0

0.2

0.4

CRU LSAT minus UKMO SST

Figure 2.6: Smoothed annual anomalies of global average sea surface temperature (°C) 1861 to 2000, relative to 1961 to 1990 (blue curve), nightmarine air temperature (green curve), and land-surface air temperature (red curve). The data are from UK Met Office and CRU analyses (adaptedfrom Jones et al., 2001, and Parker et al., 1995). The smoothed curves were created using a 21-point binomial filter giving near-decadal averages.Also shown (inset) are the smoothed differences between the land-surface air and sea surface temperature anomalies.

Land

Average Sea

Night Sea

difference sea-land

Average temperature in TallahasseeNovember 1895 - 2004

2.7 Has Climate Variability, or have Climate Extremes, Changed?

2.7.1 Background

Changes in climate variability and extremes of weather andclimate events have received increased attention in the last fewyears. Understanding changes in climate variability andclimate extremes is made difficult by interactions between thechanges in the mean and variability (Meehl et al., 2000). Suchinteractions vary from variable to variable depending on theirstatistical distribution. For example, the distribution oftemperatures often resembles a normal distribution wherenon-stationarity of the distribution implies changes in themean or variance. In such a distribution, an increase in the

mean leads to new record high temperatures (Figure 2.32a),but a change in the mean does not imply any change invariability. For example, in Figure 2.32a, the range betweenthe hottest and coldest temperatures does not change. Anincrease in variability without a change in the mean implies anincrease in the probability of both hot and cold extremes aswell as the absolute value of the extremes (Figure 2.32b).Increases in both the mean and the variability are also possible(Figure 2.32c), which affects (in this example) the probabilityof hot and cold extremes, with more frequent hot events withmore extreme high temperatures and fewer cold events. Othercombinations of changes in both mean and variability wouldlead to different results.

Consequently, even when changes in extremes can bedocumented, unless a specific analysis has been completed, itis often uncertain whether the changes are caused by a changein the mean, variance, or both. In addition, uncertainties in therate of change of the mean confound interpretation of changesin variance since all variance statistics are dependent on areference level, i.e., the mean.

For variables that are not well approximated by normaldistributions, like precipitation, the situation is even morecomplex, especially for dry climates. For precipitation, forexample, changes in the mean total precipitation can beaccompanied by other changes like the frequency of precipi-tation or the shape of the distribution including its variability.All these changes can affect the various aspects of precipita-tion extremes including the intensity of precipitation (amountper unit time).

This section considers the changes in variability andextremes simultaneously for two variables, temperature andprecipitation. We include new analyses and additional datacompiled since the SAR which provide new insights. We alsoassess new information related to changes in extreme weatherand climate phenomena, e.g., tropical cyclones, tornadoes,etc. In these analyses, the primary focus is on assessing thestationarity (e.g., the null hypothesis of no change) of theseevents, given numerous inhomogeneities in monitoring.

2.7.2 Is There Evidence for Changes in Variability or Extremes?

The issues involved in measuring and assessing changes inextremes have recently been comprehensively reviewed byTrenberth and Owen (1999), Nicholls and Murray (1999), andFolland et al. (1999b). Despite some progress describedbelow, there remains a lack of accessible daily climate datasets which can be intercompared over large regions (Folland etal., 2000). Extremes are a key aspect of climate change.Changes in the frequency of many extremes (increases ordecreases) can be surprisingly large for seemingly modestmean changes in climate (Katz, 1999) and are often the mostsensitive aspects of climate change for ecosystem and societalresponses. Moreover, changes in extremes are often mostsensitive to inhomogeneous climate monitoring practices,making assessment of change more difficult than assessing thechange in the mean.

155Observed Climate Variability and Change

(a)

Cold

Lesscold

weather

Previousclimate

Newclimate

Morehot

weather

Average

Increase in mean

Pro

babi

lity

of o

ccur

renc

e

Hot

morecold

weather

Morerecord hot

weather

(b)

Cold

Morerecordcold

weather

Previousclimate

Newclimate

Morehot

weather

Average

Increase in variance

Pro

babi

lity

of o

ccur

renc

e

Hot

Morerecord hot

weather

Less change

forcold

weather

(c)

Cold

Previousclimate

Newclimate

Much morehot

weather

Average

Increase in mean and variance

Pro

babi

lity

of o

ccur

renc

e

Hot

Morerecord hot

weather

Figure 2.32: Schematic showing the effect on extreme temperatureswhen (a) the mean temperature increases, (b) the variance increases,and (c) when both the mean and variance increase for a normal distri-bution of temperature.

Possible temperature scenarios

Consequences

Increase in temperature

sea surface temperature

on land

Increase in sea water level

Warming

water expands: 0.5 mm

Water level increases

about 2.8 mm per year

Fresh water influx:

melting glaciers

Toboggan glacier

1909

2004

McCarthy glacier: 1909 and 2004

Trivia1990s the hottest decade,

1998 and 2005 are hottest year on record (since 1861)

2002 ,2003, and 2004 are on rank 3, 4, and 5

10% loss of snow cover since 1960s.

Sea level up by 10-20 cm during the 1900s.

El Niño more frequent, persistent, and intense since 1970s (relative to past 100 years).

Consequences

Increase in temperature

sea surface temperature

on land

Increase in sea water level

Increase in El Nino frequency

Decrease in snow cover

Changes in food production (change in world climate)

Predictions

more storms

more hot summers

higher sea levels

more rain in some areas, but drier in others

sea level change will be a real threat for many town

on the gulf

Well, ....we are in for the ride

“Our ability to quantify the human influence on global climate is currently limited because the expected signal is still emerging from the noise of natural variability…”

– 1995 IPCC (2001 EPA web site)

“In the light of new evidence . . . most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations.”

– 2001 IPCC

Effect on biota

86F --> all females

93F --> all males

Janzen, F. J. 1994. Climate change and temperature-dependent sex determination in reptiles.

Proceedings of the National Academy of Science of the United States of America 91:7487–7490.

Effect on biota

demographic

range expansion, contraction

1915–1939

1940–1969

1970–1997

Parmesan, C., N. et al. 1999. Poleward shifts in geographical ranges of butterfly species associated with regional warming. Nature

399:579–583.

Effect on biota

demographic

range expansion, contraction

latitude

altitude

9 plant species in Swiss Alps with detailed records:

Observed upward shift 1–4 m per decade.

Predicted upward shift needed to keep up with temperature 8–10 m per decade

Grabherr, G., M. Gottfried & H. Pauli. 1994. Climate effects on mountain plants. Nature 369:448

Effect on biota

demographic

range expansion, contraction

latitude

altitude

Phenology (= timing of life history events)

Global warming and birds

Breeding date Pied flycatcher 13 days

Tree swallow 5-9 days

Great tit 11.9 days

Mexican Jay 10.1 days

Migration date 4 bird species 12 days

39 bird species 5.5 days

America Robin 14 days

McCarty, J. P. Ecological Consequences of Recent Climate Change.

The Journal of the Society for Conservation Biology 15 (2), 320-331.

Climate change policy

International policy

National policy

Personal policy

International policies

1988 Intergovernmental Panel on Climate Change (IPCC) established

1989 Global Climate Coalition formed by 46 corporations

1990 first IPCC Assessment Report 1992 United Nations Framework Convention on Climate Change

1996 Ministerial Declaration - official statement that climate change is a problem

International policies1997 Kyoto Protocol: Would make emissions targets legally binding (if 55% of parties sign, representing at least 55% of emissions)

2001 The United States rejects Kyoto Protocol, US delcares that it will not ratify the Kyoto agreement.

2004 Russia agrees to sign the Kyoto agreement (55% of the parties signed up)

BBC news on Feb 16 2005: The Kyoto accord, which aims to curb the air

pollution blamed for global warming, has come into force seven years

after it was agreed.

The accord requires countries to cut emissions of carbon dioxide and other

greenhouse gases. Some 141 countries, accounting for 55% of greenhouse gas

emissions, have ratified the treaty, which pledges to cut these emissions by 5.2%

by 2012. But the world's top polluter - the US - has not signed up to the treaty.

The US says the changes would be too costly to introduce and that the

agreement is flawed. Large developing countries including India, China and Brazil

are not required to meet specific targets for now.

US acceptance of the policy is still important

Trading of Carbon shares National policies

2003 Climate Stewardship Act fails in senate(McCain, Lieberman)

2004 Climate Stewardship Act introduced in the house(Glichrest, Olver)

Searching the internet about this topic, I stumbled over several “institutes” with very slick web pages

advertising scientific reasons why the global warming does not happen:

http://www.nationalcenter.org/Kyoto.html[very disturbing are their biased use of citations]

In the (old) news

Election Over, McCain Criticizes Bush on Climate ChangeBy ANDREW C. REVKINPublished: November 16, 2004

Wasting no time distancing himself from President Bush on an issue that has long

divided them, Senator John McCain yesterday called the White House stance on

climate change "terribly disappointing" and said inaction in the face of mounting

scientific data was unjustified.

Two weeks after the end of a campaign in which he stumped for Mr. Bush's re-

election, Mr. McCain, Republican of Arizona, is convening a Senate hearing

today on the human effect on climate and what to do about it.

Particularly disturbing, he went on, is the rapid pace of warming.

...

"The Inuit language for 10,000 years never had a word for robin," [McCain] said,

"and now there are robins all over their villages."

Private policies

As an individual, you can affect the emissions of about 4,800 pounds of carbon equivalent, or nearly 32% of the total emissions per person, by the choices you make in three areas of your life. These areas are the electricity we use in our homes, the waste we produce, and personal transportation. The other 68% of emissions are affected more by the types of industries in the U.S., the types of offices we use, how our food is grown, and other factors.

http://yosemite.epa.gov/oar/globalwarming.nsf/content/EmissionsIndividual.html