The United States has only 4% of the world population, and 
emits  25% of the world's CO2 emissions (year 2005).

SORTED  BY  CO2 Emissions Per Person (Grouped by Country)
Country GDP CO2 emissions GDP per Emissions Area  Population CO2 emissions per person
(in millions of US Dollars) (in thousands of metric tons) (in thousands of US Dollars per metric ton) (in sq. mi.)   (in thousands of metric tons per person)
Panama 14351 6255 2.294 177 20,579 0.30395
Qatar 31550 36450 0.866 4,416 885,359 0.04117
Trinidad and Tobago 13558 41217 0.329 1,980 1,065,842 0.03867
United Arab Emirates 103006 94163 1.094 32,000 2,602,713 0.03618
Bahrain 11781 21327 0.552 257 698,585 0.03053
Kuwait 61469 59879 1.027 6,880 2,418,393 0.02476
Luxembourg 35620 9442 3.773 998 474,413 0.01990
United States 12438873 5872278 2.118 3,718,691 298,444,215 0.01968
Australia 692436 356342 1.943 2,967,893 20,264,082 0.01758
Canada 1098446 517157 2.124 3,855,081 33,098,932 0.01562
Singapore 116326 57471 2.0241 267 4,492,150 0.01279
Saudi Arabia 284895 340555 0.837 756,981 27,019,731 0.01260
Estonia 12310 15943 0.772 17,462 1,324,333 0.01204
Norway 285604 55461 5.15 125,181 4,610,820 0.01203
Finland 204385 62659 3.262 130,558 5,231,372 0.01198
Czech Republic 125709 114563 1.097 30,450 10,235,455 0.01119
Republic of Ireland 206467 43187 4.781 27,135 4,062,235 0.01063
Israel 122987 66312 1.855 8,019 6,352,117 0.01044
Russia 755437 1432513 0.527 6,592,735 142,893,540 0.01003
Netherlands 629391 162739 3.867 16,033 16,491,461 0.00987
Germany 2906658 804701 3.612 137,846 82,422,299 0.00976
Kazakhstan 51876 147921 0.351 1,049,150 15,233,244 0.00971
Oman 25038 30118 0.831 82,031 3,102,229 0.00971
Japan 4799061 1203535 3.987 145,882 127,463,611 0.00944
South Korea 720772 446190 1.615 38,023 48,846,823 0.00913
United Kingdom 2295039 543633 4.222 94,525 60,609,153 0.00897
Greece 230684 94117 2.451 50,942 10,688,058 0.00881
Denmark 265934 47620 5.585 16,639 5,450,661 0.00874
Libya 32962 50418 0.654 679,358 5,900,754 0.00854
Cyprus 17144 6671 2.57 3,571 784,301 0.00851
New Zealand 107670 33995 3.167 103,737 4,076,140 0.00834
South Africa 226486 345382 0.656 471,008 44,187,637 0.00782
Austria 318343 63701 4.997 32,382 8,192,880 0.00778
Poland 312257 296398 1.054 120,728 38,536,869 0.00769
Slovenia 35106 15310 2.293 7,827 2,010,347 0.00762
Spain 1120312 304603 3.678 194,896 40,397,842 0.00754
Italy 1836407 433018 4.241 116,305 58,133,509 0.00745
Iceland 15388 2215 6.947 39,768 299,388 0.00740
Slovakia 50323 40061 1.256 18,859 5,439,448 0.00736
Turkmenistan 13846 34617 0.4 188,455 5,042,920 0.00686
Belgium 387840 70592 5.494 11,787 10,379,067 0.00680
Ukraine 82693 306807 0.27 233,089 46,710,816 0.00657
France 2216273 378267 5.859 211,208 60,876,136 0.00621
Malaysia 127942 150630 0.849 127,316 24,385,858 0.00618
Portugal 185091 62288 2.972 35,672 10,605,870 0.00587
Belarus 27061 59959 0.451 80,154 10,293,011 0.00583
Sweden 383816 51901 7.395 173,731 9,016,596 0.00576
Bulgaria 25959 41921 0.619 42,822 7,385,367 0.00568
Hungary 107144 56647 1.891 35,919 9,981,334 0.00568
Switzerland 384642 40854 9.415 15,942 7,523,934 0.00543
Iran 195200 360223 0.542 636,293 68,688,433 0.00524
Croatia 35102 21118 1.662 21,831 4,494,749 0.00470
Uzbekistan 11002 122330 0.09 172,741 27,307,134 0.00448
Lebanon 20699 16392 1.263 4,015 3,874,050 0.00423
Venezuela 122301 108163 1.131 352,143 25,730,435 0.00420
Romania 79848 86745 0.92 91,699 22,303,552 0.00389
Thailand 174545 231927 0.753 198,455 64,631,595 0.00359
Mexico 714530 383671 1.862 761,602 107,449,525 0.00357
Chile 101526 57320 1.771 292,258 16,134,219 0.00355
Azerbaijan 10751 27998 0.384 33,436 7,961,619 0.00352
Lithuania 23702 12565 1.886 25,174 3,585,906 0.00350
Argentina 172123 133322 1.291 1,068,296 39,921,833 0.00334
Turkey 340263 207996 1.636 301,382 70,413,958 0.00295
Jordan 11928 16782 0.711 35,637 5,906,760 0.00284
Algeria 97559 92097 1.059 919,590 32,930,091 0.00280
Latvia 15387 6306 2.44 24,938 2,274,735 0.00277
People's Republic of China 1 1843117 3513103 0.525 3,705,386 1,313,973,713 0.00267
Syria 25694 49097 0.523 71,498 18,881,361 0.00260
Dominican Republic 21476 21544 0.997 18,815 9,183,984 0.00235
Tunisia 31970 22067 1.449 63,170 10,175,014 0.00217
Ecuador 31927 24834 1.286 109,483 13,547,510 0.00183
Egypt 91688 143697 0.638 386,660 78,887,007 0.00182
Brazil 732078 313757 2.333 3,286,470 188,078,227 0.00167
Costa Rica 19558 5834 3.352 19,730 4,075,261 0.00143
Morocco 54597 43905 1.244 172,413 33,241,259 0.00132
Colombia 108731 57375 1.895 439,733 43,593,035 0.00132
Indonesia 284072 306491 0.927 741,096 245,452,739 0.00125
Uruguay 13116 4082 3.213 68,039 3,431,932 0.00119
India 749443 1220926 0.614 1,269,338 1,095,351,995 0.00111
Zimbabwe 12261 12452 0.985 150,803 12,236,805 0.00102
El Salvador 16602 6231 2.664 8,124 6,822,378 0.00091
Peru 72888 25498 2.859 496,223 28,302,603 0.00090
Guatemala 26978 10302 2.619 42,042 12,293,545 0.00084
Philippines 92586 73779 1.255 115,830 89,468,677 0.00082
Vietnam 47111 66312 0.71 127,243 84,402,966 0.00079
Pakistan 90282 108677 0.831 310,401 165,803,560 0.00066
Angola 23894 7712 3.0983 481,351 12,127,071 0.00064
Yemen 15204 12990 1.17 203,849 21,456,188 0.00061
Serbia and Montenegro 26243 46437 0.565 685,200 33,583,259 0.00138
Sri Lanka 22351 10361 2.157 25,332 20,222,240 0.00051
Nigeria 91574 52038 1.76 356,667 131,859,731 0.00039
Ghana 10340 7513 1.376 92,456 22,409,572 0.00034
Bangladesh 61944 34540 1.793 55,598 147,365,352 0.00023
Sudan 25379 8762 2.896 967,493 41,236,378 0.00021
Kenya 16900 7212 2.343 224,961 34,707,817 0.00021
Cameroon 15742 3464 4.544 183,567 17,340,702 0.00020
Tanzania 12123 3583 3.383 364,898 37,445,392 0.00010
European Union 13926873 3682755 3.782      
Hong Kong, China 172932 35438 4.88      
World 44168157 24126416 1.831      

The United States is the largest emitter of CO2 gases (of any nation;  China is 2nd)

SORTED  BY  CO2 Emissions Per Country
COUNTRY GDP CO2 emissions GDP per Emissions Area  Population CO2 emissions per person
  (in millions of US Dollars) (in thousands of metric tons) (in thousands of US Dollars per metric ton) (in sq. mi.)   (in thousands of metric tons per person)
World 44168157 24126416 1.831      
United States 12438873 5872278 2.118 3,718,691 298,444,215 0.01968
European Union 13926873 3682755 3.782      
People's Republic of China 1 1843117 3513103 0.525 3,705,386 1,313,973,713 0.00267
Russia 755437 1432513 0.527 6,592,735 142,893,540 0.01003
India 749443 1220926 0.614 1,269,338 1,095,351,995 0.00111
Japan 4799061 1203535 3.987 145,882 127,463,611 0.00944
Germany 2906658 804701 3.612 137,846 82,422,299 0.00976
United Kingdom 2295039 543633 4.222 94,525 60,609,153 0.00897
Canada 1098446 517157 2.124 3,855,081 33,098,932 0.01562
South Korea 720772 446190 1.615 38,023 48,846,823 0.00913
Italy 1836407 433018 4.241 116,305 58,133,509 0.00745
Mexico 714530 383671 1.862 761,602 107,449,525 0.00357
France 2216273 378267 5.859 211,208 60,876,136 0.00621
Iran 195200 360223 0.542 636,293 68,688,433 0.00524
Australia 692436 356342 1.943 2,967,893 20,264,082 0.01758
South Africa 226486 345382 0.656 471,008 44,187,637 0.00782
Saudi Arabia 284895 340555 0.837 756,981 27,019,731 0.01260
Brazil 732078 313757 2.333 3,286,470 188,078,227 0.00167
Ukraine 82693 306807 0.27 233,089 46,710,816 0.00657
Indonesia 284072 306491 0.927 741,096 245,452,739 0.00125
Spain 1120312 304603 3.678 194,896 40,397,842 0.00754
Poland 312257 296398 1.054 120,728 38,536,869 0.00769
Thailand 174545 231927 0.753 198,455 64,631,595 0.00359
Turkey 340263 207996 1.636 301,382 70,413,958 0.00295
Netherlands 629391 162739 3.867 16,033 16,491,461 0.00987
Malaysia 127942 150630 0.849 127,316 24,385,858 0.00618
Kazakhstan 51876 147921 0.351 1,049,150 15,233,244 0.00971
Egypt 91688 143697 0.638 386,660 78,887,007 0.00182
Argentina 172123 133322 1.291 1,068,296 39,921,833 0.00334
Uzbekistan 11002 122330 0.09 172,741 27,307,134 0.00448
Czech Republic 125709 114563 1.097 30,450 10,235,455 0.01119
Pakistan 90282 108677 0.831 310,401 165,803,560 0.00066
Venezuela 122301 108163 1.131 352,143 25,730,435 0.00420
United Arab Emirates 103006 94163 1.094 32,000 2,602,713 0.03618
Greece 230684 94117 2.451 50,942 10,688,058 0.00881
Algeria 97559 92097 1.059 919,590 32,930,091 0.00280
Romania 79848 86745 0.92 91,699 22,303,552 0.00389
Philippines 92586 73779 1.255 115,830 89,468,677 0.00082
Belgium 387840 70592 5.494 11,787 10,379,067 0.00680
Israel 122987 66312 1.855 8,019 6,352,117 0.01044
Vietnam 47111 66312 0.71 127,243 84,402,966 0.00079
Austria 318343 63701 4.997 32,382 8,192,880 0.00778
Finland 204385 62659 3.262 130,558 5,231,372 0.01198
Portugal 185091 62288 2.972 35,672 10,605,870 0.00587
Belarus 27061 59959 0.451 80,154