Climate Change 2001:
Working Group I: The Scientific Basis
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II.2: Abundances and burdens

II.2.1: CO2 abundances (ppm)

ISAM model (reference) - CO2 abundances (ppm)
Year A1B A1T A1FI A2 B1 B2 A1p A2p B1p B2p IS92a IS92a/SAR
1970 325 325 325 325 325 325 325 325 325 325 325 326
1980 337 337 337 337 337 337 337 337 337 337 337 338
1990 353 353 353 353 353 353 353 353 353 353 353 354
2000 369 369 369 369 369 369 369 369 369 369 369 372
2010 391 389 389 390 388 388 393 391 388 390 390 393
2020 420 412 417 417 412 408 425 419 409 414 415 418
2030 454 440 455 451 437 429 461 453 429 438 444 446
2040 491 471 504 490 463 453 499 492 450 462 475 476
2050 532 501 567 532 488 478 538 535 472 486 508 509
2060 572 528 638 580 509 504 577 583 497 512 543 544
2070 611 550 716 635 525 531 615 637 522 539 582 580
2080 649 567 799 698 537 559 652 699 544 567 623 620
2090 685 577 885 771 545 589 685 771 563 597 670 664
2100 717 582 970 856 549 621 715 856 578 630 723 715
Note: Emissions for OC are scaled to SRES anthropogenic CO emissions offset to year 2000.

ISAM model (low) - CO2 abundances (ppm)
Year A1B A1T A1FI A2 B1 B2 A1p A2p B1p B2p IS92a
2000 368 368 368 368 368 368 368 368 368 368 368
2010 383 381 381 382 380 380 385 383 380 382 382
2020 405 398 403 402 398 394 409 404 395 400 401
2030 432 419 433 429 416 410 438 431 410 417 423
2040 461 443 473 460 436 427 467 461 425 435 446
2050 493 466 525 493 455 446 498 495 442 454 472
2060 524 486 584 532 470 466 528 534 460 473 499
2070 554 501 647 576 480 486 557 577 479 492 529
2080 582 511 715 626 486 507 583 627 495 513 561
2090 607 516 783 686 490 530 607 686 507 536 598
2100 630 516 851 755 490 554 627 755 517 561 640

ISAM model (high) - CO2 abundances (ppm)
Year A1B A1T A1FI A2 B1 B2 A1p A2p B1p B2p IS92a
2000 369 369 369 369 369 369 369 369 369 369 369
2010 397 394 394 395 394 393 398 396 393 396 396
2020 431 422 427 427 422 417 435 429 418 424 426
2030 470 455 471 466 452 443 477 469 444 453 460
2040 513 491 527 511 483 472 521 514 469 482 498
2050 560 527 597 561 514 502 568 564 496 512 539
2060 609 560 678 617 541 534 615 620 527 543 583
2070 656 590 767 681 563 567 661 682 558 577 631
2080 703 613 863 754 581 602 706 755 586 612 682
2090 748 631 962 838 594 640 749 838 611 650 739
2100 790 642 1062 936 603 680 789 936 634 691 804

Note: A “reference” case was defined with climate sensitivity 2.5°C, ocean uptake corresponding to the mean of the ocean model results in Chapter 3, Figure 3.10, and terrestrial uptake corresponding to the mean of the responses of mid-range models, LPJ, IBIS and SDGM (Chapter 3, Figure 3.10). A “low CO2” parametrization was chosen with climate sensitivity 1.5°C and maximal CO2 uptake by oceans and land. A “high CO2” parametrization was defined with climate sensitivity 4.5°C and minimal CO2 uptake by oceans and land. See Chapter 3, Box 3.7, and Jain et al. (1994) for more details on the ISAM model.
The IS92a column values are calculated using the ISAM parametrization noted above with IS92a emissions starting in the year 2000; whereas the IS92a/SAR column refers to values as reported in the SAR using IS92a emissions starting in 1990, using the SAR parametrization of ISAM.

Bern-CC model (reference) - CO2 abundances (ppm)
Year A1B A1T A1FI A2 B1 B2 A1p A2p B1p B2p IS92a IS92a/SAR
1970 325 325 325 325 325 325 325 325 325 325 325 325
1980 337 337 337 337 337 337 337 337 337 337 337 337
1990 352 352 352 352 352 352 352 352 352 352 352 353
2000 367 367 367 367 367 367 367 367 367 367 367 370
2010 388 386 386 386 386 385 390 388 385 387 387 391
2020 418 410 415 414 410 406 421 416 407 412 413 416
2030 447 435 449 444 432 425 454 447 425 433 439 444
2040 483 466 495 481 457 448 490 484 445 457 468 475
2050 522 496 555 522 482 473 529 525 467 481 499 507
2060 563 523 625 568 503 499 569 571 492 506 533 541
2070 601 545 702 620 518 524 606 622 515 532 568 577
2080 639 563 786 682 530 552 642 683 537 559 607 616
2090 674 572 872 754 538 581 674 754 555 588 653 660
2100 703 575 958 836 540 611 702 836 569 618 703 709

Bern-CC model (low) - CO2 abundances (ppm)
Year A1B A1T A1FI A2 B1 B2 A1p A2p B1p B2p IS92a
2000 367 367 367 367 367 367 367 367 367 367 367
2010 383 381 381 381 381 380 384 383 380 382 383
2020 407 400 405 404 400 396 411 406 397 402 403
2030 432 419 432 428 417 410 437 431 410 417 424
2040 460 442 472 459 436 427 466 461 425 434 448
2050 491 464 521 492 455 445 496 495 440 452 473
2060 522 483 577 529 470 464 524 531 458 470 500
2070 548 496 636 569 479 482 550 569 475 487 527
2080 575 505 700 617 485 502 575 616 490 507 559
2090 598 508 763 671 487 522 596 670 501 528 593
2100 617 506 824 735 486 544 613 734 509 550 632

Bern-CC model (high) - CO2 abundances (ppm)
Year A1B A1T A1FI A2 B1 B2 A1p A2p B1p B2p IS92a
2000 367 367 367 367 367 367 367 367 367 367 367
2010 395 393 393 393 392 392 397 395 392 394 395
2020 436 427 433 431 426 422 441 434 424 430 431
2030 483 467 484 477 463 454 491 482 455 465 471
2040 538 514 552 533 503 491 548 538 488 504 517
2050 599 562 638 597 544 531 609 602 524 544 568
2060 666 610 743 670 584 575 675 675 566 588 624
2070 732 653 859 753 617 620 738 757 608 632 684
2080 797 689 985 848 645 668 802 851 648 680 750
2090 860 717 1118 957 666 718 863 959 682 730 822
2100 918 735 1248 1080 681 769 918 1082 713 782 902

Note: A "reference" case was defined with an average ocean uptake for the 1980s of 2.0 PgC/yr. A "low CO2" parameterisation was obtained by combining a "fast ocean" (ocean uptake of 2.54 PgC/yr for the 1980s) and no response of heterotrophic respiration to temperature. A "high CO2" parameterisation was obtained by combining a "slow ocean " (ocean uptake of 1.46 PgC/yr for the 1980s) and capping CO2 fertilisation. Climate sensitivity was set to 2.5°C for a doubling of CO2. See Chapter 3, Box 3.7 for more details on the Bern-CC model.
The IS92a/SAR column refers to values as reported in the SAR using IS92a emissions; whereas the IS92a column is calculated using IS92a emissions but with year 2000 starting values and the BERN-CC model as described in Chapter 3.
The Bern-CC model was initialised for observed atmospheric CO2 which was prescribed for the period 1765 to 1999. The CO2 data were smoothed by a spline. Scenario calculations started at the begining of the year 2000. This explains the difference in the values given for the years upto 2000. Values shown are for the beginning of each year. Annual-mean values are generally higher (up to 7ppm) depending on the scenario and the year.

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