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ß?$l Çutss Mitigation, 1% ami, . Reduction starts 2025.

'ards a net caff>on source as:

. weakening oHih. meridional ivity of all cerells ____b>

roductMty to d ity to decrease in ¡ions ~ ~ tr ~ *" ~

of global coas|pl wetlands lost each year-^-

ory, infectious diseases-->-

Fig. 1.9 Projected impacts as a function of 2100 warming (0-5°C,) from 1990; 3% early emission growth rate (Note: 3.0% growth rate to 2030. Entries are placed so the left hand side of text indicates approximate onset of impact, black lines link impacts, and dotted arrow indicate impacts increase with increasing warming)

Change in Annual Mean Temp

Models: ccsm--30 gfdlcm20 gfdlcm21 giss--eh

Fig. 1.10 Projected 1990-2100 warming for Base Case; Projected, 3% early emission growth rate

Models: ccsm--30 gfdlcm20 gfdlcm21 giss--eh

Fairbanks=8.5 C, Chicago=7.6 C, New York=5.4 C, Miami=4.4 C, Los Angeles=4.7 C

Global range 0.16 to 13.55

Global-mean dT 4.24 deg C

Scenario: New Year: 2100

Def. 2, no aerosols deg C

Fig. 1.10 Projected 1990-2100 warming for Base Case; Projected, 3% early emission growth rate

Change in Annual Mean Temp

Global range 0.10 to 8.44

Global-mean dT 2.64 deg C

Scenario: WRE550-F Year: 2100

Def. 2, no aerosols

Change in Annual Mean Temp

Global range 0.10 to 8.44

Global-mean dT 2.64 deg C

Scenario: WRE550-F Year: 2100

Def. 2, no aerosols

Models: ccsm--30 gfdlcm20 gfdlcm21 giss--eh

Fairbanks=5.1 C, Chicago=4.7 C, New York=3.7 C, Miami=2.7 C, Los Angeles=3.0 C

Fig. 1.11 Projected 1990-2100 warming for Mitigation Case (1% annual emission decrease for 75 years, starting 2025)

Models: ccsm--30 gfdlcm20 gfdlcm21 giss--eh

Fairbanks=5.1 C, Chicago=4.7 C, New York=3.7 C, Miami=2.7 C, Los Angeles=3.0 C

Fig. 1.11 Projected 1990-2100 warming for Mitigation Case (1% annual emission decrease for 75 years, starting 2025)

Change in Annual Precipitation

Global range .3 to 165.7

Global-mean dT 4.24 deg C

Scenario: New Year: 2100 Def. 2, no aerosols

Change in Annual Precipitation

Global range .3 to 165.7

Global-mean dT 4.24 deg C

Scenario: New Year: 2100 Def. 2, no aerosols

Models: ccsm--30 gfdlcm20 gfdlcm21 giss--eh

Fairbanks= +46%, Chicago= +39%, New York= + 12%, Miami= -16%, Los Angeles= -48%

Fig. 1.12 Projected 1990-2100 annual precipitation change base case, 3% early emission growth

Models: ccsm--30 gfdlcm20 gfdlcm21 giss--eh

Fairbanks= +46%, Chicago= +39%, New York= + 12%, Miami= -16%, Los Angeles= -48%

Fig. 1.12 Projected 1990-2100 annual precipitation change base case, 3% early emission growth a more realistic goal given recent increases in emissions and the unavailability of key technologies.

To more carefully explore the factors influencing the ability to constrain warming, emission scenarios were evaluated to see what reduction levels, starting in what year, would limit warming to the 2-3°C (±0.7°C) range from the pre-industrial period. Figures 1.14-1.16 were generated utilizing a large number of MAGICC runs.

Change in Annual Precipitation

Change in Annual Precipitation

Models: ccsm--30

gfdlcm20 Fairbanks +32%, Chicago +22%, New York +7%, gfdlcm21 Miami -16%, Los Angeles -30%

giss--eh

Fig. 1.13 Projected 1990-2100 annual precipitation change for mitigation case (1% annual emission decrease for 75 years, starting 2025)

Models: ccsm--30

gfdlcm20 Fairbanks +32%, Chicago +22%, New York +7%, gfdlcm21 Miami -16%, Los Angeles -30%

giss--eh

Global range -87.0 to 103.2

Global-mean dT 2.64 deg C

Scenario: WRE550-F Year: 2100

Def. 2, no aerosols

18.00 15.00 12.00 9.00 6.00 3.00 0.00 -3.00 -6.00 -9.00

Fig. 1.13 Projected 1990-2100 annual precipitation change for mitigation case (1% annual emission decrease for 75 years, starting 2025)

2 OL

Projected 2100 Warming as Function of Rate of Decrease and Start Year Atmospheric sensitivity=3.0 C

(

I.

>—

4

- J -----

1

. —-y

-----

Rate of Emission Decrease and Start Year

2010(1.6% growth rate) 2010(3% growth rate) -•k- -•-

2015(1.6% growth rate) 2015(3% growth rate)

Fig. 1.14 2100 global warming as a function of near term CO2 emission growth rates until mitigation year (1.6% or 3%), and year emission reduction starts (2010, 2015, or 2025)

They allow selection of combinations of emission growth reductions and start years needed to limit warming in 2100 to a given level. Figure 1.14 illustrates the impact of the faster 3% business as usual (BAU) growth rate, which yields additional

Projected 2100 Warming as Function of: Rate of Emission Decrease, and Start Year ra 3% to control yr. growth, BAU 2100 Warming 4.7 C deg; atmospheric sensitivity =3.0 C

Projected 2100 Warming as Function of: Rate of Emission Decrease, and Start Year ra 3% to control yr. growth, BAU 2100 Warming 4.7 C deg; atmospheric sensitivity =3.0 C

C3 cap (0%) 0.50% 1.00% 1.50% 2.00% 2.50% 3.00% Annual Emission Decrease from Start Year to 2100

C3 cap (0%) 0.50% 1.00% 1.50% 2.00% 2.50% 3.00% Annual Emission Decrease from Start Year to 2100

Fig. 1.15 2100 warming (°C) as function of annual emission decrease rate and year mitigation starts (assumes 3% growth rate until mitigation starts)

Projected 2100 CO2 ppm as function of: Rate of Emission Decrease, and Start Year Assumes 3% growth rate before control

Rate of Emission Decrease and Start Year

Fig. 1.16 CO2 atmospheric concentrations in ppm in 2100 as a function of annual emissions reduction rate and the year reductions start cap (0%) 0.50% 1.00% 1.50% 2.00%

Rate of Emission Decrease and Start Year

Fig. 1.16 CO2 atmospheric concentrations in ppm in 2100 as a function of annual emissions reduction rate and the year reductions start warming, relative to the 1.6% BAU case. As can be seen, additional warming increases as the start year for mitigation is delayed. Figures 1.15 and 1.16 focus just on the 3% base scenario and project 2100 warming and CO2 concentrations, respectively. Note that an annual decrease of 0.00% means emissions are held constant, at the start year until 2100. Also note that, in order to simplify the analysis, it is assumed that there is an immediate change in growth rate from the base case, to a decreasing emission growth rate at the control "start year". In reality, there would be a transition period between the positive and negative growth rates. Therefore, from this perspective, Figs. 1.15 and 1.16 should be considered somewhat optimistic, since emissions would not be avoided at the ultimate rate, during this transition period.

As can be seen, major annual decreases in emissions will be necessary if a warming target below 2.5 ± 0.7°C is to be achieved. Note that the earlier this reduction starts, the less the annual reduction rate has to be to meet a given warming target.

For example, if such a program would have started in 2010, reductions would need to be about 1% annually for 90 years to limit warming to about 2.5 ± 0.7°C; whereas if such a program were to start in 2025, annual reductions would need to be in the order of 3% per year for 75 years. Again, it must be noted that there is a large range of uncertainty in the resulting temperature for a given maximum CO2 concentration. Figure 1.17 illustrates this, by displaying the range of projected warming, from 1990, for a particular emission scenario (i.e., an annual decrease of 1%, starting in 2010, with a BAU growth of 1.6%, projected to constrain concentrations to the 440-480 ppm range). Note that Fig. 1.17 projects warming from 1990; about 0.4°C must be added to estimate warming from the pre-industrial era to be consistent with Figs. 1.14 and 1.15 Also, note an aggressive methane mitigation program could yield additional warming reduction of about 0.3°C in this time frame. Figure 1.18 quantifies the major challenge such reductions represent, relative to the IEA base case (1.6% growth to 2030) emission trends

It should be again noted, that if the world community continues to increase CO2 emissions at the rate of 3% per year over the next two decades, warming mitigation will be more difficult. Figure 1.19 illustrates the consequences of a higher emission o cn cn E 2

__.v-SiSS^

gglJI

IP

2050

Fig. 1.17 Projected warming range for a 1% annual decrease in CO2 emissions started in 2010

2000

2050

2100

Fig. 1.17 Projected warming range for a 1% annual decrease in CO2 emissions started in 2010

O 20

Reference: IEA Modified Base Case Policy: IEA Base 2010 1%

O 20

— Reference

— po

licy

2050

Fig. 1.18 Base case (red) and early mitigation case (green); Gt Carbon (3.67 Gt CO2 per Gt C). Note: the area between the curves represents the amount of carbon avoidance needed to achieve the target temperature versus the base case: over 1 trillion tons of carbon or over 3.7 trillion tons of CO2 over the 90-year period

2000

2050

2100

Fig. 1.18 Base case (red) and early mitigation case (green); Gt Carbon (3.67 Gt CO2 per Gt C). Note: the area between the curves represents the amount of carbon avoidance needed to achieve the target temperature versus the base case: over 1 trillion tons of carbon or over 3.7 trillion tons of CO2 over the 90-year period growth rate prior to a mitigation program started in 2025. Mitigation is less successful in moderating warming when the program is initiated after 25 years of a 3% growth rate, compared to the 1.6% growth rate of the IEA base case. As Fig. 1.13 indicated, this penalty becomes less severe the earlier the mitigation program is initiated.

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