2014 11 26 UNCLASSIFIED r 6 Temperature Targets and Timing Q What Is the relationship between emissions temperature change and when that temperature change would be realized • • • • • • • The primary driver of long-term anthropogenic warming is total cumulative CO2 emissions The relationship between total GHG emissions and temperature change is referred to as climate sensitivity There remains significant uncertainty in climate sensitivity This uncertainty exists for estimates of climate sensitivity ranging from decades to millennia Because of this and other uncertainties it is currently impossible to pinpoint a specific year • or possibly even a specific decade • when a given temperature threshold will be breached Moreover temperature change will not be regionally uniform There is very high confidence that globally averaged changes over land will exceed changes over the ocean with the Arctic region projected to warm most Some aspects of climate will continue to change even if temperatures are stabilized e g processes related to vegetation change changes in the ice sheets deep ocean warming and associated sea level rise and potential feedbacks linking ocean and the ice sheets Very generally speaking depending on how long it takes the world to emit a given amount of cumulative CO2 will largely determine appro imately when a given temperature threshold will likely be reached To put some rough numbers to the aforementioned qualitative statements A 450 ppm trajectory i e atmospheric concentrations of C02e are 450 ppm in 2100 - roughly the equivalent of RCP2 6 - puts us on a likely pace for a globally-averaged surface temperature increase above pre-industrial levels of l 5°C in 2050 range 1 1- 2 3°C l 6°C in 2100 range 1 0 - 2 s0 C 1 2°C in 2300 range 0 6 - l 6°C Note very few models have been run out this far A 550 ppm trajectory between RCP2 6 and RCP4 5 puts us on a likely pace for a globallyaveraged surface temperature increase above pre-industrial levels of l 9°C in 2050 range 1 2 - 2 4°C 2 2°C in 2100 range 1 6 - 2 8°C 3 o·c in 2300 range 1 9-3 7°C Note very few models hove been run out this far A 650 ppm trajectory roughly equivalent to RCP4 S puts us on a likely pace for a globallyaveraged surface temperature increase above pre-industrial levels of 2 l°C in 2050 range 1 6 - 2 6°C 2 6°C in 2100 range 1 8-3 1°C 3 l°C in 2300 range 2 1-4 l°C Note very few models have been run out this far The WB report is consistent with the RCP8 S scenario which is a lOOOppm trajectory and puts us on a likely pace for a globally-averaged surface temperature increase above pre-industrial of 2 4°C in 2050 range 2 0 - 3 3°C 4 6°C in 2100 range 3 6- s s·q 8 6°C in 2300 range 3 6- 12°C Note very few models hove been run out this far 2014 11 26 UNCLASSIFIED 6 12 t_ g 10 r u 8 CD n e a 12 - - hlstork aJ -RCP2 6 - 10 RCP4 5 8 RCP8 0 -RCP8 5 1 6 E 4 4 i 2 2 0 0 -2 -2 6 8 CD I en 0 C 1850 1900 1950 2000 2050 2100 2150 2200 2250 2300 Year The temperature increases depicted in the figure above are relative to the 1986-2005 average so 0 6°C needs to be added to the y-axis values to obtain warming since pre-lndustriar