New SSP-RCP database release provides excellent detail on CMIP6 scenarios which will produce an important evidence base of climate model results for the IPCC 6th Assessment - here’s how these CO2 emission scenarios compare against previous RCPs (dotted lines) - 1/13 thread 
A few things to note about specific scenarios in this thread - RCP8.5: the new SSP5-RCP8.5 scenario requires a much faster CO2 emission increase after 2030 than the old version used in IPCC AR5 - 2/13
This is because the vintage RCP8.5 had very ambitious expectations for other GHGs, and observations have supported much lower outlooks for emissions of these gases, thus more CO2 would need to be released to reach 8.5 W/m2 in 80 years - 3/13
RCP7.0-baseline: roughly consistent with continuing the post-WWII rate of growth in CO2 emissions until 2100, so if the world is headed for RCP7.0, we’d need to see a very rapid sustained acceleration of CO2 emissions + much more coal use starting in the next decade - 4/13
Otherwise we’re going to fall well under RCP7.0 (a good thing!) since technology adoption over the last 15 years has been taking us in a different direction (also an issue with 'no policy baselines' // cc @RogerPielkeJr ) - 5/13
RCP6.0: the new RCP6.0 scenario shows a much lower trajectory for CO2 emissions after mid-century than the old RCP6.0 - why is that? once again, the assumptions for other GHGs can make a big difference - more of other GHGs means less room for CO2 - 6/13
If we compare the CMIP6 RCP6.0 scenario to all of the other IAM scenarios in the SSP database consistent with staying <6.0 W/m2 by 2100, it ends the century toward the very lowest of the group and reaches 5.5 W/m2 [see figure - other IAM scenarios shown as dotted lines] - 7/13
RCP3.4: The CMIP6 RCP3.4 scenario (roughly consistent with 2˚ of warming by 2100) is one of the most ambitious for negative emissions when compared to the other IAM scenarios that do not exceed total radiative forcing of 3.4 W/m2 - 8/13
Remember that each of these CMIP6 scenarios are based on specific end-points for radiative forcing in 2100 which are useful for climate model experiments, and IAMs show us ways these levels of radiative forcing could possibly result - 9/13
The new SSP database is great because it provides detail on CMIP6 CO2 emission scenarios for specific sectors - here’s what CO2 emissions from transportation look like in the 6 main scenarios - 10/13
And here’s CMIP6 scenarios for CO2 emissions from air travel - although past passenger air travel growth has been rapid (and resilient in the face of recessions) all scenarios higher than RCP2.6 are looking at a future of even faster growth - 11/13
My take: (1) world definitely not on track for high scenarios (8.5, 7.0), but not for low scenarios either (1,9, 2.6, 3.4), and (2) many assumptions for transportation post-2050 look too ambitious, though diving into reasons would take another thread - 12/13
Overall, it is fantastic to have this level of detail available on the CMIP6 scenarios, and this data release is a significant improvement over what was published in the CMIP5 database, so kudos @IIASAVienna and CMIP6 research team - 13/13
