Its increasingly likely current policies and falling costs of clean energy lead to around 3C warming by 2100. This is a far cry from below-2C targets, but much better than 4C+ outcomes that appeared likely a decade ago. @jritch and I take a look @TheBTI: thebreakthrough.org/issues/energy/…
Two new reports – the IEA 2019 WEO and the UNEP Emissions Gap – both reflect current trends in clean energy costs and make the case that global emissions will only modestly increase over the next few decades. They project emissions at the low end of the IPCC baseline range. 2/16 
This is largely due slower growth in coal use. IEA scenarios still project future growth in fossil fuel use through 2040, but around 0.5% per year compared to 1% and 3% for most SSP baseline scenarios. 3/16
In our article we look at what this implies for 2100 warming. We consider two cases based on IEA 2040 projections: one where FF&I CO2 emissions remain flat at 2040 levels and one where they continue to increase at the 2030-2040 rate: 4/16
In the case where emissions remain flat after 2040 (and non-FF&I forcings follow a RCP4.5 trajectory), warming by the end of the century is just under 3C, with a range from around 2C to 4C reflecting uncertainties in climate sensitivity: 5/16
If we use a more conservative assumption of continued increase in emissions and RCP6.0 non-FF&I forcings warming can be modestly higher, but is still only 3C in the stated policies (STPS) and 3.4C in the current policies (CPS) scenarios: 6/16
Its important to point out a "business as usual" world where current trends continue is neither a worst case or a best case. Its quite possible to imagine a future where rising nationalism and isolationism leads to higher global inequality, pop growth, and domestic coal use. 7/16
On the other hand, it is possible for the world to reduce emissions well below 2040 levels by 2100 even in the absence of new climate policies. For example, the same IEA stated policy scenarios is often criticized as being too conservative regarding renewables. 8/16
These two contrasting possible futures set up a tension for advocates expressing optimism for clean energy but also using climate impact estimates based on very-high emission baselines. 9/16
A world where coal use could expand enough to reach SSP3-7.0 (or even SSP5-8.5/RCP8.5) levels is one of very slow growth in renewable energy, nuclear, or other decarbonization technologies. 10/16
Similarly, a world where clean energy outcompetes deployment of new fossil technologies is one where it is difficult to envision emission scenarios much above SSP4-6.0/RCP6.0. 11/16
While there is some utility in having “what might have been” scenarios that are radically divergent from the path we’re on today, these should not necessarily be used to set policy or plan for future climate impacts. 12/16
The fact that the current policy projections are on the bottom of the range of baseline scenarios in the literature is problematic if not taken into account when using baseline scenarios as a roadmap for climate policies going forward. 13/16
The benefit of having regularly updated energy models like the IEA WEO is that they can be much more responsive to recent trends in costs and deployment than energy system models initialized in 2005 or 2010 used in IPCC assessments. 14/16
The world has taken concrete steps to move away from coal in the past decade, and this progress should be reflected in our assessment of likely emissions pathways — and their resulting climate impacts — going forward. 15/16
Our business-as-usual projection of 3C of warming — rather than 4 or 5C — is a testament to progress in global decarbonization over last few decades. It also reflects that rapid growth in coal during the 2000s appears not to be characteristic of longer-term energy trends. 16/16
(These numbers are for future growth in coal use, not all fossil fuels; sorry for any confusion!)
