Coal in the US was largely replaced by natural gas, leading to reduced CO2 but higher methane. Solar and wind took up the increase in energy demand in the last few years, but did not replace existing demand - yet. In China and India coal has not been replaced at all - yet. There are good reasons to be optimistic about a transition in electricity production, as Ken Feldman and others (and Bob Wallace when he was active here) have been pointing out for quite some time. And yet, seeing is believing. I would rather see these changes taking place rather than understand that they are about to happen. I would like to see countries both developed and developing installing huge amounts of wind and solar and shutting down fossil fuel generation prematurely, so that fossil fuel use in electricity generation actually drops rather than plateaus.
As for other sectors the picture is much less rosy. In transportation we have an economic solution of EVs, currently more expensive but soon to reach parity with ICE cars. It's already being adopted by some consumers despite the cost, but
globally the numbers are still minuscule.
Sales of electric cars topped 2.1 million globally in 2019, surpassing 2018 – already a record year – to boost the stock to 7.2 million electric cars. Electric cars, which accounted for 2.6% of global car sales and about 1% of global car stock in 2019, registered a 40% year-on-year increase.
It appears the economics are there for a fast transition to occur in global sales and later in global stock. But how fast is fast? I think it will take two decades at the least to replace most stock, and that it should take one decade at most.
A lot of industry can be shifted to electricity, but not all. Construction? Agriculture? Shipping? Some of these can be shifted by using cheap electricity to produce synthetic fuels. All this will take lots of time and lots of money. The electricity system should be transitioned very very fast, and result in very cheap prices for renewable electricity, to encourage the transition of the other industries. But mindsets change slowly and investment decisions affect results years ahead, so this may take at least another decade after transitioning of electricity, which itself could take two decades to mostly complete even if politicians across the globe do the right thing, which they often don't.
Some industries cannot be transitioned at all using current technology and economics.
In the meantime, warming accumulates, with natural feedbacks kicking in and taking up some of the slack in emissions. And summer Arctic sea ice will very probably disappear in the meantime, adding to the forcing due to a strong albedo feedback. Cleanup of energy will sharply reduce amount of aerosols, whether as a spike or as a long process doesn't matter too much for the end forcing result.
Should we be optimistic? Maybe. I think yes. Are we safely out of the woods? Hell no. The main ingredient here is time, which we don't have much of.