From the report (emphasis mine):
A.2. Warming from anthropogenic emissions from the pre-industrial period to the present will persist for centuries to millennia and will continue to cause further long-term changes in the climate system, such as sea level rise, with associated impacts (high confidence), but these emissions alone are unlikely to cause global warming of 1.5°C (medium confidence). (Figure SPM.1) {1.2, 3.3, Figure 1.5}
A.2.1. Anthropogenic emissions (including greenhouse gases, aerosols and their precursors) up to the present are unlikely to cause further warming of more than 0.5°C over the next two to three decades (high confidence) or on a century time scale (medium confidence). {1.2.4, Figure 1.5}
A.2.2. Reaching and sustaining net zero global anthropogenic CO2 emissions and declining net non-CO2 radiative forcing would halt anthropogenic global warming on multi-decadal timescales (high confidence). The maximum temperature reached is then determined by cumulative net global anthropogenic CO2 emissions up to the time of net zero CO2 emissions (high confidence) and the level of non-CO2 radiative forcing in the decades prior to the time that maximum temperatures are reached (medium confidence). On longer time scales, sustained net negative global anthropogenic CO2 emissions and/or further reductions in non-CO2 radiative forcing may still be required to prevent further warming due to Earth system feedbacks and to reverse ocean acidification (medium confidence) and will be required to minimize sea level rise (high confidence).
They are saying that emissions from pre-industrial times up to now have caused effects that will last for hundreds or thousands of years. Even if we stop emitting entirely, they say, Earth's average temperature over the coming decades is going to reflect carbon already sunk into the system. They say that it is a question of avoiding further warming from the new baseline, achievable through unnamed net-negative practices. So while certain effects — ocean acidification, for instance — might stand to be reversed in the long term, others, like rising temperatures and sea levels, we can only hope to mitigate.
I'm curious for you to clarify what I'm 'glossing over' about the need for action at all levels. What I'm talking about in the original piece is the feeling of hopelessness and dread that many are dealing with, and why that shouldn't be an impediment to action, individually or at societal scales — I happen to think that people needlessly dismiss the role of individual changes in perspective and behavior, and certainly am don't mean to suggest that we not hold corporations to account, nor that anyone remain complacent. Hard for me to see how that could be read into what I wrote.
