However, that figure of 283 years remaining is for present rates of usage. If coal usage declines, then the "hubbert curve" of remaining coal is flattened and pushed further out to the right. For example, if we were using only half the amount of coal per year as we do now, then we would have 566 years of coal remaining, not 283 years. Every reduction in coal usage will extend the amount of time remaining until depletion.
Coal usage has been declining fairly rapidly in the United States, for the last 5 years or so, because renewables and gas are so much cheaper now. Coal plants are being shuttered because coal is relatively more expensive now. In fact, coal usage is down 28% in the United States over the last 5 years, because so many coal plants have been shuttered. As a result, the date of coal depletion is being pushed far out into the future. Since coal usage is down 28% already, the remaining time until coal is depleted has increased from 283 years to 388 years (= 283 / 0.72 - 5). In other words, we have “gained” 105 years of coal during the last 5 years.
This trend looks set to continue. New turbines are being developed ("supercritical CO2 turbines") to replace the old steam turbines in coal power plants. Those new turbines are 50% efficient instead of 33%, which pushes back the date of depletion another 262 years ( =393 * (0.5/0.33) ). Any further encroachment of renewables would push back the date of depletion even further, and could easily result in millennia of coal before it runs out. For example, if coal plants are gradually replaced by wind turbines during the next few decades, until coal is used only for steelmaking and also during the time when the wind isn't blowing, then coal usage could decline by more than 50%, which would result in 1,190 years total until the coal runs out (= 595/0.5). That figure is without any electricity storage technology at all for when the wind isn't blowing. Coal could still be used for electricity generation when the wind isn't blowing, but we'd still have enough coal for 1,190 years.
Of course, there are several trends happening in the opposite direction also, which could push toward increased use of coal. First, the United States looks like it will phase out nuclear power over the next several decades, and some of that lost generation may be replaced by coal. Second, south Asia is growing quickly and will increase its usage of coal. However, both of those trends are temporary. Coal usage may bounce up and down, but in the long run, it is probably headed way downwards, which implies that remaining reserves will last far longer than reserve figures suggest.
Of course, it is possible that further technological developments will occur during the next few centuries, in which case the date of depletion for coal will be pushed even further outward. If flow batteries are commercialized, for example, then coal may not be needed for electricity generation at all. If new steel-making technologies continue to progress, then coal wouldn't be needed for that purpose either.
Our civilization has at least centuries to develop technologies such as flow batteries and alternative steel-making technologies. If those technologies are developed and commercialized in the next few centuries, then the remaining coal would be left in the ground as useless.
Technology is rapidly outpacing depletion. This time to depletion for coal keeps getting further and further away, and fairly rapidly. If this trend continues for long, then coal will never run out.
*NOTE: This post was revised several times during the 24 hours after its initial publication. I also updated this article on Sept 21 to use a more realistic example of how much electricity could be generated from renewables without storage.