A juggernaut takes a lot of stopping. The present UK electricity supply system took some 40 or so years to create. It could easily take just as long to switch to a more CO2-friendly mixture of technologies, especially if we include transport and efforts to cut disproportionate per capita energy use.
This "deliverability" issue should be high on the agenda at Buenos Aires. We urgently need real commitment from the big CO2-emitters this time around.