Impacts, Mitigation, Adaptation and Energy Choices

Impacts are unevenly distributed. Warming raises sea level through thermal expansion of ocean water and the melting of land ice; it shifts the distribution of precipitation so some regions become drier and others wetter; it increases the intensity of heatwaves, heavy rainfall and tropical cyclones; it moves the ranges of species and of disease vectors; and it acidifies the ocean, because dissolved carbon dioxide forms carbonic acid, which impairs the formation of calcium carbonate shells and coral skeletons. Ocean acidification is worth naming separately because it is caused by carbon dioxide directly rather than by warming, so it would continue even if temperature were somehow stabilised. The distributional point is central to an evaluation: the countries with the lowest emissions per capita, including small island states and much of sub-Saharan Africa, face the largest impacts and have the least capacity to adapt.

Mitigation and adaptation. Mitigation acts on the cause: reducing emissions or enhancing sinks. It includes low-carbon energy, efficiency, afforestation and forest protection, carbon capture and storage, and carbon pricing through taxes or tradable quotas. Adaptation acts on the consequences: sea walls, drought- and salt-tolerant varieties, early warning systems, water storage and reuse, and planned relocation. The quickest test in an exam is to ask whether the measure changes the concentration of greenhouse gases; if it does not, it is adaptation.

Why both are necessary. The climate system has large inertia, so a degree of further warming is already committed by past emissions; mitigation alone therefore cannot avoid all impacts. Equally, adaptation alone leaves the cause untouched, so its cost rises without limit as impacts intensify, and some impacts — the loss of a low-lying state, the collapse of a reef system — cannot be adapted to at all. A further caution is maladaptation: a measure that reduces one risk while increasing emissions or transferring risk elsewhere, such as widespread air-conditioning powered by coal, or an embankment that protects one bank of a river by raising flood levels on the other.

Energy choices and energy security. Energy security means reliable, affordable access to sufficient energy. It depends on the size and location of domestic resources, the diversity of the supply mix, the reliability of imports, and the resilience of the grid. Fossil fuels offer high energy density and dispatchable output but high emissions and, for importers, geopolitical exposure. Nuclear power has very low operating emissions and provides baseload, but faces high capital cost, long build times, waste storage and public acceptance. Wind and solar have very low operating emissions and falling costs, but are intermittent, need land and critical minerals, and require storage or flexible backup. Hydroelectricity is reliable and low-carbon but displaces communities, traps sediment and, in tropical reservoirs, can emit significant methane.

Reading energy figures correctly. An installed capacity figure is not an output figure. Actual output is capacity multiplied by the hours in a year multiplied by the capacity factor — roughly 0.25 to 0.35 for onshore wind, 0.10 to 0.20 for solar photovoltaics in temperate latitudes, 0.50 to 0.80 for coal, and 0.80 to 0.90 for nuclear. Comparing a wind farm to a coal station by nameplate capacity therefore overstates the wind farm by a factor of two or three, and this is the single most common quantitative error in energy essays.