In the previous chapter we considered approaches to providing energy with near-zero emissions of carbon dioxide. While this may be technically possible, there are impediments to the adoption of these concepts. Some are political, some are economic and some are resistance to change. The alternative approach is to accept the rise in carbon dioxide concentration in the atmosphere due to continuing emissions of carbon dioxide, and to modify some other components of the climate system to maintain a desirable climate. This is known as geoengineering – engineering on a global scale. It implies exerting control over nature, a concept that comes more naturally to engineers than to others with different cultures.

Five hundred years ago, humans had made only a small dint on the global ecosystem. The land biomass was presumably in steady state, so that on the average it neither stored carbon, nor released it to the atmosphere. Then came land clearing for agriculture, with the consequent release of carbon dioxide. As the CO2 level started to rise with the Industrial Revolution, carbon flowed from the atmosphere to the sea because of Henry's Law. The ocean sink is currently estimated at 1–2GtCyr−1. One way to make this estimate is to measure the carbon dioxide partial pressure difference between the atmosphere and the ocean surface layer and use this in a flux calculation. This topic is discussed in Chapter 5.