7

Global Change

7.1 Why study global-scale environmental chemistry?

environmental chemistry?

In previous chapters of this book the chemistry of the atmosphere, oceans and

land has been dealt with largely on an individual basis. Using a steady-state model

(see Section 3.3), we can envisage each of these environments as a reservoir. In

each chapter the cycling of chemicals has been discussed, together with their

transformations within the reservoir. Where relevant, some attention has been

paid to inputs and outputs into or out of that reservoir from or to adjacent ones.

By contrast, the present chapter focuses not on individual reservoirs, but on the

ensemble of them that make up an integrated system, of air, water and solids,

constituting the near-surface environments of our planet.

As scientists have learnt more about the way chemical constituents of the

Earth’s surface operate, it has become clear that it is insufficient to consider only

individual environmental reservoirs. These reservoirs do not exist in isolation—

there are large and continuous flows of chemicals between them. Furthermore,

the outflow of material from one reservoir may have little effect on it, but can

have a very large impact on the receiving reservoir. For example, the natural flow

of reduced sulphur gas from the oceans to the atmosphere has essentially no

impact on the chemistry of seawater, and yet has a major role in the acid–base

chemistry of the atmosphere, as well as affecting the amount of cloud cover

(Section 7.3).

Since integrated systems need to be understood in a holistic way, studies of

the global environmental system and natural and human-induced changes to it

have become very important. By definition, such studies are on a large scale, gen-

erally beyond the resources of most nations, let alone individual scientists. Thus,