Global Warming

Increasing humanuse of freshwater resources 155

In this section we have considered the impacts of sea level rise for the
twenty-first century. Because, as we have seen, the ocean takes centuries
to adjust to an increase in surface temperature, the longer-term impacts
of sea level rise also need to be emphasised. Even if the concentrations of
greenhouse gases in the atmosphere were stabilised so that anthropogenic
climate change is halted, the sea level will continue to rise for many
centuries as the whole ocean adjusts to the new climate.

Increasing human use of fresh water resources

The global water cycle is a fundamental component of the climate sys-
tem. Water is cycled between the oceans, the atmosphere and the land
surface (Figure 7.5). Through evaporation and condensation it provides
the main means whereby energy is transferred to the atmosphere and
within it. Water is essential to all forms of life; the main reason for the
wide range of life forms, both plant and animal, on the Earth is the
extremely wide range of variation in the availability of water. In wet

VAPOUR TRANSPORT 40

71

EVAPORATION

PERCOLATION

Lake

River

Land

Ocean

PRECIPITATION

111

SURFACE

RUNOFF

GROUNDWATER

FLOW

RETURN FLOW

40

425

EVAPORATION

PRECIPITATION

385

TRANSPIRATION

Figure 7.5The global

water cycle (in thousands

of cubic kilometres per

year), showing the key

processes of evaporation,

precipitation, transport as

vapour by atmospheric

movements and transport

from the land to the

oceans by runoff or

groundwater flow.