Climate change in the UKOTs an overview of the ... - JNCC - Defra

Sea level and temperature: Global
average sea level has risen at an average
rate of 1.8 mm per year since 1961, with a
marked acceleration in the rate of increase
to an average of 3.1 mm per year since
1993 (Figure 10). It is too soon, however, to
know if the latter is a short-term variability
or a long-term trend. Sea level rise is the
consequence of two processes associated
with warming: inflows of water from
melting glaciers, ice caps and the polar
sheets and thermal expansion of seawater,
that is, an increase in the volume of seawater
in response to a temperature
change.
More than 80 per cent of the heat added to
the climate system is being absorbed by
40
oceans and this is affecting not just the
surface water, but water at greater depths
as well. Observations since 1961 show the
average temperature of water at depths of
up to 3,000 m has increased (IPCC, 2007).
In their latest report, the IPCC projected
that global sea level rise in the 21st century
would be at a greater rate than the period
from 1961 to 2003.
Snow and ice extent: Satellite data since
1978 show that annual average Arctic sea
ice extent has shrunk by an average of 3.7
percent per decade, with larger decreases
in summer of 7.4 per cent per decade.
Mountain glaciers and snow cover on
average have declined in both hemispheres.
Chapter summary
Climate change is any significant modification over time in the climate of a zone or
region. This change can be natural or it can have its roots in human activity. Natural
processes of change have been taking place since the Earth began evolving, but the
present day global concern is about the unprecedented rate of change over the past
60 to 100 years that is caused by human activity.
The change that is now taking place is the result of the intensification of a natural and
necessary process, the greenhouse effect. Increased emissions of greenhouse
gases are leading to an increase in the Earth’s average surface and sea temperatures.
Changes in the atmosphere are having an effect on temperature, precipitation, storm
activity and sea level. The linear warming trend over the last 50 years is nearly double
that for the last hundred years. Some parts of the world have been experiencing an
increase in precipitation while others have had a significant decline. Global average
sea level has risen at an average of 1.8 mm per year since 1961 because of melting
glaciers, ice caps and sea ice. Satellite data since 1978 show that annual average see
ice extent has shrunk by an average of 3.7 per cent per decade.
All of these consequences of warming in turn influence physical and biological systems;
this has serious implications for man and society.