1.1 What is climate change?

In this section:

Recorded changes in the weather

Snow picture

Milder winters (with snow less likely), drier summers, heavy downpours with increasing number of floods, fiercer heat waves and an apparent rise in extreme weather across the globe all point to the experience of a climate that is changing.

The most definitive source of climate change research and analysis is the Intergovernmental Panel for Climate Change (IPCC) which is sponsored by the United Nations Environment Programme (UNEP) and the World Meteorological Organisation (WMO). It has become the most comprehensive and authoritative source of material on climate change, involving the participation of thousands of scientists from around the world and a long and open review process.

(a) Global average surface temperature

According to observations from the Intergovernmental Panel for Climate Change (IPCC), the average global surface temperature over the last 50 years has increased by 0.13oC per decade which is nearly twice as much as the increase over the last 100 years. (see graphic below)

Global average surface temperature graph

Eleven of the last twelve years (1995-2006) rank among the twelve warmest years of global surface temperature recorded (since 1850).
Observations since 1961 also show that the warming rate of the average temperature of the global ocean is similar to the warming rate observed in surface temperature.

(b) Northern Hemisphere snow cover

Observed decreases in snow and ice extent are also consistent with warming:
Satellite data since 1978 show that annual average Arctic sea ice extent has shrunk by 2.7% per decade, with larger decreases in summer with 7.4%. Mountain glaciers and snow cover on average have declined in both hemispheres.

Northern Hemisphere snow cover graph

(c) Global average sea level

Increases in sea level are also consistent with warming: Global average sea level rose at an average rate of 1.8 mm per year over 1961 to 2003 and at an average rate of about 3.1 mm per year from 1993 to 2003. It is estimated than more than half of this increase is due to the expansion of the oceans as it warms up and the rest due to the melting of the ice caps and polar ice sheets.

Global average sea level graph


At continental and regional level, numerous other changes in the climate have also been observed:

According to observations from 1900 to 2005:

  • Increase in precipitation especially in eastern parts of North and South America, northern Europe and northern and central Asia whereas precipitation declined in the Sahel, the Mediterranean, southern Africa and parts of southern Asia.

According to observations over most areas in the last 50 years:

  • Less frequent cold days, cold nights and frosts while hot days and hot nights have become more frequent.
  • More frequent heat waves
  • Increase in the frequency of heavy precipitation
  • Increase in extreme high sea at a broad range of sites worldwide since 1975.
  • Increase in intense tropical cyclone activity especially in the North Atlantic since about 1970.


Graphs legend

Observed changes in (a) global average surface temperature; (b) global average sea level from tide gauge (blue) and satellite (red) data; and (c) Northern Hemisphere snow cover for March-April. All differences are relative to corresponding averages for the period 1961-1990. Smoothed curves represent decadal averaged values while circles show yearly values. The shaded areas are the uncertainty intervals estimated from a comprehensive analysis of known uncertainties (a and b) and from the time series (c).

 

Stonewall, Gay and Lesbian Charity - opens in a new windowBeacon Authority logoInvestor in People logo