Why a few degrees can cause major changes

 To understand why a few degrees of warming can cause major changes, we draw from CSIRO's Understanding Climate Change factsheet.

A shift of just a few degrees can cause major changes

Average northern hemisphere temperatures during the second half of the 20th century were the highest of any 50 year period in the past 1300 years, based on at least 10 temperature reconstructions.

However, this magnitude of warming is not unusual in the Earth's geological history.

For millions of years the planet has experienced a series of ice ages and warmer inter-glacial periods, driven mainly by changes in the Earth's orbit.

During the last major ice age, the global average temperature was only 3-5 ºC cooler than today and sea levels were more than 120 m lower than present.

About 125 000 years ago our ancestors lived through an inter-glacial period in which the polar regions were 3-5 ºC warmer than today, and sea levels were about 4-6 metres higher than in the 20th century.

This illustrates that even a few degrees change in global temperatures can create a vastly different environment.

CSIRO Fast facts

  • Global average surface temperature has risen by 0.74 ºC over the past century.
  • Greenhouse gas concentrations in the atmosphere have increased since 1750, and now exceed pre-industrial levels.
  • There is greater than 90 per cent likelihood that most of the global warming seen since the mid 20th-century is due to increases in greenhouse gas emissions.
  • Sea level is projected to rise further by the end of this century.