Climate change - comparison with the past

Temperatures and sea level

Earth has seen ice ages and the rising and lowering of sea levels in the past, but this has occurred over thousands to millions of years. Scientists have concluded that the average sea level rises that are happening now are unprecedented, and the observations of increasing land and sea temperatures over such a short time period is reason for governments across the world to start acting to reduce their emissions before the impacts of climate change become irreversible.

Some facts:

• According to historical global surface temperature records, 11 out of the 12 years from 1995 to 2006 have seen the highest temperatures recorded since 1850.
• In the Arctic, temperatures have increased at almost twice the global average rate in the past 100 years.
• Researchers have found that the oceans have been absorbing over 80% of the extra heat being added to the climate system.
• Global sea levels have correspondingly risen steadily at an average rate of between 1.8 mm to 3.1 mm per year between 1961 and 2003.¹ 

The figure above shows:

1. observed changes in global average surface temperature
2. global average sea level from tide gauge (blue) and satellite (red) data
3. Northern Hemisphere snow cover for March-April.

The shaded areas show the uncertainty, or the potential range in the predictions and all differences are relative to corresponding averages for the period 1961-1990. Smoothed curves represent averages over decades while circles show yearly values.
Source: 'Climate change 2007: Synthesis report', Intergovernmental Panel on Climate Change (IPCC), http://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_
synthesis_report.htm

Extreme weather events

Some extreme weather events, such as very hot or very cold days, heatwaves and tropical cyclones, are believed to have changed in frequency and/or intensity over the past 50 years.

This figure shows how the average area of sea ice has depleted in recent years. The yellow line shows the average extent of the ice between the years 1979 and 2000. The green line shows the minimum sea ice extent as observed in 2005, and the red line is the observed sea ice extent in 2007. These areas were reported by the USA's National Snow and Ice Data Centre (NSIDC). Read more about their research at http://nsidc.org/about/expertise/overview.html

Source: NASA, http://earthobservatory.nasa.gov/IOTD/view.php?id=8126

Scientists have agreed that it is likely that:

• cold days, cold nights and frosts have become less frequent over most land areas, while hot days and hot nights have become more frequent;
• heatwaves have become more frequent over most land areas;
• the frequency of heavy rain events (or proportion of total rainfall from heavy falls) has increased over most areas;
• the incidence of extreme high sea level has increased at a broad range of sites worldwide since 1975.¹

Return to Global observations.

¹Intergovernmental Panel on Climate Change (IPCC), Climate Change 2007: Synthesis report, 'An assessment of the Intergovernmental Panel on Climate Change', A Allali, R Bojariu, S Diaz, I Elgizouli, D Griggs, D Hawkins, O Hohmeyer, B Pateh Jallow, L Kajfez-Bogataj, N Leary, H Lee & D Wratt (eds), Cambridge University Press, Cambridge, 2007.