Temperatures are rising

The average global temperature has warmed by more than 0.7°C over the past century, and the present warming rate is 0.2°C per decade. If continued, this trend will lead to a temperature rise of about 3°C by the end of this century (relative to pre-industrial temperatures). This would be the highest global temperature rise recorded in recent PALAEOCLIMATE history. The instrumental record showing a warming earth is supported by satellite measurements of TROPOSPHERIC warming and by observations in the CRYOSPHERE and BIOSPHERE.


Global average temperature 1850-2008

Source: Met Office Hadley Centre for Climate Change © British Crown Copyright 2005, the Met Office

The global warming trend is evident from three independent sets of measurements: air temperature over land, air temperature over sea at night, and sea-surface temperature.

Annual anomalies

Source: Met Office Hadley Centre for Climate Change © British Crown Copyright 2005, the Met Office

Global warming since the 1970s has been more rapid over land than over the oceans, as would be expected from an increasing human-caused greenhouse effect. The amount of warming observed varies considerably from place to place, because natural variability of climate can add to human-caused warming in some places, or subtract from it in others. Local factors (such as cooling from aerosols of emitted fine particles in the atmosphere) may also come into play. That the earth's surface has experienced a recent warming is also supported by the widespread recession of mountain glaciers over the last few decades, and by measurements made at different depths in boreholes in sediments and ice layers that carry signatures of the climate at the time they were laid down, which can be used to estimate the historical rise in temperature.

Temperature has a direct influence on the intensity of climate and weather systems, largely related to stronger gradients between regions of higher and lower air pressure, and the ability of warmer air to hold more water vapour. Extreme events (major storms, big winds, heavy hail) are likely to increase in magnitude and/or frequency with global warming. There may also be changes in location—for example, an enlargement of the 'hurricane (cyclone) zone'. The most likely changes are an increase in the number of hot days and nights (with some minor regional exceptions), or in days exceeding various threshold temperatures, and decreases in the number of cold days, particularly including frosts.

Globally, precipitation is generally predicted to increase in high latitudes and to decrease in some mid-latitude regions, which together with a general rise in intensity of rainfall events is likely to increase the frequency of flash floods and large-area floods in many regions, especially at high latitudes. The earlier seasonal melting of snowpacks and meltwater from glaciers may accentuate the situation.

Regions where precipitation stays the same or drops are likely to experience more frequent and intense droughts, notably in Mediterranean-type climates and in mid-latitude continental interiors.

Australia, already the world’s driest inhabited continent, may become even drier in many areas—particularly in the south-east. Heat and dryness increase the risk for major bushfires.

Tropical cyclones (including hurricanes and typhoons), are likely to become more intense with sea surface temperature increases and the frequency of intense cyclones may increase, even though some modelling suggests that the total number of tropical cyclones will fall slightly.

Increasing temperature warms the oceans and causes sea level rise through expansion of sea water. Storm surges would become more common and more intense due to the combined factors of rising sea level and more intense coastal storms, especially tropical cyclones. These would likely also be associated with more intense inland rainfall and stronger winds.

Temperatures are likely to increase in Australia at a rate comparable to the global mean. The number of very hot days per year are projected to increase across Australia, particularly in the sub-tropical and tropical regions, and the number of frosts are likely to decrease. Projections of temperature changes are summarised in the table below, with columns corresponding to projections for 2030 under a mid-range emissions scenario and projections for 2070 under low and high emissions scenarios:

2030 Mid emissions
2070 Low emissions
2070 High emissions
Average temperature increase
Average number of days per year above 35°C in temperate coastal capital cities
Average number of days per year above 35°C in Brisbane
Average number of days per year above 35°C in Darwin

Source: Climate change in Australia—observed changes and projections, CSIRO, October 2007.

Also see more extreme weather.

Further reading:

CSIRO, Climate Change in Australia, Technical Report, 2007.

Intergovernmental Panel on Climate Change, Working Group I Contribution to the Fourth Assessment Report, Climate Change 2007: The Physical Science Basis, Chapter 3, Observations: surface and atmospheric climate change.

Intergovernmental Panel on Climate Change, Working Group II Contribution to the Fourth Assessment Report, Climate Change 2007: Impacts, Adaptation and Vulnerability, Chapter 19, Assessing key vulnerabilities and the risk from climate change, Table 19.1 and p. 795.

1 September, 2009