The Earth's climate has exhibited marked natural variation, with time scales varying from many millions of years down to a few years. During periods of a few years up to a decade, fluctuations in global surface temperatures of a few tenths of a degree are common. The El Niño-Southern Oscillation phenomenon, and major volcanic eruptions have had some effects.

Changes in land and ocean floor topography have had major influences on global climate at time scales of 50 million to 150 million years. These changes influenced the patterns of absorption of incoming radiation from the sun, and affected circulation patterns in the atmosphere and oceans.

Over the last two million years the onset and recession of the great Ice Ages were probably influenced by changes in the earth's orbit and the tilt of its axis, which caused systematic variations in the amount and distribution of solar radiation. The difference in globally averaged temperatures between glacials (or ice ages) and interglacials is about 5°C.

Since the end of the last ice age (14,000-10,000 years ago) globally averaged surface temperatures have fluctuated over a range of up to 2°C on time scales of centuries or more. Causal elements included fluctuations in the radiation output from the sun, and changes in ocean circulation and overturning. These temperature variations through the Holocene period (the last 10,000 years) have been small compared with those during ice ages. In fact the Holocene has probably been the longest warn, stable period during the past 400,000 years.

CSIRO states, "There are a number of changes of slope over short periods in the Global Mean Sea Level record. This variability is at least partly related to El Niño and La Niña (sea level rises during El Niño and falls during La Niña) and associated changes in the hydrological cycle." This is one of many examples of variablity in the climate cycle.

CSIRO Fast facts:

• Climate variability, climate change and drought in eastern Australia remains a complex issue

• It is important that these complexities are understood so that Australian industry and local communities can respond to drought in appropriate ways

 

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