Title: 2. How has climate changed? | Australian Academy of Science
Headings: 2. How has climate changed?
2. How has climate changed?
Past climate has varied enormously on a variety of time-scales
Past records demonstrate that global climate is sensitive to small but persistent influences
Box 2.1: How do we detect climate change?
Box 2.2: Has climate warming recently stopped?
Global average temperatures have increased over the past century
Changes are evident in many parts of the climate system
There are regional differences to climate change including within Australia

Content: The last 8,000 years, which includes most recorded human history, have been relatively stable at the warmer end of this temperature range. This stability enabled agriculture, permanent settlements and population growth. Most past changes in global temperature occurred slowly, over tens of thousands or millions of years. However, there is also evidence that some abrupt changes occurred, at least at regional scales. For example, during the last ice age, temperatures in the North Atlantic region changed by 5°C or more over as little as a few decades, likely due to sudden collapses of Northern Hemisphere ice sheets or changes in ocean currents. Figure 2.1: Past changes in temperature align with changes in CO2 at a variety of time scales. These graphs show the changes from long‑term average temperature (oC) and average atmospheric CO 2 concentration (parts per million) over the last (a) 800,000 years, (b) 2,000 years and (c) 160 years. The temperature changes in (a) are for Antarctica, while for (b) and (c) they are global averages. Source: