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: None of these influences is likely to continue over the long term. Moreover, despite the slowdown in warming at the surface, there have been continuing increases in heat extremes and in the heat content of the oceans, as well as rising sea levels, shrinking Arctic sea-ice, and ongoing melt of ice sheets and glaciers. Some models predict that, when the current slowdown ends, renewed warming will be rapid. Scientists use ice core samples to reconstruct climatic records over hundreds of thousands of years. by NASA/Lora Koenig
Global average temperatures have increased over the past century
Climate and sea level were relatively stable over thousands of years of recorded human history up to the 19th century, although with some variations (Figure 2.1b). However, globally averaged near-surface air temperature rose by around 0.8°C between 1850 and 2012 (Figure 2.1c). The rate of warming increased in the mid-1970s, and each of the most recent three decades has been warmer than all preceding decades since 1850. The last decade has been the warmest of these. Satellite observations and direct measurements also show warming in the lower atmosphere over the past three decades. In contrast, the atmosphere above about 15 km elevation (the stratosphere) has cooled over this time.