Climate scientists have provided the strongest evidence yet that human activities are causing climate change, according to a Lead Author of the Intergovernmental Panel on Climate Change’s (IPCC’s) 4th Assessment Report.
CSIRO Marine and Atmospheric Research scientist, Dr Penny Whetton, contributed to the report as a Lead Author on the chapter dealing with regional climate projections. She was also an author of the report’s Summary for Policy Makers, released in Paris this evening.
Dr Whetton says evidence from global air and ocean temperatures, melting snow and ice, and rising sea level show that warming of the climate system is now unequivocal.
“We now have improved understanding of how the climate is changing, based on improved datasets and analyses with broader geographical coverage, a wider variety of measurements and better understanding of uncertainties,” she says.
“It is very likely that most of the rise in global average temperatures since the mid-20th century has been caused by increased greenhouse gas concentrations in the atmosphere. In other words, there is a greater than 90 per cent chance that temperatures are rising due to human activities. Human influences are also evident in changes to some types of extreme weather.”
The report states that atmospheric concentrations of the main greenhouse gases, carbon dioxide and methane far exceed concentrations over the previous 650,000 years, primarily due to combustion of fossil fuels, agriculture and land-use changes.
Depending on how humans emit greenhouse gases in future, Dr Whetton says the range of projected globally-averaged surface warming for the end of the 21st century is between 1.0 and 6.3 degrees Celsius. Warming over Australia will be similar to the global rate.
“We also have a better understanding of how precipitation patterns are likely to change,” Dr Whetton says.
“Increases in the amount of precipitation are very likely in high latitudes, while decreases are likely in most subtropical land regions, including southern Australia.”
“Dr Whetton says evidence from global air and ocean temperatures, melting snow and ice, and rising sea level show that warming of the climate system is now unequivocal.”
The IPCC Working Group 1 report, Climate Change 2007: The Physical Science Basis, assesses the current scientific knowledge of the natural and human drivers of climate change, observed changes in climate, the ability of science to attribute changes to different causes, and projections for future climate change.
The IPCC represents the consensus view of about 2500 climate scientists from around the world. More than 100 Australian experts have been involved in the IPCC process since 2001.
Dr Whetton is one of 15 CSIRO authors who contributed to the IPCC Working Group 1 report. She will join a panel of Australian report contributors and climate experts to present results from the report at a media conference on Saturday 3 February at 10.30 am, at the Rydges Hotel (186 Exhibition Street, Melbourne).
Background
IPCC AR4 Global and regional climate projections
In this assessment report projections of future climate are based on a much broader range of global climate models. The findings have confirmed that substantial warming is expected during the 21st century. Over the next two decades, the globe is projected to warm at about 0.2°C per decade. Depending on how humans emit greenhouse gases in future, the range of projected global warming for the end of the 21st century is between 1.0 and 6.3 degrees. Sea level is projected to rise by between 19 and 58 cm by 2100, although further increases are considered possible due to uncertainty surrounding ice sheet dynamics and other contributors to sea-level rise.
The fourth assessment report of the IPCC has given increased attention to how climate is likely to change at the regional level. The ability of models to simulate regional climate has improved and the results of many more models have become available. The picture is now clearer than it was in previous reports.
Warming is expected to be greater over land areas and the high northern latitudes and least over the Southern Ocean and North Atlantic Ocean. Increases in the amount of precipitation are very likely in high-latitudes particularly in winter. Decreases predominate over subtropical land regions such as southern Australia, Southern Africa and the Mediterranean. Changes to tropical precipitation are more uncertain. Heat waves and extreme heavy rainfall is likely to increase in most regions and areas affected by drought are also likely to increase. Tropical cyclones are likely to decrease in numbers, but be more intense.
The IPCC findings for projected climate change over Australia reflect the picture that has been evident for some time. Warming over Australia is likely to be larger than the surrounding oceans and, on average, comparable to the global mean. Warming will be less in the south, especially in winter. Precipitation is likely to decrease in southern Australia in winter and spring and is very likely to decrease in Southwestern Australia in winter. Rainfall changes in northern, central and eastern Australia are less certain.
Increased frequency of extreme high daily temperatures is considered very likely for Australia. Extremes of daily precipitation are very likely to increase in many areas. There is also likely to be an increased risk of drought in southern areas of Australia.
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