Climate change science
Climate scientists say that the pivotal question regarding climate change is not whether the climate is changing and will continue to change in response to human activities, but rather how much, how fast and where.
Scientists are certain that climate change is already happening. Global average surface temperature increased over the past 100 years by about 0.7°C. There has also been an increase in heatwaves, a reduction in frosts, warming of the lower atmosphere and deep oceans, retreat of glaciers and sea ice, a rise in sea level of approximately 17 cm and increased heavy rainfall in many regions. There is extensive evidence of the impacts of global warming on the growth and distribution of plants and animals, as well as changes in events such as floods and droughts in some regions.
Once carbon dioxide—the main greenhouse gas increasing through human activity—is released into the atmosphere, it stays there for between 50 and 200 years. Hence further warming is already in the pipeline, regardless of what we do in the future. This is also because the deep ocean and the polar ice caps have massive thermal inertia, or heat-storing capacity, so they warm and cool more slowly than the atmosphere.
It is very likely that the warming will exceed 1°C over the next century. To quantify future warming, scientists have developed scenarios. These represent possible futures based on various assumptions about human behaviour, economic growth and technological change. Some scenarios assume ‘business as usual' without actions specifically aimed at reducing net greenhouse gas emissions. These scenarios lead to a projected global-average warming of 1.1-6.4°C from 1990 to 2100. Other scenarios include actions to slow global warming by stabilising carbon dioxide concentrations. These scenarios will require substantial global greenhouse emissions reductions over the 21st century.
The level of action required to address the problem depends on the degree of climate change we are prepared to accept. Article 2 of the United Nations Framework Convention on Climate Change requires stabilisation of greenhouse gases at a level that prevents “dangerous human interference with the climate system”. At this stage, “dangerous” is not well defined and will involve a mixture of scientific, economic, political, ethical and cultural considerations. However, a number of scientific assessments and governments have adopted a threshold for “dangerous” climate change of 2°C above pre-industrial levels. After accounting for the 0.7°C of warming that has already occurred, this allows less than 1.5°C of additional warming before the threshold is exceeded. Avoiding this level of warming by the year 2100 will require substantial global emissions reductions within the next 20-40 years.
The Australian Government is investing $3.4 billion on climate change action, including helping Australia to adapt to the impacts of climate change as well as finding ways to reduce greenhouse gas emissions, domestically and globally through a range of international partnerships.
