How do we know that global warming is caused by human activities?
The present atmospheric concentration of carbon dioxide is the highest it has been for 420,000 years. For the past 1000 years global atmospheric carbon dioxide has been quite stable. However, since the beginning of the Industrial Revolution, about 1750, the concentrations of greenhouse gases in the atmosphere have increased dramatically.
Human activities, such as burning fossil fuels (coal, oil and gas), land clearing and agricultural practices have increased carbon dioxide by 31% (to about 360 parts per million), nitrous oxide levels by about 17% and methane concentrations have more than doubled. The current rate of increase in carbon dioxide is unlikely to have been experienced during the past 20,000 years at least.
The observed changes in climate, especially temperature increases since about 1970, cannot be explained by natural causes such as solar activity. Reconstructions of climate data for the past 1000 years indicate that this recent warming is unusual and is unlikely to have resulted from natural causes alone.
If people around the world do not act to control global warming, scientists have predicted:
- a rise in the Earth's temperature of between 1.4ºC and 5.8ºC by 2100";
- higher sea levels as oceans expand and glaciers melt - between 9 and 88 centimetres by 2100; and
- "complicated changes in weather patterns, such as more severe droughts and floods, and higher rainfall intensity".
Will a few degrees temperature increase have a significant impact on our climate?
During the last ice age, between 10,000 and 20,000 years ago, surface temperatures were on average about 5°C cooler than today.
Sheets of ice covered almost one-third of the world's land. Half of the world's oceans were covered by floating ice. As sea level was much lower than it is now, it was possible to walk from mainland Australia to Tasmania.
The projected global warming of just a few degrees in the 21st century is likely to result in more heat waves and droughts in some regions of the world and more intense rainfall and resultant flooding in other areas.
The impacts of climate change will vary from region to region and are difficult to predict on a local scale. In some regions of the world a small degree of global warming may have negligible or even positive impacts (eg. Canada), while in others, such as tropical countries, it may be disastrous.
Developing countries that have fewer resources are likely to be the hardest hit, as they will have less capacity to adapt to climate change impacts. As sea levels rise, as a result of thermal expansion and melting glaciers, some low-lying coastal areas and islands will be more prone to inundation from storm surges.
Many plants and animals are unlikely to be able to migrate or adapt quickly enough to survive in a warmer world. For example, alpine animals and plants can only migrate upwards to cooler locations. Habitat clearing means that many animals will not be able to adapt to increasing temperatures by moving to other locations.
Human-induced climate change is another major stress in a world where natural and social systems are already experiencing pollution, increasing resource demands and unsustainable management practices.
How do we know that global warming is caused by human activities?
The present atmospheric concentration of carbon dioxide is the highest it has been for 420,000 years. For the past 1000 years global atmospheric carbon dioxide has been quite stable. However, since the beginning of the Industrial Revolution, about 1750, the concentrations of greenhouse gases in the atmosphere have increased dramatically.
Human activities, such as burning fossil fuels (coal, oil and gas), land clearing and agricultural practices have increased carbon dioxide by 31% (to about 360 parts per million), nitrous oxide levels by about 17% and methane concentrations have more than doubled. The current rate of increase in carbon dioxide is unlikely to have been experienced during the past 20,000 years at least.
The observed changes in climate, especially temperature increases since about 1970, cannot be explained by natural causes such as solar activity. Reconstructions of climate data for the past 1000 years indicate that this recent warming is unusual and is unlikely to have resulted from natural causes alone.
If people around the world do not act to control global warming, scientists have predicted:
- a rise in the Earth's temperature of between 1.4ºC and 5.8ºC by 2100";
- higher sea levels as oceans expand and glaciers melt - between 9 and 88 centimetres by 2100; and
- "complicated changes in weather patterns, such as more severe droughts and floods, and higher rainfall intensity".
Will a few degrees temperature increase have a significant impact on our climate?
During the last ice age, between 10,000 and 20,000 years ago, surface temperatures were on average about 5°C cooler than today.
Sheets of ice covered almost one-third of the world's land. Half of the world's oceans were covered by floating ice. As sea level was much lower than it is now, it was possible to walk from mainland Australia to Tasmania.
The projected global warming of just a few degrees in the 21st century is likely to result in more heat waves and droughts in some regions of the world and more intense rainfall and resultant flooding in other areas.
The impacts of climate change will vary from region to region and are difficult to predict on a local scale. In some regions of the world a small degree of global warming may have negligible or even positive impacts (eg. Canada), while in others, such as tropical countries, it may be disastrous.
Developing countries that have fewer resources are likely to be the hardest hit, as they will have less capacity to adapt to climate change impacts. As sea levels rise, as a result of thermal expansion and melting glaciers, some low-lying coastal areas and islands will be more prone to inundation from storm surges.
Many plants and animals are unlikely to be able to migrate or adapt quickly enough to survive in a warmer world. For example, alpine animals and plants can only migrate upwards to cooler locations. Habitat clearing means that many animals will not be able to adapt to increasing temperatures by moving to other locations.
Human-induced climate change is another major stress in a world where natural and social systems are already experiencing pollution, increasing resource demands and unsustainable management practices.