Human activities are increasing the concentrations of greenhouse gases in the atmosphere, leading to an 'enhanced' greenhouse effect and causing surface temperatures to rise.
To maintain stable temperatures at the Earth’s surface the incoming energy from the Sun must be balanced in the longer-term by an equal amount of heat radiated back to space.
Greenhouse gases in the atmosphere absorb some of this re-radiated heat, which increases the temperature of the Earth’s surface, ocean and atmosphere. This is what is termed the “greenhouse effect”.
Without any greenhouse gases, the Earth’s average surface temperature would be much lower, about -18 °C rather than today’s average of about 14 °C.
For many centuries before the industrial era (i.e. prior to 1750), the incoming sunlight and outgoing heat were balanced, and global average temperatures were relatively steady.
Human activities, especially the burning of fossil fuels and changes in land use, are increasing the concentrations of greenhouse gases in the atmosphere, leading to an “enhanced” greenhouse effect and causing an energy imbalance of around 0.7–0.8 Wm–2 (i.e. extra heat is building up in the Earth system) averaged over the global surface of the Earth.
This is causing the surface temperatures to increase.
The atmosphere and oceans will continue to warm until enough extra heat can escape to space to allow the Earth to return to balance. Because increased levels of carbon dioxide and other long-lived greenhouse gases persist in the atmosphere for hundreds of years, further warming and sea-level rise will occur.
Monitoring past and future changes in atmospheric greenhouse gas concentrations, including those measured and monitored at Cape Grim in remote north-western Tasmania, is important because of the influence these gases have on the Earth’s climate.
Concentrations of greenhouse gases continue to rise, with the global average carbon dioxide concentration now above 410 parts per million (ppm).
Before the industrial era, the average carbon dioxide concentration was around 280 ppm for several thousand years.