Human activities are increasing the concentrations of greenhouse gases in the atmosphere and causing surface temperatures to increase, leading to an “enhanced” greenhouse effect.

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.

Without any greenhouse gases, the Earth’s surface would be much colder, about -18 °C. This is what is termed the “greenhouse effect”.

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 at a little under 15 °C.

Human activities, especially the burning of fossil fuels and changes in land use, are increasing the concentrations of greenhouse gases in the atmosphere and causing surface temperatures to increase, leading to an “enhanced” greenhouse effect. There is now an energy imbalance of around 0.7–0.8 Wm–2 averaged over the global surface of the Earth.

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 is inevitable.

Tracking past and future changes in atmospheric greenhouse gas concentrations, including those measured and monitored at Cape Grim is important because of the role these gases play in the Earth’s climate.

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