Energy ________________________________________________________________ 16. Causes of climate crisis
Figure 6.24. Natural greenhouse effect and enhanced greenhouse effect (click on the image to make it bigger)TheEarth’s atmosphere works something like a giant glass greenhouse.
As the Sun’s rays enter our atmosphere, most continue right down to the planet’s surface. As they hit the soil and surface waters, those rays release much of their energy as heat. Some of the heat then radiates back out into space.
Greenhouse gases absorb and re-emit some of the heat radiation given off by the Earth’s surface and warm the lower atmosphere.
The most important greenhouse gas is water vapor, followed by carbon dioxide and methane, and without their warming presence in the atmosphere the Earth’s average surface temperature would be approximately -20°C.
While many of these gases occur naturally in the atmosphere, humans are responsible for increasing their concentration through burning fossil fuels, deforestation and other land use changes.
Records of air bubbles in ancient Antarctic ice show us that carbon dioxide and other greenhouse gases are now at their highest concentrations for more than 800.000 years.