Colonization of Venus
Venus's atmosphere is made mostly out of carbon dioxide, which, after filtering from sulfuric acid, can be used to grow food. Because nitrogen and oxygen are lighter than the carbon-dioxide that makes the atmosphere, breathable-air-filled balloons will float at a height of about . At this height, the temperature is a manageable ; or if we could get higher (see ).
Greenhouse effect
The greenhouse effect on Venus is particularly large because its dense atmosphere consists mainly of carbon dioxide.
"Venus experienced a runaway greenhouse in the past, and we expect that Earth will in about 2 billion years as solar luminosity increases".