2. Impact on climate

$CO_{2}$ is a greenhouse gas. Sunlight hitting the Earth warms the ground. Normally much of this heat would be radiated back into space. However, certain greenhouse gases can absorb and reemit the heat, warming the Earth.

Greenhouse gases include carbon dioxide, water vapor, methane, and nitrous oxide. Carbon dioxide is a key greenhouse gas since it accumulates in the atmosphere in large quantities. We say that increasing $CO_{2}$ levels cause a global warming (though the preferred term nowadays is climate change, since the overall effects will be varied). – jsu

[1]

More details on carbon dioxide as a greenhouse gas causing global warming. – jsu

Rising ocean levels. Global warming causes ocean levels to rise, because water expands when heated, and because polar ice caps and ice sheets melt, releasing water and possibly more greenhouse gases.

Ocean levels have been rising at 1.7 millimeters per year in the 20th century, and this rate has nearly doubled since 1993. Some areas will see even higher rises, such as the United States east coast, and China's Yellow River Delta. A few degrees higher, and Greenland will melt irreversibly away; South Florida will vanish entirely. – jsu

Greenland is melting away. – jsu

Do icebergs melting cause ocean levels to rise? – jsu

No -- icebergs float in water, and they displace just as much water as they contain. Ice sheets and glaciers melting are another story though!

Low-lying Florida is especially vulnerable to rising ocean levels (as is New Orleans, and the coast of New York). – jsu

[2]

An in-depth article about rising ocean levels due to global warming. – jsu

Ocean acidification. Carbon dioxide is a gas, and if one tries to add it to water, most of it just bubbles out. Still, a little bit of it is soluble in water. Higher pressures cause more carbon dioxide to dissolve, which can bubble back out when the pressure is relieved (think of your soda).

Carbon dioxide is much more soluble in water than other gases, e.g. it 50 times more soluble than oxygen. This is because water can react with dissolved $CO_{2}$ to form a new species, carbonic acid:

$$CO_{2} + H_{2}O \rightarrow H_{2}CO_{3}$$

The carbonic acid in turn transfers protons to water, causing the overall pH to drop. Rising $CO_{2}$ levels have caused the world's oceans to become more acidic, threatening coral reefs and marine life. – jsu

The oceans absorb 25% of the $CO_{2}$ we emit, slowing global warming, but causing the pH of the ocean to drop from 8.25 to 8.14. By 2100, it is estimated the pH will drop to 7.7, with catastrophic effects on coral reefs and other marine life. – jsu

Habitat and vegetation changes. In 2012, the U.S. Department of Agriculture released an updated version of its "Plant Hardiness Zone Map," showing which plants can grow where. Although they don't make any specific reference to global warming, many of the zones have shifted hundreds of miles upward, and two entirely new warm zones have been created.

As the globe warms up, fish that thrive in cold water die off; migratory birds find that anticipated food sources have bloomed at the wrong time; and animals that store food away for the winter find that their supplies have spoilt. – jsu

[3]

Global warming effects on wildlife and habitats. – jsu

[4]

Changes in the gardening map, released 2012. – jsu

Extreme variations in climate. As the Earth warms, we expect to see more extremes of temperature -- both hot and cold -- which coupled with rising sea levels cause more rain, more droughts, more floods, more hurricanes and tornadoes, more wildfires, etc.

This is not an absolute prediction, but is based on the increase of several risk factors. – jsu

[5]

Global warming makes it more likely that extreme climate events will occur. – jsu

[1] http://climate.nasa.gov/causes
[2] http://e360.yale.edu/feature/rising_waters_how_fast_and_how_far_will_sea_levels_rise/2702/
[3] http://www.nwf.org/wildlife/threats-to-wildlife/global-warming/effects-on-wildlife-and-habitat.aspx
[4] http://www.npr.org/blogs/thesalt/2012/01/25/145855948/gardening-map-of-warming-u-s-has-plant-zones-moving-north
[5] http://www.skepticalscience.com/extreme-weather-global-warming-intermediate.htm