From the “shmeaty” goodness of a test-tube hamburger to the glimmer of water on Mars, it’s been a year in science to remember—and in some cases (yep, we’re talking to you, comet ISON) to forget. Here are some of our picks for the year in science. We’ll share one of our top science stories each day of the first week of 2014. See them all at #2013SciencePicks.
2. Record-High Carbon Dioxide
In May, atmospheric levels of carbon dioxide measured at the Mauna Loa Observatory reached a new high, surpassing 400 parts per million for the first time since data-taking began there in 1955. The last time CO2 levels reached this level was roughly 4.5 million years ago, during the Pliocene Epoch, when the earth was roughly 6° F warmer and sea level ranged between 16 to 131 feet higher. http://www.esrl.noaa.gov/news/2013/CO2400.html