Each year, the planet balances its budget. The carbon dioxide absorbed by plants in the spring and summer as they convert solar energy into food is released back to the atmosphere in autumn and winter. Levels of the greenhouse gas fall, only to rise again.But the budget has gotten bigger. Over the last five decades, the magnitude of this rise and fall has grown nearly 50 percent in the Northern Hemisphere, as the amount of the greenhouse gas taken in and released has increased. Now, new research shows that humans and their crops have a lot to do with it, highlighting the profound impact people have on the Earth’s atmosphere.