In 2011 Greenfield relocated to San Diego, California, where he founded The Greenfield Group, an environmentally active marketing company.

In 2013, Greenfield cycled 4,700 miles (7,600 km) across America on a bicycle made of bamboo to inspire Americans to live more sustainably. On this 104-day ride he used 160 US gallons (610 l) of water, created two pounds (0.9 kg) of trash, traveled via his own power except for one mile (1.6 km) on a ferry into New York City, plugged into five electrical outlets, and never turned on a light switch.

From April 2013 to April 2014 Greenfield spent a year bathing only in natural water sources such as rivers, lakes, waterfalls and in the rain. The average resident of San Diego consumes around 100 US gallons (380 l; 83 imp gal) of water per day. During the first four months of the campaign Greenfield used an average of two US gallons (7.6 l; 1.7 imp gal) a day, and when he returned to his home he managed to use just ten to twenty US gallons (38 to 76 l; 8.3 to 16.7 imp gal) per day.

In October 2016, Greenfield spent a month walking around New York City wearing on his body all the trash he produced during the month by storing the trash in a suit of clear plastic sheeting, designed by trashion designer Nancy Judd, which hung on his torso and limbs. It was another attempt “to inspire people to think about how our little daily actions affect the world around us”.

From November 2018 to November 2019, Greenfield lived in Orlando, Florida and ate only food that he could grow and forage. He grew over 100 different foods in gardens and foraged more than 200 foods from the wild, using skills he learned from local teachers. At the same time he lived in a tiny house (his second—his first was in San Diego) that he built from recycled materials.

In 2020 Greenfield toured Europe as part of his “World Solutions Tour”.