>>12531001At current technology levels? Less than 2 billion. Current level are only possible because we burn tremendous fossil fuel energy to create nitrogen fertilizer and create chemical pesticides and clear and plow and plant massive fields without human labor. With human labor and only yearly solar energy input, some 200 million in Europe, some 300 million in China, some 300 million in India, another 100 million throughout Asia, some 100 million - 300 million in Africa. Some 200-300 million in North America, and some 100-300 million in South America . Australia? Probably negligible.