Historians have estimated the total human population back to 10,000 BC.[8] The figure on the right shows the trend of total population from 1800 to 2005, and from there in three projections out to 2100 (low, medium, and high).[6] The United Nations population projections out to 2100 (the red, orange, and green lines) show a possible peak in the world's population occurring by 2040 in the first scenario, and by 2100 in the second scenario, and never ending growth in the third.