Refer to the figure.
The figure shows the temperature (in °C, relative to modern temperature) and the concentrations of carbon dioxide (in ppm) and methane (in ppb) over the past 400,000 years.
- The current concentration of carbon dioxide is 404 ppm (not shown on the figure). Use the data in the figure to determine the highest carbon dioxide concentration levels that occurred over the past 400,000 years. At that point, the concentration of carbon dioxide was about _______% of the current concentration.