There has been about a _____ increase in carbon dioxide in the atmosphere in the last 250 years

There has been about a _____ increase in carbon dioxide in the atmosphere in the last 250 years

• A. 5%
• B. 25%
• C. 50%
• D. 75%

Answer: (B)

Understanding how percent change works for a long-term atmospheric change helps here. Carbon dioxide levels rose from about 280 parts per million in the pre-industrial era to around 350–410 ppm today due to human activities like burning fossil fuels. That translates to roughly a quarter to half again as much CO2 as there was 250 years ago. In many introductory contexts, a rough, single-number estimate of the increase is given as about 25%, which captures the idea of a substantial rise without getting into the more precise range. The other options would either understate or overstate the commonly cited rough increase. So the best single figure to pick from the choices is about a 25% increase.

Understanding how percent change works for a long-term atmospheric change helps here. Carbon dioxide levels rose from about 280 parts per million in the pre-industrial era to around 350–410 ppm today due to human activities like burning fossil fuels. That translates to roughly a quarter to half again as much CO2 as there was 250 years ago. In many introductory contexts, a rough, single-number estimate of the increase is given as about 25%, which captures the idea of a substantial rise without getting into the more precise range. The other options would either understate or overstate the commonly cited rough increase. So the best single figure to pick from the choices is about a 25% increase.