In recent decades, the level of Carbon Dioxide (CO2) in Earth's atmosphere.
Group of answer choices
a. has increased dramatically to a new high level
b. is difficult to measure reliably
c. has increased, but not by much compared to historical records
d. is lower than 100 years ago
Group of answer choices
a. has increased dramatically to a new high level
b. is difficult to measure reliably
c. has increased, but not by much compared to historical records
d. is lower than 100 years ago