Climate scientists claim that CO2 has risen recently to levels that have not been seen in the history of humankind. How do they know this? Group of answer choices 1 They run computer models backwards from the present into the past; no direct measurments are made 2 They are extrapolating backwards from measurements made in the last few years 3 From the dawn of humankind, people have made measurements of atmospheric CO2, and archeologists have recently discovered these records 4 They are basing this on direct measurements of the atmosphere over the last 60 years or so, and overlapping ice-core data that extend back about 800,000 years 5 It comes from tree ring studies, using a theoretical relationship between temperature and CO2 concentration.

1. Climate scientists claim that CO2 has risen recently to levels that have not been seen in the
history of humankind. How do they know this?
Group of answer choices
1 They run computer models backwards from the present into the past; no direct measurments
are made
2 They are extrapolating backwards from measurements made in the last few years
3 From the dawn of humankind, people have made measurements of atmospheric CO2, and
archeologists have recently discovered these records
4 They are basing this on direct measurements of the atmosphere over the last 60 years or so, and
overlapping ice-core data that extend back about 800,000 years
5 It comes from tree ring studies, using a theoretical relationship between temperature and CO2
concentration