Over the last several decades, what have researchers discovered about atmospheric co2 levels? 1 they have decreased.2 they have increased.3 they have remained the same.4 they increased for a period, but have now stabilized.

they have increased

Explanation:

What happens with pollution is that every day are tons of CO2 liberated to the atmosphere. those tons of pollution supose to be regulated by the states, but that is not what actually happens in third world countries there is an almost uncontrolable increase of CO2 liberation at the atmosphere. In the first world countries it's more controlled but still haven't decreased the CO2 levels released into the atmosphere.

The CNN (an spanish daily paper) said: the CO2 levels are the highest in the last 3 million years, in a new released the past april.