Such predictions received relatively little notice until the 1950's. They also pointed out that the CO 2 would remain within the atmosphere for a very long time because of how slowly it is absorbed by the oceans. Since then there has been a growing acknowledgment of the increasing concentrations of not only CO 2 but also the other greenhouse gases and their potential impact on the global climate. Media and a few scientists speculated publicly that the drought and heat wave affecting much of U.S. were evidence of climate change. As impacts from the drought diminished, and cooler heads prevailed, the realization that this drought was in fact within the established range of climate variability triumphed over the wild speculation raging within the media.
Carbon dioxide is responsible for approximately half of the increase.
Concentrations of CO 2 have been systematically monitored at the Mauna Loa Observatory in Hawaii since 1958. Scientists can determine the CO 2 concentrations from before 1958 using data collected from air bubbles within ice cores around the world. By 1990, these levels were at 353 ppm and they are increasing at 0.5 percent per year. 2 O, and CFCs are also increasing at a similar rate. Four major GCMs have been developed by research institutions.