Abstract: A 2-dimensional climate model is established, which considers the radiant energy transfer process. Through using it, the relationship between the ice line latitude and concentration of CO2 as well as the curve of mean global surface temperature change with concentration of CO2 are analytically gained. And then an explicit analysis has been made and some interesting results have been obtained. It is suggested that if the concentration of CO2 increases from the level of 280×10-6 in pre industrial era to 700×10-6, the ice line will recede northward by several latitudes (in the North Hemisphere); while the concentration continues to increase, there will be a quick receding and even no ice covers the earth eventually. Accompanying with this, the mean global surface temperature will rise, with a slowed down increasing velocity before the level of 700×10-6 reached but an accelerating rate after 700×10-6. To verify the impact of albedo, the different albedo values ranged from 0.1 to 0.32 are tested. It is found that with the change of albedo the results vary little. The model does not have much sensitivity to albedo. According to the calculation, the warming effect incited by CO2 seems to tend to approach a quasi saturated state in the current situation, that is, the climate sys tem will not transform fast to a warming globe due to the increase of CO 2. A more realistic circumstance might be that the global temperature will rise robustly after an andante increasing. According to the computational results, this critical value is near 700×10-6. However, that does not mean the warming effect of C02 can be ignored. It can be implied from the results that the climate will be in a very warm state and the temperature will rise robustly after exceeding the critical value.