Global warming and cooling are the result of natural climate change, which is clearly evident from the historical evidence. All scientists agree that the huge temperature swings that have occurred in the past are completely, 100% natural, cyclical behavior.
Likewise, research and the data are confirming that the warming periods of the 20th century follow this same historical, natural, cyclical pattern, regardless of human CO2 emissions. The two 20th century time periods below show almost identical warming, despite the earlier 30-year period having little CO2 emission growth. (click on images to enlarge)
Per the National Climate Data Center (NCDC) temperature data, the large influx of human CO2 emissions may, at best, have added another 0.05 degrees Centigrade to the most recent global warming century trend, versus the century warming trend that ended during mid-1940's (see above charts). In layperson's language, the human CO2 impact on temperatures has been about 'squat', per the NCDC data.
It is important to recognize and remember, as the actual modern 20th century data depicts (review above charts), global warming/cooling naturally occurs during both low and high CO2 growth regimes. The human CO2 impact on global temperatures has not been of any significant consequence, even over the longer periods, such as 30 years.
Additional current temp charts here. Historical temp charts here.