In April 2015 the US measuring station at Mona Loa in Hawaii measured 403.26 parts of carbon dioxide per million in the atmosphere compared with 401.29 ppm in April 2014. The US National Oceanic and Atmospheric Administration state that world atmospheric carbon dioxide levels exceeded 400 ppm across the whole of the earth. The statement is based upon only 40 measuring sites, so it may be inaccurate, but for the first time all 40 sites reported measurements in excess of 400 ppm.
There has been a rise of 120 ppm since pre industrial times and half of that rise has occurred since 1980. There is a great deal of scepticism amongst many people who are not climatologists that a rise in what is, after all, a trace gas in the atmosphere could affect our climate.
I shall not set out the processes that are believed to make increasing carbon dioxide a serious contributor to global warming; I have done that elsewhere. We may not see the proof of the theory of climate change in our lifetimes, at least those of us who are old may not see it, but I fear for future generations. The proof of that pudding will certainly be in its eating.