Atmospheric carbon dioxide levels pass 400 ppm everywhere and every month

El Nino is responsible for many climatic effects from droughts to torrential storms and warming oceans. It's also likely to be responsible for CO2 levels passing the 400 ppm (parts per million) concentration for every month this year for the first time in 2-3 million years. The carbon cycle has many components and while human-generated CO2 levels are still increasing globally (despite agreements to attempt to limit their rate of increase), after an El Nino event (which occurs every 4-7 years) the climatic consequences of this natural phenomenon can lead to CO2 levels being even higher. Drought in tropical zones can reduce biomass growth which means less CO2 is absorbed from the atmosphere. Additionally, natural forest fires are more numerous, releasing stored CO2 from the biosphere into the atmosphere. Both make for higher-than-normal CO2 levels in what is known as the 'fast carbon cycle'. Though 'normal' is becoming a rising float on steady trajectory upwards.

Read more on the El Nino impact affecting the carbon cycle in this BBC News article

In an extension to this, the Antarctic has recently recorded a CO2 concentration over 400 ppm for the first time in 4 millions years as global concentrations of the gas diffuse throughout the upper atmosphere. Most human-released CO2 occurs in the northern hemisphere where the greatest concentration of population, industry, traffic and urbanisation occurs. But the atmospheric cycling of constituent gasses has now spread the rising peaks of CO2 to the furthest reaches of the planet, suggesting it is much higher than 400 ppm over the northern hemisphere. You can read about this Antarctic CO2 milestone in this Guardian article.