Last year was supposedly unprecedentedly warm, if you don’t count anything more than three or four years ago. It was rich fodder for the climate hysterics, not that they need anything to prompt their ceaseless panicked delirium. We already know that one likely factor impacting global temperatures in the last couple of years was the Tonga volcano explosion, which injected massive amounts of water vapor, one of the most potent greenhouse gases, into the atmosphere. That is a purely natural phenomenon and volcanoes regularly have powerful eruptions which affect global climate. Turns out that another major factor was likely human-induced, but not in the way you might imagine.
Ships often used a very heavy oil fuel, one that had lots of sulfur emissions. Those emissions led to formation of aerosols, very small particles. Aerosols have a number of impacts on climate and one is to spur cloud formation, and clouds can cool the Earth by blocking sunshine from reaching the surface. They can also having warming effects. Sulfur is considered a pollutant and developed nations agreed to ban high-sulfur shipping fuel beginning in January 2020. So far fewer sulfate-based aerosol particles were observed, a 90% drop in fact. New research finds that this change in turn caused fewer clouds and greater surface temperatures, enough to account for all the above-trend warmth last year. (ESD Article)
The climate is very complex, and natural impacts likely predominate, but some human actions can impact it, at least in the short term. The multifactorial feedback processes at work in short and long-term climate dynamics tend to keep climate on its natural long-term trend. As I used to read all the time when I was a child, an ice age is coming. That really will be something to get hysterical about.