There are loads of ways that we humans play a major part of climate change, however, to keep it short, I'll name two.
1. Agribusiness
Agribusiness is defined as "agriculture conducted on commercial principles, especially using advanced technology." While this massive commercial industry, especially the cattle industry, would seem to be more of a moral and health violation, the biggest toll it takes is on the planet. Cattle release a massive amount of methane gas. While no matter where the cattle are they excrete gases, humans fuel the methane release by overfeeding cattle to produce better meat and also overcrowd farms. The population of cattle has skyrocketed since agribusiness began to boom, leading to more methane than normally and naturally excreted into the environment.
The reason that methane is important is that of how serious it is in comparison to carbon emissions–the focus of many studies regarding climate change. Methane gas is approximately 30% more potent than carbon dioxide and stays in the atmosphere much longer than carbon. This leads to a very rapid increase in temperature because of this potency.
So while cattle already produce this gas, humans accelerate and multiply the effects it has on the environment.
2. Fossil Fuels & Non-renewable Energy
This is the one most people think of when they think of humans affecting the environment. The burning of fossil fuels causes carbon dioxide (CO2) to be released into the atmosphere. In small amounts, CO2 is relatively harmless, however, the massive amount currently being released into the environment is quite problematic because of the greenhouse gas theory. Ways to minimize this include carpooling, biking, and walking, or perhaps switching to an electric car.
I'd strongly suggest reading about how planetary albedo affects climate change since it is also a major non-human but also human-related factor. NASA has some good information on it. Hope I could help!
