Since the thermometer is only about 150 years or so, not more than 200 years, the historical records really don't exist, so climate change is based upon analysis and theory, and only that. but long term is really more than 200 years. . . .
The most likely reason for long term climate change is most likely related to changes which are too small to measure over thousands of years. . .
Milankovitch (Orbital) Cycles and Their Role in Earth's Climate – Climate Change: Vital Signs of the Planet
however, there are regional climates which change due to human behavior, such as creating more heat sinks from city construction, so if anything might be the recent cause of surface global temperature rise, it comes from the heat sinks which humans have created by turning cattle fields into roads and houses. . .
remember, anything related to money or funding of any sort is subject to abuse. .