Volcanoes and hot springs contribute to climate change because both add carbon dioxide (CO2) to the atmosphere. The CO2 released by volcanic eruptions and hot spring activity comes from carbon stored in deep rocks and sediments, which form the largest reservoir of carbon on Earth.
CO2 inputs to the atmosphere from volcanoes and hot springs are normally balanced (in the absence of humans) by removal of CO2 from the atmosphere by chemical weathering. The main way by which this occurs is hydrolysis, a process in which water reacts with certain minerals and CO2 is consumed. The CO2 is transformed into other compounds, which eventually end up stored in the ocean and rocks.
Both of these processes (input of CO2 by volcanoes and hot springs, and removal of CO2 by weathering) take place over very long time scales, and will only noticeably alter the climate over millions of years.
CO2 inputs to the atmosphere from volcanoes and hot springs are normally balanced (in the absence of humans) by removal of CO2 from the atmosphere by chemical weathering. The main way by which this occurs is hydrolysis, a process in which water reacts with certain minerals and CO2 is consumed. The CO2 is transformed into other compounds, which eventually end up stored in the ocean and rocks.
Both of these processes (input of CO2 by volcanoes and hot springs, and removal of CO2 by weathering) take place over very long time scales, and will only noticeably alter the climate over millions of years.