The start of the Industrial Revolution marked the beginning of the large-scale exploitation of fossil fuels. The small dip in temperature in the early 1800s was caused by volcanic eruptions which reduced the amount of sunlight reaching the Earth's surface. After 1958, the data are from annual air measurements, not ice core proxies, and are therefore of higher quality. It shows how temperatures and CO2 concentrations have increased in recent times. But we don't know that the trend is linear.
Recent research indicates that it is probably exponential .
Or it may be that peak temperatures are more important than mean temperatures. It's not a matter of whether, it's only a matter of when and how.