Figure 1~13 below shows the total amount of energy (in EJ, 10^18 J) produced worldwide each year, from 1973 - 1995. It also shows the amount of primary energy resources used each year.
The total global energy use in 1995 was 383 EJ. For comparison, about 5.5 million EJ of sunlight strikes the upper atmosphere of the Earth each year, and about 250,000 EJ of that makes it to Earth's surface. So humans used the equivalent of less than 0.2% of the Sun's energy striking the Earth's surface in 1995. (That number doesn't take into account energy uses that aren't included in the U.S. DOE's figures, such as sunbathing and solar heating of homes, swimming pools, and other structures.)
Energy-wise, then, people use only a tiny fraction of the solar energy available at the Earth's surface each year. If we used only renewable energy resources, there would probably be no cause for concern. However, most of the energy we used in 1995 came from non-renewable energy resources, in particular the fossil fuels.