Carbon dioxide is transparent to light but rather opaque to heat rays. At this point, the answer depends on limited data and what assumptions you plug into your computer models. The very activities that deposit CO 2 in the air also deposit dust particles that impede the passage of light through the atmosphere so more is reflected back into space. Air pollution thus appears to reduce the arrival of energy as well as its departure. Whether these opposing effects cancel each other out is not yet known.
Average temperatures do seem to have increased slightly in recent decades.
Many glaciers and ice sheets are receding. Many species of birds and butterflies are moving north and breeding earlier in the spring. Whether the present change is a result of human activities or of long-term changes over which we have no control is still uncertain. But a developing consensus is telling us that it is better to be safe than sorry. The marked warming of the earth that occurred at the end of the Paleocene epoch is thought to have been caused by the release of large amounts of methane from the sea floor.