We can observe exoplanets, but is it possible with today's technology to observe if there is life as we know it on an exoplanet? What do you look for when doing this kind of observation?
Direct observation of exoplanets (and then of traces of life on them) is still a big challenge.
Up to now, there are several indirect methods (effects on the parent star or on other stars), and direct detection is performed by using devices such as coronagraphs on faint stars, where very bright planets are imaged.
A way to image things such as as "forests" is very far in the future, and could be achieved by using extreme coronagraphy in space interferometers .
Another way is to use spectroscopy to find traces of biological activity in the athmosphere. This solution is very tricky due to the faint light reflected by extrasolar planets.
It is anyway a field where progresses are very quick, so stay tuned!