Is it possible for an entire planet to have the same climate? So lets for example say an entire world with a northern european (scandinavian) climate and accompanying geography. (No deserts, no rainforests, no polar ice)
This concept is known as a "Single-Biome Planet" and they are a fictional concept.
It is impossible for a planet that orbits a star to have only one biome while remaining anything akin to Earth, however it is possible for a planet to have reduced extremes of temperature compared to Earth.
The thicker a planet's atmosphere, the more heat will be distributed around the planet, so you could have a planet with a warm equator and poles that are only a little cooler.
Additionally, having lower topography would result in rain-bearing air being able to transport moisture further from the sea, so a flatter planet will have reduced continental aridity.
You must be aware though, that if the atmosphere is too thick, it will have consequences for human survival. Likewise, low topography suggests that the planet has either greater surface gravity, or reduced tectonics, both of which have consequences for life. (e.g. reduced carbon cycle)
One way to do this would be to ensure each unit of area on the planet absorbs the same amount of energy. Normally the poles receive less energy because the surface of the planet is at an angle to the sun's rays. The solution could be an extraordinarily unique geology. If the rocks near the equator were almost entirely white, and they shifted towards almost entirely black at the poles, you could counteract the effect of this incidence angle.
It'd be one heck of a bespoke planet!
Alternately if by biome you mean across all land area. There are several examples of this during earth's own history.
- Molten earth (everything was still lava)
- Snow Ball earth (everything was covered by snow and ice).
- The Permian (particularly close to the extinction) everywhere was essentially arid scrub/desert.
Alternately pick any biome of your choosing. Make a small landmass at the right latitude. Everywhere else is ocean (conveniently not a Biome for the purpose of this definition).