An Alternative Earth: Warmer Siberia

This question concerns this Alternative Earth.

To make a certain fictional country which occupies the northern part of Russia more interesting, I want to make agriculture feasible in Siberia and to increase the population density of this region. This will require several climatic changes.

Let's start with the situation in Real Life. Siberia is mainly covered in forests that slowly turn into forest tundras and tundras when travelling northwards. Siberia's climate is relatively harsh - temperatures can reach -40 degrees celsius in winter and 40 degrees celsius in summer.

As you can see, Siberia and northeastern Europe are not very good areas for agriculture.

I want the northern part of Eurasia to look like this:

Brown - important mountain ranges (hills and smaller mountain ranges have not been accounted for)

Light brown - Tundra/grassland. Dirt permafrost tundra in the north that slowly turns into a grassland tundra with some shrubs and reindeer and sheep pastures.

Pale brownish green - Forest tundra with reindeer, sheep and cattle pastures. Slow southward transistion from barren tundra landscape to forest landscape with some agriculture.

Dark green - Taiga landscape. While forestry (logging) prevails over agriculture, large cities are surrounded by "agricultural islands" that become more and more common when travelling southwards.

Light green - Loose agricultural landscape interrupted by coniferous and birch forests; transistion from taiga to farmland.

Yellow - Farmland. Wheat and barley prevail; some large pastures (especially close to mountain ranges). Hops gardens, apple orchards and even wineyards appear in the southernmost (coastal) parts; slow transistion to forest steppe and steppe in the south. Coniferous (coastal) and mixed forests.

My question is:

• What geographical or climatical factors need to change to allow for such a landscape distribution (Consider the higher Urals!)? I imagine something similar to a gulf stream in the Polar Sea or in the Pacific Ocean or reducing the axial tilt of the Earth. It is necessary to somehow move the permafrost border northward.

• How would this affect the climate of other parts of the world? After all, I reduced the area of the taiga and increased population density. Will Europe have to turn into a steppe or a desert?