 Nyora kupfuurira kweiyi ndima - Karlsson akasarudzwa semudziviriri akanakisa wemutambo pa2008 IIHF World U18 Championships. Akanga ari mutungamiri wemutambo a hrefPlus-minus2028ice20hockey29plusminusa aine huwandu hwepamusoro. Akatungamira timu yeSweden mukubatsira, achipedza wechitatu pakupedzisira mumutambo aine manomwe mumitambo mitanhatu, izvo zvakamufananidzawo nenzvimbo yekutanga mukudzivirira zvibodzwa. Munguva ye2008 U20 4-Nations makwikwi ayo Sweden yakakunda, Karlsson akarova chinangwa chimwe uye imwe inobatsira iyo yakamufananidza naDavid Rundblad, Viktor Ekbom naTim Erixon semutungamiri weSweden anotsigira zvibodzwa. PaWorld Junior Ice Hockey Championships muna 2009, Karlsson akasarudzwa kuchikwata chenyeredzi dzese, uye semudziviriri akanakisa wemutambo. Nezvibodzwa zviviri uye zvinomwe zvinobatsira mumitambo mitanhatu, akatungamira vatambi vese veSweden mumapoinzi, uye akabatanidzwa mukutungamira kwemutambo pakati pevadziviriri. 