  The Compact Linear Collider (CLIC) targets a nanometre beam size at the
collision point. Realising this beam size requires the generation and transport
of ultra-low emittance beams. Dynamic imperfections can deflect the colliding
beams, leading to a collision with a relative offset. They can also degrade the
emittance of each beam. Both of these effects can significantly impact the
luminosity of CLIC. In this paper, we examine a newly considered dynamic
imperfection: stray magnetic fields. Measurements of stray magnetic fields in
the Large Hadron Collider tunnel are presented and used to develop a
statistical model that can be used to realistically generate stray magnetic
fields in simulations. The model is used in integrated simulations of CLIC at
380GeV including mitigation systems for stray magnetic fields to evaluate their
impact on luminosity.
