  Space Weather is the portion of space physics that has a direct effect on
humankind. Space Weather is an old branch of space physics that originates back
to 1808 with the publication of a paper by the great naturalist Alexander von
Humboldt (von Humboldt, 1808). Space Weather is currently experiencing
explosive growth, because its effects on human technologies have become more
and more diverse. Space Weather is due to the variability of solar processes
that cause interplanetary, magnetospheric, ionospheric, atmospheric and ground
level effects. Space Weather can at times have strong impacts on technological
systems and human health. The threats and risks are not hypothetical, and in
the event of extreme Space Weather events the consequences could be quite
severe for humankind. The purpose of the review is to give a brief overall view
of the full chain of physical processes responsible for Space Weather risks and
hazards, tracing them from solar origins to effects and impacts in
interplanetary space, in the Earth's magnetosphere and ionosphere and at the
ground. The paper shows that the risks associated with Space Weather have not
been constant over time; they have evolved as our society becomes more and more
technologically advanced. The paper begins with a brief introduction to the
Carrington event. Next, the descriptions of the strongest known Space Weather
processes are reviewed. The concepts of geomagnetic storms and substorms are
briefly introduced. The main effects/impacts of Space Weather are also
considered, including geomagnetically induced currents (GICs) which are thought
to cause power outages. The effects of radiation on avionics and human health,
ionospheric effects and impacts, and thermosphere effects and satellite drag
will also be discussed. Finally, we will discuss the current challenges of
Space Weather forecasting and examine some of the worst-case scenarios.
