High tides will be extra high everywhere around the world this week.
These so-called "king tides" are occurring now because the sun and the moon are very near Earth, as meteorologist Dan Satterfield reports on his blog hosted by the American Geophysical Union. Tides are caused by the pull of the moon and the sun on masses of water. Combined with the peculiarities of different coastlines, they result in differing local sea levels around the world. King tides happen when the gravitational forces of the sun, Earth and moon are aligned.
This combined force is being asserted now because the Earth was at perihelion, the point in its orbit at which it is closest to the sun, on Jan. 2, and this week the moon is reaching its perigee for January, the point during the month when it is closet to our planet, according to Satterfield.
"King tides" is a non-scientific term to describe these exceptionally high tides, which occur twice per year. These higher-than-usual tides can cause flooding if storms arrive when water levels are elevated, as happened in California in 2011.
In 2009, a group of concerned citizens formed the King Tides Initiative, in which people worldwide were invited to take photos of local water levels during these high tides and to share them online. One such initiative is sponsored by the Maryland Department of Natural Resources; photos can be seen on their Flickr page.