For the record, climate change is real — but that's nothing new.  Just ask a wooly mammoth or a dinosaur.  Atmospheric heat-trapping is also real, or else everything around us would freeze solid every night — just as it does on our airless moon.  And sea level is the best way to tell if the Earth is warming or cooling because it is a truly global indicator, rather than a stew of various local measurements.

It is also important to understand the well known cycles that bring us seasons and weather patterns.  The seasons change from equinox to solstice over and over because the Earth's rotational axis is tilted relative to its orbital plane.  During winter in the northern hemisphere, the sun appears in the sky farther in the south.  It moves north until it reaches the summer solstice — as the weather warms.  Due to the elliptical nature of our orbit around the sun, the northern summer finds the Earth farther away from its heat source than it is in the winter, which tends to moderate the seasonal temperature change. 

The opposite is true for the southern hemisphere.  Closer to the sun in the summer and farther in the winter would make for more severe weather down there, except for the much greater amount of the southern surface being covered by oceans, which also serve to moderate the weather.

Another axiom of climatology is that the west coasts of the continents have noticeably milder weather than the east coasts.  This is probably due to the rotational direction of the Earth, which is counterclockwise when looking down at the north pole.

Back to sea level and climate change.  Previously at this site, Viv Forbes posted a link to NASA's website showing a graph of annual sea level measurements going back to 1993.  The overall accumulated increase is 102.5 millimeters.  This site is also sprinkled, nonetheless, with all kinds of dire climate change warnings.  But if you do the math, it comes out to a little under 3.7 millimeters per year.  At this rate, it would take about 82 years for the sea level to be raised by one foot.  Also, the graph forms what is mostly a straight line even if you scroll down to see the same plot going back all the way to 1900.  No "hockey sticks" here...just a steady increase.  This is because we are in an interstitial warm period known as the Holocene — which began about ten to twelve thousand years ago when the last ice age, the Pleistocene, ended.

During ice ages, glaciers and polar ice caps expand.  During interstitial warm periods, they melt, and the sea level rises.  Should the sea level stop rising and start declining, it would likely be an indicator that a new ice age is beginning.  Exactly why ice ages happen remains an incompletely solved mystery, though much effort is being applied to the quest.  Orbital, rotational, and solar cycles are the most likely causes. 

Now to the politics of the issue.  "Global warming" entered the public policy debate in a serious way when the midterm election of 2006 made Nancy Pelosi speaker of the House of Representatives.  Knowing of the general public's pervasive ignorance of Earth science, the demagogues of the left seized the opportunity to wage war on fossil fuels as a convenient stand-in for capitalism.  After losing out to technology when it came to smog and acid rain, global warming had to be their next best line of attack.  Add to this the compelling appeal that doomsday cults have for those who are looking for any excuse to avoid facing the drudgery of ordinary life.

And lastly, we are seeing climate change being woven into just about every weather-related news report.  The current prolonged deluge that may be ending California's three-year drought is a prime example.  The term "atmospheric river" is used prolifically, as it was some years back in a Scientific American article that discussed the flood of 1862.  This flood is seldom mentioned in today's reportage concerning the current situation, even though it was of tremendous historic importance.  The (ahem) inconvenient truth is that sediment analysis shows that such floods to have regularly occurred about every 165 years, give or take, going back thousands of years.  Doing the arithmetic, the last occurrence was 161 years ago.  Close enough for weather forecasting.

Image: Hans Grobe/AWI.