I am very happy to see a very unwelcome visitor go away: La Niña is dead.
Over time, the pattern of ocean and atmospheric circulation changes. When cooler water in the eastern Pacific Ocean is brought to the surface at the Equator, it’s called La Niña, and when that water is warmer it’s El Niño. This changes the way winds blow and water evaporates, and during La Niña Australia gets torrential rains and floods, while the US gets drought conditions, especially in the southwest.
This year, the jet stream was also held up near the US/Canada border, so the winter was very mild, and many states suffered severely dry conditions. But finally, after two years, equatorial waters are warming up. As you can see in the image above, the water near the Equator was cooler (blue) in January 2012, and now a stream of warmer water (red) has appeared north of it. This means neutral conditions will take hold (and eventually lead to an El Niño).
All winter here in Boulder it’s been far warmer and drier than usual, and in my travels these past few months the story has been the same nearly everywhere. The mountains to my west have been nearly free of snow, something I haven’t seen since moving here. But literally, as I type this it’s raining steadily outside, again something I haven’t seen in many months.
It’s very welcome! Well, I’m rather hoping it doesn’t interfere with the talk and star party I’m doing in Boulder this coming Saturday, but in the meantime it’ll be nice to see the creeks rising, the snow pack increasing, and the trees looking a little bit peppier.
Image credit: NASA Earth Observatory/Jesse Allen and Kevin Ward, using JASON-2 data provided by Akiko Kayashi, NASA/JPL Ocean Topography Team.
Over the past 10 years at least, sea levels have been rising relatively steadily. This is mostly due to melting glaciers and ice sheets, and is a natural — if detrimental — consequence of global warming. The rate of ocean level rise has been a little over 3 millimeters per year (about 1/8th of an inch per year)… until last year. The rate of increase suddenly reversed itself in 2010, and the sea levels actually dropped a bit, by about 6 mm. What happened?
La Niña happened. Equatorial ocean temperatures fluctuate on a cycle; when they are warmer it’s called an El Niño, and when they’re cooler it’s La Niña. As you might expect, this affects how water evaporates off the ocean surface, and therefore rainfall across the world as well. Right now we’re in a La Niña, characterized by drought conditions in the southern US (like in Texas), and heavier than usual rainfall in Australia, northern South America, and other locations:
That map is from the NASA/German Aerospace Center’s Gravity Recovery and Climate Experiment (GRACE) satellites, which map where water is on the Earth and how it moves around. This change in rainfall is the culprit for the lowering sea level:
So where does all that extra water in Brazil and Australia come from? You guessed it–the ocean. Each year, huge amounts of water are evaporated from the ocean. While most of it falls right back into the ocean as rain, some of it falls over land. "This year, the continents got an extra dose of rain, so much so that global sea levels actually fell over most of the last year," says Carmen Boening, a JPL oceanographer and climate scientist. Boening and colleagues presented these results recently at the annual Grace Science Team Meeting in Austin, Texas.
That’s pretty interesting! I didn’t realize it could rain so much that sea levels could be affected, but there you go. Doing the math, I find that a 6 mm drop is equivalent to a volume of very roughly 700 billion cubic meters of water, or 700 cubic kilometers (about 180 cubic miles). That is a lot of water! Read More