The two main reasons why 2008 was the coolest year since 2000 was that the Pacific ocean was in its La Niña phase, and the sun was remarkably inactive and showed us a blank face for essentially the whole year. Both of these factors (oceanic and solar) exert a mild to strong influence on year-to-year climate variability. The forcing effect of additional greenhouse gases is more subtle in the short term, but ultimately dominates because it is inexorable (until we mitigate our emissions) and accumulative (due to long residence times).
In the first half of 2009, La Niña conditions persisted, despite a brief excursion to a more neutral phase. Now, however, the relevant signs — such as the southern oscillation index (SOI) and Pacific sea surface temperatures — point to the return of El Niño in the second half of 2009 (and perhaps continuing through 2010). There are also clear signs that the sunspots are returning in 2009, after the particularly extended period of quienscence, which recently had some speculating that we may be entering a new Maunder-Mininum-like period (more here).
The Bureau of Meteorology in Australia runs an excellent webpage on the El Niño-Southern Oscillation , updated weekly, called ENSO Wrap-Up. They have concluded the following:
“More evidence of a developing El Niño event has emerged during the past fortnight, and computer forecasts show there’s very little chance of the development stalling or reversing…
Another adverse sign for southeastern Australian rainfall is the recent trend to positive values in the Indian Ocean Dipole (IOD), as measured by the Dipole Mode Index (DMI)…
The sub-surface of the equatorial Pacific has also continued to steadily warm through June. A large volume of warmer than normal sub-surface water is evident across the entire tropical Pacific…
All international climate models predict the tropical Pacific to continue to warm and to be above El Niño thresholds throughout most of the second half of 2009.”
Both the oncoming El Niño, and the positive values of the IOD, is bad news for the rainfall outlook in eastern Australia. As reported in The Age, “Such an event could send Melbourne’s water storages, already at a record low level of 26 per cent, plummeting well below 20 per cent by next year and force stage 4 restrictions. Rivers — especially the Yarra — farmlands and crops look set to be stressed further. The prediction comes as the bureau confirmed that Melbourne had a record dry start to the year, with just 126.2 millimetres of rain falling from January to June — eight millimetres below the previous record set in 1967 and less than half the long-term average of 307 millimetres.”
Look out for the next update of ENSO Wrap-Up in 3 days time (as of this post).
In related news, a recent paper published in Science has demonstrated that there are at least two distinct types of El Niño with different relative influences on hurricane formation in the Atlantic, with one type (El Niño Modoki) being more inherently predictable. Forming in the central, rather than eastern Pacific, it is associated with a higher storm frequency and a greater potential for making landfall along the Gulf coast and the coast of Central America. Read more here and here.
The return of El Nino suggests that 2009 and 2010 will be considerably warmer than 2008. An additional +0.01 to 0.05C boost in global mean temperature may also come from increasing activity in the sun over this period. Current predictions are for a smaller than usual peak in sunspot activity (the lowest since 1928) during cycle 24, maxing out in mid-2013. What’s particularly interesting is the proposition from solar physicists that they have uncovered a new mechanism which may be influencing the progress of sunspot activity — a migrating jet stream from deep within the sun. To quote from the NASA press release:
“Rachel Howe and Frank Hill of the National Solar Observatory (NSO) in Tucson, Arizona, used a technique called helioseismology to detect and track the jet stream down to depths of 7,000 km below the surface of the sun. The sun generates new jet streams near its poles every 11 years, they explained to a room full of reporters and fellow scientists. The streams migrate slowly from the poles to the equator and when a jet stream reaches the critical latitude of 22 degrees, new-cycle sunspots begin to appear… Howe and Hill found that the stream associated with the next solar cycle has moved sluggishly, taking three years to cover a 10 degree range in latitude compared to only two years for the previous solar cycle. The jet stream is now, finally, reaching the critical latitude, heralding a return of solar activity in the months and years ahead.”
There is still not likely to be much activity in 2009, but as the report notes with regard to those Maunder Minimum fears, “The sun’s internal magnetic dynamo is still operating, and the sunspot cycle is not ‘broken’.“.
In other news, the Arctic sea ice is now well on its way to its summer minimum for 2009. A lot of people are interested to see whether the record low of 2007 will be beaten this year (we’ll know by late September), or whether there is some recovery due to the persistent effect of the cooler 2008. Current conditions are tracking about the same as 2008, and still fairly close to the 2007 level, so it’s really anybody’s guess as to what’ll happen next.
The rapid loss of old, thicker multi-year sea ice over the last few years is one major reason to be concerned that a tipping point in this system has already been crossed. My suspicion is that we’ll just miss the 2007 record this year due to the lingering cooler conditions of 2008, but that it’ll be broken in 2010. But such year-to-year records are really besides the point — the long-term decline in Arctic summer sea ice is beyond dispute, and the projections of total summer sea ice loss within the next 40 years now seem absurdly optimistic.